DEVELOPMENT OF SEAL RING CARBON

NASA

CR-I2O955

o

DEVELOPMENT

OF

SEAL RING

CARBON

-

GRAPHITE MATERIALS

(TASKS

Y

t

m,andTni)

by

N.J. Fechter

and

P.S. Petrunich

UNION CARBIDE CORPORATION

Carbon

Products Division

12900

Snow

Road

Parma,

Ohio

44130

prepared

for

NATIONAL AERONAUTICS

AND

SPACE

ADMINISTRATION

NASA

Lewis Research Center

Contract

NAS

3-13211

Lawrence

P.

Ludwig, Project Manager

1.

Report

No.

CR-120955

2.

Government

Accession

No.

4.

Title

and

Subtitle

DEVELOPMENT

OF

SEAL

RING

CAR

BON

-GRAPHITE

MATERIALS

(TASKS

V, VI, AND VU)

7.

Author(s)

N. J.

Fechter

and P. S.

Petrunich

9.

Performing

Organization Name

and

Address

Union

Carbide

Corporation

Carbon Products

Division

12900 Snow

Road

Parma,

Ohio

44130

12.

Sponsoring

Agency Name

and

Address

National

Aeronautics

and

Space

Administration

Washington

D. C.

20546

3.

Recipient's Catalog

No.

6.

Report

Date

August

10,

1972

6.

Performing Organization

Code

8.

Performing Organization Report

No.

10.

Work

Unit

No.

11.

Contract

or

Grant

No.

NAS-3-13211

13.

Type

of

Report

and

Period Covered

Contractor

Report

14.

Sponsoring

Agency

Code

16.

Supplementary

Notes

Project

Manager, Lawrence

P.

Ludwig,

Fluid

System Components Division,

NASA

Lewis Research Center, Cleveland,

Ohio

16.

Abstract

Carbon-graphite

seal

ring bodies

for

operation

at air

temperatures

to

1300°F

(704°C)

were manufactured

from

three

select

formulations. Selection

was

based

on the

results

of

screening studies

and an

analysis

of

prior work. Mechanical

and

thermal

properties,

porosities,

and

oxidation

rates

were

measured.

The

results

have shown:

1.

Major

property improvements anticipated from

the

screening studies

were,

not

realized

because

of

processing problems associated

with

the

scale-up

in

material

size

and

probable

deterioration

of a

phenolic

resin

binder.

2.

The

mechanical

properties

of a

phenolic resin-bonded, carbon-graphite

material

can

be

improved

by

applying high

pressure

during carbonization.

3. The

textile

form

of

graphite fiber used

as the

minor filler component

in a

carbon-

graphite

material

can

beneficially

affect

mechanical

properties.

17. Key

Words

(Suggested

by

Author(s))

19.

Security

dassif.

(of

this report)

Unclassified

18.

Distribution

Statement

20.

Security Classlf.

(of

this

page)

21. No. of

Pages

22.

Price*

Unclassified

* For

sale

by the

National Technical Information

Service,

Springfield, Virginia 22151

NASA-C-168

(Rev. 6-71)

FOREWORD

The

work described herein

was

conducted

at the

Parma

Technical

Center, Carbon Products,

Division

of

Union

Carbide Corporation, under

NASA

Contract NAS3-13211. Mr.. Lawrence

P.

Ludwig,

Fluid System

Components Division,

NASA

Lewis Research Center,

was the

Project

Manager.

Mr.

Leonard

W.

Schopen,

NASA-^Lewis

Research

Center,

was

the

Contracting Officer.

TABLE

OF

CONTENTS

Page

ABSTRACT

. i

FOREWORD.

. . ii

SECTION

I 1

SUMMARY

1

SECTION

II . 4

INTRODUCTION

-. . . . 4

SECTION

III

-....'

' " 7

CONCLUSIONS

-....'

7

SECTION

IV 8

SCREENING

STUDIES

AND

SEAL RING CARBON-GRAPHITE

MATERIAL FORMULATION (TASK

V) 8

A.

Screening Studies

8

1.

Study

of

Resin

Impregnants

17

2.

Study

of

Baking

Techniques

18

3.

Material

Subsystem Study

23

B.

Seal

Ring Carbon-Graphite

Material

Formulation

27

SECTION

V 31

MANUFACTURING

OF

CARBON-GRAPHITE MATERIALS

(TASK

VI) .31

A.

Identification

of

Materials

Manufactured

31

B.

Processing

of

Material,

Formulations

. 33

1.

Formulation-No.

1Y . . . 33

2.

Formulation

No. 1Z 36

3.

Formulation

No. 5 37

-----

-4.

Formulation

No.-

6

......

. . . . . . . . ; 7 7 . . . ' "39

5.

Formulation

No. 6Y 40

SECTION

VI 42

MATERIAL

PROPERTIES

(TASK VII)

42

A.

Property

Requirements

of

Seal

Ring

Carbon-

Graphite

Materials

42

B.

Mechanical

Properties

43

C.

Thermal

Properties

54

D.

Porosities

60

E.

Oxidation

Tests

83

.

111

TABLE

OF

CONTENTS (Cont'd)

Page

SECTION

VII 92

DISCUSSION

OF THE

RESULTS

. 92

APPENDIX

I 97

PROCEDURES USED

TO

CHARACTERIZE

RAW

MATERIALS

... 97

APPENDIX

II 98

PROCEDURES USED'TO MEASURE MATERIAL

PROPERTIES.

. . 98

APPENDDC

III .' 100

DEFINITION

OF

STATISTICAL TERMS

100

REFERENCES

102

DISTRIBUTION

LIST

104

IV

LIST

OF

TABLES

Table.

Page

I

Material Formulations Developed

Under

Tasks

I

Through

IV 9

II

Mechanical

Properties

-Resin

Impregnated

Materials

19

III

Mechanical Properties-Pressure

Cured

and

Baked

Formulation

No. 3

Material

21

IV...

Identification

of

Material Subsystems SS-47

to

SS-51

24

V

Mechanical Properties

-

SS-47,

SS-50,

and

Formulation

No.

4

Materials

26

VI

Oxidation

Test Results

27

VII

Material Formulations Nos.

1Y, 5Y, and 6Y . 28

VIII

Identification

of the

Three Basic Material Formulations

and

Their Impregnated Versions

32

IX

Mechanical Properties

-

Formulation

No. 1Z

material

....

45

X

Comparison

of

Mechanical Properties

-

Formulations

Nos.

1, IX, and 1Z

Material

46

XI

Mechanical Properties

-

Formulations

No. 5

Material. ....

48

XII

Comparison

of

Mechanical Properties

-

Formulations

Nos.

3 and 5

Material

49

XIII

Mechanical Properties

-

Formulation

No. 6Y

Material .....

51

XIV

Comparison

of

Mechanical Properties

-

Formulations

Nos.

4, 4X, and 6Y

Material

53

XV

Thermal

Conductivities

—-Formulations

Nos. IX,-

hZr - '

4X,

and 6Y

Material

. . . 55

XVI

Percent Total Porosities

-

Formulations Nos.

1, IX, 1Z,

4, 4X, and 6Y

Material

61

XVII

Pore

Volume

and

Distribution

by

Mercury Intrusion-

Formulation

No. 1Z

Material

63

XVIII

Pore

Volume

and

Distribution

by

Mercury Intrusion-

Formulation

No. 6Y

Material

66

LIST

OF

TABLES

.(Cont'd)

Table

Page

XIX

Pore

volume

and

Distribution

by

Mercury Intrusion

-

Grade

CDJ . 70

XX

Pore

Volume

and

Distribution

by

Nitrogen Desorption

-

Formulation

No. 1Z

Material

73

XXI

Pore

Volume

and

Distribution

by

Nitrogen Desorption

-

Formulation

No. 6Y

Material

.

.......;..

75

XXII

Pore

Volume

and

Distribution

by

Nitrogen Desorption

-

Grade

CDJ 78

XXIII Weight

Pickups

for

Materials

Impregnated with

No. 121

Oxidation-Inhibiting

Treatment

80

XXIV

Bulk Densities

of

Materials

Impregnated with

No. 121

Oxidation-Inhibiting Treatment (Grams/Cubic Centimeter)

... 82

XXV

Oxidation

Test

Data

for

Materials

Impregnated with

No. 121

Oxidation-Inhibiting Treatment

90

VI

LIST

OF

FIGURES

Figure

Page

1

Mean

Coefficient

of

Thermal

Expansion

-

Formulation

No. 1Z

Material

57

2

Mean

Coefficient

of

Thermal

Expansion-

Formulation

No. 6Y

Material

58

3

Mean

Coefficient

of

Thermal

Expansion-

Grade CDJ-83

59

4

Pore

Volume Versus

Pore

Diameter

by

Mercury

Intrusion-Formulation

No. 1Z

Material

. 64

5

Cumulative

Pore

Volume Versus

Pore

Diameter

by

Mercury

Intrusion-Formulation

No. 1Z

Material

...

T

....

65

6

Pore

Volume Versus.Pore Diameter

by

Mercury

Intrusion-Formulation

No. 6Y

Material

67

7

Cumulative

Pore

Volume Versus

Pore

Diameter

by

Mercury Intrusion-Formulation

No. 6Y

Material

68

8

Pore

Volume Versus

Pore

Diameter

by

Mercury

Intrusion-Grade

CDJ 71

9

Cumulative

Pore

Volume Versus

Pore

Diameter

by

Mercury IntrusionrGrade

CDJ 72

10

Percent

Pore

Volume

and

Cumulative

Percent

Pore

Volume

Versus

Pore

Diameter

by

Nitrogen Desorption-

Formulation

No. 1Z

Material

, 74

11

Percent

Pore

Volume

and

Cumulative

Percent

Pore

Volume

Versus

Pore

Diameter

by

Nitrogen Desoprtion-

Formulation

No. 6Y

Material

76

12

Percent

Pore

Volume

and

Cumulative

Percent

Pore

Volume

Versus

Pore

Diameter

by

Nitrogen Desorption-

Grade

CDJ 79

13

Oxidation Testing Apparatus

. . 84

14

Percent

Weight

Loss

Versus Exposure

Time

at

1300°F

(704°C)-Formulation

No.

1Z-121

Material

86

15

Percent

Weight

Loss

Versus Expsoure

Time

at

1300°F

(704°C)-Formulation

No.

5-121

Material.

87

16

Percent

Weight

Loss

Versus Exposure Time

at

1300°F

(704°C)-Formulation

No.

6Y-121

Material

88

SECTION

I

SUMMARY

The

purpose

of

this Contract

is to

develop

a

carbon-graphite

seal

ring

material

which will have significantly greater

life

than conventional carbon-

graphite

seal

materials

at

ambient

air

temperature

up to

1300T

(704°C).

The

carbon-graphite

material

is

being developed

for use in a

self-acting

seal

in ad-

vanced

gas

turbine engines.

.

Although high oxidation resistance

is the

primary

requirement

of the

materials

being developed, high

strength

and

good

wear

resistance

are

also

needed.

Good

wear resistance

is

necessary, since self-

acting

seals

experience relatively high speed sliding contact

during

limited

periods

of

operation. High

thermal

conducti-vity

also

is a

very

desirable

prop-

erty

for the

carbon-graphite

seal

material,

since

it

will provide rapid dissipa-

tion

of the

frictional heat generated during periods

of

sliding contact.

Topical .Reports

NASA

CR-72799

(Tasks

I and II) and

NASA

C-R-72986

(Tasks

III and IV)

cover

the

earlier

work

done

under this program.

Tasks

I

and II

included

the

selection

of

four

base

material:: systems

from

a

total

of

12

which were derived from

a

literature

survey

and

bench-scale

tests.

Task III'.

covered

the

fabrication

of

seal

rings made from seven carbon-graphite

mate-

rials

whose final heat-treatment temperature

was

2800°C:

the

four

formulations

selected

above plus resin-impregnated versions

of

three

of the

four

formulations.

Four

of the

formulations were selected

for

property

and

performance evaluation

which

was

performed

in

Task;IV.

Three

of the

materials

had

oxidation

resist-

ance,

thermal

conductivity,

and

thermal

expansion superior

to

that

of a

widely

used

commercial grade. Strength.and hardness were

low but

could

be

satisfac-

tory

for the

self-acting

seal.

This

Topical Report covers

Tasks

V, VI, and VII of the

program. Task

V

efforts

were directed

at

improving

the

strength, mechanical erosion

resistance

(hardness)

and

uniformity

of the

best

materials

from

Task

IV,

while maintaining

oxidation

resistance.

.

Eight

material/process

systems were

studied

of

which

three

were selected

for

manufacture

of

seal

rings under

Task

VI.

Selected prop-

erties

of the

three

materials

were determined under

Task

VII and

samples

were

delivered

to

NASA-Lewis

Research Center

for

evaluation.

The

Task

V

screening studies covered various resin impregnants

and

baking techniques. Graphite fibers were investigated

as a

minor filler com-

ponent

in a

carbon-graphite

seal

r.ing

material.

The

following

conclusions

were drawn:

a.

Bakelite

BRP-5095 phenolic

re-sin-furfuryl

alcohol

appears

to be

a

rnore suitable

resin

.impregnant than

the

Bakelite BRP-5095 resin-acetone

solution used during Task^III.

.

b.

Pressure

baking improved

the

mechanical properties

of a

resin-

bonded,

carbon-graphite

material;.

c. The

density

and

hardness

of

a.resin-bonded

material

containing

fibers

as its

minor filler component

can be

increased

by

substituting

Union

Carbide Corporation (UCC) Grade

WFA

graphite fibers

for

those pre-

pared from

UCC

Grade

WCA

graphite cloth.

For

Task

VI,

three

formulations listed below were selected

for the

manufacture

of

improved carbon-graphite

seal

ring bodies.

Particulate

raw

materials

included

UCC

Grade

CHP

artificial

graphite,UCC Grade

WFA

graphite fibers,

and

Commercial Solvents Corporation Thermax furnace

black.

Formulation

Filler

Material Binder Material

No.

1Y CHP

Artificial Graphite

(80

pbw)

Barret

No.

Medium

Pitch

Thermax

(20

pbw)

(60

pph)

No.

5Y CHP

Artificial Graphite

(80

pbw) Bakelite BRP-5095

Thermax

(20

pbw) Resin

(58

pph)

No.

6Y CHP

Artificial Graphite

(80

pbw) Bakelite BRP-5095

WFA

Graphite

Fibers

(20

pbw) Resin

(70

pph)

Compacts baked

to

1000°C

were impregnated with BRP-5095 resin

(35

pbw)-furfuryl

alcohol

(50

pbw) before heat-treatment

at

2800°

C.

pbw =

parts

by

weight

pph =

parts

(by

weight)

per

hundred

parts

filler

Several major processing problems resulted

from

the use of the

furfuryl

alcohol-Bakelite BRP-5095 resin-impregnant.

The

impregnant filled

the

open

porosity

of the

large

1000°C

baked compacts

so

completely that some

of

them

cracked

during

rebaking

as the

volatiles from

the

resin-impregnant tried

to

escape. This problem prevented

the

manufacture

of the

formulation

No. 1Y and

some

of the

formulation

No. 6Y

compacts.

Formulation

No. 1Z was

substituted

for

formulation

No. 1Y. The

resin impregnation

for

formulation

No. 1Z was

applied

to

2800°C

baked compacts

of the

base

material

and was

followed

by a

very

slow rebaking schedule.

Processing problems

also

were encountered during

the

attempt

to

manu-

facture

seal

ring bodies

from

formulation

No. 5Y. The

formulation

No. 5

compacts were prepared

from

one-year-old

mix

remaining

from

one of the

Task

III

formulations.

The

BRB-5095

resin binder

in the mix

apparently

had

deteriorated,

causing most

of the

formulation

No. 5

compacts

to

crack

and

laminate

during baking

to

1000°C.

The

deterioration

of the old mix was

first

noted

during

the

Task

V

screening studies

of

baking techniques. Only

a few

seal

ring bodies

of

formulation

No. 5

were successfully

manufactured

during

Task

VI.

None

of the

compacts were resin-impregnated prior

to

final heat-

treatment

at

2800°C.

Before

testing, some

of the

formulations were

given

the No. 12 L

oxidation

inhibiting

treat.

The

formulation

No.

1Z-1Z1

material

had

comparable mechan-

ical

and

thermal properties

and was at

least

as

oxidation resistant

as a

similar

material

manufactured during Task III. Formulation

No.

6Y-1Z1

material

had

comparable mechanical properties

and

oxidation

resistance_aLong

Iwith

a'higher

thermal

conductivity

and a

lower

coefficient

of

thermal

expansion than those,

of

a

similar

material

manufactured during Task III. These improvements indicate

that

the

materials

manufactured

from

formulations Nos.

1Z-121

and

6Y-121

may

be

better suited

for use as

rings

for

self-acting

seals

than

the

similar

ma-

terials

manufactured during Task III.

SECTION

II

INTRODUCTION

Introduction

of the gas

turbine engine

has

produced

sealing problems

so

severe that carbon-graphite

is one of the few

engineering materials

which

can

meet

the

requirements

of

this application. Operating conditions will become

more severe

as gas

temperatures

and

seal

sliding speeds increase. Increased

temperatures

result

from

the

higher

flight

speeds

or

higher

gas

temperatures

used

to

improve engine

efficiency;

increased

seal

sliding speeds result

fromthe.

use

of

larger

engines. Contact

type

seals

with

carbon-graphite

seal

rings

are

used

in

many current

gas

turbine engines;

however,

the

limited pressure, speed,

and

temperature capability

of the

contact

seal

restricts

this

use to

operation

below

125 psi (86

N/cm

E

)

sealed pressure

differential,

350-ft/sec.

(107 meter/sec.

)

/

) *

sliding speed,

and

800°F

(427°C)

sealed

gas

temperature.

— For

more severe

operating conditions, labyrinth

seals

are

used.

The

labyrinth

seal

systems have

higher

gas

leakage than contact

seals

and, therefore, contribute

to

easier

passage

of

debris

and to

greater

losses

in

engine

efficiency.

Recent

studies have resulted

in the

production

of a

face

seal

with

self-

acting

lift

augmentation. Since this

seal

operates

without

rubbing contact

(except

at

start

and

stop),

it has

higher pressure, speed,

and

temperature capability than

a

conventional face contact

seal.

For

this

new

generation

of

seals,

pads

are

machined

on the

seal

face

which,

during

engine operation,

act as a

thrust bearing

and

cause

the

seal

to

lift

off the

seal

seat

and

ride

on a

thin

gas

film.

— The

seal

with

self-acting

lift

augmentation ideally will experience mechanical wear

only

during

start-up

and

shut-down

of the

engine.

However,

momentary periods

of

high speed sliding contact

may

occur because

of the

close dimensional tolerances

associated

with

the

thin

gas

films.

-^

Therefore,

the

importance

of

wear resistance

cannot

be

neglected when

a

carbon-graphite formulation

is

developed

for use as a

self-acting

seal

ring

material.

*

Denotes Reference Number

High

hardness, strength,

and

modulus,

together with

the

proper selection

of

impregnants

and

mating

materials,

are

necessary

for

producing wear

resist-

ant

carbon-graphite

seal

ring

materials.

—

Increased" oxidation

resistance

will

become

a

major requirement

of

carbon-graphite

seal

rings

as

engine

gas

tem-

peratures

rise

to

1200°F

(649°C)

and

above. Development

of

improved carbon-

graphite

seal

ring

materials

which

can

operate

in

ambient

air

temperatures

up

to

1300°F

(704°

C)

will make feasible

seal

designs which will contribute

to im-

provements

in

engine performance.

Conventional

carbon-graphite

seal

ring

materials

are

prepared

by

mix-

ing

selected sizes

and

types

of

carbon

and

graphite fillers

with

a

binder such

as

coal

tar

pitch.

The

mixtures

are

formed

into

compacts

and

baked

to

tem-

peratures

which

are

adjusted

to

produce

the

desired physical properties

of the

finished

material.

Usually,

the

finished carbon-graphite

seal

ring contains

additives

or

impregnants which help

the

seal

to

meet particular performance

requirements (e.g., oxidation resistance). Specific

raw

materials

or

process-

ing

techniques

are

employed

to

obtain desired properties

of the

finished car-

bon-graphite

material.

Detailed descriptions

of the raw

materials

and

processes employed specifically

for the

preparation

of

carbon-graphite

seal

rings

are not

available

in the

literature.

Topical Report

NASA

CR-72799

-

covered

the

work

done

duringTasks

I

and II of

this Contract. Task

I

included

a

literature

search

for

information

relevant

to

carbon -graphite

materials

for

high-temperature

seal

ring applications.

Task

I

also

provided

for

selection

of

four

particulate

and

four

binder

raw

mate-

rials

for

experimental studies

and for the

selection, preparation,

and

screen

testing

of 12

material

systems. Forty-seven material/process subsystems

were

produced

and

evaluated

to

optimize

the

selected

12

material

systems.

Small

compacts measuring

2. 5

inch

x 1. 25

inch

x 1. 0

inch

(6.

35 cm x 3. 18 cm x 2. 54 cm)

were

prepared

from

the 12

optimized

material

systems

and

used

for all the

screen studies

conducted

during

Task

I. The

screen

testing

of the

compacts

of the 12

optimized

material

systems consisted

of

meas-

uring

their

bulk densities, flexural strengths,

and

hardnesses

at

room tempera-

ture

and

their

oxidation

rates

in air at

1300°F

(704°C).

The

experience gained during Task

I was

used

to

select

four

approaches

to the

manufacture

of

seal

ring carbon-graphite bodies during

Task

II.

Tests

indicated that

the

compacts prepared during

the

screen testing were significantly

more oxidation

resistant

than commercial

seal

ring Grade CDJ. Since

seal

ring

materials

must

be

made

as

strong

and

wear resistant

as

possible,

the

four

for-

mulations

that

would

produce

materials

with

the

best

combination

of

strength,

hardness,

and

oxidation resistance were selected.

Topical Report

NASA

CR-72986^-' covered

the

work

done

during Tasks

III

and IV of

this Contract. Task

III

included

the

manufacture

of

carbon-graphite

seal

ring bodies

from

the

four

formulations selected during Task

II. The

number,

size,

and

shape

of

these bodies were determined

by the

delivery requirements

of

Task

III and the

testing requirements

of

Task

IV.

Seven

materials

were ultimately

produced

during

Task

III:

the

selected

four

formulations

and a

second version

for

three

of

those formulations

in

which

the

1000°C

baked compacts were impregnated

with

a

phenolic

resin

prior

to

final heat treatment

at

2800°

C.

During

Task

IV,

four

of the

seven

materials

manufactured under Task

III

were selected

and

their

material

properties determined.

The

selection

was

based

on the

preliminary

mechanical property measurements made

on all

seven

materials.

This

Topical Report covers-Tasks

.V, VI, and VII of the

Contract.

The

scope

of

work

for

Task

V

consisted

of the

screen testing

of up to

eight

material/

process

systems

or

subsystems

for the

purpose

of

optimizing

the

particulate

systems, binder concentrations, carbonizable impregnants,

and

processing

techniques studied during Tasks

I

through

IV. The

experience gained during

the

Task

V

screening studies

was

used

to

select

three approaches

to the

manu-

facture

of

seal

ring

carbon-graphite

bodies with improved

properties.

Seal

ring

bodies were manufactured

during

Task

VI, but

processing problems necessitated

some

modification

of the

formulations. Selected

material

properties were

determined

for the

manufactured

materials

during

Task VII.

SECTION

III

CONCLUSIONS

1.

Improvements

in

mechanical properties anticipated

from

the

screen-

ing

studies were

not

realized

because

of

processing problems encountered during

scale-up

in

material

size.

Problems

Included

rupture

and

chipping

of

compacts

during

pyrolysis

of a

furfuryl

alcohol-phenolic resin^impregnant

and

lamination

during

baking

of

compacts

bonded

with

a

phenolic

resin.

2.

Pressure

curing

and

pressure baking

of a

phenolic resin-bonded

carbon-graphite

material

effects

improved

mechanical

properties.

3. A

phenolic resin-bonded,carbon-graphite

material

prepared with

chopped

graphite yarn

has

better mechanical

and

thermal

properties than

a

similar

material

prepared with chopped graphite cloth.

4.

The

materials

manufactured

from

formulations Nos.

1Z

(pitch binder)

and 6Y

(phenolic

resin

binder)

show

potential

as

useful

primary rings

for

self-

acting

seals.

.

Both formulations incorporate artificial graphite

as the

major

filler

component

(80

weight percent);

the

former contains

furnace

black

and the

latter

chopped graphite yarn

as the

minor filler component

(20

weight percent).

A

furfuryl

alcohol-phenolic

resin

impregnant

is

Introduced

prior

to

final heat-

treatment

at

2800°C.

SECTION

IV

SCREENING

STUDIES

AND

SEAL

RING

CARBON-GRAPHITE

MATERIAL

FORMULATION

(TASK

V)

A.

Screening Studies

The

carbon-graphite

seal

ring materials

developed

during

Tasks

I

through

IV

——

of

this Contract (Table

I)

have oxidation resistance several

times greater than that

of a

widely

used commercial grade,

but

their flex-

ural

strengths

are 40 to

50.percent lower than that

of the

commercial grade.

These oxidation

resistant

carbon-graphite materials were

developed

.for

use

as

self-acting

seal

rings.

Since self-acting

seals

normally employ metal

-

retaining bands,

the

strengths

of

these materials were

judged

acceptable.

Erosion resistance

may

also

be an

important requirement

for

self-acting

seal

materials.

.

Debris passing

through

the gas

film

formed

between

the

sealing

dam and the

seat

is

responsible

for the

erosion

of the

seal

face.

In-

creases

In

strength

would

mitigate

the

necessity

of

metal-retaining

bands

and

increases

in

hardness

would

improve erosion resistance. These

im-

provements

would

enable broader application

of the

carbon-graphite

seal

ring materials.

The

purpose

of

this phase

of the

Contract

was

thus

to im-

prove

the

uniformity,

strength,

and

hardness

of the

materials

manufactured

during

Task

III

—while

maintaining

or

improving

their oxidation resistance.

Included

in the new

effort

was a

review

and

analysis

of the

work

and a

screening

study

to

optimize

the

particulate systems, binder con-

centrations, carbonizable impregnants,

and

processing

techniques

studied

during

Tasks

I

through.IV.

^-'^

The

Task

V

screening

study

consisted

of

three

parts.

A

study

of

vari-

ous

resin impregnants

and

baking techniques comprised

the

first

two

parts.

The

third part consisted

of the

manufacture

and

characterization

of

five

ma-

terial

subsystems aimed

at

improving

the

uniformity

and

properties

of the

formulation

No. 4

material.

The

composition

of the

formulation

No. 4 ma-

terial,

along

with

those

of the

other materials

produced

during Task III,

—is

displayed

in

Table

I. All the

materials

presented

in

Table

I

were

manufactured

from

particulate

and

binder

raw

materials that

had

been characterized

during

Task

I.

*-§-'

The

results

for the

characterization

of the raw

materials also

are in-

cluded

in

this section

of the

report. Descriptions

of the

test procedures

used

to

characterize

the raw

materials

are

presented

in

Appendix

I.

8

w

n

I

Through

tn

x

to

ri

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(11

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Temperature

=

rtions

are

parts

by w

r

proportions

are pai

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solve

resin,

in an eqi

re at 150 "C,

rebake

1

ipregnate

with

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2

Some

of the

carbon-graphite

materials

produced

during

the

Task

V

screening study employed

two

particulate

raw

materials

which

had

previously

not

been

used

during

the

Contract work.

The two new raw

materials

were

Grade VEA. carbon fibers

and

Grade'WFA graphite fibers. Both types

of

fibers

are

produced

by

pyrolyzing

continuous

filament rayon yarn which

is

subsequently

chopped

to the

desired lengths.

The

fibers previously used

for

the

Contract work were prepared

from

Grade

WCA

graphite cloth which

is

produced

by the

pyrolysis

of

rayon

cloth.

Although

the two new

types

of

fibers

were

not

characterized

during

Task

V,

some

of

their

properties were obtained

from

"Union Carbide Corporation Technical Information Bulletin

No.

465-213 cj."

The

brochure

lists

a

density

(water

immersion)

of 1". 8

g/cc and.a weight percent

ash of 0. 8 for the

Grade

VFA

carbon fibers. Grade.

WFA

graphite fibers

are

reported

to

have

a

density (water immersion

) of 1.4

g/cc,

a

surface

area

of

2m

2

/g, and.

a

weight percent

ash of 0. 01.

10

1.

Union

Carbide Corporation Grade

CHP

Artificial Graphite

Helium

Density

=

2.22 g/cc

Surface

Area

= 6.7

m

2

/g

Chemical

Analysis

%

Ash =

0.066

%

Moisture

=

0.039

Emission Spectrographic

Analysis

(Semi-Quantitative)

Screen Analysis

On 35

mesh

= 0%

On 65

mesh

= 0%

On

100

mesh

= 0%

On

150

mesh

=

0.08%

On

200

mesh

=

3.30%

On

Pan =

96.62%

Al

Ti

V

Fe

Ni

Cr

Si

Ca

Mg

Pb

Sn

Ag

B

Na

Cu

7 ppm

37

ppm

23

ppm

44

ppm

5 ppm

5

ppm

60

ppm

162 ppm

5

ppm

5

ppm

5

ppm

5

ppm

6 ppm

5

ppm

5

ppm

11

2.

Commercial Solvents Corporation Thermax Furnace Black

Helium Density

=1.84 g/cc

Surface Area

= 8.1

m

2

/g

Screen Analysis*

On

35

mesh

=

3.97%

On

65

mesh

=

36.91%

On

100

mesh

=

15.74%

On

150

mesh

=

13.44%

On

200

mesh

=

10.84%

On

Pan =

19.10%

Chemical

Analysis

%

Ash

=0.022

%

Moisture

=

0.027

Emission Spectrographic

Analysis

(Semi-Quantitative)

Al <

Ti <

V <

Fe <

Ni <

Cr <

Si

=

Ca

=

Mg

=

Pb

=

Sn <

Ag <

B =

Na

=

Cu <

5

33

11

5

23

5

ppm

* The

presence

of

aggregates

appears

to

have

a

significant

effect

on the

results

of the

screen

analysis.

12

3.

Lockheed

Company

LMSC

Glassy Carbon

(Ground)

Helium

Density

=

1.91

g/cc*

Surface

Area

= 5.6

m

2

/g

Screen Analysis

On 35

mesh

= 0%

On 65

mesh

= 0%

On 100

mesh

=

0.41%

On

150

mesh

=

18.42%

On 200

mesh

=

21.98%

On Pan =

59.19%

Chemical

Analysis

%

Ash

=0.92

%

Moisture =0.85

Emission

Spectrographic

Analysis (Qualitative)**

+

Major-

+

Minor-

+

Trace-

•Fe

Cr

Ni

Mn

Sn->-

Si

Al

Ca

Cu

Mg

Ag-

* A

prolonged period

was

required

for the

Beckman

pycnometer

to

reach equilibrium conditions and,

therefore,

the

results

are

questionable.

** No

standards

available

to run

semi-quantitative

analysis.

13

4.

Union

Carbide Corporation Grade

WCA

Graphite Cloth

Helium

Density

=

1.43

g/cc*

Surface

Area

= 1.3

m

2

/g

Chemical

Analysis

%

Ash

=0.04

-

%

Moisture

=

0.03

Emission

Spectrographic

Analysis

Semi-Quantitative

Al <

Ti

=

V <

Fe <

Ni <

Cr <

Si

=

Ca <

Mg <

Pb <

Sn <

Ag <

B <

Na

=

Cu <

5

7

5

13

5

ppm

ppm.

* A

prolonged period

was

required

for the

Beckman

pycnometer

to

reach

equilibrium conditions and,

therefore,

the

results

are

questionable.

14

5.

Barrett

No. 30

Medium Coal

Tar

Pitch

Helium

Density

=

1.33 g/cc

Coking Value

=

57.4%

Benzene Insoluble

=

32.1%

Quinoline Insoluble

=

13.1%

Softening Point

=

100.3°C

Elemental Chemical Analysis

C =

93.62%

H =

4.29%

0 =

1.56%

N

=

0.92%

S =

0.44%

Emission Spectrographic Analysis

(Qualitative)*

+

Major-

+

Minor-

+

Trace-

Fe

Pb-»-

Si

Al

Ca->-

Zn->-

Mg

Mn

Cu-*-

Differential

Thermal Analysis

Endotherm

at

55°C.

Endotherm

at

440°C.

Exothermic jump

at

535°C.

which

is

coincidental with

3%

weight

loss.

Exothermic rise maximum

at

645°C.

Thermal Gravimetric Analysis

Essentially

constant weight

to

200°C.

Gradual loss between 200°C

and

260°C.

-1%

at

260°C.

Increasing rate

of

loss

between 260°C

and

335°C

Steady

rate

of

loss from

335°C

to

460°C

and

605°C

to

800°C with

a

slightly

lower rate

of

loss between

460°C

and

605°C.

-10%

at

370°C.

Overall loss

of 83% at cut

off of

800°C

Volume Change After Baking**

1000°C

Baked Volume

Green Volume

2800°C

He

at-Treated

Volume

Green Volume

=

0.871

=

0.843

* No

standards available

to run

semi-quantitative analysis.

**

Measured

for

compacts containing

80 pbw CHP

graphite,

20 pbw

Thermax,

and 60 pph No. 30

Med. Pitch.

15

6.

Bakelite BRP-5095 Phenol-formaldehyde Resin

Helium

Density

=

1.28 g/cc

Coking Value

=

65.4%

Elemental Chemical Analysis

C =

75.86%

H =

6.13%

0 =

16.80%

N

=

2.44%

S =

None

Emission Spectrographic Analysis

(Qualitative)*

+

Major- +Minor-

Si-

Mg

•fTrace-

t-Fe

Cu

Al

«-Ni

Cr-»-

Mn-»-

'Differential Thermal

Analysis

.

Small

exotherm

at

165°C

which

is

just

at the

beginning

of 5%

weight

loss.

Very

broad exothermic rise

beginning

at

540°C.

Thermal Gravimetric Analysis

Essentially constant

weight

to

160°C.

Gradual loss between

160°C

and

265°C.

Plateau between 265°C

and

370°C

at

approximately

5%

loss.

-10%

at

445°C.

Steady loss between 370°C

and

540°0....

Increasing rate

of

less

to

600°C.

Steady

loss rate

to cut

off

at

750°C.

Overall loss

of 88% at

cut

off of

750°C.

Volume Change After Baking**

1000°C

Baked Volume

Green Volume

2800°C

Heat Treated

Volume

Green

Volume

=

0.704

0.649

* No

standards available

to run

semi-quantitative analysis.

**

Measured

for

compacts containing

80 pbw CHP

graphite,

20 pbw

Thermax,

and 58 pph

Bakelite

BRP

5095 resin.

16

1.

Study

of

Resin-impregnants

Carbonization

of a

resin-impregnant

was

found

during

Task

III

—

to

significantly improve

the

strength,

hardness,

and

modulus

of a

carbon-

1

t \

graphite

material.

The

resin-impregnant used during

Task

III—

was a

solu-

tion

of

Bakelite BRP-5095

resin

(50 pbw [

parts

by

weight])

and

acetone

(50

pbw).

After

the

compacts were baked

to

1000°C,

they were impregnated

with

the

resin

solution

by

using

a

vacuum-pressure technique.

The

resin-

impregnated compacts were subsequently pressure-cured

at

150°C

and

rebaked

to

1000°

C

prior

to

final

baking

to

2800°

C.

A

screening

study

of

various resin-impregnants

was

conducted

during

Task

V to

find

a

more

suitable

resin-impregnant than that used during

Task

III.

— The

principal objective

of

this

investigation

was to

find

a

liquid

resin

to

replace

the

acetone

as the

vehicle

for

dissolving

the

Bakelite

BRP-5095

resin.

A

liquid

resin

would

contribute

to the

coking value

of the

resin-impregnant, whereas,

the

acetone contributes nothing,

since

it is

com-

pletely driven

off

during curing.

The

investigation

was

begun

by

determining

the

solubility

of the

Bakelite

resin

in

various liquid

resins.

Varcum 8251

(partially polymerized

furfuryl

alcohol)

was

found

to be a

poor

resin

for

dis-

solving

the

Bakelite

resin.

Only

25 pbw of the

Bakelite

resin

could

be

dissolved

in 50 pbw of the

Varcum

8251

resin,

and the

resultant

solution

was too

viscous

to be

used

as an

impregnant.

Furfuryl

alcohol

monomer

was

found

to be

better

than

the

Varcum

8251

resin.

A

solution

suitable

for use as an

impregnant

was

obtained

by

dissolving

35 pbw of the

Bakelite

resin

in 50 pbw of the

furfuryl

alcohol.

A

second

solution

suitable

for use as an

impregnant

was

prepared

by

dissolving

50 pbw of the

Bakelite

resin

in 50 pbw of

furfural.

The

second portion

of the

resin-impregnation study consisted

of

impregnating

small

(4

-inch

x 1/2

-inch

x

1/4-inch [10.2

cmx 1.3

cmxO.6 cm])

1000°C,baked

samples

of the

formulation

No. 1

material

(Table

I).

Three

resin-impregnants were investigated:

the two in

which

furfuryl

alcohol

and

furfural

were used

to

dissolve

the

Bakelite

BRP-5095

resin

and a

third con-

sisting

of

Varcum 8251

(98

pbw)

and

oxalic

acid

(2

pbw).

The

formulation

No. 1

samples

were vacuum evacuated, impregnated, pressure-cured

to

150°C

or

pressure-baked

to

550°C,

and

rebaked

to

1000°C.

The

results

of the

resin-

17

impregnation studies

are

displayed

in

Table

II.

After

the

samples, were

re-

baked

to

1000°Cj

the

measured

increases

in

weight ranged between

4. 5 and

6.

5

percent

for the

three

types

of

resin-impregnated

materials.

These

in-

creases

in

weight resulted.in improvements

of 26 to 45

percent

in the

1000°C

baked"flexural

strengths.

The

Bakelite BRP-5095

resin

(50

pbw)

and

acetone

(50

pbw) solution used during

Task

III—

effected

only

a 1.6

percent increase

in the

weight

of the

formulation

No. 1

material

after

it was

rebaked

to

1000°C.

The

higher yields

of

residual carbon

from

the

three

resin impregnants thus

produced

greater

improvements

in

physical properties than

did the

Bakelite

resin-acetone

solution used during Task

III.

—

Although these improvements

were determined

for

1000°C

baked

material,

they were expected

to

carry

over

to

the

2800°C

baked

material

as

well.

The

goal

of

this investigation

was to

find

a

resin

impregnaht

which

would

effect

large

improvements

in the

strength, hardness,

and

modulus

of

a

carbon-graphite

material.

Of the

resin

impregnants studied,

the one

con-

sisting

of

furfuryl

alcohol

(50

pbw)

and

Bakelite BRP-5095

resin

(35

pbw)

•appeared

to be the

best

for

fulfilling

this goal.

This

investigation

also

showed

that

pressure-curing

a

resin

impregnant

to

150°C

produced

the

same

strength

and

hardness

as

that obtained

by

pressure baking

to

550"C. This observation

was

made

for the

formulation

No. 1

samples

impregnated

with

the

furfural

(50

pbw)-Bakelite BRP-5095

resin

(50

pbw) solution (Table

II).

2.

Study

of

Baking Techniques

Pressure

curing

and

pressure baking were

two

techniques

in-

vestigated

to

improve

the

properties

of the

materials

developed

under

Tasks

I

through

IV.

——

The

baking

of a

pitch-bonded, carbon-graphite

body

while

subjecting

it to a

mechanical constraint

at

elevated pressure exerted

by ah

inert

gas has

been

shown

to

result

in an

improvement

in

mechanical

proper-

ties.

— The

improvements

are due in

part

to an

increased coke yield

from

the

pitch binder

phase.

18

TABLE

II

Mechanical

Properties

- Re

sin-Impregnated

Materials

1000°C

Baked

Density

(g/cc)

Flexural

(psi)

Strength

(N/cm

2

)

Rockwell

Rs

Hardness

Rm

Formulation

No.

1-No Impregnant

Maximum

Minimum

Average

Standard Deviation

n

1.657

1.650

1.653

0.003

4

5430

4880

5170

231

4

3740

3360

3560

159

4

97

94

96

1

8

61

55

59

2

8

Formulation

No.

1-Impregnated With Varcum 8251

(98

pbw)

+

Oxalic

Acid

(2

pbw)-Pressure Cured

Prior

to

Baking

to

lOOO'C

Maximum

1. 750

Minimum

1. 722

Average

1. 742

Standard Deviation

0. 013

7350

6150

6750

556

4

5060

4240

4650

383

4

118

116

117

1

8

Formulation

No.

1-Impregnated

With

Furfuryl Alcohol

(50

pbw)

+

Bakelite

BRP-5095

(35

pbw)-Pressure Cured

Prior

to

Baking

to

1000

0

C

Maximum

Minimum

Average

Standard Deviation

n

1. 748

1. 740

1.744

0. 004

4

7890

7160

7500

301

4

5440

4930

5170

207

4

116

108

114

3

8

Formulation

No.

1-Impregnated

With

Furfural

(50

pbw)

+

Bakelite BRP-5095

(50

pbw)-Pressure Cured

to

150"C

Prior

to

Baking

to

1000°C

Maximum

Minimum

Average

Standard Deviation

n

1.759

1. 754

1. 757

0.002

4

7050

6080

6510

411

4

4860

4190

4490

283

4

118

116

117

1

8

Formulation

No.

1-Impregnated

With

Furfural

(50

pbw)

+

Bakelite BRP-5095

(50

pbw)-Pressure Baked

to

550"C

Prior

to

Baking

to

1000"C

Maximum

Minimum

Average

Standard Deviation

n

1. 767

1. 763

1. 765

0. 002

4

7250

5740

6510

641

4

5000

3950

4490

442

4

-

-118

116

117

1

8

99

94

96

2

8

96

88

95

3

8

98

96

97

1

8

99

96

98

1

8

Note:

Density, flexural strength,

and

hardness measured

on

1/4"

x

1/2"

x 4"

(0.

6 cm x 1. 3 cm x 10. 2 cm)

samples.

Flexural

samples broken

on 1.

875"

(4.

76 cm)

span.

R

6

Scale

-

1/2" (1.3

cm)

Diameter

ball

and 100 Kg

Maj.

load.

Two

readings

per

sample.

R

m

Scale

=

1/4" (0.6

cm)

Diameter

ball

and 100 Kg

Maj. Load.

Two

readings

per

sample.

Pressure-curing

done

using

100

psig Air. While under

pressure,

temperature

maintained

for 1

hour

at

125°C

and 1

hour

at

150°C.

During

pressure-baking, temperature rushed

to

150°C,

followed

by a

10°C/hour

rate

between

150°C

and

550°C.

Temperature held

4

hours

at

550°C.

19

During

the

Task'V

baking.studies,-,.

the

.one-year -old

r,e,sinrhorid:e.d

formulation

No. 3 mix

(Table

I)

remaining

from

Task

III—

was

used. Twelve

green compacts measuring

2.

5-inch

x 1.

25-inch

x 1.

0-inch

(6.

35 cm x 3. 18 cm x 2. 54 cm)

were molded from

the

formulation

No. 3

mix.

The

compacts were molded

to a

green bulk density range

of

1.400

to

1.415 g/cc,

a

range

which

had

been determined during Task

III—

to be the

optimum molding

condition

for the

formulation

No. 3

material. Four

of the

green compacts sub-

sequently were pressure-cured

at

150°C

and

four

were pressure-baked

to

550°C,

These

eight compacts

and the

remaining

four

green compacts were then baked

to

1000°C

by

employing

the

standard packing procedure-and baking schedule

(10°C/hr)

used

to

bake

the

formulation

No. 3

material

during Task III.

^—'

The

twelver"

compacts were

not

baked

to

2800°C

but, .instead, were analyzed after

they

had

been baked

to

1000°C.

The

mechanical properties

of the

three

variations

of the

formu-

lation

No. 3

material

are

displayed

in

Table

III.

The

results

show

that both

the

pressure-curing

and

pressure-baking techniques yielded

improved

mechanical

properties.

Incorporation

of the two

techniques

into

the

processing

of the

for-

mulation

No. 3

material

resulted

in

increased coke yields

and

greater shrinkage

during

baking, both

of

which contributed

to the

improvements

in

mechanical

properties. However,

the

pressure baking

to

550°C

prior

to

baking

to

1000°C

resulted

in the

greater

improvement.

The

results presented

in

Table

III do

show

the

benefits

of em-

ploying

pressure baking,

but the

1000°C

baked density listed

for the

formulation

No.

3

standards

was

much lower than that

(1. 519

g/cc) measured

for the

same

material

during

Task

III.

— The

reduction

in

baked density indicated that

the

resin

in the

formulation

No. 3 mix may

have deteriorated during

the

one-year

period between

mix

manufacture (Task

III

—)

and the

Task

V

work.

20

r—

1

'£n

1)

nj

^

ro

o"

z

f—t

j

o

C^J

i~i

^

£

M

O

f

T1

T3

<l)

«J

pQ

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l

r"j

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Mechanical

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n

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1.413

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1.407

1.410

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n

No.

3-Green Compacts

Pressure

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1.403

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1.406

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4

lities

Calculated

From

Physical

Dimens

ural

Strengths Measured Using 0.200"

x

Flexural

Samples Broken

on a 0.

950"

(

tale

=

1/2"(1.

3cm) Diameter

Ball

and 1(

Pressure

Curing Done Using

100

psig

Ai

for

1

Hour

at

125°C

and I

Hour

at

150'

During

Pressure

Baking Temperature

R

150°

C

arid

550°C.

Temperature Held

uj

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Q

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21

The

pressure baking

(550°C)

analysis discussed thus

far in-

volved

the use of the

small

samples

of the

formulation

No. 3

material.

No

problems were encountered

when

pressure-baking

the

small

samples.

Prob-

lems

occurred during

the

initial

pressure-baking

trials

with

large

compacts

of

the

formulation

No. 3.

material.

Several

of the

5-inch (12.

7 cm)

diameter

greenplugs :and

the

large

green ring blanks molded

from

the

formulation

No. 3

mix

during

Task

111^-'were pressure-baked

to

550°C

during

Task

V.

.All

the

large

compacts were

found

to

have cracked and/or laminated during pressure-

baking,

and

they

all

possessed

a

pungent

odor

characteristic

of

ammonia.

Ammonia

is one of the

compounds

formed

when

the

hexamethylene-tetramine

("hexa") hardening agent reacts

with

the

thermoplastic novolac

of the

first

stage

of the

Bakelite BRP-5095 resin binder

raw

material. Apparently,

the

products

of

reaction were given

off

suddenly

during

pressure-baking, resulting

in

cracking

and

laminating

of the

compacts.

The

large compacts

of the

for-

mulation

No. 3

material

could

be

successfully

pressure-baked

to

550°C

if

they

were

first pressure-cured

at

150°C

for

several hours.

The

pressure-curing

partially

decomposes

the

"hexa"

and

allows

the

reaction

by-products

to be

evolved

without

disrupting

the

internal structure

of the

molded

material.

The

formulation

No. 3

material

had the

lowest

oxidation rate

of

the

carbon-graphite materials characterized

during

Task

TV, — but

its.

mechanical properties

and

related wear resistance were rather poor.

The

results

of the

Task

V

study

of

baking techniques indicated that

the

pressure-

baking might

be

used

to

Improve

the

properties

of the

formulation

No. 3

material

in

spite

of the

apparent resin deterioration. Incorporation

of

pressure-baking

into

the

processing

of the

formulation

No. 3

material

would

increase

the

coke

yield

and

shrinkage

of the

material during baking, thus

producing

an

improvement

in

mechanical properties

and a

reduction

in

total

open

porosity. Increased oxidation resistance

should

result from

the

reduc-

tion

in

total

open porosity.

22

3.

Material

Subsystem

Study

The

compositions

of the

five

material

subsystems analyzed

during

Task

V are

listed

in

Table

IV. The

five

materials

were processed

in

an

attempt

to

optimize

the

composition

of the

formulation

No. 4

base

material

(Table

I).

Specifically, changes

in the

minor filler component

and

binder con-

centration were investigated which could yield improvements

in the

uniformity,

strength, hardness,

and

oxidation

resistance

of the

resultant

material.

All

five

material

subsystems were

similar

to

formulation

No.

4 in

that they included some form

of

fiber

as a

minor filler component.

Grade

WFA

graphite fibers chopped

from

yarn were used

in

subsystems SS-47,

SS-48, SS-49,

and

SS-51

rather

than

the

fibers prepared

from

Grade

WCA

graphite cloth.

The

latter

type

of

fiber

was

used

as the

minor filler component

in the

formulation

No. 4

material.

Subsystem SS-50 incorporated Grade

VFA

chopped

carbon fibers

as the

minor filler component.

The

individual Grade

VFA

and WFA

fiber filaments were approximately 1/4-inch (0.64

cm)

long

prior

to

milling.

Subsystems. SS-47

to

SS-51 were

all

bonded

with

Bakelite

BRP-5095

resin.

Small

green compacts measuring

2.

5-inch

x 1.

25-inch

x

1.0-

inch

(6. 35 cm x 3. 18 cm x 2. 54 cm)

were molded

from

the

mixes manufactured

from

subsystems SS-47

to

SS-51.

After

the

compacts were baked

to

1000°C,

their

bulk densities were measured

and

their

internal

structures examined.

The

1000°C

baked compacts

of

subsystems SS-48, SS-49,

and

SS-51 were

all

found

to be

extremely porous, apparently

due to an

outgassing problem.

This

same

outgassing problem

had

been noted during

Task

I,

\r_but

was

remedied

at

that time

by

revising

the

baking schedule.

The

binder levels

of

subsystems

SS-48, SS-49,

and

SS-51 were apparently

too

high

for the

respective particulate

filler

systems, since

the

revised baking schedule

did not

prevent

the

outgassing

problem. Based

on the

analysis

of the

1000°C

baked compacts, molding

pres-

sures

of

15,000

psiU-Q

340

N/cm

2

)

and 10, 000 psi

(6890

N/cm

2

)

were selected

as

the

optimum molding conditions

for the

SS-47

and

SS-50

materials,

respectively.

The

compacts molded

at

these

pressures were subsequently final baked

to

2800°C.

23

1—

i

w

PQ

H

»—

t

ui

i

CO

co

o

4-J

r~

tt<

co

w.

Cfl

6

(L)

j *

10

>,

CO

,0

3

CO

1—1

flj

• rH

!H

0)

4->

S

<*H

O

C

O

.^

.)-»

Ri

o

VH

JJ

c

<D

TD

i—

(

A)

u *

o a,

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&o

.

T3 fi

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5*

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0)

m

(0

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A^

Mja

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o

in

ii

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2K

IL

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o3

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ro

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la "I

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:

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to to £ to

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M (M (M <-< M

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W

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w w tn w to

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h

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to I

°5™

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bfi

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m

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13

ra n

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h h M

<u

n) rt

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<•§,&

0)

o

Z

24

Table

V

displays the.

mechanical

properties measured

for the

small,

2800°C

baked compacts

of

subsystems SS-47

and

SS-5Q

(the properties

measured

for

small

compacts

of

formulation

No. 4

have been included

for

com-

parison).

The

SS-47

material

was

found

to

shrink

more than

the

formulation

No.

4

material

during baking.

The

total porosity

of the

SS-47

material

was

17.

6

percent compared with

22. 1

percent

for the

formulation

No. 4

material.

(The

procedure

for

calculating

the

percent total porosity

of a

material

is ex-

plained

in

Section VI-D

of

this report.

) The

SS-47

material

also

had a

higher

2800°C

baked bulk density

and

hardness,

and the

properties

were

more

uniform

than

those

of the

formulation

No. 4

material.

The

mechanical properties

of the

SS-50

material,

which contained Grade

VFA

carbon fibers, were

not so

uniform

nor

quite

so

good

as

those

of the

SS-47

material.

Table

VI

presents

the

1300°F

(704°C)

oxidation test results

generated

when untreated

samples

of

materials

SS-47, SS-50, formulation

No. 4,

and

commercial Grade

CDJ

were examined.

The

oxidation test procedure

was

the

same

as

that used during

Tasks

I and IV.

-Si

1

—

Due to the

required rebuilding

of

the

furnace used

for

oxidation testing,

— it

would

be

misleading

to

compare

the

Task

I

oxidation test results with those displayed

in

Table

VI. The

oxidation

rate

determined

for the

SS-47

material

was the

same

as

that measured

for the

formulation

No. 4

material.

.

Since Grade

VFA

carbon fibers

are not so

crystal-

line

as

Grade

WFA

graphite fibers, they should

not be so

oxidation resistant.

Therefore,

the

lower oxidation

rate

determined

for the

SS-50

material

probably

can be

attributed

to the

higher binder level

(80

pph)

of the

material

rather

than

the use of

Grade

VFA

carbon fibers.

The

purpose

of the

Task

V

subsystem

study

was to

produce

a

formulation

No. 4

type

material

with improved

and

more uniform

material

properties.

The

SS-47

material

was

found

to be the

best

one for

fulfilling

the

goal

of the

subsystem study. Although

no

further

improvement

in

oxidation

resistance

was

achieved, subsystem SS-47 resulted

in a

material

with more

uniform

and

slightly better mechanical properties than those

of the

formulation

No.

4

material.

25

TABLE

V

Mechanical

Properties

-

SS-47, SS-50,

and

Formulation

No. 4

Materials

Material

Bulk

Density*

Green Density

(g/cc)

Maximum

Minimum

Average

Standard Deviation

n

1000°C

Density

(g/cc)

Maximum

Minimum

Average

Standard Deviation

n

2800

°C

Density

(g/cc)

Maximum

,

Minimum

Average

Standard Deviation

n

Flexural

Strength**

Maximum

Minimum

Average

Standard Deviation

n

Rockwell

"S"

Hardness***

Maximum

Minimum

Average

Standard Deviation

n

SS-47

1.445

1.442

1.444

0.002

3

1.442

1.428

1.434

0.007

3

1.494

1.485

1.490

0.005

3

(psi)

4610

4080

4270

199

6

(N/cm

2

)

3180

2810

2940

137

6

51

43

49

3

8

SS-50

1.343

1.334

1.

338

0.005

3

1.352

1.

330

1.343

0.012

3

1.489

1.449

1.472

0.021

3

(psi)

(N/cm

2

)

4480

3090

3390

2340

3860

2660

392 27Q

6 6

39

21

32

7

8

Formulation

No.

4

1.431

1.426

1.428

0.002

3

1.364

1.

345

1.356

0.007

3

1.437

1.416

1.428

0.008

3

(P*i)

4590

3680

4020

325

6

(N/cm

2

)

3160

2540

2770

224

6

38

23

32

6

8

*

Calculated from physical dimensions

and

weights measured

for

compacts'.

**

Measured using

0.

200"xO.

200"x2. 00"(0. Slcmx

0. 51 cmx 5.

1cm)

samples.

Flexural

samples broken

on

0.950" (2.41

cm)

span.

*** R

s

Scale 1/2"

(1.

3cm) diameter

ball

and 100 Kg

Maj. load.

Four

readings

on

two

samples

of

each

material.

26

TABLE

VI

Oxidation

Test Results

Average

Cumulative.

Material

SS-47*

SS-50*

Formulation

No. 4**

CDJ**

1/2 Hr

5.47

3. 02

7.

99

8. 84

1

14

7

18

26

Hr

.25

. 56

.20

. 33

1-1/2

Hr

23.

12.

26.

43.

15

45

58

16

Percent

Weight

Loss

2

35

19

36

59

Hr

.42

.63

.56

.40

2-1/2

Hr

45.

28.

45.

72.

84

46

22

17

3

53

34

53

80

Hr

. 14

. 33

.06

. 70

*

Three untreated

samples

tested.

** Two

untreated

samples

tested.

Sample

size 1/2"

x

1/2"

x

1/2"

(1. 3cm

x.l.

3cm

x;l. 3cm).

Oxidation

temperature 1300°F

(704°C).

B.

Seal

Ring Carbon-Graphite Material Formulation

At

the

conclusion

of the

Task

V

screening studies, three approaches were

selected

for the

manufacture

of.

seal

ring carbon-graphite bodies.

The

selection

of

the

three

material

formulations, which included

the

required processing tech-

niques,

was

based

on the

results

of the

Task

V

screening studies

and

review

of

r

( \

the

work

done

under

T.aslcs

I

through

TV.

^=U

—

The

three selected formulations

represented

the

most promising approaches

for

improving

the

uniformity,

strength,

and

oxidation resistance

of the

seal

ring

materials

manufactured

during Tasklll.—

TWO

of the

formulations were

to be

manufactured

by

using-

i-n-process

material

re-

maining

from

Task III.

—

Table

VII

displays

the

compositions

of the

selected three

material

formulations.

27

vO

cU

>

H

PQ

H

W

O

en

C

o

•

-H

-l->

nt

r-H

'I

0)

4->

iti

Baking

Procedure

i

.36

™

4)

» K

«

n) •-<

(V <4

OH

.H

Binder

Mater

T)

^^,

53

» M

S <o

13

•iH

>

•M t>

M rt

(S^

_g

7J

^

gl

h^

™

SJ o t i

o

^

**

^

AJ

gj fl) °

&

"^ 0

Bake Green Compacts

tc

1000°C.

Impregnate

Cot

with

Re sin

-Solution,

Pr<

Cure

at

150°C,

and

Reb;

1000°C.

Final

Bake

to 2f

7.S

43 to

(X H)

O

^

in

m

Qfv

oS

"o

'

1—

1

p[J

<rt

3

U3 43

**<•**

in

^ rtj ^**

^4 pQ >Ii

•2^

*o

p,

* •*-*

7

(X

o

00

u

•"••

"?

•S 43

5s

^H

rt M

'o *^

•M

«

<H

X

o

i-H

JS

'

n)

M U

L CQ 4> *J °

g

<U

<D

a, C

rt

0

Pressure

Cure Green

Ci

pacts

at

150°

C.

Pressui

Compacts

to

550°

C. Bal

Compacts

to

1000°

C. Im

nate Compacts with Res:

Solution,

Pressure

Cur«

150°

C, and

Rebake

to 1C

Final

Bake

to

2800°C.

7.s

43 to

O. 0)

o "4

in m

~"

o-

"o

°

t

ftf'

**^

H •-* rQ

t£n <U Ct

^ .^i

S)

n) JJj

«.a

0)

S —

7

"fx

o

oo

<u

•S

"?

0^43

rt *^

oS

la

" 6

*^j

t;

<H

X

o

in

Same

as

that used

for

Formulation

No. 5Y.

T.S

(X V

u">

m

o^

"o

"^

_

1 Q*

<«

a

3

43

<«

a> P.

0

rt ^

Uj

D3

^

&

«.s

0}

a»

S^-

•H«5-S.

i-H

"

P<

«ui ft

l°°

03

mC

7^

tx

5

0

43

00

^

—

o

4)

d

'S <n

43 ™

(5e

2

*

2'2

<H

P.

*^j rt

^^

S

^

o

^

>o.

m

0)

d

fi

ft

rt

M

D

I

y

d

(X

^J*

43

00

'w

.0

m

i

0

o

l-H

V

o.

•«

?

00

43

'«

3 ?

77 >»

00

.^"

••-1

m

Q)

-M

I R

43

to M

S.

§

SI

C

0

0 fH

M

L,

o

5

2

1

p. (Q

0)

«

28

Formulation

No. 1Y is the

same

as

formulation

No. IX

(Table

I)

except

for

the

resin

impregnant.

The

letter

"Y"

following

the

formulation number

was

used

to

denote impregnation

of the

1000°

C

baked compacts with

a

solution

consisting

of

furfuryl

alcohol

(50

pbw)

and

Bakelite BRP-5095

resin

(35

pbw).

The

resin

impregnant

was

found

to be the

best

of

those studied during

Task

V

for

producing significant improvements

in the

density, strength,

and

hardness

of

the

formulation

No. 1

base

material.

Impregnation

of the

formulation

No. 1

base

material

with

the

furfuryl

alcohol

-

Bakelite

resin

solution yielded con-

siderably more residual carbon after baking

to

1000"C

than that obtained when

the

same

material

was

impregnated with

the

Bakelite BRP-5095

resin

(50

pbw)-

acetone

(50

pbw) solution during

Task

III.

— The

formulation

No.

IX.material,

which

was

impregnated with

the

Bakelite resin-acetone solution,

was

felt

to be

the

best

material

of

those characterized during Task

IV

—for

meeting

the re-

quirements

of a

self-acting

seal

material.

Due to the

higher residual carbon

yield resulting from

the use of the new

resin

impregnant,

the

formulation

No.

1Y

material

was

expected

to be a

significant improvement over

the

formu-

lation

No. IX

material.

The

formulation

No. 1Y

material

was to be

manufac-

tured

from

the

formulation

No. 1 mix

remaining

from

Task. III.

—

The

formulation

No. 5Y

material

was to be

manufactured,

from

the

for-

mulation

No. 3

mix.(Table

I)

remaining from Task.III.

— As

mentioned

previously

in

Section'IV^A-2,

the

resin

binder

in the

one-year-old formulation

No.

3 mix

apparently

had

degraded during

the

time

between

manufacture

of the

mix and

reuse during

the

Task

V

baking studies. Although

the

"aged"

formu-

lation

No. 3 mix

produced

a

low-density baked

material,

the use of the mix in

the

manufacture

of the

for-mulation

No. 5Y

material

was

felt

to be a

valuable

addition

to the

further

development

of

the

:

pressure baking

and

resin-impreg-

nation techniques.

The

formulation

No. 5

base

material

was the

same

as

that

manufactured

from formulation

No. 3

with

the

exception that formulation

No. 5

incorporated pressure curing

and

pressure baking,

in its

processing.

Pressure

baking

was

included.in

the

formulation

No. 5

processing, since that technique

had

been

found

during Task

V to

yield significant improvements

in the

mechani-

cal

properties

of the

resin-bonded formulation

No. 3

material.

Pressure

curing

was

included, since

it had

been

found

during

Task

V to be a

required step before

pressure

baking

large

compacts.

The use of the

furfuryl

alcohol-Bakelite BRP-

5095

resin

impregnating solution

was to be

extended

to the

processing

of the

formulation

No. 5Y

material.

29

Formulation

No. 6Y was

similar

to

formulation^No.

-4X

(Table

I)

from

whichmaterial

was

manufactured

during Task III.

— The

formulation

No. 6Y

material,

however,

was to be

impregnated

with

the

furfuryl

alcohol-Bakelite

BRP-5095

resin

solution rather than

the

Bakelite BRP-5095 resin-acetone

solution used

in the

processing

of the

formulation

No. 4X

material.

The use

of

pressure

curing

and

pressure

baking

was

extended

to the

processing

of the

formulation

No. 6

base

material. Unlike

the

formulation

No. 4

base

material

which

contained

a

minor filler

component

(20

pbw)

of

fibers prepared

from

Grade

WCA

graphite cloth,

the

formulation

No. 6

base

material

included

Grade

WFA

chopped graphite fibers

as a

minor filler

constituent

(20

pbw).

The

Task

V

subsystem

study

revealed

that

the use of

Grade

WFA

fiber

results

in

an

increase

in the

shrinkage

of the

material

during

baking.

Due to the in-

crease

in

shrinkage

and

reduction

in

porosity,

the

material

(SS-47)

containing

the

Grade

WFA

graphite fibers

had

more

uniform

and

slightly better mechani-

cal

properties than those

of the

formulation

No. 4

material.

Although

the

formulation

No. 6

base

material

also

was to be

bonded

with

Bakelite BRP-5095

resin,

its

binder level

(70

pph)

was

slightly higher than that

of the

formulation

No.

4

material

(67.

5

pph).

. The

binder level

was

increased

in an

attempt

to

further

improve

material

properties.

30

SECTION

V

MANUFACTURING,

OF

CARBON-GRAPHITE MATERIALS

(TASK

VI)

A. .

Identification

of

Materials

Manufactured

Carbon-graphite

seal

ring

bodies were

to be

manufactured during

Task

VI

from

material

formulations Nos.. 1Y,.

5Y, and 6Y.

Since processing

problems were encountered

during"

the

manufacture

of the

three

materials,

some adjustments

in

processing

had to

be.made.

The

processing problems

and

the

required, revisions

in the

processing procedures

are

discussed

in

Section

V-B

with

detailed descriptions

of the

techniques

employed

to

manu-

facture

the

carbon-graphite

materials

during

Task

VI. The

manufacturing

problems resulted primarily

from

the

scale-updn

the

size

of the

compacts

being

manufactured.

Many

of the

processing techniques employed

during

Task

VI had

been

developed

during

the

Task

V

sceening studies

in the

prep-

aration

of

small

2.

5-inch

x 1.

25-inch

x 1.

0-inch

(6.

35cm

x 3.

18cm

x 2.

54cm)

compacts.

Although

these processing techniques

had

been

used

successfully

to

.manufacture

the

small

compacts, they resulted

in

some problems

during

Task

VI

when

attempts were made

to

manufacture

considerably

larger

conn-

pacts: 5-inch (12.

7 cm)

diameter

x 1.

4-inch

(3. 6 cm)

thick solid plugs

and

8.

6-inc (21.

8 cm) o. d. x 5.

8-inch (14.

7 cm) i. d. x. 1.

3-inch

(3. 3 cm)

thick

ring

blanks.

All

dimensions

listed

are for the

green compacts.

Table VIII presents

the

identification

of the

three basic formulations

and

their impregnated versions

from

which carbon-graphite

seal

ring bodies

were.manufactured

during

Task

VI.

Formulation

No, 1Y was

replaced

by

formulation-No.

1Z

when

processing problems prevented

the

manufacture

of

the for

mulation.No.

1Y

material.

Except

for the use of the

Grade

WFA

graph-

ite

fibers,

the

carbon-graphite

materials

produced

during

Task

VI

were manu-

factured

from

the

particulate

and

binder

raw

materials characterized

during

Task

I. — The

results

of the

Task

I—characterization

tests

and

some

of the

properties

of the

Grade

WFA

graphite fibers were presented previously

in

Section IV-A

of

this

report.

31

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f

n

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1

w

pq

*i^

H

rt

o

CO

H

>

T3

(U

4-)

n)

W)

a

r—

i

<U

^C

H

T3

C^

rt

CO

C

O

or

mulati

bn

3

?-t

^ ,

4-J

(TJ

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I^H

a

CO

rt

CQ

(L)

CU

t.

fH

H

^d

mtification

of t

<u

S

B

rt

00

41

a

&

DO

C

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X

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No. 1

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No. 5

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Temperature

=

tions

are

parts

by v

proportions

are pai

gnate

2800

°C

baked

agnate

1000

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32

B.

Processing

of

Materials Formulations

Two

different

types

of

compacts were prepared,

for

the.

materials

manu-

factured

during Task

VI:

5-inch (12.

7. cm)

diameter

x

1.4-inch (3.6

cm)

thick

solid plugs

and 8.

6-inch (21. 8cm)

o. d. x 5.

8-inch (14.

7 cm) i. d. x 1.

3-inch

(3.3

cm)

thick ring blanks.

The

dimensions listed.are

for the

green compacts.

The

material

property

samples

and the rod

specimens submitted

to the

NASA

Project Manager were machined

from

the

solid plugs.

Several test bakes were

conducted

to

determine

the

best molding con-

ditions

for

each

of the

materials

manufactured during

Task

VI. The

mixes

of

formulations

Nos.

1 and 3,

which were employed during Task

VI for the

manu-

facture

of two

materials,

had

been test baked

when

they were

manufactured

during

Task III.

— The

formulation

No. 6 mix was

manufactured

and

test baked

during

Task

VI. The

test bake procedure consisted

of

molding

small

compacts

of

each

material

at

5000

psi

(3450

N/cm

2

) pressure increments between

10, 000

psi

(6890

N/cm

2

)

and 35, 000 psi

(24,

100

N/cm

2

).

After

the

compacts were baked

to

1000"C,

their densities were measured

and

their internal structures were

examined,

for

laminations.

The

green density that resulted

in a

1000°C

baked

compact having

the

highest baked density

and

sound

internal structure

was se-

lected

as the

molding condition

for

each

material.

The

processing techniques

employed

to

manufacture

compacts from

the

materials:produced during Task

VI

are as

follows:

1.

Formulation

No. 1Y - CHP

Artificial Graphite

(80

pbw)-

Thermax

(20

pbw) -No.

30

Medium Pitch

(60

pph)

-

1000°C

Baked

Compacts Impregnated

with

Solution

Consisting

of

Furfuryl

Alcohol

(50

pbw)

and

Bakelite BRP-5095 Resin

(35

pbw)

a)

Blend filler

raw

materials

for one

hour.

.

b)

Preheat

filler

and

mixer

to

150°C,

add

pitch,

and mix

filler

and

binder

in

sigma blade mixer

for one

hour.

c)

Crush cooled

mix by

using

a

hammer pulverizer.

d)

Micromill crushed mix.

e)

Blend milled

material

for one

hour.

f)

Mold

the

milled

material

at

room temperature

by

using

a

hydraulic

press.

33

g)

Pack

green compacts with coke

in a

sagger, place

a

layer

of

charcoal

on the top of the

pack,

and

bake green com-

pacts

between

room temperature

and

1000°C

at a

rate

of

5°C

per

hour,

followed

by a

4-hour hold

at

1000"C.

h)

Impregnate

100Q°C

baked compacts

with

a

furfuryl

alcohol

(50

pbw)

-

Bakeli.te BRP-5095

resin

(35

pbw) solution

by

using

the

following

procedure.

1.

Place-compacts

in

autoclave

and

evacuate

for 1

hour

at 27 to

29-inch (9.1

to 9. 8

N/cm

2

)

Hg

vacuum.

.

2.

Impregnate compacts with

resin

solution.

3.

Pressurize

autoclave containing compacts with

80

to

85

psig

(55 to 59

N/cm

2

)

air for 1

hour.

4.

Remove

compacts

from

solution.

5. .

Place

compacts

in an

autoclave, pressurize

with

100.psig

(69

N/cm

2

) air, rush temperature

to

125°C

and

hold

1

hour,

and

rush temperature

to

150°C

and

hold

1

hour.

.

Remove compacts

from

autoclave

and

.

place them

in a

150°C

circulating-air

oven

for 2

hours

to

complete

resin

cure.

i)

Pack

resin impregnated compacts

with

coke

in a

sagger

and

rebake

to

1000°C

according

to the

following

schedule: rush,

to

150°C,

150°C

to

1000°C

at

10°C

per

hour,

and

hold

4

hours

at

1000°C.

j)

Using graphite

particles

as the

packing medium, fire

the

1000°C

baked compacts

to

2800°C

in an

induction

furnace,

using

the

following

schedule: room temperature

to

900°C

at

400°C

per

hour,

900°C

to

1600°C

at

200°C

per

hour,

1600°C

to

2800"C

at

300°

C per

hour,

and

hold

1

hour

at

2800°C.

34

Processing problems were encountered during

the

manufacture

of the

formulation

No. 1Y

compacts. Eight 5-inch (12.

7 cm)

diameter

x

1.4-inch

(3.

6 cm)

thick

solid

green

plugs were successfully baked from room

tempera-

ture

to

1000°C.

The

1000°C

baked compacts were then impregnated

with

the

furfuryl

alcohol

-

Bakelite BRP-5095

resin

solution.

A 7. 7

percent average

increase

in

weight

was

measured

for the

resin-impregnated compacts

following

pressure curing

at

150°C.

After

they were pressure cured, these compacts

were

rebaked

to

1000"C

at a

rate

of

10*C

per

hour.

The

baking schedule

was

apparently

too

fast,

since

large

chips

of

material

broke

off

during baking.

The

force

produced

by the

volatiles

from

the

resin-impregnant trying

to

escape

through

the

internal structure

of the

compacts probably caused

the

shipping

..

The

10°C

per

hour

rate

was the

same

as

that used during

the

Task

V

resin

im-

pregnation studies

in

which

smaller

resin-impregnated samples

(4.

0-inch

x 0.

5-inch

x 0.

25-inch (10.

2 cm x 1. 3 cm x 0. 6

cm))

of

formulation

No.

1Y

were successfully rebaked

to

1000°C.

Final

baking

(Z800*C)of

the

damaged

1000°C

rebaked formulation

No. 1Y

compacts resulted

in

their com-

pletely breaking

apart,

apparently

due to

undetected

microcracks

which

had

formed

during

the

rebaking

of the

compacts

to

1000°C.

The

formulation

No. 1Y

compacts were being

manufactured

from

the

limited

quantity

of

formu-

lation

No. 1 mix

remaining

from

Task III.

—

This supply

of mix was

exhausted

with

the

manufacture

of the

solid plugs

of

formulation

No. 1Y.

The

processing problems encountered during

the

manufacture

of the

formulation

No. 1Y

compacts necessitated

the

revising

of the

original work

plan

for

Tasks

VI and

VII. Formulation

No. 1Y was

replaced

by

formulation

No.

1Z.

Formulation

No. 1Z was

basically

the

same

as

formulation

No. 1Y

with

the

exception that formulation

No. 1Z

specified

resin

impregnation

of

2800°C

baked compacts

and a

much slower baking schedule

to

rebake

the

resin-impregnated compacts

to

1000°C.

35

2.

Formulation

No. 1Z - CHP

Artificial Graphite

(80

pbw)

-

Thermax

(20

pbw)

- No. 30

Medium

Pitch

(60

pph)

-

2800°C

Baked Compacts Impregnated with Solution Consisting

of

Furfuryl

Alcohol

(50

pbw)

and

Bakelite BRP-5095 Resin

(35

pbw):

a)

Bake compacts

to

2800°C

by

using

the

same

processing

as

that used

for

formulation

No. 1Y

except

for the

elimination

of

steps

h and i.

b)

Impregnate 2800°C baked compacts with

the

furfuryl

alcohol

(50

pbw)

-

Bakelite

BRP-5095

resin

(35

pbw) solution, using

same

procedure

employed

to

resin

impregnate

1000°C

baked compacts

of

formulation

No. IY

(Step

h). ' . .

c)

Pack

resin impregnated compacts

with

coke

in a

sagger

and

bake

to

1000°C

according

to the

following

schedule: room temperature

to

500°C

at 2. 5°C per

hour,

500 to

1000°C

at 5°C per

hour,

and

hold

4

hours

at

1000°C.

d)

Using graphite

particles

as the

packing medium, fire

1000°C

baked compacts

to

2800°C

in an

induction-furnace

according

to the

firing

schedule

used

for the

formulation

No. IY

compacts.

Three

of the

large

ring

blanks

and

seven solid plugs were manu-

factured

from formulation

No. 1Z.

Existing

2800°C

baked formulation

No. 1

compacts remaining from Task

III—

were used

to

manufacture

the

formulation

No.

1Z

material.

A 10. 6

percent average increase

in

weight

was

measured

for

the

compacts following

resin

impregnation,

and

pressure curing

at

150°

C.

Although

the

resin-impregnated formulation

No. 1Z

compacts were rebaked

to

1000°C

by

using

a

very slow baking schedule,

the

large

resin

pickup resulted

in the

chipping

of

some

of the

compacts during baking. However,

the

resin-

impregnated compacts

of

formulation

No. 1Z

were

in

much better condition after

rebaking

to

lOOO^C

than those

of

formulation

No. IY. The

formulation

No. 1Z

compacts experienced

no

further damage

during

final baking

to

2800°C.

Although

some

of the

formulation

No. 1Z

compacts experienced chipping problems during

processing,

the

quantity

of

material

that

was

successfully manufactured

was

sufficient

to

fulfill

the

delivery

and

testing requirements

for

Tasks

VI and

VII.

36

3.

Formulation

No. 5 - CHP

Artificial Graphite

(80

pbw)

^

Thermax

(20

pbw)

-

Bakelite BRP-5095 Resin

(58

pph):

a)

Blend filler

raw

materials

for one

hour.

b)

Dissolve Bakelite BRP-5095

resin

binder

in

equal volume

of

acetone

and mix

with

filler

in a

sigma blade mixer

for one

hour

at

room

temperature.

c)

Dry

mixed

material

at

.75°C

for 16

hours.

d)

Crush

material

by

using

a

hammer pulverizer.

The

material

may

still

be

rather

soft

and

pliable

after Step

c, due to

entrapped acetone,

in

which

case

the mix

must

be

chilled

at

-20°C

to

harden

it

before

crushing.

e)

Place

crushed mix:in

an

autoclave

and

vacuum

-

evacuate.;

for

16

hours while maintaining

the

temperature

at

50"C.

The

step will remove

the

residual acetone.

f)

Crush

material

again

by

using

a

hammer pulverizer.

The

step

can be

omitted

if the mix

does

not

agglomerate during Step

e.

g)

Micromill crushed

material.

h)

Blend milled

material

for 1

hour.

i)

Mold

the

milled

material

at

room temperature

by

using

a hy-

draulic

press.

j)

Pressure

cure green compacts

at

150°

C by

using the,

follow-

ing

procedure: place compacts

in

autoclave, apply

100

psig

(69

N/cm

2

)

air

pressure, rush temperature

to

125°C, hold

for 1

hour, rush temperature

to

150°C

and

hold

3

hours.

. The

cure

Is

completed

by

heating

the

pressure cured

compacts

in a

circulating-air oven for-1 hour

at

100*C,

1

hour,

at

125°C,

and

3

hours

at

150°C.

k)

Pressure

bake cured compacts according

to the

following

schedule: rush

to

150°C

and

hold

1/2

hour,

raise

at 5°C per

hour between

150°C

and

550*C,

and

hold

at

550°C

for 4

hours.

.

During pressure baking,

an

inert

gas'

is.oisied.

to'apply

50

tp'.lOO

atmospheres

pressure;

;

37

1)

Pack

pressure baked compacts

with

coke

in a

sagger, place

a

layer

of

charcoal

on

the.

top of the

pack,

and

bake

to

1000°C

according

to the

following

schedule: rush

to

150°C,

raise

at

10*C.per

hour between

150°C

and

500

a

C, hold

2

hours

at

500*C,

.

raise

at 5°C per

hour

between

500°C

and

1000"C,

and

hold

4

hours

at

1000°C.

m)

Using graphite particles

as the

packing medium, fire

the

1000°C

baked compacts

to

2800°C

in an

induction

furnace

according

to the

firing

schedule used

for the

formulation

No. 1Y

compacts.

Since major processing pro.blems were encountered during

the

manufacture

of the

formulation

No. 5

base

material,

no

attempt

was

made

to

manufacture

the

resin

impregnated version

of the

material

(formulation

No.

5Y).

As

reported

for the

Task

V

baking'studies

(Section

IV-A-2),

scale

up in the

size

of the

compacts resulted,

in

cracking, problems.

The

large

green formulation

No.

3

compacts fractured when they were

pressure

baked

to

550°C.

At

that

time,

it was

discovered that

the

large green compacts

could

be

successfully pressure

baked

to

550°C

if

they

were first pressure cured

at

150°C.

The

large

green

formulation

No. 3

compacts

used

during

the

Task

V

baking studies

had

been

molded

a

year

before

during Task

III—

and had

since been resting

on a

bench

in an

air-conditioned room.

The

formulation

No. 3 mix

from

which

the

formu-

lation

No. "6

compacts were molded during Task

VI,.had

spent

the

past year

in

an

unheated storage

area.

Hence,

the mix had

been exposed

to

temperatures

ranging from 100°F

(38°C)

during

the

summer

to

below

0°F

(-18°C)

during

the

winter.

The

large

variation

in

temperature

may

have

affected

the

Bakelite

BRP-5095

resin

used

to

bond

the

formulation

No. 3 mix or the

resin binder

may

have deteriorated with age.

The

result

was

that

all 20 of the

5-inch (12.

7 cm)

diarnter

x

1.4-inch (3.6

cm)

thick green formulation

No. 5

compacts cracked

and/or

laminated

when

pressure cured

at

150"C

followed

by

pressure baking

to

550°C.

Absorbed

moisture

was

also

.suspected

as a

possible cause

of the

processing problems encountered during

the

manufacture

of the

formulation

No.

5

material.

However,.

an-

analysis

of

the'one-year-old

formulation

No. 3

mix

showed that

It

contained only

0. 6

percent

(by

weight)

absorbed moisture.

38

This

value

was

obtained

by

weighing

a

sample

of the mix

before

and

after

it had

been

vacuum

evacuated

for 7

hours

at a

temperature

of 50° C.

Furthermore,

the

dried sample

of mix was

found

to

re-absorb

0. 5

percent moisture during

its

first hour exposure

to

room temperature conditions.

Due to the

relatively

small

amount

of

absorbed moisture present

in the

mix,

it was

ruled

out as

being

a

major cause

of the

processing problems experienced during

the

manu-

facture

of the

formulation

No. 5

material.

In

view

of the

processing

difficulties

experienced

during

the

manufacture

of the

formulation

No. 5

material,

the

NASA

Project Manager

requested

that

the

work

on

this material

not be

continued.

The

remaining pro-

gram

efforts

were

to be

directed

to

completion

of the

manufacture

and

charac-

terization

of the

other

two

materials

(formulations Nos.

1Z and

6Y).

Only,

a

few

formulation

No. 5

compacts were completely processed through baking

to

2800°C.

The

compacts included

two

ring blanks

and

several

small

pieces

salvaged

from

the

solid plugs which

had

experienced cracking problems during

pressure baking.

The

formulation

No. 5

compacts were

not

resin-impregnated

prior

to

final

baking

to

2800°

C to

avoid

any

further

processing problems which

might

result

from

the use of the

furfuryl

alcohol-Bakelite BRP-5095

resin

im-

pregnant. Because

of the

processing problems encountered during Task':VI,

.,

the

quantity

of

formulation

No. 5

material

which

was

produced

was not

sufficient

to

fulfill

the

delivery requirements.

4.

Formulation

No. 6

-CHP Artificial Graphite

(80

pbw)-

WFA

Fibers

(20

pbw)

-

Bakelite BRP-5095 Resin

(70

pph):

a)

Blend Grade

WFA

chopped graphite fibers

with

the CHP

artificial graphite

for one

hour.

-

-.--_--__..

b)

Micromill

the

blended filler

material.

c.

Blend

milled

filler

material

for one

hour.

d)

Follow

the

other processing steps listed

for

formulation

No.

5,

starting

at

mixing (Step

b).

39

5.

Formulation

No. 6Y

--CHP Artificial Graphite

(80

pbw)-

WFA

Fibers

(20

pbw) -.Bakelite BRP-5095 Resin

(70

pph)-

1000°C

Baked Compacts Impregnated

with.

Solution Consisting

of

Furfuryl Alcohol

(50

pbw)

and

Bakelite BRP-5095 Resin

(35

pph):

;

'

a)

Bake

the

green compacts

to

1000°C

in the

same

manner

as

that used

for

formulation

No. 6.

b)

Follow

the

other processing steps listed

for

formulation

No.

1Y,

starting

at the

impregnation

of the

1000°C

baked compacts (Step

h).

Ring

blanks were

manufactured

.from

formulation

No. 6

after

processing problems prevented

the

manufacture

of the

resin-impregnated

formulation

No. 6Y

ring blanks.

The

processing problems resulted

from

the

large

resin

pickup experienced

by the

formulation

No. 6Y

ring blanks.

An in-

crease

in

weight

of 11. 1

percent

was

measured

for the

1000°C

baked ring

blanks

following

resin

impregnation

and

pressure curing

at

150°C.

This

resin

pickup

was ten

times

that measured

for the

5-inch (12.

7 cm)

diameter solid

plugs

of the

formulation

No. 6Y

material

at the

same

stage

in

processing.

The

impregnant apparently filled

the

open porosity

of the

1000°C

baked

ring

blanks

so

completely that they broke

apart

during rebaking

to

1000°C

as the

volatiles

from

the

resin

impregnant tried

to

escape

through

the

internal structures

of

the

compacts.

Due to

their

low

resin

pickup,

no

problems were encountered

during

the

processing

of the

formulation

No. 6Y

solid plugs through final baking

to

2800°C.

The

resin

pickups measured

for the

solid plugs

and

ring blanks

of

formulation

No. 6Y

indicated that there may. have been

a

difference

Ln the

surface

condition

of the two

types

of

compacts prior

to

impregnation.

The

1000°

C

baked solid plugs

of the

formulation

No. 6

base

material

apparently

had

a

very

low

porosity surface

condition

which prevented

the

res.in solution

from

freely

entering

the

stock during impregnation.

The

1000°C

baked ring blanks

of

the

formulation

No. 6

base

material

did not

appear

to

have

the low

porosity

surface

condition, since they readily accepted

the

resin during impregnation.

40

If

indeed

there

was a

difference

in the

surface porosity

of the two

types

of

compacts,

the

difference

would

probably

be

difference

in

their

surface-to-volume

ratios.

The

surface-to-volume

ratio

of the

ring blanks

was

approximately

1.4

times

that

of the

solid plugs, indicating

that

the

vol-

atiles

would

experience

greater

difficulty

in

escaping from

the

resin

binder

through

the

solid plugs during baking.

The

difficulty

of

removing

the

vol-

atiles

and the

fact

that phenolic

resins

yield

low

porosity carbonaceous

:

materials

after pyrolysis possibly could account

for the

formation

of a low

porosity envelope around

the

solid

plugs

of

formulation No..

6

during baking

to

1000°C.

41

SECTION

VI

MATERIAL

PROPERTIES

.:•

(TASK

VII)

A.

Property Requirements of.Seal Ring-Carbon-Graphite Materials

The

goal

of

this contract

is the

development

of a

carbon-graphite

ma-

terial

for use as a

self-acting

seal

in

advanced

gas

turbine engines. High

oxidation resistance

is a

primary requirement

of the

material

if it is to

withr

stand

the

high operating temperatures. Since self-acting

seals

experience

relatively high speed sliding contact during limited periods

of

operation,

good

wear

resistance

is

also

a

requirement. High hardness, strength,

and

modulus',

.

together

with

the

proper selection

of

impregnants

and

mating

materials,

are

necessary

for

producing wear-resistant carbon-graphite

seal

ring

materials.

High

hardness

also

is

required

to

ensure

the

erosion resistance

of the

material.

Erosion

resistance

is an

important requirement

for a

self-acting

seal

material,

since

debris

passing through

the gas

film

formed

between

the

self-acting

seal

and

the

seat

during engine operation tends

to

score

and

erode

the

primary ring.

A

carbon-graphite

material

used

as a

self-acting

seal

must also have

a

high

thermal

conductivity

to

provide rapid transfer

of

deleterious

fricti-pnal'

heat

which

can

develop during periods

of

sliding contact. Dimensional stability

is

a

desirable property

of a

seal

ring

material,

although thermal expansion

is not

critical

for

this application, since

the

carbon will

be

controlled

by an

outer

shrink

ring during operation.

Aside

from

the

material

properties that

are

essential

for

good

performance,

a

seal

ring

material

should

also

be

readily machinable, since

seal

dam

widths

as

small

as 0.

020-inches

(. 05 cm)

often

are

present

in

seal

design.

The

compacts

manufactured

from

formulations Nos.

1Z, 5, 6, and 6Y

during

Task

VI

were

all

found

to be

more

easily

machinable than commercial

seal

ring Grade CDJ.

The

good

machinability

of the

carbon-graphite

articles

manufactured

during Task

VI

resulted from

the use of a

large

proportion

of

particulate graphite

in the

filler

systems

and a

final heat-treatment temperature

of

2800"G.

42

Under

the

scope

of

Task VII,

the

Contractor determined

the

following

material

properties

for the

carbon-graphite

seal

ring bodies

manufactured

during

Task

VI:

1.

Mechanical

Properties

a.

Density

before

and

after

impregnation

with

an

oxidation

inhibiting

treatment.

b.

Flexural

strength.

c.

Elastic

modulus.

2.

Thermal Properties

a.

Thermal

conductivity.

b.

Coefficient

of

thermal expansion.

3.

Oxidation Resistance

and

Related Porosity

a.

Oxidation resistance compared with that

of

carbon-graphite

seal

material

currently

in

use.

b.

Total

porosity, pore size

and

size distribution,

uniformity

of

impregnation,

and

structural

uniformity.

This section

of the

report

is

divided

into

subsections,

The

next sub-

section

discusses

the

mechanical properties determined

for the

materials

manufactured

during Task

VI. The

remaining subsections cover

the

thermal

properties,

the

porosities,

and the

oxidation

rates

determined

for the

materials.

B.

Mechanical

Properties

The

literature search

conducted

during

Task

I—

indicated

that high hard-

ness, strength,

and

modulus

are

necessary requirements

for

producing

wear-

resistant carbon-graphite

seal

ring materials. Hardness greatly

affects

performance,

since

the

load-carrying capacity

of a

carbon-graphite

seal

ring

material

is

directly related

to its

hardness. High hardness also

is

needed

to

prevent

scoring

and

erosion

of the

seal

face

when

debris

passes

between

the

self-acting

seal

and the

seat

during engine operation. Although

no

goal

was

established

for the

strength

of the

material

to be

developed

under

the

scope

43

of

this

Contract,

the

operating pressures, dimensional stability requirements,

and the

configuration

of the

seal

ring (7-12 inches (18-30

cm) in

diameter,

1/2-inch

(1. 3 cm) in

thickness,

and 0.

020-inch

(. 05 cm) in dam

width)

require

a

material

with maximum strength

and

hardness consistent with high oxidation

resistance.

Tables

IX, XI, and

XIII display

the

green,

1000°C

baked,

and

2800°C

baked bulk densities;

the

flexural strengths;

the

elastic moduli,

and the

hard-

nesses

determined

for the

carbon-graphite

seal

ring bodies manufactured

from

formulations Nos.

1Z, 5, and 6Y.

Except,for the.

hardness

measurement,

.these

mechanical

properties were

the

ones which

the

Contractor

was

required

to

measure.

The

hardness

measurement

was

included,

since

it is one of the

phys-

ical

properties commonly specified

for

commercially available carbon-graphite

seal

ring

materials.

Appendix

II

described

the

procedures used

to

determine

the

material

properties.

The

ASTM methods were used where applicable.

A

complete listing

of the

mechanical properties determined

for the

formu-

lation

No. 1Z

material

is

displayed

in

Table

IX.

Table

X

presents

a

comparison

of

the

average mechanical properties measured

for the

formulation

No. 1Z ma-

terial

with those determined during Task

IV

—

for the

materials

manufactured

from

formulations Nos.

1 and IX

(compositions listed

In

Table

I).

Although

the

formulation

No. 1Z

material

had a

significantly higher

2800°C

baked bulk density,

its

other mechanical properties were

not

quite

so

good

as

those determined

for

the

formulation

No. IX

material.

The

mechanical properties

of the

formulation

No.

1Z

material

were slightly more uniform than those

of the

formulation

No..

IX

material.

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46

The

strength, hardness,

and

modulus

of the

formulation

No. 1Z

material

initially

had

been expected

to be

better than those

of the

formulation

No. IX

material.

This result

was

expected since

the

formulation

No. 1Z

resin

impreg-

nant yielded three

times

more residual carbon

(by

weight)

after baking

as

that

obtained

from

the

formulation

No. IX

resin

impregnant.

The

large

amount

of

residual carbon resulting from

the

resin impregnant

was

reflected

in the

2800°C

baked bulk density

measured

for the

formulation

No. 1Z

material.

The

lack

of

improvement

in the

strength, hardness,

and

modulus

of the

formulation

No. 1Z

material

may

have been

the

result

of a

number

of

different

factors.

Perhaps

the

furfuryl

alcohol-BRP-5095

resin

solution

did not wet nor

adhere

to the

sub-

strate

carbon

so

well

as did the

BRP-5095 resin-acetone

solution

used

to

manu-

facture

the

formulation

No. IX

material.

The

lack

of

improvement

also

might

indicate

that

the

residual carbon

formed

from

the

resin

impregnant

in the

formu-

lation

No. 1Z

material

may

have

had a

higher degree

of

crystallinity after baking

to

2800°C

than that

formed

in the

formulation

No. IX

material. This increased

degree

of

crystallinity, which

could

have resulted from

the

impregnation

of

2800°C

baked

rather

than

1000°C

baked formulation

No. 1

compacts,

would

cause

the

Residual carbon

to be

softer

than that

formed

in the

formulation

No. IX

material,

thus contributing

little

to the

strength

and

hardness.

The

lack

of im-

provement

could

also

be due to a

difference

in the

pore size distribution

of the

formulation

No. 1Z

material

as

compared

with

that

of the

formulation

No. IX

material.

This possibility will

be

discussed

further

in

Section VI-D

of

this

report.

Table

XI

displays

a

listing

of the

mechanical properties determined

for the

formulation

No. 5

material-. Table

Xllpresentsa

comparison

.of.the

average mechani-

cal

properties measured

for the

formulation

No. 5

material

and

those determined

during

Task

IV— for the

material

manufactured

from

formulation

No. 3

(compo-

sition listed

in

Table

I).

Although

pressure baking

was

included

as a

part

of the

processing,

the

formulation

No. 5

material

was

found

to

have mechanical properties

similar

to

those determined

for the

formulation

No. 3

material.

This result

was

probably

due to the

fact

the

formulation

No. 5

compacts were

manufactured

from

the

one

-year -old

formulation

No. 3 mix

remaining from Task III.

—

The

Bakelite

BRP-f

resin

used tobond

the for

mulationNo.

3 mix

apparently

had

deteriorated with age.

47

TABLE

XI

Mechanical

Properties

-

Formulation

No. 5

Material

Bulk

Density

Green

(g/cc)

550°C

Pressure

Baked

(g/cc)

1000'C

Baked

(g/cc)

2800"C

Baked

(g/cc)

5"

(12.

7 cm)

Diameter

Plugs

Maximum

Minimum

Average

Standard Deviation

1.410

1.406

1.408

0.001

13

1.682

1.649

1.668

0.012

10

R.ing

Blanks

Maximum

Minimum

Average

n

Flexural

Strength

Maximum

Minimum

Average

Standard Deviation

n

Elastic

Modulus

Maximum

Minimum

Average

Standard Deviation

n

1.406

1.405

1.406

2

si)

3780

2950

3390

278

6

(10

6

psi)

1.24

1. 10

1.20

0.05

6

1. 502

1.496

1.499

2

(N/cm

2

)

Z600

2030

2340

192

6

(10

5

N/cm

2

8*54

7.58

8.27

0.34

6

1.565

1.554

1.560

2

1.659

1.656

1.658

2

Rockwell

"S"

Hardness

***

Maximum

Minimum

Average

Std.

Dev.

69

37

57

10

6

*

Calculated

from

physical dimensions

and

weights measured

for

compacts.

2800°C

baked bulk densities

listed

for 5"

(12.

7 cm)

diameter plugs were

determined

for

segments salvaged

from

solid

plugs damaged during

pressure

baking.

**

Measured using

4. 5" x 1. 0" x 0. 5"

(11.

4 cm x 2. 5 cm x 1. 3 cm)

samples.

Flexural

samples broken

on a 3. 0" (7. 6 cm)

span

per

ASTM

procedure

C651-70.

*** R

g

Scale

=

1/2" (1.3

cm)

diameter

ball

and 100 KG

Maj. load.

Two

measure-

ments made

on

each

of the 6

flexural

samples.

48

TABLE

XII

Comparison

of

Mechanical

Properties

-

Formulations

Nos.

3 and 5

Material

Formulation

No. 5

Flexural

Strength

Average

Standard Deviation

**#

Elastic

Modulus

Average

Standard Deviation

n

Rockwell

"S"

Hardness

Average

Standard Deviation

n

****

(psi)

3390

278

6

(10*

psi)

1.20

0.05

6

Formulation

No. 3

&&

Bulk

Density (g/cc)

Green (average)

Standard Deviation

n

2800°C

Baked (average)

Standard Deviation

n

1.408

0.001

13

1.668

0.012

10

1.407

<0. 001

6

1.644

0.005

6

57

10

6

(N/cm

2

)

2340

192

6

(10

5

N/cm

2

)

8.27

0.34

6

(psi)

3480

118

6

(10

6

psi)

1.

15

0.02

6

58

2

6

(10

5

N/cm

2

)

7.92

0. 14

6

***

Material

manufactured during

Task

III. Composition

of

formulation

No.

3 was

presented

in

Table

I of

this

report.

Calculated'from

physical dimensions

and

weights measured

for

com-

pacts.

2800°C

baked bulk density

listed

for

formulation

No. 5 was

measured

for

segments salvaged from solid plugs damaged during

pressure

baking.

Measured using

4. 5" x 1. 0" x 0. 5"

(11.

4cm x 2. 5cm x 1.

3cm)

samples.

Flexural

samples

broken

on a 3. 0" (7.

6cm) span

per

ASTM

Procedure

C651-70.

****

R

g

Scale

=

1/2" (1.3cm)

diameter

ball

and 100 Kg.

Maj.

load.

Two

measurements made

on

each

of the

flexural

samples.

49

The

apparent deterioration

of the

resin binder

was

reflected

in the

1000°C

baked

densities measured

for the

small

formulation

No. 3

compacts manufactured dur-

ing the

Task

V

baking studies (Section

IV-A-2).

These compacts,

which

had

been

molded

from

the

one-year-old formulation

No. 3

mix,

had an

average

1000°C

baked bulk density

of 1. 427

g/cc.

Although

the

same processing techniques

had

been

employed,

the

compacts

manufactured

from

the

formulation

No. 3 mix

dur-

ing

Task

III-

had an

average

1000°

C

baked bulk density

of 1. 519

g/cc.

The

apparent

deterioration

of the

resin

binder prohibited

the

formulation

No. 5 ma-

terial

from

gaining

the

full

benefit

of

pressure baking.

Since complete property characterization

of the

formulation

No. 5 ma-

terial

was not

warranted, only selected mechanical properties

and

oxidation

rate

were determined.

The

oxidation testing,

which

is

discussed

in a

later

section

of

this

report,

was

conducted

by

using

samples

impregnated

with

the No. 121

oxi-

dation-inhibiting treatment.

A

complete listing

of the

mechanical properties

of the

formulation

No. 6Y

material

is

presented

in

Table XIII. These mechanical properties were deter-

mined

for

samples

prepared

from

the

2800"

C

baked solid plugs

of

formulation

No.

6Y. Due to the

apparent formation

of a low

porosity surface

condition

dur-

ing

processing,

the

solid plugs

of

formulation

No. 6Y

experienced only

a 1. 1

percent average increase

In

weight after

resin

impregnation.

The

average increase

in

weight decreased

to>0.26

percent

after

the

resin-impregnated solid plugs were

rebaKed

to

1000°C.

Since

the

solid plugs

of

formulation

No. 6Y

experienced such

a

small

resin

pickup,

the

mechanical properties displayed

in

Table

XIII

are

essentially

the

same

as

those

which

would

be

measured

for the

solid plugs

of the

non-fesin-impregnated

formulation

No. 6

base

material.

The

formulation

No. 6

ring blanks

manufactured

during Task

VI had

2800°

C

baked bulk densities ranging

between

1. 564 and 1. 569

g/cc.

The

larger

surface-to-volume

ratio

of the

formu-

latioii

No. 6

ring blanks

may

have been responsible

for

their

2800°C

baked bulk

density being

higher

than

that

measured

for the

solid plugs

of the

same

material.

50

(

—

I

.5

<u

1

^

O

2

ri

o

i

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K-(

ti

t—

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w £

t-J O

CQ fa

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P*

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ni

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is.*

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2

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Calculated

from

]

Measured using

4

broken

on a 3. 0"

R

Scale

=

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(

each

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flex

#

# «•

fe W

Table

XIV

shows

a

comparison

of the

average mechanical properties

measured

for the

formulation

No. 6Y

material

and

those determined

during

Task

IV—

for

similar

materials

manufactured

from

formulations Nos.

4.and

4X

(compositions listed

in

Table

I). . The

mechanical properties

of the

formu-

lation

No. 6Y

material

were significantly better than those determined

for the

non-resin-impregnated formulation

No. 4

material.

The

formulation

No. 6Y

material

had

mechanical properties

similar

to but

more

uniform

than those

of

the

resin-impregnated formulation

No. 4X

material,

even

though

the

latter

had

gained considerably more residual carbon

from

the

carbonization

of its

resin

impregnant.

An

average increase

of 4

percent

had

been measured during

Task

III—

after

the

resin-impregnated

formulation

No. 4X

compacts were

re-

baked

to

1000°C.

As

mentioned

.previously,

the

mechanical properties

of the

formulation

No. 6

base

material

should

be

approximately

the

same

as

those

measured

for the

resin-impregnated

formulation

No. 6Y

material. Formulation

No.

6

thus results

in a

non-resin-impregnated

material

with

properties

similar

to

those

of the

resin-impregnated formulation

No. 4X

material. This improve-

ment

is

significant,

since deletion'

of

resin-impregnation reduces processing,

The

goal

of the

Tasks

V, VI, and VII was to

develop

carbon-graphite

materials

having improved strength, hardness,

and

uniformity.

The

goal

was

not

completely achieved, since

the

scale-up

in the

size

of the

compacts prod-

uced

during Task

VI

resulted

in

processing problems. These processing prob-

lems

prevented

the

gains

in

mechanical properties anticipated

from

the

techniques

developed

during

the

Task

V

screening

study.

Seal ring bodies

manufactured

from

formulations

Nos.

1Z and 6Y

possessed mechanical properties

similar

to

those

determined

for the

compacts

of

formulations Nos.

IX and 4X,

respectively.

The

mechanical properties

of the

latter

two

materials

had

been

judged

during

TaskI"\r—•

to

be

adequate

for use as a

self-acting

seal

ring material.

Although

no

improve-

ments

in

strength

and

hardness were obtained,

the

formulation

No. 6

material

was

more

uniform

than

the

formulation

No. 4X

material

manufactured

during

Task

III.

— The

mechanical properties determined

for the

carbon-graphite

seal

ring

bodies

manufactured

from

formulations

Nos.

IX, 1Z, 4X, and

6.Ywere,

however,

all

lower than

the

corresponding values specified

for

commercial

seal

ring Grade

CDJ

-83.

52

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1—

1

rt

*t

cu

n)

S

vO

3

rtf

X

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w

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J k

CP i

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**l CO

H <u

•_£

IH

cu

o

QJ

r"i

"I!

O

• •-i

£

rd

u

0)

5

Comparison

of

X

N

<

o

2

g

rd

1

g

M

0

•*

.

o

2

c

o

*^j

cd

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t<

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fn

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5.°°

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r~

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Average

Standard Deviation

n

ikwell

"S"

Hardness*

Average

Standard Deviation

u

o

ff!

D

CO

O O

T S

^H

^

in H

•O

vO ^

01

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O <U <U JJ

£ gl o

C

fli >

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d r, *

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bo

w P< ^

30

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rj » sO

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•-' .

i-H

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<n

•

—

'*-'

cd ??

fi - - -°

JH

.2

ib M &

n

. . o H

C

om

•*••

_*

d

« ^

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•OOO^g

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§

.JJ

-X-J^

- C ^

2,

=

£ CO

jd

"*. -

0

• S

ft

•*

m C*

n

Calculated

from

Measured using

Flexural

sample

R

Scale

=

1/2"

made

on

each

of

#

* *

53

Grade-,CDJ-83

has a

nominal bulk density

of 1. 76

g/cc,

a

flexural strength

of

8800

psi

(6100

N/cm

z

)

5

an

elastic

modulus

of 3. 2 x 10

6

psi (2. 2 x 10

6

N/cm

2

),

and a

Rockwell

"E"

hardness

of

105.

As

discussed

in

Topical Report

NASA

CR-72799

,

some sacrifice

in

strength

and

hardness

was

necessary during

the

development

of the

oxidation

resistant,

carbon-graphite

materials.

C.

Thermal

Properties

As

a

part

of the

material

characterization

program,

the

Contractor

determined

the

thermal

conductivities

and the

coefficients

of

thermal

expan-

sion

for the

materials

manufactured from formulations Nos.

1Z and 6Y.

Both

of

the

thermal

properties

affect

the

performance

of a

carbon-graphite

seal

ring

material.

.

Self-acting

seals

experience limited periods

of

sliding contact.

However

to

mitigate

thermal

deformation,.

they

require

:a

carbon-graphite

material

having

a

high

thermal

conductivity

so

that

any

frictional heat genera-

ted

during sliding contact will

be

rapidly dissipated

ahdothus';prbper-tiite"rfacial

geometry will

be

maintained

to

prevent high speed rubbing contact.

— A low

coefficient

of

thermal

expansion

is

thus very

desirable,

even

though

the ex-

pansion

of

some self-aicting

seals

will

be

controlled

by an

outer

metal

shrink

ring.

Table

XV

lists

the

thermal

conductivities measured

for the

carbons-graphite

seal

ring bodies manufactured

from

formulations Nos.

1Z and 6Y. The

table

also

displays

the

thermal

conductivities measured during

Task

IV—

for the

materials

manufactured

from formulations Nos.

IX and 4X

(compositions presented

in

Table

I. ) The

materials

manufactured

from

similar

formulations Nos.

IX and 1Z

had

approximately

the

same

with-grain

thermal

conductivity,

but the

latter

ma-

terial

had a

considerably higher thermal

conductivity

in the

across-grain

direction.

This

improvement

in

across-grain

thermal

conductivity

may

have resulted from

the

higher 2800°C baked bulk density

of the

formulation

No. 1Z

material

(1. 792

g/cc)

as

compared with that

of the

formulation

No. IX

material

(1. 733

g/cc).

Formu-

lation

No. 6Y

resulted

in a

more isotropic

material

with

higher with-grain

and

across-grain

thermal

conductivities than those

of the

similar

material

manufac-

tured from formulation

No. 4X. All the

thermal

conductivities listed

in

Table

XV,

which

were measured

at

room temperature

by

using

the

laser

flash method

(Appendix

II),

are

considerably higher than

the

typical value

of 4.4

BTU-ft/ft

2

-hr-°F

(0.

018

cal/cm-sec-°C)

for

commercial

seal

ring Grade CDJ-83.

54

g

H

rH

PQ

<;

H

nt

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14

0)

NO

Tl

s

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1—4

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X

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to

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00 00 t^ ' ^^

i—

1

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z

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XJ

5

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CO

1

Formulation

O fvj ^ t^

• • • •

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rH r-t rH

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•

• • •

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^

with

grain

across grain

easured

during Task

i

i ^

• e

O O

• t

^ <J ^

0)

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z

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o

^

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lisotropy

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__.

•ft

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55

Figures

1 and 2 are

plots

of the

coefficients

of

thermal expansion

deter-

mined

for the

compacts

of

formulations Nos.

1Z and 6Y.

Each plot represents

the

average

of two

tests

conducted

on

samples machined

on the

with-grain

direction.

.

Figure

3 is a

plot

of the

coefficient

of

thermal expansion

of

com-

mercial

seal

ring Grade CDJ-83, which

has

been

included

for

purposes

of

comparison.

All the

materials analyzed

showed

an

increasing

coefficient

of

thermal

expansion

with

increasing temperature.

The

coefficient

of

thermal

expansion

of

Grade CDJ-83

is

considerably higher than those

of the

other

ma-

terials

tested. Figure

1

presents

a

comparison

of the

coefficient

of

thermal

expansion

of the

formulation

No. 1Z

material

to

that determined during

Task

IV

—for

the

formulation

No. IX

material.

The

coefficients

of

thermal

expansion

of the two

materials

are

comparable. Figure

2

shows that

formu-

lation

No. 6Y

resulted

in a

material

having

a

considerably lower

coefficient

of

thermal

expansion than that

of the

similar

formulation

No.

4X--jnaterial.

Based

on the

measured thermal properties,

the

material

manufactured

from

formulation

No. 6Y is a

potentially better

seal

ring

material

than that

prepared

from

the

comparable formulation

No. 4X. The

higher thermal con-

ductivity

of the

formulation

No. 6Y

material

as

compared

with

that

of the

formulation

No. 4X

material will

provide

more rapid

dissipation::.of?

the

fric-

tional

heat

generated

during

periods

of

sliding contact.

The

lower

coefficient

of

the

thermal expansion

of the

formulation

No. 6Y

material

is

beneficial

from

a

thermal

deformation

standpoint.

Although

a

metallic shrink ring con-

trols

the

thermal

deformation

of the

carbon ring

in

some

cases,

if no

shrink

ring

is

used

(as on

small

turbine engine seals), thermal

deformation

is

miti-

gated

by

using high

thermal

conductivity

and low

thermal expansion carbon-

graphite

materials.

56

POOOOOOOOOO

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g

W

5

i—i

nt

6

h

u

rU

H

VI ^_ ^

°U

4

9

Note:

Each mean C.T.

E.

measured

in the

with

grain direction

between

room temperature

(22°C)

and the

final tem-

perature indicated.

B

i . " i i ' '" a

^___

100

200

300 400

Final

Temperature (°C)

500

600

Figure

3.

Mean

Coefficient

of

Thermal Expansion

-

Grade

CDJ-83.

G

710432

59

D.

Porosities

Carbon-graphite

seal

ring bodies must

be low

porosity

materials

so

that

they

will

be

impervious

to the

fluids which they

seal.

As

demonstrated

during

the

experimental portion

of

Task

I,

—the

mechanical

properties

and

oxidation

resistance

of a

carbon-graphite compact

are

greatly

affected

by the

choice

of raw

materials,

composition,

and

final baking temperature used

for

its

manufacture. Although

the

degree

of

crystallinity

of a

carbon-graphite

body

greatly

affects

its

material

properties,

the

porosity

of the

compact

also

has

some

effect.

Reducing

the

porosity

of a

formed

article

should

result

in

an

improvement

in the

mechanical

and

chemical properties.

The

carbonization

of

a

resin

Lmpregnant

has

been

found

to be a

good

way to

reduce

the

porosity

of

a

carbon-graphite compact. Resin impregnation

has

been

found

to be

better

than

the

conventional pitch-type impregnation, since

the

resins,

with

their

lower viscosities

and

increased

wettingn,

tend

to

block

the

pores,

as

well

as

the

larger

open volumes.

^Decreasing

the

porosity

of a

compact reduces

the

number

of

interconnected voids,

and the

remaining isolated voids

are

less

damaging

to the

mechanical properties.

Reducing

the

porosity

of a

carbon-

graphite compact

also

should

increase

Lts

oxidation

resistance.

Table

XVI

presents

the

percent total porosities calculated

for the

com-

pacts

of

formulations Nos.

1, IX, 1Z, 4, 4X, and 6Y. The

values presented

for

'the

materials

manufactured

from

formulations Nos.

1, IX, 4 and 4X

were

determined during Task.IV,

— but

have been

included.for

purposes

of

com-

parison.

Table

XVI

also

displays

the

percent total porosity determined

for

commercial

seal

ring Grade CDJ. These values were calculated

by

using

the

following

equation:

Helium

Density

-

Bulk Density

Percent

Total Porosity

=

100X

'•

Helium Density

>

The

value obtained

by

using

this

equation

is the

ratio

of the

total open pore

.volume

to the

volume

occupied

by the

pores

and the

carbonaceous

material

in the

compact being analyzed.

60

TABLE

XVI

Percent

Total

Porosities-Formulations

Nos.

1, IX, 1Z, 4, 4X, and 6Y

Material

Formulation

No.

1

IX

1Z

4

4X

6Y

Grade

CDJ

Helium Density

(g/cc)

2.

1.

2.

1.

050

940

042

900

765

790

841

Bulk

Density

(g/cc)

1.

710

730

790

441

466

496

756

Percent

Total

Porosity

16.

10.

12.

22.

16.

4.

6

8

3

1

9

4

6

Formulations Nos.

IX and 1Z

were resin-impregnated versions

of

formulation

No. 1.

Formulation

No. IX

involved

the

impregnation

of

1000°C

baked formulation

No. 1

compacts

with

a

Bakelite BRP-5095

resin

(50

pbw)-

acetone

(50

pbw) solution. Formulation

No. 1Z

involved

the

impregnation

of

2800°C

baked formulation

No. 1

compacts

with

a

furfuryl

alcohol

(50

pbw)-

Bakelite BRP-5095

resin

(35

pbw) solution.

As

mentioned

during

the

discussion

of

mechanical properties (Section

VI-B),

the

carbonaceous residue remaining

after

the

formulation

No. 1Z

resin

impregnant

was

baked

to

2800°C

may

have

had a

higher degree

of

crystallinity than that obtained from

the

formulation

No.

IX

resin

impregnant.

A

more

"graphitizable"

resin

impregnant

could

account

for the

formulation

No. 1Z

material

having

a

higher bulk density with

a

higher

total

porosity than those

of the

formulation

No. IX

material.

Although

a

higher helium density generally indicates

a

greater

degree

of

crystallinity

for

a

fine

particulate

material,

this result

may not

necessarily occur

for

bulk

carbon-graphite

materials.

Rather than indicating

a

difference

in the

degrees

of

crystallinity

of the two

materials,

the

difference

in the

helium densities

of

the

materials

manufactured from formulations Nos.

IX and 1Z

could

be a

result

of

a

difference

in the

accessibility

of

helium into

the

pore structures

of the two

materials.

61

The

formulation

No. 1Z

material

may be

more oxidation resistant than

formulation

No. IX

material,

even

though

the

total

porosity

of the

former

is

slightly

greater.

The

helium density measurements indicate

the

formulation.;

No.

1Z.

material

is

less

accessible

to

helium than

the

formulation

No. IX ma-

terial

and, therefore,

may be

less

accessible

to

oxidizing gases. Greater

oxidation

resistance

also

would

be

expected

if the

formulation

No. 1Z

material

is

more

"graphitic"

than

the

formulation

No. IX

material,

since

the

degree

of

crystallinity greatly

affects

the

rate

at

which

a

carbon-graphite

material

oxidizes.

The

data displayed

in

Table

XVI

show

that

the

percent total porosity

of

the

formulation

No. 6Y

material

was

similar

to

that measured

for the

formu-

lation

No. 4X

material (Table

I) and

lower than that

of the

formulation

No. 4

material

(Table

I). The

reduced

porosity

of the

formulation

No. 6Y

material

was

probably primarily

effected

through processing changes other than

resin

impregnation,

since

the

resin pickup

of the

formulation

No. 6Y

compacts

was

low.

The

total porosities

of the

materials

manufactured

from

formulations

Nos.

4X and 6Y

their

mechanical

properties:

both

materials

had

significantly

better mechanical properties than those

of the

formulation

No. 4

material.

, The

total porosities

of all

these

materials

are

significantly

higher

than that

of

commercial Grade CDJ.

Tables:

XVII

and

XVIII

present

the

results

of the

pore

volume

and

pore

size distribution measurements made

on

compacts

of

formulations Nos.

l.Z

and 6Y by

using mercury intrusion. Figures

4 to 7 are the

corresponding

plots

of the

pore volume

and

cumulative pore volume versus pore diameter

for

the two

materials.

The

mercury

intrusion method

is

used

to

determine

the

distribution

of the

pores ranging between

0. 02 and

100.

0

microns

.(n.)

in

diameter.

For the

range

of

pores measured,

the

formulation

No. 1Z

material

was

found

to

have

the

largest

average pore diameter

(5.

2|J.)

with

an

intruded

pore volume

of 0. 082

cc/g.

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(LOG

SCALE)

Pore

Diameter,

by

Mercury

No.

6Y

Material.

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PORE

DIAMETER

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Figure

6.

Pore Volume

Versus

]

Intrusion

-Formulation

68

The

similar

material

manufactured

from

formulation

No. IX had

been

found

during

Task

IV— to

have

an

average pore diameter

of 4.

4H-

with

an

intruded pore

volume

of 0. 076

cc/g.

The

larger

average pore diameter

and

greater intruded

pore volume

of the

formulation

No. 1Z

material

could

account

for the

slight

re-

duction

in

strength

and

hardness compared

with

those

of the

formulation

No. IX

material

(Section VlrB). Formulation

No. 6Y

produced

a

material having

an

average pore diameter

of 2. 6^,

which

was

approximately half

the

average pore

diameter

(5. 6^)

determined

during

Task

TV—

for the

similar

formulation

No.4X

material.

The

formulation

No. 6Y

material

had an

intruded pore volume

of

0.

156

cc/g, which

was a

little

larger

than

the 0. 139

cc/g value determined

for

the

formulation

No. 4X

material.

The

material

manufactured

from

formulation

No.

6Y

appears

to

have

a

larger

volume

of

pores measuring

less

than

0.

060u.

in

diameter than does

the

formulation

No. 4X

material.

Since

the

mercury intru-

sion method does

not

accurately measure

the

distribution

of

pores

smaller

than

0.

060u.

in

diameter,

a

more accurate determination

of

this

difference

was

made

by

the

nitrogen desorption method.

Table

XIX

displays

the

pore volume

and

pore size distribution determined

by

mercury intrusion

for

Grade CDJ. Figures

8 and 9 are the

corresponding

plots

of

pore volume

and

cumulative pore volume versus pore

dia^meter.

The

sample

of

Grade

CDJ had an

average pore diameter

of 1.

2fo.

and an

intruded

pore

volume

of 0. 025

cc/g, both

of

which

are

significantly

smaller

than

the

corres-

ponding

values determined

for the

seal

ring bodies

of

formulations Nos.

IX, 1Z,

4X,

and 6Y.

Tables

XX and XXI

display

the

results

of

nitrogen pore volume measure-

ments made

on

compacts

of

formulations Nos.

1Z and 6Y.

Figures

10

"and

IT are

the

corresponding plots

of

percent pore volume

and

cumulative

percent pore

volume

versus pore diameter..

The

nitrogen desorption method

is

used

to

measure

the

size distribution

of

pores with diameters

in the

range

of

20-600

Angstroms (A).

For the

range

of

pore sizes measured

by

nitrogen desorption (too

small

to be

accurately

measured

by

mercury

intrusion),

the

formulation

No. 1Z

material

was

found

to

have

an

aver

age

pore diameter

of 12 5 A

with

a

total pore volume

ofO.

0011 cc/g.

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73

74

TABLE

XXI

Pore

Volume

and

Distribution

by

Nitrogen

Desorption-

Formulation

No. 6Y

Material

Sample

Weight

= 14

BET

Surface

Area

=

Total

Pore

Volume

.

68020

grams.

0.

17

square

meters

per

gram.

=

0.00106

ml per

gram.

Range Average

Pore

„

Pore

0

Diameter,

A

Diameter,

A

600-

500

500-

450

450-

400

400-

350

350-

300

300-

280

280-

260

260-

240

240-

220

220-

200

200-

180

180-

160

160-

150

150-

140

140-

130

130-

120

120-

110

110-

100

100-

95

95- 90

90- 85

85- 80

80- 75

75- 70

70- 65

65- 60

60- 55

55- 50

50- 45

45- 40

40- 35

35- 30

30- 25

25- 20

Below

20

550.0

475.0

425.0

375.0

325.0

290.0

270.

0

250.0

230.0

210.0

190.

0

170.

0

155.0

145.0

135.0

125.0

115.0

105.0

97.5

92. 5

87.5

82.5

77.

5

72.

5

67.5

62.5

57. 5

52.5

47.5

42.5

37.5

32.5

27.

5

22.5

10.

0

Percent

Pore

Volume

cc/g

8.930

5. 123

4.983

5.904

5. 925

2. 527

3.011

2. 727

3.216

3.014

3.918

3.586

2.228

1.985

2.409

2. 135

2.262

2.513

1.343

1. 372

1.329

1.902

1.913

2.421

2.423

2. 195

2. 225

2.492

2.098

2.688"

7.976

0.464

0.000

0. 743

Percent

Pore

Volume

CC/R/A

0.0893

0.

1024

0.0996

0.

1180

0.

1185

0.

1263

0.

1505

0.

1363

0.

1608

0.

1507

0.

1959

0.

1793

0.2228

0.

1985

0.

2409

0.2135

0.2262

0.2513

0.2687

0.2745

0.2659

0.

3804

0.

3827

0.4843

0.4847

0.4390

0.4450

0.4985

0.4197

0.5377

1.

5953

0.0929

0.

0000

0.0000

0.0371

Percent

Cumulative

Pore

Volume

cc/g

8. 930

14.054

19.038

24.

943

30.868

33.396

36.407

39. 135

42.351

45.366

49. 284

52.871

55. 100

57.086

59.495

61.631

63.893

66.407

67.751

69. 123

70.453

72.356

74.269

76.691

79. 115

81.310

83.535

86.027

88. 126

90.

815

98.792

99.256

99. 256

100.000

75

Y

76

The

similar

formulation

No. IX

material

had

been

found

during

Task

IV —

to

have both

a

larger

average pore diameter

and a

larger

total pore volume

(average

pore diameter

=

240A,

total pore volume

is 0.

0014 cc/g).

The

for-

mulation

No. 6Y

material

had an

average pore diameter

of

180A, which

was

considerably

larger

than

the 50A

value measured

during

Task IV*-

for the

similar

formulation

No. 4X

material.

However,

the

total pore volumes

of

the

materials

manufactured

from formulation Nos.

4X and 6Y

were very

similar,

i. e. , 0.

00099 cc/g

and 0. 001 1

cc/g, respectively.

Table

XXII presents

the

results

of the

nitrogen pore volume measure-

ment made

on a

sample

of

Grade CDJ.

Figure

12 is the

corresponding plot

of

percent pore volume

and

cumulative percent pore volume versus pore dia-

meter.

The

sample

of

Grade

CDJ was

found

to

have

an

average pore diameter

of

240A

and a

total pore volume

of 0.

0013 cc/g.

The

microporosity determined

for

Grade

CDJ is

almost identical

to

that

of the

formulation

No. IX

compact

examined during

Task

IV. —

The

internal structures

of the

carbon-graphite

seal

ring bodies manu-

factured

from

formulations Nos.

1Z and 6Y

appeared

by

visual examination

to

be

very homogeneous

and

fine-grained.

No

large

pores

or

voids

were

noted

in

the

compacts examined.

The

formulation

No. 5

compacts,

however,

were-found

to

have internal structures containing localized

areas

of

relatively high porosity.

These

!

'punky"

areas

were visible

to the

naked eye.

A

measure

of the

uniformity

of

the

structures

is

obtained

by

examining

the

percent Increases

in

weight

of the

compacts after impregnation with

the No. 121

oxidation-inhibiting treatment.

The

uniformity

of

impregnation reflects

the

uniformity

of the

internal structure

of

the

impregnated

material.

Table XXIII

lists

the

treat

pickups measured

for

the

1/2-inch ("1.3

cm)

cubes

of

formulations Nos.

IX, 1Z, 3, 5, 4X and 6Y

after

impregnation

with

the No. 121

oxidation-inhibiting treatment.

The

materials

im-

pregnated

with

the

oxidation-inhibiting treatment were

identified

(Tables

I and

VIII)

by the

formulation number

followed

by the

Number

121 (e. g. ,

formulation

No.

1X-121).

Table XXIII displays

the

coefficient

of

variation

for the

treat

pick-

ups

("V"

in

Table

XXIII).

Based

on the

calculated

coefficients

of

variation,

the

formulation

No. 1Z

material

was

more

uniform

than

the

similar

formulation

No.

IX

material,

the

formulation

No. 5

material

was

considerably

less

uniform

than

the

similar

formulation

No. 3

material,

and the

uniformity

of the

formulation

No.

6Y

material

was

comparable

with that

of the

formulation

No. 4X

material.

77

TABLE XXII

Pore

Volume

and

Distribution

by

Nitrogen

Desorption

-

Grade

CDJ

Sample

Weight

= 24.

03020

grams.

BETSurface

Area

= 0. 2

square

meters

per

gram.

Total

Pore

Volume

= 0.

00126

ml per

gram.

Range

Pore

Diameter,

A

600-

500

500-

450

450-

400

400-

350

350-

300

300-

280

280-

260

260-

240

240-

220

220-

200

200-

180

180-

160

160-

150

150-140

140-

130

130-

120

120-

110

110-

100

100-

95

95- 90

90- 85

85- 80

80- 75

75- 70

70- 65

65- 60

60- 55

55- 50

50- 45

45- 40

40- 35

35- 30

30- 25

25- 20

Below

20

Average

Pore

0

Diameter,

A

550.0

475.0

425.0

375.

0

325.0

290.0

270.0

250.0

230.0

210.0

190.0

170.0

155.0

145.0

135.

0

125.0

115.0

105.0

97.5

92.5

87.5

82. 5

77.

5

72.5

67.5

62. 5

57.5

52.5

47.5

42.5

37.5

32. 5

27.5

22.5

10.0

Percent

Pore

Volume

CC/B

13.880

6.967

6. 706

6. 502

6.296

2.386

2.439

2. 207

2.951

2.496

3. 136

2. 879

1.

831

2. 195

1.551

2. 158

2. 134

2.458

1.

121

1.412

1.

091

1.

516

1.

563

1.001

1.998

2.029

1.478

3.280

0. 364

2.

504

4.392

1. 372

0.000

0. 000

3.688

Percent

Pore

Volume

cc/g/A

0.

1388

0.

1393

0.

1341

0.

1300

X

0.

1259

0.

1193

0.

1219

0.

1103

0.

1475

0.

1248

0.

1568

0.

1439

0.

1831

0.2195

0.

1551

0.2158

0.2134

0.2458

0.2243

0.2825

0.2183

0.3033

0.3127

0.2002

0.

3996

0.4058

0.2957

0.

6560

0.0728

0.

5008

0.

8785

0.2745

0.

0000

0.

0000

0.

1844

Percent

Cumulative

Pore

Volume

cc/g

13.880

20.

848

27.554

34.057

40. 353

42. 740

45. 179

47.387

50.339

52.835

55.972

58.851

60.682

62.878

64. 430

66. 589

68. 723

71. 181

72.303

73.716

74.

808

76.325

77.

889

78. 890

80. 888

82.918

84.397

87.677

88.041

90. 545

94. 938

96.311

100.000

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80

Comparison

of the

pore volume data determined

by

mercury intrusion

(Table

XXIII)

with that

of the No, 121

oxidation-inhibiting

treat

pickups shows

the

expected trend

of

increasing

treat

pickup with increasing pore volume.

As

noted

during

Task

IV,

—normalization

of the

data presented

in

Table

XXIII

with

respect

to the

formulation

No.

1X-121

material

shows

a

disproportionately

high

treat

pickup

for the

formulation

No. 4X

material

based

on its

intruded pore

volume.

The

similar

material

manufactured from formulation

No. 6Y

experi-

enced

a

treat

pickup directly proportional

to its

pore volume determined

by

mercury intrusion,

i. e. , the

formulation

No. 6Y

material

had a

normalized

intruded

pore volume

of 2. 05 and a

normalized

treat

pickup

of 2. 06.

This

phe-

nomenon

is

probably

large

difference

in the

average pore dia-

meters

of the

materials

manufactured

from

formulations Nos.

4X and 6Y. The

treat

pickups

for the

for.mulations Nos. 1X-121, 1Z-121,

and

3-121

materials

also

were directly proportional

to

their respective pore volumes determined

by

mercury intrusion.

The

data listed

in

Table

XXIV

show

that

the

impregnation

of the

samples

of

formulations Nos.

1Z, 5, and 6Y

with

the No. 121

oxidation-inhibiting

treat-

ment increased

their

respective final densities.

The

impregnation with

the

No.

121

treatment probably

had

little

effect

on the

strengths

and

hardness

of

the

materials,

since

the

pickups

are

relatively

low and

since

no

additional

carbonaceous

material

was

added

to the

compacts

as in the

case

when

a

resin-

impregnant

is

carbonized.

The

densities listed

in

Table

XXIV

were measured

for

the

treated 1/2-inch (1.3

cm)

cubes which were

later

used

during

the

oxi-

dation

testing

of the

three

materials.

The

pore structures determined

for the

seal

ring bodies

of

formulations

Nos.

1Z and 6Y

indicate

that

both

are

potentially

good

carbon-graphite

seal

ring

materials.

Both

of the

formulations resulted

in

fine-grain

materials

with

relatively

low

porosity.

81

TABLE

XXIV

Bulk Densities

of

Materials

Impregnated

with

121

Oxidation-Inhibiting Treatment

(Grams/Cubic Centimeter)

Formulation

No. 1Z

Formulation

No.

1Z-121

Maximum 1.794 1.825

Minimum 1.783 1.816

Average

1.789 1.821

Standard

Deviation 0.004 0.004

n 6 6

Formulation

No. 5

Formulation

No.

5-121

Maximum 1.696 1.729

Minimum 1.653 1.703

Average 1.675 1.717

Standard Deviation 0.016 0.010

n

66

Formulation

No. 6Y

Formulation

No.

6Y-I21

Maximum

'

1.514 1.574

Minimum 1.501 1.547

Average 1.507 1.556

Standard Deviation 0.005 0.011

n 6 6

82

E.

Oxidation

Tests

High

oxidation resistance

is a

primary requirement

for a

carbon^

graphite

seal

ring material which

is

exposed.to ambient

air

temperatures

up

to

1300°F

(704°C).

A

material

with

a

high degree

of

crystallinity

is

needed,

since

the

crystallinity

of a

carbon-rgraphite

material

greatly

affects

the

rate

at

which

it

oxidizes. Formulation Nos.

1Z.~,

5, and 6Y

were designed

to

yield

carbon-graphite

seal

ring bodies

with

high degrees

of

crystallinity.

Further

increases

in

oxidation resistance

are

obtained

by

impregnating

the

seal

ring

bodies with oxidation-inhibiting treatments, such

as the No. 121

treatment.

Oxidation

tests

were

conducted

at

1300°F

(704°C)

with

1/2-inch

(1. 3 cm)

cubes

prepared

from

the

seal

ring bodies

of

formulation Nos.

1Z, 5, and 6Y.

Com-

mercial

seal

ring Grade

CDJ was

used

as a

standard

for the

oxidation testing.

The 1/2

T-ihch

(1. 3 cm)

cubes were impregnated

with

the No. 121

treatment

before

being exposed

to the

oxidizing conditions;

the No. 121

treat

pickups

were presented

in

Table XXIII.

The

oxidation test procedure

and

equipment employed during

Task

VII

were

the.same

as

those

us'ed

during the'-Tasks

land

IV

oxidation studies,

-

21

—

The

samples

were placed

in

one-inch

i. d.

quartz tubes, which subsequently were

supported

in a

small

electrically

heated furnace.

The

quartz tubes were used

to

keep

the

samples

from contacting

the

metal

support (which might have

acted

as an

oxidation catalyst)

and to

allow

the

removal

of the

oxidation

samples

from

the

furnace

without

damaging them.

Figure

13 is a

schematic

of the

oxidation

testing apparatus.

The

furnace

has a

split

door

which

was

propped open during

oxidation testing

so

that

a

3/8-inch

(0. 95 cm) gap was

maintained

across

the

entire

face

of the

furnace

between

the

upper

and

lower halves

of the

door.

The

quartz tubes containing

the

samples

were supported

so

that

the

samples

were

in

line

with

the gap

between

the two

sections

of the

door..

Air

passing through

the

gap

in the

door

also

flowed

around

the

samples,

as

shown

in

Figure

13. At the be-

ginning

of the

test,

the

samples

were weighed

and

placed into

the

quartz tubes, after

which

the

tubes containing

the

samples

were weighed

and

placed inside

the

1300°F

(704°

C)furnace

chamber.

After

1/2-hour exposure

to the

oxidizing condition,

the

quartz tubes containing

the

samples

were removed

from

the

furnace,

cooled

to

room temperature, weighed,

and

placed back inside

the

furnace

for

another 1/2-

hour period.

This

procedure

was

continued until

the

samples

had

been exposed

to

the

oxidizing conditions

for a

total

of

three hours.

A

preliminary testhad shown

that

the

weight

of the

empty quartz tubes remained constant

when

exposed

to the

1300°F

(704°C)

temperature.

83 '

9

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QUARTZ

TUBE

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FURNACE

TEMPERATURE

MAJNTAINED

AT

1300°F

(704°C)

)

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84

Three

oxidation

tests

were conducted during

Task

VII

using

the No. 121

treated

samples.

During

each

test,

one

sample

of

each

of the

formulations Nos.

1Z-121,

5-121,

and

6Y-121

and one

sample

of

Grade CDJ-121 were exposed

to

the

1300°F

(704°C)

temperature

for a

three-hour period.

The

relative

positions

of

the

four

materials

in the

furnace were changed

for

each

test

to

avoid

any

possible

position-to-position variation

in the

oxidizing conditions.

One of the

tests

was

extended

to

include weight measurements after 4-1/2 hours:

and six

hours

of

exposure,

and two

tests

were extended

to

include seven-hour

readings.

The

agreement

between

the

oxidation

rates

determined

for the

Grade CDJ-121

standards during

the

Tasks

IV and VII

oxidation studies indicated that

the

oxida-

tion

results

from

the two

series

of

tests

can be

compared directly.

Figures

14 to 16 are

semi-logarithmic plots

of the

average percent

weight

loss

versus exposure time

at

1300°F

(704*0)

for the

samples

of

formu-

lations Nos. 1Z-121, 5-121,

and

6Y^121.

Each

figure

includes

the

control

Grade CDJ-121 oxidation curve.

The

oxidation

rates

for all

three

of

theNo.

121

treated

materials

manufactured during

Task

VI

were significantly lower than

that

of

Grade CDJ-121. Also included

in

each

figure

is the

oxidation curve

de-

termined during

Task

IV — for a

similar

material

manufactured

during

Task

III.

^

Figure

14 is a

plot

of the

oxidation

rate

for the

formulation

No.

1Z-121

material.

This

material

oxidized

at a

slower average

rate

than that determined

for

the

similar

formulation

No.

1X-121

material

manufactured during

Tasklll.

—

The

presence

of a

slightly greater amount

of

absorbed moisture probably

accounted

for the

higher weight

losses

experienced

with

the

formulation No.lZ-121

material

during

the

initial one-half hour

of

exposure. One" common method

of

characterizing

the

oxidation

resistance

of a

carbon-graphite

material

is to

specify

the

exposure time

at

temperature required

to

produce

a

5-percent

loss

in the

weight

of the

material.

The

formulation

No.

1Z-121

material

experienced

a

5-per-

cent weight

loss

after being exposed

to the

1300°F

(704°C)

ambient

air for 6. 7

hours.

This

result

was an

improvement over

the

formulation

No.

IX-121

material,

which

required only

4. 7

hours

to

achieve

the

5-percent weight

loss

when

tested under

the

same

conditions.

85

Sample Size

=

l/Z"x l/2"x 1/Z"

(1.

3cmx

1.

3cmx

1.

3cm)

I

I I I I

I I I

II II

o

1.5

2.0 2. 5 3.0 3. 5 4.0 4.5 5.0 5.5

Exposure

Time

(Hours)

6. 5 7. 0

Figure

14.

Percent

Weight

Loss

Versus

Exposure Time

at

1300°F

(704°Q

-

Formulation

No.

1Z-121

Material.

G720399

86'

Sample Size

=

1/2"

x

1/2"

x

1/2"

(1.

3cmx

1.

3cmx

1.

3cm)

I

I I

II I I I II I I

0.3 h—

0.2

0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4. 5 5.0 5. 5 6. 0 6.5 7.0

Exposure

Time

(Hours)

Figure

15.

Percent

Weight

Loss

Versus

Exposure Time

at

1300°F

(704

9

C)

-

Formulation

No.

5-121 Material.

G720398

87

100.

0

90.0

80.0

70. 0

60. 0

50. 0

40.0

30. 0

20.

0

10.0

9.0

« 8.0

S

7.0

^ 6. 0

4-*

§5.0

<u

^ 4.0

4J

8

3.0

2.0

1.0

0.9

0.8

0. 7

0.6

0.5

0.4

0.3

0.2

Sample Size

=

1/2"

x

1/2"

x

1/2"

(1.

3cmx

1.

3cmx

1.

3cm)

I I I I I I I I I I I I I

0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0

Exposure Time

(Hours)

Figure

16.

Percent

Weight

Loss

Versus

Exposure

Tirrie

at

1300°F

(704°C)

-

Formulation

No.

6Y-121

Material.

•'.-••••

G720397

88

Figure

15 is a

plot

of the

1300°F

(704°

C)

oxidation

rate

determined

for

the

formulation

No.

5-121

material.

The

initial

weight

losses

measured

for

the

formulation

No.

5-121

material

were considerably

larger

than those deter-

mined during

Task

IV — for the

similar

formulation

No.

3-121

material.

The

weight

pickups measured after impregnation with

the No. 121

oxidation-

inhibiting

treatment

indicated

that

the

formulation

No. 5

material

was

more

porous

and

considerably

less

uniform than

the

material

manufactured from

formulation

No. 3. The

greater

porosity

of the

formulation

No. 5

material

and

the

resultant

higher

treat

pickup probably

increased

the

amount

of

adsorbed

moisture removed during

the

initial

one-half hour

of

exposure.

This

expulsion

of

moisture

may

account

for the

higher

initial

oxidation

rate

of the

formulation

No.

5

material

as

compared with that

of the

formulation

No. 3

material.

Although

their

initial

weight

losses

were different, both

the

formulation

No.

5-121

material

and the

formulation

No.

3-121

material

experienced

a

5-percent

weight

loss

after approximately

six

hours

of

exposure

to the

1300°F

(704°C)

ambient

air.

The

.oxidation curve

for the

formulation

No.

6Y-121

material

is

pre-

sented

in

Figure

16.

Comparison

of

this

oxidation curve with

that

determined

for

the

similar

formulation No.4X-121

material

during

Task

IV —

shows

that

the

two

materials

have

comparable

oxidation

resistance.

The

formulation

No.

6Y-121

material

experienced

a

5-percent

loss

Ln

weight after

5.4

hours

of

exposure

and the

formulation

No.

4X-121

material

required only

4. 7

hours

to

achieve

this

weight

loss.

The

difference between

the

oxidation

rates

of the

materials

manufactured

from formulations Nos. IX-121, l-Z-121,

3-121,

5-121,-

4X-121,

and6Y-121

were

relatively

small.

A

statistical

analysis

of

these oxidation data

was

con-

ducted

to

determine whether

the

observed differences were significant.

Table

XXV

lists

the

differences

in

percent weight

loss

measured after

1/2

hour

and

three

hours

of

exposure

to the

oxidizing conditions.

This

procedure

for

specifying oxi-

dation

losses

was

adopted during

Task

I

%•

when

the

evaporation

of

absorbed

moisture

was

found

to

distort

the

incremental

weight

losses

measured after

the

first

1/2

hour

of

exposure.

89

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,

Chemic

udent

' s t

ithematical

;rimentation

of

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iuction

to N

iustrial

Ex;

r

explanatic

°a 2

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90

Table

XXV

also

displays

the

results

of the

Student's

t

distribution

15

''

1

^

used

to

compare

the

weight

losses

(A

Percent

Weight

Loss

1/2-3 hours)

deter-

mined

for the six

materials.

The

statistical

analysis

indicates

that

the

apparent

difference

in the

oxidation

rate

of

formulations

No.

1X^121

material

and

that

of

the

formulation

No.

1Z-121

material

is not

significant.

No

significant differences

were indicated

in the

oxidation

rates

of the

materials

manufactured from formu-

lations

Nos. 1X-121, 1Z-121, 3-121, 5-121, 4X-121, and6Y-121.

The

oxidation

rates

determined

for the

samples

of the

materials

manu-

factured

from formulations Nos. 1X-121, 5-121,

and

6Y-121

indicate

that

the

three

materials

are

potentially

good

carbon-graphite

seal

ring

materials.The

materials

manufactured from formulations Nos. 1Z-121

and

6Y-121

showed

oxidation

resistances

at

least

comparable

with those

of the

similar

materials

manufactured during

Task

III.

—'

91

SECTION

VII

DISCUSSION

OF THE

RESULTS

An

overall comparison

of the

material

properties

measured

for the

seal

ring

bodies

of

formulations Nos.

1Z, 5, and 6Y is

needed

to

determine which

materials

are

best

suited

for use as

self-acting

seals

which will

be

exposed

to

ambient

air

temperatures

up to

1300°F

(704°C).

The

results

of

Task

VII

have

shown that

the

materials

manufactured

from formulations Nos. 1Z-121

and

6Y-121

are

potentially better

seal

ring

materials

for

high temperature

use

than

commercial

Grade

CDJ-121. Although

the two

materials

are not so

strong

and

hard

as

Grade CDJ-121, they have much better

thermal

properties.

The

high

thermal

conductivities

of the

seal

ring bodies

of

formulations Nos.

1Z and 6Y

will provide

rapid

transfer

of the

deleterious frictional heat

which

can

develop

during periods

of

sliding

contact

After

they have been impregnated with

the

No.

121

oxidation-inhibiting treatment,

the two

materials

have significantly

better oxidation

resistance

than Grade CDJ-121.

The

seal

life

of the two ma-

terials,therefore,

should

surpass

that

of

Grade CDJ-121 under high ambient

air

temperature conditions where oxidation

is the

limiting performance factor.

Both

of the

materials

have

the

further advantage

of

being much more machinable

than Grade CDJ.

Good

machinability

is

very desirable

for a

seal

ring

material,

since

seal

dam

widths

as

small

as 0. 02

inches

(. 05 cm)

often

are

necessary

in

seal

design.

The

material

properties determined

for the

seal

ring bodies

of

formu-

lation

No..

1Z

indicate

that

it is a

potentially

good

material

for

meeting

the

goal

of

the

Contract.

In

some

respects,

the

formulation

No. 1Z

material

is a

better

seal

ring

material

than that manufactured from

the

similar

formulation

No. IX

during

Task

III.

— The

formulation

No. IX

material

had

been

judged

during

Task

IV— to be the

best

material

manufactured during Task

III—

for

meeting

the

goal

of

this Contract.

After

impregnation with

the No. 121

oxidation-inhibiting

treatment,

the

formulation

No. 1Z- 121

material

had an

oxidation

rate

at

least

as

low

as

that

of the

material

manufactured from formulation

No.

lX-121.The narrow

spread

in the No. 121

treat

pickups measured

for the

compacts

of

formulation

No.

1Z-121 indicates that

it was the

most

uniform

material

manufactured thus far.

Formulations Nos.

IX and 1Z

yielded carbon-graphite

materials

with

similar

thermal

and

mechanical

properties.

92

Formulation

No. 1Z was not

among

the

three

material

formulations

originally selected

for

the. manufacturing

of

carbon-graphite

seal

ring bodies

during

Task

VI.

Formulation

No. 1Z was

substituted

for

formulation

No. 1Y

after

processing, problems prevented

the

manufacture

of the

latter

.material.

Although

a

sufficient

quantity

of the

formulation

No. 1Z

material

was

success-

fully

produced

to

fulfill

the

.testing

and

delivery requirements prescribed

by

the: Contract,,

a

processing problem

also

was

encountered

during

its

manufacture.

This problem consisted

of the

chipping

of the

resin-impregnated

2800°C

baked

compacts

during

rebaking

to

1000°C.

The

chipping problem

was

attributed

to

the

furfuryl

alcohol

(50

pbw)-Bakelite BRP-5095

resin

(35

pbw) impregnant.

The

resin

solution apparently filled

the

open porosity

of the

large

compacts

so

com-

pletely that,

during

pyrolysis, volatiles

could

not

escape

without

disrupting

the

stock.

Although

this resin impregnant

was

successfully used during Task

V to

produce

small

(4 - in ch x 0. 5

-inch

x 0. 2 5-

inch (10.

2cm x 1.3 cm x 0. 6

cm))

1QGG°C

baked samples

of

formulation

No. 1Y, it is not a

good

impregnant

for

manufacturing

large

(5-inch (1Z.

7 cm)

diameter

x 1.

4-inch

(3. 6 cm)

thick)

compacts.

The

disruption

of the

large

resin

impregnated, compacts during

rebaking

to

1000°C

prevented

the

manufacture

of the

formulation

No. 1Y ma-

terial

and the

formulation

No. 6Y

ring blanks

during

Task .VI.

The

chipping

of

the

formulation

No. 1Z

material

was

reduced

to a

tolerable level

by

using

a

very slow

firing

schedule

to

rebake

the

resin

impregnated compacts

to

1000°C.

No

further damage

was

sustained

by the

formulation

No. 1Z

compacts during

final baking

to

2800°C.

Formulation

No.

5'was

the

base

material

for one of the

three formu-

lations

(No.

5Y)

originally

selected.for

the

manufacture

of

seal

ring bodies

during

Task

VI. The

formulation

No. 5

material

was the

same

as

that manu-

factured

from

formulation-No.

3

during Task

III—

except that formulation

No. 5

included

pressure

curing

and

pressure baking

as a

part

of its

processing.

The

two

baking procedures

had

been

found

during

the

Task

V

screening, studies

to

be

good

ways

to

improve

the

mechanical properties.

.

Major-processing problems

were encountered during

the

manufacture

of the

formulation

No. 5

material.

These

processing problems most probably resulted

from

the use of the

one-year-old

.formulation

No. 3 mix

remaining

from

Task

III.

—

The

Bakelite BRP-5095

resin

binder

in

this

mix.apparently

had

deteriorated

with

age.

The

apparent deterioration

93

of

the

resin

binder

had

first

been noted during the. Task

V

screening,

study.

The

1000°C

baked density

(1.427

g/cc)

of the

compacts prepared during Task

V

from

the

one-year-old

mix was

considerably lower than that

(1. 519

g/cc)

of the

formuv

lation

No. 3

compacts

produced

during

Task

III.

— In

view

of the

processing

difficulties

experienced,

only

a few of the

formulation

No. 5

compacts were com-

pletely processed during Task

V

through baking

to

2800°C.

The

formulation-No.

5

compacts were

not

resin-impregnated

prior

to

final baking

to

2800°C,

since

the

Contractor

wanted.to

avoid

any

further

processing

problems which might

result

from

the use of the

furfuryl

alcohol-Bakelite

BRP-5095 resin-impregnating

solution.

The

formulation

No. 5

material

was not

completely characterized during

Task

VII, since

the

apparent deterioration

of the

resin

binder

had

prevented

the

material

from gaining

the

full

benefit

of

pressure baking. Only

the

mechanical

properties

and

oxidation

rate

of the

formulation

No. 5

material

were determined.

The

oxidation testing.was.,carried

out by

using

samples

impregnated with

the

No.

121

oxidation-inhibiting treatment..

The

material

properties measured

for

the

pressure

baked formulation

No. 5

material

were approximately

the

same,

as

those measured during Task

IV—

for the

similar,

formulatipn

No. 3

material.

The

material

properties determined

for the

formulation

No. 6Y

material

indicate that

it is a

potentially better

seal

ring

material

than that manufactured

from

the

similar

formulation

No. 4X

during Task III;

—

Formulation

No. 6Y re-

sulted

in a

material

with mechanical

properties

approximately

the

same

as

those

determined

for the

formulation

No. 4X

material.

However,

the

formulation

No.

6Y

material

had

a.higher

thermal

conductivity than that measured

.for

the

formulation

No. 4X

material

and a

considerably lower

coefficient

of

thermal

expansion.

The

higher thermal,

conductivity

indicates that

the

formulation

No. 6Y

material

will

more rapidly, dissipate

the

frictional heat generated during limited

periods

of

sliding contact.

The

lower

coefficient

of

thermal expansion measured

.for

the

formulation

No. 6Y

material

is

beneficial

from

a

thermal

deformation

standpoint.

The

formulation

No.

6Y-12

1.

material

and

that manufactured

from

formulation

No.

4X-121 oxidized

at

approximately

the

same-rate.

94

No

manufacturing problems were encountered during

the

processing

of

the

solid plugs

of

formulation

No. 6Y

through final baking

to

2800°

G.

Formu-

lation

No. 6Y

specified

the

impregnation

of

1000°C

baked

formulation

No. 6

compacts'with

the

furfuryl

alcohol

(50

pbw)-Bakelite BRP-5095

resin

(35

pbw)

solution

prior

to

final baking

to

2800°C. However,

the

apparent formation

of

a low

porosity surface

on the

solid plugs during processing impeded

the

pene-

tration

of the

resin

impregnant.

Due to the low

resin

pickup.

(1.

1-percent),

very

little

carbonaceous

material

was

gained from

the

resin

Lmpregnant

after

rebaking

the

solid plugs. Since

the

solid plugs

of

formulation

No. 6Y

experi-

enced such

a

small

resin

pickup,

the

material

properties

determined

for the

formulation

No. 6Y

material

during

Task

VII

should

be, for all

practical

pur~

poses,

the

same

as

those which

would

be

measured

for the

non-resin-impreg-

nated formulation

No. 6

base

material.

Ring

blanks

were manufactured from formulation

No. 6

after processing

problems

prevented

the

manufacture

of the

resin-impregnated formulation

No.

6Y

ring

blanks.

The

processing problems resulted from

the

large

resin

pickup

(11.

1%)

obtained

for the

formulation

No. 6Y

ring

blanks.

Unlike

the

solid plugs

of the

formulation

No. 6Y

material,

the

ring

blanks

apparently

did

not

form

the low

porosity surface during processing;

a

result

which accounted

for

the

large

resin

pickup.

The

larger

surface-to-volume ratio

of the

ring

blanks,

as

compared with that

of the

solid plugs,

was

probably

in

some

way

responsible

for

preventing

the low

porosity surface condition from developing.

Due

to the

large

resin

pickup,

the

formulation

No. 6Y

ring

blanks

broke

apart

during

rebaking

to

1000°C.

The

processing experience

and

material

properties

determined

for the

seal

ring

bodies

of

formulations Nos. 1X-121, 1Z-121, 4X-121, and6Y-121

have been examined

and the

materials

ranked

as to

their suitability

for

fulfilling

the

goal

of

this

Contract. These

four

materials

were

the

best

of all the ma-

terials

manufactured during

Tasks

III—

and VI for use as

self-acting

seal

rings.

The

four

materials

can be

ranked

in the

following order

of

decreasing suitability.

This

comparison

is

exclusive

of

wear

effects,

since

the

materials

manufactured

from

formulations Nos. 1Z-121

and

6Y-121

were

not

wear-performance tested.

'95

1.

Formulation

No.

1Z-121.

2.

Formulation

No.

1X-121.

,3.

Formulation

No.

6Y-121.

4.

Formulation

No.

4X-121.

The

materials

manufactured

from

formulations Nos. lZ-121.and

1X-121

are

listed

first

and

second, since they

are

approximately twice

as

hard

as the

materials

manufactured

.from

formulations Nos.

6Y-121

and

4X-121.

. Due to

their-increased hardness,

the

first

two

materials

should

be

more erosion-

and

wear-resistant than

the

other

two

materials.

The for

mulation

No. 1Z - 121

material

is

listed

first, since

it is

more

uniform

and at

least

as

oxidation-

resistant

as the

formulation

No.

IX-121

material.

Of the two

materials,

however,

the

formulation

No.

1Z-121

was

found

to be the

more

difficult

to

manufacture.

Formulation

No.

6Y-121

is

listed third,

since

it

produced

a

material

with better

thermal

properties than that

of

the.

material

manufactured

from

formulation

No.

4X-121;

the

oxidation-resistance.was equal

to

that

of

formulation

No.

4X-121.

The

materials

manufactured from formulations

Nos. 4X-121

and

6Y-121

have approximately

the

same

mechanical properties.

Further

improvements

in the

strength,

uniformity,

hardness,

and

oxidation

resistance

of the

materials

developed

during

Tasks

I

through

VII

would

enable

broader

application

of

these

materials.

The use of

finer

par -

ticulate filler

materials

might

be one

method

of

obtaining

the

required

Im-

provements. Intensive mixing

may

also

be

beneficial, and,

when

used

in

combination

with

warm molding, might allow

for a

reduction

in the

binder

level

required

for

processing with attendant improvements

in

properties.

Pressure

baking

also

warrants

further

study.

The

pressure-baked formu-

lation

No. 5

material

might have been

one of the

best

materials

manufactured

thus

far if it had

been

produced

with

a

"fresh" batch

of the

Bakelite BRP-5095

resin

as the

binder

material.

96

APPENDIX

I

PROCEDURES

USED

TO

CHARACTERIZE

RAW

MATERIALS

Helium

Density-

Surface

Area-

Screen Analysis-

Chemical Analysis-

Emission Spectrographic

Analysis

-

Coking

Value

-

Benzene Insoluble-

Quinoline

Insoluble-

Softening

Point

-

Elemental Chemical

Analysis

-

Differential

Thermal

Analysis-

Thermal

Gravimetric

Analysis-

Measured

with

Beckman pycnometer

B.

E. T.

method

Tyler standard screen sieve

analysis

Ash

measured

per

ASTM C561 except

680°C

overnight

Moisture

measured

by

drying

at

105°

C

overnight

Modification

of

ASTM

C562

Conducted

using

Jerrell

Ash

emission

spectrograph

Modified

Conradson technique

(ASTM

D-189-52).

Modification

is

furnace

instead

of gas

burner

for

heat

Method

based

on

ASTM

D2317

Method

based

on

ASTM

D2318

Method

based

on

ASTM

D2319

(C)

Combustion techniques using gravi-

metric

analysis

(H)

Combustion techniques using gravi-

metric

analysis

(O)

LECO oxygen analyzer

(N)

Kjeldahl method

(S)

X-ray fluorescence

Mettler

thermal

analyzer

Mettler thermal analyzer

97

APPENDIX

II

PROCEDURES

USED

.TO

MEASURE MATERIAL PROPERTIES

Bulk Density-

Helium Density

-

Flexural

Strength-

Elastic

Modulus

-

Hardness

-

Thermal

Conductivity-

Coefficient

of

Thermal

Expansion-

Determined

by

direct physical measurement

of

mass

and

volume.

Measured with Beckman pycnometer.

ASTM

C651-70

through

use of a 4.

5-inch

x 1.

0-inch

x 0.

5-inch

(11.4cmx2.5cm

x 1.3 cm)

ground sample.

Determined

by a

sonic resonance method

by

utilizing

a

variable

frequency

oscillator,

amplifier,

frequency

counter, oscilloscope,

filter,

and

transmitting

and

receiving

trans-

ducers. Measured

at

room temperature

by

using

a 4.

5-inch

x 1.

0-inch

x 0.

5-inch

(11.4

cm x 2. 5 cmx 1.3 cm)

ground

sample.

Measured

with

a

Rockwell Hardness

Tester

by

using

a 0.

5-inch

(1. 3 cm)

diameter

ball,

a 100 Kg

major load,

and the R

scale.

Calculated from

a

measured thermal dif-

fusivity

by

using

a

sample

of

known

density

and

specific

heat.

Thermal

diffusivity

is

measured

by a

laser

flash method

by

using

a

pulsed ruby

laser

with associated

mirrors,

filters, thermocouples, oscilloscopes,

and

camera.

Measured

at

room temperature

by

using

a 0.

5-inch

(1. 3 cm)

diameter

x

0.

080-inch

(. 20 cm)

thick sample.

Measured

by an

elongation method

by

using

a

tube

furnace,

twin

telescopes, thermo-

couples

and

optical pyrometers. This

measurement

was

carried

out

from

room

temperature

to

1000°

C in an

argon

atmos-

phere

by

using

a 0.

5-inch

x 0.

5-inch

x

2.

5-inch (1.3

cmx 1.3

cmx6.4

cm)

ground

sample.

98

APPENDIX

II

(Cont'd)

Pore

Volume

and

Distribution

by

Mercury Intrusion-

Pore

Volume

b.yNitrpgen

Desorption-

The

sample

is

placed

in a

chamber

and

evacuated.

Mercury

from

an

external

reservoir

is

induced

into

the

sealed

chamber

as the

system

is

allowed

to

come

back

up to

atmospheric

pressure.

When

equilibrium

is

reached, increasing

amounts

of

pressure

are

applied

to the

mercury

in the

reservoir

and the

corres-

ponding

changes

in the

volume

of the

mercury

in the

reservoir

are

recorded

as the

mercury

is

intruded

into

the

sample.

Knowing

the

corresponding reservoir

volume

and

pressure changes allows

one

to

calculate

the

pore volume

and

distribution

of

the

sample, since

the

size

of the

pores

filled

by

mercury

is

inversely proportional

to the

applied

pressure.

Mercury does

not

wet

carbon-graphite

material.

o

The

volume

of

pores

smaller

than

600A

in

diameter

was

determined

from

the

nitrogen

desorption

isotherm

by

using

the

exact

form

of

the

equation attributed

to

Barrett, Joyner,

and

Halenda ^-'^-

with

no

simplifying

assumptions.

99

APPENDIX

III

DEFINITION

OF

STATISTICAL TERMS

F

Distribution

(1$)

A

calculated

n

X

- 1

Where

cr

2

and <r

2

are. unbiased

estimates

of

the

two

sample

variances,

a

2

will always

denote

the

larger

of the two

estimates.

n.

Where

x =

samples.

n-

x

;

ri is

the. size'

of the

random

Similarly:

n

- 1

y

After

calculating

the

value

of F, it is

compared

to the 2. 5%

critical

value

of F

obtained from

a

statistical

F

distribution

table.

To

deter-

mine

the 2. 5%

critical

value

of F

from

the

table,

the two

degrees

of

freedom

are

necessary.

The two

degrees

of

freedom

are

calculated

as

follows:

v

] = n

- 1 ,

The 2. 5%

critical

value

of F is for a

double

tail

analysis

at a 95%

confidence

level.

If the

calculated value

of F is

less

than

the 2. 5%

critical

value

of F

obtained from

the

statistical

table,

then

the

Student's

t

distribution

can be

used

to

compare

the

means

of the two

samples

as

follows.

100

APPENDIX

III

(Cont'd)

Student's

t

Distribution

(is,,

16.J

The

Student's

t

distribution

is

used

to

determine whether

the

mean

of

one

sample

is

significantly

different

from

the

mean

of a

second

sample,

or

whether

the two

sample means

can be

regarded

as

drawn

from

one

population.

n.

n

yi

x =

<r

2

=

, y —

v»nt;iri;

3

n

- ' n ,

x y

sample

["

n,

r

y

S

(y.*)

-

n \

y

\

S

(y-)

n

1=1

> + -^

f,-

2

^

n

+

r.

U

i '

L

1-1 y 1-1

(.

ia LUG iax gci L

means.

(

n \

x I

S

(x.)

2

i=l

1

/

n

x

(n

+ n - 2)

x y

calculated

After

calculating

the

value

of t, it is

compared

to the

value

of t

obtained

from

a

statistical

t

distribution table.

To

obtain

the

value

of

t

from

the

table,

the

degrees

of

freedom

must

be

calculated using

the

following

equation:

Degrees

of

freedom

=n + n - 2.

6

x y

After

calculating

the

degrees

of-freedom,

the

corresponding

value

of

t can be

found

in the

table

using

a

value

of P

(probability)

equal

to

0.

05 for a

single tail analysis

at a 95%

confidence

level.

The

differ-

ence

between

the

means

of the two

sample

populations

is

significant

only

if the

calculated

value

of t is

greater

than

the

value

of t

from

the

table. That

is:

t ' i i .. j > t , ,, =

significant

calculated

table

6

t

i i -i j < t . , , = not

significant

calculated

table

6

101

REFERENCES

1.

Parks,

A. J. ,

McKibbin,

R. H. , and Ng, C. C. W. ,

"Development

of

Main

Shaft

Seals

for

Advanced

Air

Breathing Propulsion Systems,

"

NAS3-7609,

Final

Report

Phase

I

(August,

1967),

NASA

CR-72338,

page

49.

2.

Johnson, Robert

L. , and

Ludwig, Lawrence

P. ,

"Shaft

Face

Seal

with Self-

Acting

Lift

Augmentation

for

Advanced

Gas

Turbine Engines,

"

NASA-TN-

D-5170,

NASA

Lewis Research Center, Cleveland, Ohio, April, 1969.

3.

Strom,

Thomas

N. ,

Allen, Gordon

P. , and

Johnson, Robert

L. ,

"Wear

and

Friction

of

Impregnated Mechanical Carbons

at

Temperatures

to

1400°F

(760°C)

in Air or

Nitrogen, "NASA-TN -D-3958, page

2,

NASA

Lewis

Research

Center,, Cleveland, Ohio, May, 1967.

4.

Lauzau,

W. R. ,

Shelton

, B. R. , and

Waldheger,

R. A.,

"The

Use of

Carbon-Graphite

in

Mechanical

Seals,"

Lubrication Engineering, Volume

19,

pages 201-209, May, 1963.

5.

Fechter,

N. J. , and

Petrunich,

P. S. ,

"Development

of

Seal

Ring Carbon-

Graphite

Materials

(Tasks

I and

II),

"

Union

Carbide Corporation, Topical

Report

NASA

CR-72799

(Contract

NAS3-13211),

January, 1971.

6.

Fechter,

N. J. , and

Petrunich,

P. S. ,

"Development

of

Seal

Ring Carbon-

Graphite

Materials

(Tasks

III and

IV), "Union Carbide Corporation, Topical

Report

NASA

CR-72986

(Contract

NAS3-13211),

August,

197.1.

7.

"Pressure

Baked Graphite

Materials,"

Great

Lakes

Research Corporation,

Technical

Documentary Report

No.

ML-TDR-64-175 (Contract

No.

AF33

(657)-11738),

June, 1964.

8.

Loc. cit.

,

Reference

5,

pages 75-77.

9.

Loc. cit., Reference

5,

pages

84-89.

10.

Loc. cit.

,

Reference

6,

pages 77-87.

11.

Loc. cit., Reference

6,

page

79.

12.

Loc. cit., Reference

2,

page

17.

13. The

Industrial Graphite Engineering Handbook,

Union

Carbide Corporation,

pages

5A. 08.

OZ-5A.

08.

03,.

C1969.

102

REFERENCES

(Cont'd)

14.

JLoc.

cit.

,

Reference

6,

pages

73-75.

15.

Brownlee,

K. A.,

Industrial Experimentation, Chemical Publishing

Co. ,

Inc.

, New

York,

pages

28-32,

C1947.

16.

Hoel,

Paul

G. ,

Introduction

to

Mathematical Statistics,

John

Wiley

&

Sons,

Inc.,

New

York-London,

pages

271 to

288,

C1962.

17.

Barrett,

E. P. ,

Joyner,

L. G. , and

Halenda,

P. B. , The

Determination

of

Pore

Volume

and

Area Distributions

from

Nitrogen Isotherms, Journal

of

the

American Chemical Society, Volume

73,

page

373, 1951.

18.

Roberts,

B. F. , .A

Procedure

for

Estimating

Pore

Volume

and

Area

Distributions

by

Sorption Isotherms, Journal

of

Colloid

and

Interface

Science, Volume

23,

pages

266-273,

1967.

103

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R. E.

Burcham

1

62.

Sealol

Inc.

P. O. Box

2158

Providence,

RI

02905

Attn:

Justus Stevens

1

63. .

Sikorsky Aircraft

United

Aircraft Corp.

North

Main

St.

Stratford,

CT

06497

Attn:

L.

Burroughs

1

110

Addressee

No. of

Copies

64.

Sinclair

Refining

Co.

600

Fifth Ave.

. .

New

York,

NY

10020

•

Attn:

C. W.

McAllister

.. 1

65.

Sinclair

Research

Inc.

400

E.

Sibley Blvd.

Harvey,

IL

60426

Attn:

M. R.

Farille

1

66.

SKF

Industries, Inc.

1100

First

Ave.

King

of

Prussia,

PA

19406

Attn:

L. B.

Sibley

. 1

67.

Socony

Mobil

Oil

Company

Research Dept.

Paulsboro

Lab

Paulsboro,

NJ

08066

Attn:

E.

Oberright

1

68. St.

Marys

Co.

1939

State Road

.

St.

Marys,

PA

15857

Attn:

J. E.

Lanzel

. 1

69.

Director

Government

Research

Lab .

Esso

Research

&

Engineering

Co.

P. O. Box 8

Linden,

NJ

07036

1

70.

Southwest Research Institute

P. O.

Drawer

28510

San

Antonio,

TX

78284

Attn:

P

r

M. Ku 1

71.

Stanford Research Institute

Menlo

Park,

CA

94025

Attn:

R. C. Fey 1

72.

Stein

Seal

Company

20th

St. &

Indiana Ave.

Philadelphia,

PA

19132

Attn:

Dr. P. C.

Stein

. 1

73.

Sun Oil

Company

Automotive

Laboratory

Marcus Hook,

PA

19061

Attn:

J. L.

Griffith

1

111

Addressee

. •. No. of

Copies

74.

Ultra

Carbon Corp.

St.

Marys,

PA

15857

Attn:

Dr. E. I.

Shobert

1

75.

Ultra

Carbon

Corp.

1300

N. '

Madison Ave.

Bay

City,

MI

48706

Attn:

Del

Hughes

. 1

76.

United Aircraft Corp.

Pratt

&

Whitney Aircraft

East

Hartford,

CT

06108

Attn:

R.

Shevchenko,

Engr.

Bldg.

1

77.

United

States

Graphite

Company

1620

Holland

Saginaw,

MI

48601

Attn:

F. F.

Ruhl

1

78.

Westinghouse

Electric

Corp.

5100

W.

164th

St.

Cleveland,

OH

44142

Attn:

Lynn

Powers

1

79.

Wright-Aeronautical Division

Curtiss-Wright Corp.

333

West

First

St.

Dayton,

OH

45402

y

Attn:

D.

Lombardo

1

80.

Pennsylvania

State University

Dept.

of

Chemical

Engineering

University

Park,

PA

16802

Attn:

Dr. E. E.

Klaus

1

81. The

University

of

Tennessee

Dept.

of

Mechanical

&

Aerospace

Engr.

'

Knoxville,

TN

37916

Attn:

Prof.

W. K.

Stair

1

Dr. C.

Fisher

1

112