The carbon-phenolic composite ablative material used on the Solid Rocket Motor (SRM) nozzle is known to absorb moisture from the atmosphere. This could cause problems such as pocketing during firing. Several moisture barrier coatings were tested on the SRM nozzle material. Data are presented for six of the 12 coatings to be tested. The data were obtained from immersion of coated samples in an environmental chamber at 100 F and 100% relative humidity and by using a modified TGA (thermal gravimetric analysis) technique. The TGA technique involved allowing wet nitrogen (25 C, 80% relative humidity) to flow across a small sample at about 65 cu cm per minute while continually monitoring the weight increase. These preliminary results show Kel-F-800, a material supplied by 3M Corporation to be the better moisture barrier. A second task was to collect data on the relative absorption of water and kerosene into the carbon-phenolic SRM nozzle material. These data indicate that water absorbs into the nozzle material to a much greater extent than kerosene. Thus kerosene is the more likely solvent in which to make specific gravity measurements on the SRM nozzle material

Mcnutt, Ronald C.

English

NASA Technical Reports Server

1986
N87- 16773
I"
!
NASA/ASEE FACULTY FELLOWSHIP PROGRAM
MARSHALL SPACE FLIGHT CENTER
EVALUATION OF MOISTURE BARRIER COATINGS
ON CARBON-PHENOLIC SRH
NOZZLE MATERIALS
Prepared by:
Academic Rank:
University and Department:
Laboratory:
Division:
Branch:
MSFC Coileagues:
Date:
Contract No.:
Ronald C. McNutt, Ph.D.
Professor
Athens State CoIiege
Chemistry Department
Materiais and Processing
Non-Metallic Materials
Ceramics and Coatings
R. L. Nichols
R. G. Clinton
August 22, 1986
NGT 01-002-099
The University of Alabama
XXX I
https://ntrs.nasa.gov/search.jsp?R=19870007340 2020-03-20T12:55:11+00:00Z
EVALUATION OF MOISTURE BARRIER COATINGS
ON CARBON-PHENOLIC SRM
NO77LE W_TE_!ALE
by
Ronald C. McNutt
Professor of Chemistry
Athens State College
Athens, Alabama
ABSTRACT
The carbon-phenolic composite ablative material used on the
Solid Rocket Motor Nozzle is known to absorb moisture from the at-
mosphere. This could cause problems such as pocketing during firing.
Part of this work was to test several moisture barrier coatings
on the SRM nozzle material. This report shows data on six of about
twelve coatings to be tested. The data were obtained from immersion
of coated samples in an environmental chamber at lO0°F and lO0_
relative humidity and by using a modified TGA (thermal gravimetric
analysis) technique. The TGA technique involved allowing wet nitrogen
(25°C, 804 relative humidity) to flow across a small sample at about
65 cm 3 per minute while continually monitoring the weight increase.
These preliminary results show Kel-F-800, a material supplied by
3M Corporation to be the better moisture barrier.
A second task was to collect data on the relative absorption
of water and kerosene into the carbon-phenolic SRM nozzle material.
These data indicate that water absorbs into the nozzle material
to a much greater extent than kerosene. Thus kerosene is the more
likely solvent in which to make specific gravity measurements on
the SRM nozzle material.
XXXl-i
ACKNOWLEDGEMENTS
I want to thank Mr. R. L. Nichols and Dr. R. G. Clinton for
offering me a second summer appointment. I want to express my
appreciation to my NASA co-worker, Mrs. Linda Jeter, for beginning
this work, for working with me, and for continuing the project
after my ten weeks are comp|eted. Everyone in the Non-MetalIics
Division has been extreme]y helpful. I must, however, mention
some people who have gone out of their way to help: Mr. Donald
Morris, without whom very little could have been accomplished;
Mr. Roger Harwell and Mr. David Webb, who instructed us in coating
techniques, among other things; Mr. Benjamin Goldberg who wi]]ing]y
shared hls ideas; and Mr. Robert Durham for a marvelous suggestion
on how to coat small samples.
°
XXXI-iI
Table
Number
LIST OF TABLES
Title
List of names and companies for moisture barrier
coatings to be tested.
List of moisture barrier coating materials.
Percent weight gain, based on weight of coating,
for moisture barrier coatings on 4" x 4" AI
plates.
XXXl-6
xxxl-7
VVVl_ 8AAAI
XXXl-iii
LIST OF FIGURES
Figure
Number
3
4
5
Title
Typical carbon-phenolic block from which samples
were taken and machined.
Comparison of weight gain for carbon-phenolic
samples immersed in water at room temperature
to those exposed to wet nitrogen flowing at
65 CM3/min at 25°C.
TGA plots; percent weight gain vs time at 25°C,
80% R.H. for I/8" cubes of carbon-phenolic
material coated with moisture barrier candidates
Percent weight gain vs time at IO0°F, 100%
nil . , • . ,
R.H. for l" x I" x L _mpies coacea wlcn
moisture barrier candidates.
Percent weight gain vs time for carbon-phenolic
sample immersed in water and kerosene
XXXl-9
XXXI-IO
XXXl-ll
XXXl-12
XXXI-13
XXXl-iv
INTRODUCTION
IDI_IGINAL PAGE i3
POOR QUAUTY
- hl__
The a_lative material • u,, L,,= =_ .................. 1_u_=u -Alid -^-"-* --_" .......
is a carbon-phenolic composite known to absorb water from the atmos-
phere, especially under warm humid conditions. This absorbed water
could cause problems such as pocketing during firing or it could
cause general degradation of the composite over a period of time.
(References)
This work should test the efficiency of various coating mate-
rials which could be used as moisture barriers on the surface of
the carbon-phenolic composite. The carbon-phenolic materials from
two 404 rings were obtained From Morton-Thiokol _,,,po,,yr....... • _-_,,,vles
were cut out and machined into two sizes I" x I" x 2" for exposure
to 100% relative humidity at lO0°F in a controlled humidity chamber
and I/8" cubes for a modified TBA (Thermal Gravimetric Analysis)
analysis. This modified TBA analysis consisted of allowing wet
nitrogen gas flow isothermally across the sample for about two
days while monitoring the weight gain.
A secondary task was to immerse carbon-phenolic samples into
water and in kerosene to compare the relative absorption of each
into the carbon-phenolic material.
XXXI-I
OBJECTIVES
The objectives of this work were to:
I • Subject coating materials From several candidates
conditions oF high humidity, and possibly recommend
one or more as moisture barriers with which to coat
the carbon-phenolic SRM nozzle material.
2. Obtain data on the relative absorption of water and
kerosene into the carbon-phenolic SRM nozzle material.
tO
XXXI-2
PROCEDURES
The material to be tested was obtained from Morton-Thiokol
Company. The gross samples (carbon-phenolic nozzle material) were
from two 404 rings of the SRM. They consisted of eight blocks,
four from each ring. Each of the four blocks represents about 45 °
taken From alternate 45 ° sections around the ring (Fig. I). Blocks
A, B, C, & D came from ring number 42. Blocks E, F, G, & H came
from ring number 45. Samples were taken in such manner as to get
representative material from each block. The samples to be tested
at 100°F, lO0_ relative humidity were cut to I" x I" x 2", a
convenient size For possible diffusion studies and consistent with
the amount of material available, coating, case, etc. The small
samples (I/8" cubes) were cut to be compatible with the TGA apparatus.
The I/8" cubes were also used to test relative absorption of water
and kerosene into the carbon-phenolic material. It should be noted
that this material was not the same as that used in the TGA and
humidity chamber work but was from nozzle material already on hand.
Mixing, curing and coating procedures followed were generally
those set down by the suppliers. Duration of exposure in the humidity
chamber has not been determined because data acquisition will continue
for at least another month beyond the date of this report. The
time limit on TGA analysis was determined by what was reasonable
in terms of available instrument time and the Fact that total
immersion and TGA data were very similar For about two days (Fig.
2). The only technique, other than essentially standard procedures,
was coating the small cubes. They were lightly adhered to two-sided
tape on an aluminum plate. Five exposed sides of the cubes were
cQated and cured. The samples were turned to expose the uncoated
side which was then coated, cured'and the samples placed in a dry
environment to await testing.
The procedure followed in weighing the small cubes immersed
in water and in kerosene was to remove each individually with
tweezers, touch the sample to absorbent tissue quickly to remove
adsorbed solvent, weigh, and return it to the solvent container.
Most of these tests were done using three replicate samples.
xxx1-3
RESULTS AND OISCU$SION
There were originally eleven moisture barrier candidates (Table
I and 2). The time available allowed dat_ _o be reported on six
of these. A complete report on all coatings listed (possibly more)
will probably be available in November 1986. .Table 3 shows data
on the absorption of moisture by the coatings themselves; only one,
scuffcoat, absorbed significant amounts _f water. Poly/Ep and
Kel-F-800 absorbed moderate amounts but other data (Fig. 3 and 4)
showed them to be Fairly good moisture barriers, especially Kel-F-800.
Figure "3 compares the weight gain For each of the six coatings tested
to that For an uncoated sample using the TGA apparatus. All coatings
absorbed less moisture than the uncoated control. Three coatings,
Poly/Ep, Desoto Green, and KeI-F-800 appeared to be about equally
efficient moisture barriers in this test. However, Ke)-F-800 is
the best moisture barrier considering the results from the
environmental chamber (lOO°F, lO0_ Rel. Hum.) shown in Figure 4.
An interesting Feature of the results shown in Figure 4 is the fact
that the uncoated control absorbs moisture at a slower rare after
a couple of days than two of the coated samples. One explanation
could be that the uncoated control more nearly follows Fick's law
of diffusion than the coated samples.
Figure 5 concerning the relative absorption of kerosene and
water into carbon-phenolic material shows water to absorb to
considerable more than kerosene. One of the concerns here was which
solvent would be preferable For specific gravity measurements.
These data (Fig. 5) indicates kerosene to be the solvent of choice.
Further tests will be done weighing the samples in the two solvents
over a period of time using a modified Westphal balance.
XXXl-4
CONCLUSIONS AND RECOMMENDATIONS
iU=iII,_ _he daL= uv=il=.];i ,_¢ i-r-uvv i3 LII¢ be5_ moisture
barrier of the six tested so far. The coating mater{al is a copolymer
of chlorotrlfluoroethy]ene(CTFE) and vinylidene fluoride (VF 2) supplied
by the 3M Corporation. This coating has a long pot-life and is
easy to apply.
Considering water and kerosene as solvents in which to do
specific gravity measurements on carbon-phenolic SRM nozzle material
the data shows kerosene to be the more likely choice. One point
brought out in oral presentation was the need to perform flame tests
- _a_ing materials. It is recommended that this be uone before0,, _,,e
a final selection is made.
XXXl-5
TABLE I
LIST OF COATINGS TO BE TESTED
I, Poly/EP Polyamide Epoxy Coating
(Degraco Company)
2. EPON RESIN 828/TETA
(Shell/Union Carbide)
3. Fluorad Brand Surface Modifier FC-723
(3M Corporation)
4. KEL-F Brand 800 Resin
(3M Corporation)
5. FIuorad Brand Conformal Coating FC-725
(3M Corporation)
6. Integral Fuel Tank Coating, Green
(DeSoto, Inc.)
7. Fuel Barrier Coating 473-13
(Sikkens)
8. HysoI Adhesive EA 934 Non-Asbestos
(Dexter Hysol Aerospace and Industrial Adhesives)
9. Chemglaze Z 302
(Lord Chemical Products)
10. Scuffcoat
(Mixture of Products)
11. EXXON Butyl Rubber
XXXl-6
TABLE 2
L!ST OF COAT!N_ NATFR!AL_
I. Poly/EP Polyamide/Epoxy theromsetting coating.
2. Epon Resin 828/TETA
Epon 828 a reactive ]ight colored liquid epoxy resin.
TETA Tetraethylene-tetramine.
3. FC-723 is an oleophobic-hydrophobic f]uorochemical polymer dissolved
in a Fluorinated inert material.
4. KEL-F 800 is a copolymer of chlorotrifluroethylene (CTFE) and
vinylidene fluoride (VF2).
5. FC-725 is a clear mobile solution of a Fluorine containing polymer
that dries to a transparent acrylic coating.
6. integral Fue] Tank Coating Green, is a chemica]ly cured acid
resistant and fluid resistant urethane.
7. 473-13 iS a two component high build epoxy system.
r_ • p• _ 934 NA consists of a gray thixotropi_ paste and an amber
liquid amine curing agent.
CheBg]aze Z302 is an oil-free, moisture curing polyurethane.
Scuffcoat is a blend. The base is Epon 828 with NER-OIO and the
curing agent is Versamid 115 and 125. Epon 828 is a reactive light
colored liquid epoxy resin. NER-010 is a mixture of glycerol di-
and tri- glycidyl ether. Versamid !15 and 125 are polamide resins.
EXXON Butyl Rubber is a complex material containing EXXON BUTYL
268, zinc oxide, stearic acid, N-770 Black, Hydrogenated Resin
Ester, Sulfur, P-Quinone dioxime, Lead oxide, Heptane (solvent),
and Isopropanol.
ll.
xxxl-7
TA_E 3
WEIGHT GAIN FOR COATINGS OR ALUMINUH PLATES
4" x 4" Coated AI Plates
Placed in Chamber IO0°F 1OO¢ Relative Humidity
Coatinq
Poly/EP
DeSoto Green
473-13
_L-r -ovu
Scuffcoat
Chemglaze-Z302
Percent Wt. Gain
(Eased on Wt. of Coating)
4.61
0.34
0.87
4.22
10.40
I .07
Days
in Chamber
30
28
28
23
21
18
xxxl-8
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XXXI-10
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XXXl-13
Springer, G.S., "Environmental Effects on Composite Materials",
Vol. 1, Technomic Publ. Co., (1981).
Ibid, Vo]. 2, (1984).
R. G. Clinton, "Effects of Hygrothermal Environments on Graphite-
Epoxy Composites", Thesis Appendix B, Georgia Institute of
Technology (1983).
J. P. Galica, "Evaluation of Barrier Haterials to Stop the Higration
of Organic Liquids, Moisture and Corrosive Chemicals in Solid
Rocket Motors", Report, Contract Number F04611-84-C-0033,
Springborn Labs. Inc., Enfield, Ct, Dec. 1985.
XXXl-14


Evaluation of moisture barrier coatings on carbon-phenolic SRM nozzle materials

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