NASA/TM-2000--209897

Material Total Mass Loss in Vacuum Obtained from

Various Outgassing Systems

John Scialdone, Peggy Isaac, Carroll Clatterbuck, and Ronald Hunkeler

National Aeronautics and Space Administration

Goddard Space Flight Center

Greenbelt, Maryland 20771

July 2000

https://ntrs.nasa.gov/search.jsp?R=20010038656 2018-05-15T06:54:33+00:00Z
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NASA/TM-2000-209897

Material Total Mass Loss in Vacuum Obtained from

Various Outgassing Systems

John Scialdone, Peggy Isaac, Carroll Clatterbuck, and Ronald Hunkeler

NASA's Goddard Space Flight Center

Greenbelt, MD 20771

National Aeronautics and Space Administration

Goddard Space Flight Center

Greenbelt, Maryland 20771

July 2000
Available from:

NASA Center for AeroSpace Information

7121 Standard Drive

Hanover, MD 21076-1320

Price Code: A17

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ABSTRACT

Several instruments including the Cahn Microbalance, the Knudsen Cell, the micro-CVCM, and the vacuum Thermogravimetric Analyzer (TGA) were used in the testing of a graphite/epoxy (GR/EP) composite that is proposed for use as a

rigidizing element of an inflatable deployment system. This GR/EP will be cured in situ. The purpose of this testing is to

estimate the gaseous production resulting from the curing of the GR/EP composite, to predict the resulting pressure, and to

calculate the required venting. Every test was conducted under vacuum at 125 degrees C for 24 hours. Upon comparison of

the results, the ASTM E-595 was noted to have given readings that were consistently lower than those obtained using the

other instruments, which otherwise provided similar results. The GR/EP was tested using several different geometric arrangements.

This paper describes the analysis evaluating the molecular and continuum flow of the outgassing products issuing from the

exit port of the ASTM E-595 system. The effective flow conductance provided by the physical dimensions of the vent

passage of the ASTM E-595 system and that of the material sample were investigated, among other factors, to explain the

reduced amount of outgassing released during the 24-hour test period.

°°.

111

1.0 INTRODUCTION

Materials selected for space applications must maintain

structural and chemical integrity when exposed to the

environmental conditions of space. They should have low

outgassing rates at normal operating temperatures and the

outgassing should consist of a minimum of materials

condensable at the temperatures of nearby surfaces.

The observation of distant sources of radiation or the

measurement of the space medium is affected minimally

with the spacecrafts having low outgassing. In addition,

voltage breakdowns and undesirable heat transfer regimes

at certain critical regions of the spacecraft are minimized by

limiting material outgassing. The requirement on

condensables reflects the potentially degrading effect of

materials deposits on radiating surfaces and on elements of

optical instruments. Deposits may change the thermal

properties of a surface and attenuate, reflect, and disperse

the incoming radiations to be measured.

Materials with the desirable characteristics have been

screened by a test developed in [1] and used at various

organizations including Goddard Space Flight Center

(GSFC), European Space Research Organization (ESRO),

and Jet Propulsion Lab (JPL). The test, described by [1-3],

consists of maintaining samples of about 200 mg of the

materials under consideration at a temperature of 398 K

(125°C) for 24 hours in a vacuum of about 10-6torr. The

sample mass loss and the amount of that mass which

condenses on a collector plate held at 298 K (25°C) and

located near the sample are used as some of the criteria for

the selection of these materials for space use. The test

temperatures were purposely designed to be extreme; these

temperatures can only be encountered in exceptional

applications. The pressure of 10.6 torr is sufficiently low to

prevent collisions between molecules leaving a surface. In

general, the material is considered acceptable if the total

mass loss (TML) is less than 1% and the volatile condensable mass (VCM) is less than 0.1% of the initial sample

mass. The criteria arise from the observation that certain

materials show mechanical and physical degradation when

they have lost 3 to 5% of their mass. For others, such as

elastomers, a 1% TML is usually detrimental to their

mechanical properties. A more definite interpretation can be

given to the 0.1% VCM criteria. The 0.1% condensate of a

1-kg material would cover 100m 2of surface with a uniform

10.6g/cm 2 layer corresponding to about 20 monolayers and

to a thickness of about 10.6cm.

Material coatings of these dimensions can be detrimental

for optical and thermal applications. Regardless of these

considerations, the selection criteria appear to provide

sufficient protection against the use of objectionable

materials. However, the test and its selection criteria do not

provide direct data that a designer requires to ensure against

contamination and the performance of certain systems. The

designer must know the materials' outgassing rates as a

function of temperature, time, and surface area and the

condensation of this outgassing at temperatures other than

298 K (25°C). With this data, the designer can select the

materials to use and can estimate the pressure versus time in

compartments and the deposits and contamination which

may occur on critical surfaces [4-6].

The criteria and the testing methods employed to qualify a

material for space application have worked well and

continue to do so. A targe number of materials have been

tested according to those criteria. Goddard Space Flight

Center provides a website with the outgassing data for

various materials [7]. ESTEC, located in the Netherlands,

also reports data on materials outgassing according to the

ASTM E-595 [8]. Other important characteristics of

materials, such as flammability, toxicity, and thermo-optical

properties are reported in other documents. This paper

discusses the use of the TML and CVCM obtained from the

ASTM E-595 tests for purposes other than general material

selection for space applications. These standard test data

have been used to get results about distribution, amount of

contaminant deposits, and other data at temperatures and

pressures other than those of the ASTM E-595 test.

The TML and CVCM have been employed to obtain the

outgassing activation energy, the vapor pressures, and the

outgassing rates of that material at different temperatures

and as a function of time. These extrapolations have been

used to compensate for the absence of difficult and expensive tests to obtain kinetic data on the materials. The

purpose of this paper is to ward against the indiscriminate

use of those data. As an example, the author was recently

requested to estimate the gaseous release from a graphite/

epoxy composite (see fig. 1) when heated at 121°C in a

vacuum and to indicate the vent(s) needed to prevent

excessive pressures within the confined volume containing

the material. The available data on the material for the

calculations were the TML from the E-595 test at 125°C.

Figure 1. Graphite/Epoxy Weave Sample
No data were available on the rate, the temperature, and the

length of time during which the major release of gas

occurred. The TML from the many standard tests carried

out on this material at 125°C for the 24 hours at 10_ torr

averaged about 1.8%. The author employed that value for

the requested evaluation. Meanwhile, a fully operational

Cahn microbalance that includes a residual gas analyzer and

a quartz crystal microbalance became available at the

author's laboratory. That facility was employed to test the

composite material. The facility, which shows the real-time

mass loss and the rate of mass loss as a function of time and

temperature as seen in fig. 2, indicated that at 121°C for 24

hours, the %TML was in excess of 13% (see fig. 3). It also

indicated that practically all of the mass loss occurred early

in the test and lasted for about 23 minutes. This TML result

confirmed by many tests of the same material, indicated a

much larger production of gas than that obtained using the

E-595 result. As a consequence, a study was initiated to

verily and compare the TML results given by the ASTM E595 facility, the Cahn Microbalance, the Vacuum TGA, and

the Knudsen Cell.

The analysis that follows is an attempt to obtain a better

understanding of the parameters affecting the micro-CVCM

tests. The analysis points to some of the reasons for the

different results obtained for the same materials by different

instruments. Most importantly, it gives some insight on the

utilization of the test results for the use of the designer.

Figure 2. Cahn/QCM/RGA Outgassing Facility
T

Figure 3. Graphite/Epoxy Outgassing Test

2.0 EXPERIMENTAL

Material tests according to the E-595 method are carried out

by placing chips or thin slices of the material with thicknesses of less than 3.1 mm (1/8 in) in a 10xl2x6-mm

container (fig. 4). This container boat is placed inside a

receptacle within a temperature controlling heated copper

bar. The receptacle has a venting port facing a collector. For

the test, the copper bar and the materials under test are held

at 125°C and the collector at 25°C. The assembly is located

within a vacuum chamber providing pressures of about 10.6

torr. The TML and CVCM are measured after the 24-hour

test. Other facilities not of the E-595 design can provide

direct measurements of the TML and CVCM for a 125°C/

25°C, 24-hour test. These facilities provide results that are

not affected nor controlled by the fixture design. Those

used here are a Vacuum Thermogravimetric Analyzer

(TGA), a Cahn microbalance, and a Knudsen cell. The TGA

provides an isothermal change of the mass of a small

sample of material and records it as a function of time. The

Knudsen cell holds a sample of material at a desired

temperature. A collector surface facing the cell exit collects

the mass lost from the sample at a desired temperature. The

TML is obtained by measuring the weight of the sample

before and after the test and then subtracting the final

weight from the initial weight. The Cahn microbalance

records the mass loss of the sample and the rate of change

at the chosen temperature as a function of time. These three

facilities were employed to obtain the TMLs of the sample

materials at 125°C or at 12 I°C for 24 hours in vacuum and

to compare the results.
NOMENCLATURE

A - SAMPLE BOAT

B - HEATER BAR

C - SAMPLE COMPARTMENT

D - COVER PLATE

E - HEATER ELEMENT

F - SEPARATOR PLATE

G - COLLECTOR DISK

H - RETAINING NUT

I - COOING PLATE

J - COOLING COIL

A

SPECIMEN

COMPARTMENT

COPPER HEATER BAR

SEPARATOR PLATE

}

/

/

f

I

/

II

II

II

II

II

ill "--

_11 II

iii II

)VER

PLATE

M

t<.- 12 mm --),

SAMPLE BOAT

ABOAT = 0.72 cm 2

_ 4 D. 0.31 = 0.2cm 2

ATUBE - _"

I AM == 6.3 16 mmmm diadia

IL = 8mm

J = 12.7mm

K = 1.6 mm

ATUBE ° A BOAT

= 0.15 cm 2

Figure 4. Micro-CVCM Apparatus
The results of the many tests done on the same material using

three different facilities are shown in Table 1. The TML test

results obtained with the E-595 averaged 1.67% with the

exception of one test. The Cahn system results averaged

15.86% for a 6.45 cm 2(lin 2) sample. Staking samples of the

material resulted in smaller average TMLs: five-staked

samples produced an average TML of 5.9%; four-staked

samples produced an average of 7.23%; three-staked samples

produced an average of 8.6%; a single sheet of material

fitting the E-595 boat produced a 18.63% average TML. The

results obtained from the Knudsen cell indicated a 16.94%

average for a 6.45 cm 2( l in 2) sample and a 6.1% TML for a

single test consisting of 6 sheets. The TGA indicated a 15.7%

TML for a single 1.5 cm diameter sample and 11.8% for a

stack of three of the same samples. The table shows the

temperature, the initial mass mo, the mass loss Am for the 24-

hour tests, and the resulting TMLs. A small symbol shows

the sample arrangement.

The samples used in these tests came from the same batch of

materials, but it may have been possible that some differences may have existed among them due to the non- uniformity of the epoxy coatings on the graphite filaments. With

regards to the sizes and dimensions, those for the E-595 were

in accord with the recommendations in the standard for the

E-595 tests. For the Cahn and Knudsen tests, the samples

were 1 in 2 (6.45 cm2). They were made of stacked layers of

the same dimensions. The samples for the TGA tests were of

round shapes made to fit the small instrument pan.

Table 1: Test Results of Mass Losses & TMLs of Graphite/Epoxy Weave

Test

Average:

Cahn Microbalance

Average (1 cm 2 ):

Knudsen Cell

Average (lcm2):

Vacuum TGA

I T (oc) l A (cm 2) I mo (rag)

125 121.77

125 118.90

125 145.14

125 140.25

125 149.34

125 266.73

157.02

Am (mg)

I ME

(percent) Sample Confi_quration

2.90 2.38 II/

1 .g7 1.65 III

2.63 1.81 ///

2.16 1.54 III

2.16 1.44 /11

3.25 1.22 /11

2.51 1.67

121.0 6.45

121.9 6.45

122.5 6.45

125.0

125.0

126.4 6.45

125.0

125.0

125.0

125.0

125.0

125 6.45

125 6.45

125

243.00 32.58 13.40

240.70 40.70 16.90

240.90 39.54 16.40

254.00 14.97 5.89

126.90

230.80

243.80

256.00

103.36

38.10

39.40

9.70

38.80

41.39

24.47

7.47

7.10

6.26

238.85 37.89

7.64

16.80

16.98

9.56

7.23

18.63

15.90

15.86

251.20 41.03 16.33

257.70 44.90 17.42

218.50 13.32 6.10

254.45 42.96 16.87

1.53 I 16.90 5353

2.66 15.70

6.34 11.86

I-1

El

IS]

i : 5 pieces 0.95cm x 0.95cm

I=_1: 3 pieces 0.95cm x 0.95cm

[]

III : 3 pieces 2.54cm x 0.83cm

----__: 3 Pieces 0.95cm x 0.95cm

I,=1 : 4 pieces 0.95cm x 0.95cm

: 1 piece 0.95cm x 0.95cm

I/I : 1 piece 0.95cm x 0.95cm

E3

[]

IIIIII

0

=
3.0 ANALYSIS

Table 1 shows the average test results from the Cahn Microbalance, the Knudsen Cell, and the TGA, and compares them

to the average TML result of 1.67% from the E-595 test. The

average results from the Cahn Microbalance, the Knudsen

Cell, and the TGA are 9.49, 10.10, and 8.25% higher,

respectively, that those of the ASTM E-595. This indicates

that the results from the non-E-595 facilities were on the

average about 9.28% higher than those of the E-595. The

justification for the difference could be found on the sampleexposed area and the mass released during the 24 hours. In

the case of the E-595, the sample is within a boat and the

outgassing leaves the cavity via a tubular passage. The flow

must proceed through a series of passages from the boat and

through the tube. The second consideration must be the

nature of the flow, either molecular or viscous flow. The

molecular density created in the cavity by the outgassing of

the E-595 test dictates the nature of the flow. The mass flow

from the other facilities is not restricted by the geometry or

by the gas mean free path conditions above the sample. The

samples are in an environment where the pressure is less than

10.6 torr and the flow of escaping gas is molecular. In both

types of testing facilities, the quantity of released gas is

affected by the staking and the percentages by the sample

masses as shown by the results produced by the restrictions

among layers.

On the basis of the above, two flow analyses have been

considered for the E-595 system. First, the flow may be

molecular. If so, the flow conductance is either a series

conductance made up of the boat passage area and the tubular

passage or the conductance is that of the tubular passage

alone. Alternatively, the assumption that the flow is a viscous

flow controlled by the tubular passage or by the boat open

area. These altematives have been compared to the losses

indicated by the other facilities operating in the molecular

region without area restrictions. The ratios of the mass losses

from the two systems, E-595 and the others, are then compared to the TML ratios obtained from the tests.

In the systems other than the micro-CVCM, the outgassed

molecules leave the surface of the sample according to the

cosine distribution law. The mass loss in a time t from the

material at temperature T is given according to the kinetic

theory as 1

m = -4PvAt (1)

where p (g/cm 3) is the mass density of the molecules moving

with velocity v=(3kT/mm)m where k (erg/K) is Boltzman's

constant, T is the surface temperature in K and m m(g/molec)

is the molecular mass [9-10]. The outgassing area A (cm 2) is

the exposed surface of the sample.

The outgassing releasing area for the sample in the E-595

m = pvAet (2)

will be an equivalent area A t resulting from the effective

conductance of the passages. The mass loss for the cotinuum

flow when the flow when sufficient gas is released is

For viscous conditions in the cavity, the tubular passage may

control the flow. Its diameter d is 0.63 cm, providing an area

0.31 cm 2, and the length L is 1.27 cm. The open area of the

boat is 0.72 cm 2, larger than that of the tube. A discharge

coefficient can be applied to the tube passage. For an orifice,

the discharge coefficient for viscous flow can be assumed to

be 0.6. For the pipe, the Clausing factor _ for molecular flow

is approximately 4/3 D/L=0.66. The effective area A ewith

ct_---0.6can be taken as 0.6x0.3 l=0.20cm 2. A possibility that

the effective area for the flow out of the cavity is a series

combination of the boat opening area and the tubular passage

can be considered. In that case, the equivalent area of the exit

is 0.31 cm 2, which modified by the Clausing factor or

discharge coefficient, becomes A u_=0.2. The boat's equivalent area Ahoy,is 0.72 cm 2 and the series combination of the

two can indicate an equivalent A =Atu_AboJAt,_+A_a =0.157

cm 2. Another alternative for the viscous flow is that the

effective area is simply the open area of the boat (0.72 cm2).

In the following, the assumption has been made that for the

micro-CVCM, the equivalent area A is 0.15 cm 2and the

flow is viscous. These assumptions have been verified by the

calculations comparing mass losses and TML. The mass loss

m 2from the open systems tests will be expressed by the

molecular flow leaving the exposed area A 2 of the sample

during the time t2as 1

= _ pvA2 t2 (3)

and the TML when the initial mass of the sample is m2o by

TML2 = rn 2 = _.1/gvAzt 2 (4)

m2o 4 m2o

The results of the two types of tests have been compared as

follows: for the same outgassing rates (pv) released by the

same material samples at the same temperature, the masses

are equal when 1

aet I = --4A2t 2 (5)

The TML_ and TML 2are equal when

Aett=_.l AzI 2 (6)

m_o 4 mzo
and the ratio of the TMLs is given by

TML l 4Aet t m2o

TML2 Azt2 mlo

(7)

Using the value of 0.15 cm 2 for A°, the ratio of the test times

based on the TML value is

t, _ 1 A 2 m,,, _ _ m,,, _ 1.66Az ml(___L (8)

t 2 4 A, mzo 0.6 m2o m2o

where the subscript I refers to the micro-CVCM and 2 to the

open systems.

As an application, one may want to know when the mass

losses are the same. For example, for testing a sample with an

exposed surface A2=6.45 cm 2 (lin 2) on the Cahn Microbalance for t2=24 hours, the same mass loss will be produced

with the micro-CVCM when t,=l.66x6.45x24=256.9 hours

and the TML will be the same when from equation 8,

tl=l.66A2tz(mJm2o)=256.9(mJmzo). Note that the times for

the two tests to produce the same mass are nearly the same if

A2=0.72 (the area of the boat). Then for tz=24 hours,

h=l.66x0.72x24 hours and if one makes the mz0=l.2m_0 the

test times and the TML will be the same since (TML)_/

(TML)2 =4Ae/A(t_/t2)(mz0/m_0)=4x0.15/0.72x 1x 1.2= 1.

Table 2 shows the test results for the graphite/epoxy material

for a scotchweld 2216 sample and a jonal rubber sample.

The calculated results for the scotchweld and jonal rubber

were obtained using the micro-CVCM equivalent area of A

=0.15 cm 2. The result for the graphite/epoxy was obtained

using a continuum viscous (pvA) flow originating at the

sample surfaces (i.e., A_=0.72 cm 2 for the micro-CVCM and

6.45 cm 2 for the Cahn system) for both the open systems and

the micro-CVCM. These assumptions were needed to justify

the large difference in TML results obtained for this material. The justification of continuum viscous flow in both tests

may reside in the sudden, short (about 25 minutes) release of

the outgassing from the weave, as shown in figure 3. A test

attempting to justify the TML difference based on the test

time proved erroneously. The weave was tested for 150

hours using the micro-CVCM system and the results showed

again that its TML was again about 1.6% as obtained for the

24-hour tests.

Table 2: Test Results & Calculated TML

Outgassing Facility

&Test Material

1. Graphite/Epoxy

Cahn Test

MicroCVCM Test

2. Scotchweld 2216

Cahn Test

MicroCVCM Test

3. Silicone Rub. Jonal

Cahn Test

MicroCVCM Test

Test Results:

A (cm 2) mo (rag) t {hr)

6.45 238.85 24

0.72 157.02 24

0.72 297.68 24

0.15 221.13 24

1.00 1633.70 24

0.15 "1200.30 24

Calculated

t_=tm=24h

%TML %TML

15.80 16.20

1.60 2.67

1.15 1.15

1.34 1.54

0.65 0.65

0.36 0.53

Notes: general case

TML1 _ 4A_tL m2o

TM_ A2t 2 m,,_) , AI=Ao=0.15 cm 2

TM I-a Al t , m2o

forGraph/Epoxy -TML2 - A2 t mloo • AI= 0.72 cm 2 (boat area)
4.0 CONCLUSIONS

The micro-CVCM test has been appropriate and effective for

the selection of acceptable materials for space applications. It

has protected against excessive outgassing and deterioration

of materials when they are exposed to vacuum, excessive

temperatures, and radiation in the space environment. It has

provided indications on material stability and on its volatility.

Those test results, however, should not be used to quantify

the outgassing and its condensable content or to perform

estimates with regard to pressure conditions in and about a

system. These conclusions have been conf'trmed by tests on

several sample materials showing the difference in the results

for the TML and the mass losses obtained using the microCVCM in comparison with those from the other facilities.

They show that the micro-CVCM results can be considerably

less than those from the other tests.

The difference in results has been attributed to the narrow

exhaust passage and the variable flow, either viscous or

molecular, that may exist within the micro-CVCM sample

cavity.

The equivalent exhaust vent area resulting from the series

combination of the boat vent area and the tubular passage of

the cavity has been calculated to provide an effective area for

the outgassing of about 0.15 to 0.20 cm 2. This is the effective, limiting outgassing surface area of the sample.

Simple relationships have been proposed for the equivalence

of the results of the micro-CVCM and those of the open

systems. The equivalence for the mass losses and the total

mass loss percentages (%TML) have been based on a set of

considerations. First, the effective exposed outgassing area of

the sample in the micro-CVCM is 0.15 cmL Next, the flux of

outgassing per unit of area (fly) is the same since the sample

materials and their testing temperatures are the same. In

addition, the flow out of the micro-CVCM system is viscous

due to the small dimensions of the cavity and the resulting

small molecular mean free path offered to a reasonable

outgassing quantity. Last, the flow leaving the high vacuum

exposed surface of the samples in the open tests is molecular

and the molecules leave according to the cosine distribution.

An exception to the consideration of the flow being molecular in an open system has been found for the case of the

graphite/weave outgassing. In that case, the sudden and large

loss of mass of the material in a few minutes has indicated a

condition of continuous viscous flow for both the open and

the micro-CVCM systems.

In general, the equivalence for the mass losses for the two

methods of tests should occur when 0.15h=l/4A2t 2 and the

equivalence for the TML when 0.15tt/m_0=l/4m20(A2t2). In

these equations, the subscript 1 refers to the micro-CVCM

and 2 to the others and ml0 and m:0 refer to the initial masses

of the samples. The dimensional units are the same and the

outgassing fluxes (pv) in the equations have been cancelled

out based on the considerations given above. The difference

in the results obtained using the equations and those obtained

by the Cahn Microbalance and the micro-CVCM were

indicated.

5.0 REFERENCES

1. Muraca, R. E and J. S. Whittick, September 1967,

"Polymers for Spacecraft Applications," SRI Project ASD5046, Stanford Research Institute.

2. Dauphin, J. G., et al., 1962, "Some Contamination

Problems in European TD Satellite," Paper No. 53, NASA

SP-298, Proceedings Space Simulation Symposium, New

York.

3. Park, J. J., et al., 1973, "Outgassing Tests in Support of a

Proposed ASTM Specification," Paper No. 33, NASA SP336 Proceedings Space Simulation Symposium, Los

Angeles.

4. Scialdone, J. J., 1974, "Environment of a Spacecraft

Produced by Its Own Outgassing," International Conference on Evaluation of Space Environment on Materials,

Centre National d'Etude Spatials, Toulouse.

5. Scialdone, J. J., August 1996, "Some Sources of Contaminants in the Shuttle Bay," SPIE Prceedings, The Intern.

Society for Optical Eng., Paper No. 208, Vol. 2864,

Denver.

6. Scialdone, J. J., August 1976, "An Equivant Energy for

the Outgassing of Space Materials," NASA TN D-8294.

7. Walter, N. A. and Scialdone, J. J., 1997, "Outggassing

Data for Spacecraft Materials," NASA Ref. Publ. 1124,

Rev. 4.

8. Zwaal, A., October 1996, "Verification of Baking Efficiency Using MicroVCM Test Data," Proceedings NASA

Conference, Publication No. 3341, p. 25, Baltimore.

9. Dushman, S. and J. M. Lafferty, 1962, Scientific Foundation of Vacuum Techniques, J. Wiley & Sons, Inc., New

York.

10. Santeler, D. J., et. AI., 1966, Vacuum Technology and

Space Simulation, NASA SP-105.
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4. TITLE AND SUBIHLE 5. FUNDING NUMBERS

Material Total Mass Loss in Vacuum Obtained from Various Outgassing

Systems

6. AUTHOR(S)

John Scialdone, Peggy Isaac, Carroll Clatterbuck, and Ronald Hunkeler

7.PERFORMINGORGANIZATIONNAME(S)ANDADDRESS(ES)

Goddard Space Right Center

Greenbelt, Maryland 20771

9. SPONSORING / MONITORING AGENCY NAME(S) AND ADDRESS (ES)

National Aeronautics and Space Administration

Washington, DC 20546-0001

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REPORT NUMBER

2000-03654-0

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TM-2000-209897

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13. ABSTRAChT (Maxim(Jm 200 words)

_ieveral instruments including the Cahn Microbalance, the Knudsen Cell, the micro-CVCM,

and the vacuum Thermogravimetric Analyzer (TGA) were used in the testing of a graphite/epoxy (GR/

EP) composite that is proposed for use as a rigidizing element of an inflatable deployment system.

This GR/EP will be cured in situ. The purpose of this testing is to estimate the gaseous production

resulting from the curing of the GR/EP composite, to predict the resulting pressure, and to calculate

the required venting. Every test was conducted under vacuum at 125 degrees C for 24 hours. Upon

comparison of the results, the ASTM E-595 was noted to have given readings that were consistently

lower than those obtained using the other instruments, which otherwise provided similar results. The

GR/EP was tested using several different geometric arrangements.

This paper describes the analysis evaluating the molecular and continuum flow of the outgassing products issuing from the exit port of the ASTM E-595 system. The effective flow conductance

provided by the physical dimensions of the vent passage of the ASTM E-595 system and that of the

material sample among other factors were investigated to explain the reduced amount of outgassing

released durinp the 24-hour test neriod.

14. SUBJECT TERMS

micro-CVCM, Thermogravimetric Analyzer (TGA), graphite/epoxy, ASTM

E-595, outgassing, total mass loss (TML), Knudsen cell, Cahn microbalance

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Unclassified

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9

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