CARBON-CONTAINING BLACK GLASS MONOLITHS

MONOLITHES DE VERRE NOIR RENFERMANT DU CARBONE

English Abstract

ABSTRACT OF THE INVENTION
Carbon-containing black glass compositions of
matter having the empirical formula SiCxOy in which x ranges
from about 0.5 to about 2.0, and y ranges from about 0.5 to
about 3.0, wherein the carbon content of the black glass
ranges from about 10% to 40% by weight, are prepared by
pyrolysis of a cyclosiloxane polymer in a non-oxidizing
atmosphere at a temperature from bout 750°C to about
1400°C.

Claims

24
WE CLAIM AS OUR INVENTION:
1. A carbon-containing black glass ceramic
composition of matter having the empirical formula SiCxOy
wherein x ranges from about 0.5 to about 2.0, and y ranges
from about 0.5 to about 3.0 .
2. The composition of matter of Claim 1 further
characterized in that x ranges from about 0.6 to about 1.9,
and y ranges from about .55 to about 2.6.
3. The composition of matter of Claim 1 further
characterized in that x ranges from about .75 to about 1.75,
and y ranges from about .65 to about 2.2.
4. The composition of matter of Claim 1 further
characterized in that x ranges from about 0.9 to about 1.60,
and y ranges from about 70 to about 1.8.
5. The composition of matter of Claim 1 further
characterized in that x ranges from about 1.0 to about 1.5,
and y ranges from about 0.8 to about 1.4.
6. A process to produce a black glass comprising
making a polymer by reacting, in the presence of a catalytic
effective amount of a hydrosilylation catalyst, (a) a
cyclosiloxane monomer of formula
<IMG>
where n is an integer from 3 to about 20, R is hydrogen, and
R' is an alkene of from 2 to about 20 carbon atoms in which
one vinyl carbon is directly bonded to silicon of (b)
reacting of two or more different cyclosiloxane monomers of
said formula and said n integer range where for at least one
monomer R is hydrogen and R' is an alkyl group having from 1
to about 20 carbon atoms, and for the other monomers R is an

alkene of from 2 to about 20 carbon atoms in which one vinyl
carbon is directly bonded to silicon and R' is an alkyl
group of from 1 to about 20 carbon atoms, heating the
resulting polymer in a non-oxidizing atmosphere to a
temperature in the range of from about 800°C to about 1400°C
to produce a black glass, and recovering said black glass.
7. The process as described in Claim 6 further
characterized in that said polymer is formed in a
temperature range of from about 10°C to about 300°C.
8. The process as described in Claim 6 further
characterized in that polymerization takes place at a
pressure range of from 14 psi to about 30,000 psi.
9. The process as described in Claim 8 further
characterized in that said pressure range is from 14 psi to
about 300 psi.
10. The process as described in Claim 6 further
characterized in that said monomer reaction takes place in
the presence of a hydrosilylation catalyst selected from the
group consisting of platinum, cobalt, or manganese, which is
present in an amount which has a range of from 1 ppm by
weight to about 200 ppm by weight.
11. The process as described in Claim 6 further
characterized in that conversion of the polymer to black
glass takes place a heating rate range of from about 10°C per
hour to about 800°C per hour.
12. The process as described in Claim 11 further
characterized in that said heating rate range is from 10°C
per hour to 200°C per hour.
13. The process as described in Claim 6 further
characterized in that the black glass is a monolith with a
bulk density in the range of from about 1.40 g/ml to about
2.20 g/ml.
14. The process as described in Claim 6 further
characterized in that said polymer contains a filler
selected from the group consisting of silicon nitride,

26
silica, silicon carbide, alumina, hafnia, titania and
zirconia.
15. The process as described in Claim 14 further
characterized in that said silicon carbide is selected from
the group consisting of hexagonal silicon carbide and cubic
silicon carbide.
16. The process as described in Claim 14 further
characterized in that said filler is in a form selected from
the group consisting of powder, fiber, and whisker.
17. The process as described in Claim 6 further
characterized in that said cyclosiloxane monomer is
1,3,5,7-tetravinyltetramethylcyclotetrasiloxane.
18. The process as described in Claim 6 further
characterized in that said cyclosiloxane is 1,3,5,7-
tetramethyltetrahydrocyclotetrasiloxane.
19. The process as described in Claim 6 further
characterized in that said cyclosiloxane is 1,3,5,7-
tetravinyltetrahydrocyclotetrasiloxane.
20. The process as described in Claim 6 further
characterized in that said cyclosiloxane is 1,3,5-
trivinyltrimethylcyclotrisloxane.
21. The process as described in Claim 6 further
characterized in that said cyclosiloxane is 1,3,5-
trimethyltrihydrocyclotrisiloxane.
22. The process as described in Claim 6 further
characterized in that said black glass is impregnated with
said monomer and then pyrolyzed to afford a black glass with
increased density.
23. The product of the process of Claim 6.
24. The product of Claim 23 further characterized
in that the silicon content is in a range of from about 35
wt. % to about 55 wt. %, the carbon content is in a range of
from about 10 wt. % to about 40 wt. %, and the oxygen
content is in a range of from about 15 wt. % to about 50 wt.%.

27
25. The product of Claim 23 further characterized
as thermally stable in air up to about 1400°C.
26. A process to produce a crack free polymer
precursor to black glass from cyclosiloxanes comprising the
steps of:
(a) mixing a hydrosilylation catalyst with (a) a
cyclosiloxane monomer of formula
<IMG>
where n is a value from 3 to about 20, R is hydrogen, and R'
is an alkene from 2 to about 20 carbon atoms which has a
vinyl carbon bonded directly to silicon or (b) two or more
different cyclosiloxane monomers of said formula and said n
integer range where for at least one monomer R is hydrogen
and R' is an alkyl group having from 1 to about 20 carbon
atoms, and for the other monomers R is an alkene of from 2
to about 20 carbon atoms in which one vinyl carbon is
directly bonded to silicon and R' is an alkyl group of from
1 to about 20 carbon atoms; and
(b) polymerizing said monomeric mixture at
reaction conditions under pressure; and
(c) recovering said crack free polymer precursor
to black glass.
27. The process of Claim 26 further characterized
in that said reaction conditions include a temperature in
the range of from about 10°C to about 300°C, a time in the
range of from about one minute to about 600 minutes, and
said pressure is in a range of from about 14 psi to about
30,000 psi.
28. The process of Claim 26 further characterized
in that said hydrosilylation catalyst is selected from the

28
group consisting of platinum, cobalt, or manganese and is
present in said monomeric mixture in an amount of from about
1 ppm to about 200 ppm.
29. The process of Claim 26 further characterized
in that said monomeric mixture contains a filler selected
from the group consisting of si;icon nitride, cubic: silicon
carbide, hexagonal silicon carbide, alumina, hafnia, silica,
titania, and zirconia.
30. The process of Claim 29 further characterized
in that said filler is in a form selected from the group
consisting of powder, fiber and whisker.

Description

" 3 ~ ~3 7 ~
CAR~3CIN--CONTAINING BLACR GLASS MONOLITHS
B_CKGROUND OF THE INVENTION
Ceramics have been known for many hundreds of
years and hav~ been u~ed as coatings or a~ fabricated parts
and are employed wherever their charact~ristics SUC}I as
durability, nonporo~ityr electrical conductivity or
nonconductivity, and heat protection are required. One of
th~ more recent ceramic material~ i~ a silicon-carbon-oxygen
system, named as a black glass, which can find use in
certain situat~on~ where extremely high temperatures are
present.
Traditionally; the introduction of carbon in
glasses was made by impregnating porou~ glas~ with a
concentrated solution of an organic compound and
subsequently firing in a reducin~ or n~u~ral atmosphere.
The carbon-containiDg product is generally regarded as a
composite containing carbon and ~ilica. Elme~ and Meissner
( ~ , 59, 2~6, 1976) of
Corning Gla~ Work~ repor~ed that the annealing poin~ of
recon~tructea 96% sllicon dioxide glasse~ is markedly
increa~d by in~orporating carbon in porous glass. Furfuryl
alcohol w~ u~d a~ the pyrolyzabl~ organic compound. They
attributed th0 increa8e of about 100C in annealing point to
the effect of hydroxyl removal from ~he internal ~urface of
the porou~ gla~ by hydroxyl reaction wi~h carbo~. The
resistivi~s of sample~ with le~3 ~han ~% carbon content
approaohed that of the gla~ wh~reas the electrical
re~istivi~ie~ of carbon-~ontain~ng silica with ear~on
be~ween 4.5-7% are in the rangs of 1-3 ohm-cm, thu~
producinq elec~rically conduotive glas~e~. The highest
carbon cont~n~ i~ th~ final gla~ses ~hey could produce is
~.5~%O
r
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' ' ' ' : ' ". ' '

2 ~2`37~
Smith ~ Cra~dall reported in U.S Patent 3,378,431
a method of making carbon--containing Iylass by hot~pressing
to sintering temperature a mixture of colloidal silica and
an organic compound known in khe txadle as "Carbowax'~
~polyethylene glycol) in an oxygen-free atmosphere. The
black gla~s ob~ain~d from the mix~ure of 33~ "Carbowax" and
67~ silicon dioxide show~d the presenc~ o~ 1.2~ by weight of
carbon. A devitriication-r2sistant bonded ma~s of vitreous
silicon dioxide and carbon physically in~eparable and
micro~copically indis~inguishable from cilica waY ob~ained.
The black glasq has a low thermal diffuivity and more
resistance t~ cry~tallization than pur~ vitreous silica.
Devitxi~ication temperature increased by 150C to 1250C as
compared with colloidal silica.
Carbon-modified ~ilica glas~ ha~ been used as a
composite matrix by Larsen, Harada and Nakamum (Report No.
AFWAS-TR~3-4134, December, 1983~ Wrigh~-Patterson hFB,
Ohio)~ In producing fiber-r~inforced composite~, the
proces.~ng sequence include~ slurry impregnation of silicon
carbide fiber in an a~ueous slurry of a carbowax
Ipolyeth~lene glycol) and a silicon-contain~ng compound
know~ in the trade a Cab-0-Sil (a ~illcon dioxide powder
manufactur~d by Gabot), layout o~ prepregyed fiber tow~, and
hot-pressing. The compo~ites thu~ obtained exhibited high
porosity and brittle fracture indicativ~ of low toughness.
They con~lud~d that the sllicon carbid~/blaGk gla~s fib~r
compo~ite i~ a promising ma~erlal, although the proper~y
goal~ were no~ achiev~d. There i su~pi~ion ~ha~ ~he
silicon carbide fiber~ may hav~ degraded.
More rec~ntly, formation of carbonaceou~ ceramics
has be~n carri~d out through the use o~ the sol-gPl process.
January di~lose~ in U.S. Patent No. 4,472,510 ~h~ use of
th~ sol g~l proce~s to form monolithic glass~s containing
carbo~ ~hrough pyrolysis of the gel~ of
org~no~ilse~quio2carles ~ metal oxide3 and metal alkoxide3 .
:
'

-
3 ~ 7 ~
~onomann in Great ~ritain Patent 1,3~9,576 disclosed the
formation of silicon and quartz fi~ers using silses~uioxanes
as precur~ors. Their gelling process used selected
organosilicon compounds for the prepara~tion of the ceramic
precursor ba ed on ~he following reaotion:
- Si-OR ~ ~2 ~ - Si-OH ~ RO~ (l)
_ Si-OH + HO-Si-- ~ - Si-O-~Si- ~ ~2~ (2)
in which R represents an organio radical such as alkyl
groups and aryl groups such a~ phenyl group.
The uniqueness o the sol-ael process is the
ability to obtain homogeneous, purer glassy Products b~ low
temperature processe Al~o, the use of a liquia svl as the
starting materials allows the preparation of intractable
monoliths of complicated shape~ utilizing a li~uid path.
The advantages of su~h a procedure over the powder
consolidation techniques, such as sinter~ng and hot
isostatic pressing, are th~ir formabilitY of complicated
shape~ and low temperatur~ operationO ~owever, monolithic
black glas~e~ produced via hydroly~is and condensation of
organoalkoxy~ilane~ are not practical because of the
requirement for ~ery long dxyins periods and delicate
gelling conditions. For example, ~anuary prepared a~0.~6
cubic centimoter methyltrim~thoxy~ilane gel monolith over a
drYing period of about three weeks, which, upon pyrolysis,
yielded a carbon containing black gla~s monolith of density
1.6 gram~ p~r milllliter.
The very slow drying rate is n~c~ssary for
reducing crack-~ during the gelation period. These cracks
form as a result of the non-uniform surface tensions created
by the evaporation of tha ~pli~-of~ wa~er or al~ohol
mol~cule3 in th~ hydroly~is (1) and condensation ~2~
reaction~. In th~ ln~tant in~ention, a hydrosilvlation
reaction w~ u~d ~or the gelation ~rocess in plac~ of the
hydrolysis~ond~nsation routP~ The hvdro~ilylation involves -`
addition of ~ilan~ H) to vinyl silane (Si~C~=C~) to
.
,~

4 2~337~ ~
-
form an ethylene linkage as illustrated in the following
equation:
- Si-H + CH2 - CH Si ~ SiC~CH2Si ~ (3)
The features of the hydrosilylation reaction are such that
there is neither a small molecule reac~ion product nor a
weight los~ during yelation and that ~he carbons in the
ethylene linkage are bonded to the silicon a~om~O This
gelation reaction completely eliminates the drying problem
inherent in the hydrolysi~ of organoalkoxysilan~ process.
We also unexpectedly found that cyclosiloxan~ gels cro3s-
linked by hydro~ilylation reaction produced upon pyroly~is
to high temperature in a non oxidizing atmo~phere high
carbon content, high yield and high den8ity black glasses.
Monomann in Great ~ritain Patent 1,359,576
disclosed the u e of a phenyl group rather than a methyl
group as R i~ order to increase the carbon content of their
products. By choosing phenyl group a~ R, the carbon weight
percent can be increased to as high as ca. 30%. How0ver, we
have shown in our simulation exp~riments that thP carbon
present ~arted to oxidize at 550C in flowing air and was
completely removed before 1000C. Th~refore, the carbon
derived fro~ pyroly~i~ of the phenyl group ~s free carbon
susceptible to oxidatio~ while our inv~ntion produces carbon
content~ with the carbon bonded to silicon rather than
~iexi~ting as fr~e carboD, resulting in a carbon-containing
material that i~ oxidation resi~tant up ~o about 1400C.
Okamura ~t al. reported in U.S. 4,618~591 a method
of making silicon carbide-carbon compo~it~ mold~d product by
using polycarbosilane as ~he precursor for 2 matrix
material~ The polycarbosilane on pyrolysis ~orms
microcry~t~lline silicon carhide with inclusion of low
oxyg~n perc~ntage, as indicated by their X-ray diffraction
patt~rn~. In contxadistinction to this work~ this inYention
produce~ materials that have different composltion ranges
::; : ~ ' :
:~
:: : : : ~:

~02337~
and that are overwhelmingly amorphous with a few small
diffraction p~3aks different from silicon carbide.
N. ~?arada and M. Tana}ta ln U.S~ Patent 3,~57,717
described and claim~d an organopoly~iloxane gel prepared
from cyclosiloxanes and H . Lamoreaux in U . S . Patents Nos .
3 ,197, 432 and 3 ,197, 433 claimed the prodllc~ gel from
reaotins eyclosiloxane~ conkaining hydxogens and vinyl
gxoups. The basi~ idea of reac~ing silyl hydrogen groups
with silyl vinyl groups i~ found in U ~ S, Patent~ Nos .
3,439,014 and 3,271,362.
The ~ability of a . oluble polymer was s~udied by
thermogravimetric analysi~ by A. Zhdanov e~ alO and reported
i n the ~,
Serie~ A, 16 ~10~, 2345-50 (1974). They precipitated the
highly branched, soluble polymer from the reaction mixture
as powders by adding aleohols into the reaction vessel
before the gel point . Their polymer wa~ dif ferent ~rom a
network gel produced from a sol-gel process in that it
contained a large amount of unr~acted Si-E~ and Si-CH=C~?2
group~ ansS wa~ readily ~oluble in aromati~ ~olvents. P,lso,
the polym~r powd~r did no~ melt when heated up to snoc.
They heatQd the ~oluble polymer~ at 1 nc per minute up to a
m~ximum of 780C in both Argon and air an~ reported the
thermogravimetric results a~ to weight loss at various
stages oiE hea~ing and 2~3 to the ~e)tal weigh~ lo~s involved.
No weight chang~ wa~ observed beyond 7S0C wh~n hea~d in
Argon at a rat~ of 10C/min. with a final yield of 879~. The
Russian~ did no1: eharac~erlze ~he re~u~tan~ product of ~his
analy~is and appeared to have no in~erest iD thi~ product.
In eontradi~tinetiorl to this prior work, this
invention i~ eoneern~d with the produot of pyroly~i~ of the
qel polymer~ ~ormed from eyelo~iloxanes as w~ll as with the
pro.-ess to produe~ sueh a produet. Th~ prc~duet of our
invention i~ a hardS ~la~y material whl~h w~ call a black
., ~
.. .

6 ~ 3 ~7 ~
glas~ having carbon directly ~onded to silicon and which is
very useful when cast as a monolith, or one pie~e object.
BRIEF SUMMARY OF T~E INVEMTION
This invention relates to a composi~ion of matter
in which ~reater amount~ of carbon are incorporated by
bonding to ~ilicon than were possibl2 utilizing prior art.
More ~pecifically, the invention is co~cerned wi~h a carbon-
containing black gla~ composition of matter in which about
10% to about 40% carbon is incorporated by we~ght to produce
an oxidatively stable and high melting subqtance.
Ag was hereinbe~ore di3cus3ed, there ls a need for
a thermally stable, oxidative-resistant, and
devitrification-resi~tant black gla~. Such a matsrial
would find high temperature u~ and would be economically
attractive when pr~pared by the present method in whic:h a
polymer would be foxmed at a low temperature followed by
pyroly~is at temperatur~ ln the range of abou~ 700C to
about 1400C. Our invention ha~ the advantag~ of producing
a silica modif~ed glas~ having a higher melting point than
cristobalite and having greater r2si~ t:ance to
devitrif~c~tion than pure vi reou~ silica and previou~ly
kno~m carbon-c:ont~lning gla~es. Our inv~nt:Lon also yields
a car~on-~onta~r.iRg gla~s having higher th~rmal ~tabili~y in
air than kno~n nonoxlde ceramic~ containing carbon.
It i3 therefore an object o~ this invention to
provi;d2 an amorphou~ carbon ;con~a~ning 3ili ::a-ba~ed cexamic
with a high me~lting point that is r~ tant to oxidation and
crys~alli~a~iorl l
a further object of ~he pre~ent in~ention to
provide a proceR~ whereby any moldable shape can be obtained
in the form of a black glass monolith.
' :
.~
:: :

~3~78
It is a still further object: of the pxesent
invention to provid~ a proces~ in whic:h a filled ~lack glass
monolith can be produced.
IA one aspe~t, an embodim~nt: of ~his invention
resides in a carbon-containing black gla33 ceramic
composition o~ matter having the empirical formula SiCx0y
wherein x rznges from about 0.5 to ab~ut 2.0, and y ranges
from about 0.5 to about 3Ø
Another aspect of this invention is found in a
process to produ~e a black gla~s comprising making a polymer
by reacting, i~ the presenca of a catalytic ~f~ective amount
of a hydro~ilylation cataly~t, (a) a cyclosiloxane monomer
of formula
~ ' ~
where n ~ an integer from 3 to abou~ 20, R is hydrogen, and
R' is an alken~ of from 2 to about 70 carbon atoms in which
on~ vinyl carbo~ i~ direc~ly bonded to silicon or ~)
reacting of ~wo or more d~ffeE~nt cycloslloxane monomers of
the formula and the n int~ger range where for at least one
monom~r R i~ ~ydrogen and R' i~ an alkyl group having ~rom 1
to ~bout 20 Garbon a~om~, and for the oth~r monomer~ R is an :.
alXene oP from 2 ~o about 20 carbon a~oms in which one-vinyl
carbon is dir~¢tly bonded to ~ilicon and R~ is an alkyl
group of from 1 to about 20 caxbon atoms, hea~.ing the
resulting polymer in a non-oxidizi~g atmosphere to a
tempera~ure in ~he range of from abou~ 800C to about 1400C
: to produ~e a bl~ck glas~.
Other object~ and embodimen~ will be found in the
following further detailed des~ription of the pre~en~
invention.
~:~
,
: - ` ` `
.
.

2~2337~
D~TAILED DESCRIPTION OF THE INVENTION
As hereinbefor~ set for~h, the present invention
is conc~rned with carbon-containing black glass compositions
of matter having varying percents by weigh~ of carbon, w.ith
high melting points, resistant to devitrifica~ic)n, and
possessing oxidative stability.
A carbon-containing black glass compositioD of
matter may be prepared by any method kno~ in the art.
Examples of this art would be the physical blending a~d
sintering of mixtures of silica and pyrolyzable orqanic
compounds or the sol-gel proces~. The ~ol-gel process is
very attracti~re due to the homogensity of the sol produced,
the ease of forming a gel from the sol, and the fact that
such a pro~ess ca~ be carried out at low temp~ratures,
thereby reducing production costs. As described in ~he
bac}cground o~ the invention, other WOEICer8 have been able to
prepare a polymer from cyclosiloxane~, and, in some cases,
forrn thi~ };olymer into a monol~ th, but no prior work has
shown th~ manu~ac~ure of a black glass mox~olith, eithe:r
filled or ua~illed, util~zing the cyclosiloxane polymer
method. Our invention, ~hereore, comprise3 the pyrolysis
in a~a lnert at~o.~phere of a polymer made from t:yc~losiloxanes
to tempera~cur~ of about 1400C to produce a hard, glassy
material whlch we call a black glas~. ~he shape o~ thi~
black gla~s deriv~s dlrectly from the shape o~ the precursor
polymer with th~ strength dependent on whether th~ monomer
is filled with ~ powdex, whisker, or fiber prior to
polymeri~ation. A ~onol~thic shape can he produced
u~ilizi~g a molding or an ex~rusion step prior to or
conco~i~ant wi~h a final polymeriza~ion. ~f~er the polymer
is ~haped, t~e pol~mer ls pyrolyzed up ~o about 1400~C to
for~ a blacX gla~ with retention of the b~ic ~tarting
~'`
..
.
. . . ' , .: ~ ~ ~ :

~23~78
shape~ but with decreased dimensions due to thermal
shrinkage.
The polymer precursor of the present invention is
prepared in one instance at reaction conditions by
subjec~ing a cyclosiloxane mixture con~aining cyclosiloxanes
of from 3 to about 20 silicon atoms to h~a~ing to a
~emperatur~ in the range of from about 10C to about 300C
in the presenc~ of a platinum hydrosilylation catalyst
present at 1-200 ppm for a time ln the range of from about I
minute to about 600 minutes. The poly~er is then placed in
nitrog~n and pyrolyzed at a temperature in the range from
about 800C to about 1400C for a time in the range of from
about 1 hour to about 300 hours to produce the black glass.
The polymer formation step from the monomer takes advantage
of the fact that a silicon~hydride will react with a
~ilicon~villyl group to form a silicon-carbon-carbon-silicon
bonded chain~ thexeby forming a network polym~r. For ~his
reason, each monomer cyclo~iloxan~ mu~t contain ~ither a
silicon-hydrid~ bond or a silicon-vinyl bondO For purposes
of thi~ application and the appended claim~ a silicon-
hydride bond refer~ ~o the presence of a silicon atom bonded
directly to a hydrogen atom and a silicon-vinyl bond refers
to the pr~sen~ of a ~ con atom bonded directly to a
carbon a~o~, call~d an alkene carbon, that i~ doubly bonded
to a~oth~r carbon atom in an alken~ moiety.
Co~v~rsion of the gel polym~r ~o black gl~ss takes
place..b~tween 430C and g50C~ Three major pyrolysis stPps
were iden~ified by ~hermogravimetric ana~ysis at 430-700C,
680~800C and 780-g50C. The yield of the gel-gla~s
conversion is 83~; the hlrd pyrolysis mech~ni~m o~ourring
between 785C ~nd ~50~C contributed the final 2.5% weight
los~ ~o ths final produc~. Thu~, the pyrolysis chemis~ry of
th~ gel polymer in thi~ invention i~ dis~inctly diff~rent
from that reported by A. Zhdanov et al. in ~ha~ ~heir
. .
,

lo ~23~78
soluble polymer did not have any reacti.on above 78~C in a
~ast heating of 600C per hour. As discussed hereinbefore,
thiq soluble cyclosiloxane precursor is al~o chemicall~
different from a gel polymerO ~he gel polymers in this
invention cannot be dissolved in solvents such a~ toluene.
The invention can be prac~iced by u~ilizin~ a
polymer pr~cursor cyclosiloxane wherein both the recluisite
silicon-hydride bond and the silicon-vinyl bond are present
in one molecule. For example, 1,3,5,7-tetravinyl-, 1,3,S,7-
tetrahydrocyclotetrasiloxane would operate within the scope
of this invention since this molecule has the basic
requirement of a silicon~hy~ride bond and a silicon~vinyl
bond and would polymerize to give a black gla~s polvmer
precursor of use in this inv~ntion.
One of the most us~ful method~ utili~ed in the
process of this invention is to fabricate the polymer
precursor into a monolith using procedures liXe tape
casting, in~ection molding/ rea~t~on in~ection molding, and
compr~sion molding. For instance, ~he polymer orming
cyclosiloxane mixture may he introd-lced into a mold and then
heated to form the polym~r monollth black yla~ precur50r or
extruded through a heated dle to form a precursor polvmer
monolith~ The monoli~h would then be pyrolyze~ up to about
1 400C to form the! black glaY3 mon~lith~
A1 o considered as wlthin the s~o~e of thi~
inv2n~ion is impx~gnating ths black gla~ product of thi3
invention with cyclo~iloxane monomer rea~ion mixture, the
best results coming from pre sure or vacuum impr~nation
with subsequent pyrolysi~ to afford a black glass product
with less cracks and voids and with yreater density.
Impregnation can be rep~ated to furth~r increase the density
of the black gla~ produ~t of this inventionO

2337~
While the reaction works best if platinum is the
hydrosilylation ~atalyst, other catalysts such a~ cobalt and
manganese carbonyl will perform adequately, The ca~alyst
can be dispersed as a solid or can be used as a ~olution
when added to the ~yclosiloxane monomer.
Cy~losiloxane~ are the preferred ~ilicon
containing compounds ox ef~ecting the gel monoliths~
Examples of cyclosiloxanes include, but are not limited to,
1,3,5,7-tetramethyltetrahydrocyclotetrasiloxane,
1,3,5,7-tetravinyltetrahydrocyclotetrasiloxane,
1,3,5,7~tetravinyltetraethylcyclotetrasiloxan~,
1,3,5,7-tetravinyltetramethylcyclotetra~iloxane,
1,3,5-trimethyltrivi~ylcyclotrisiloxane,
1,3,5-trivinyltrihydrocyclotrisiloxane,
1,3,5-trimethyltrihydrocyclotrisiloxane,
1,3,5,7,9-pe~t~vinylpentahydrocy~lopentasiloxa~e,
1,3,5,7,9-penta~lnylpentamethylcyclopentasiloxane,
1,1,3,3,5,5,7,7-octavinylcyclotetrasiloxane,
1,1,3,3,5,5,7,7-octahydrocyclotetrasiloxane,
1,3,5,7,9~ hexavinylhexamethylcyclohexasiloxane,
1,3,5,7,9,11-haxame~hylhexahydrocyelohexa~iloxane,
1,3,5,7,9,11,13,15,17,19-
dec~vinyld~aahydro~yclodecasiloxan~,
1,3,5,7,9,11,13,15~17,19,21,23,25,27,29~p~ntadecavinyl-
pentadecahydrocyclopentad~ca~iloxan~,
1,3,5,7-t~rapropenyltetrahydrocyclotetra~iloxane,
1~3,5~,7-t~txap~ntenyltetrapentylcyclotetrasiloxan~ and
1,3,5,7,9-pentadecenylpen~apropylcyclopentasiloxa~eO
The monomeric mixture can include a ~iller such as
cubic or hexago~al silicoD carbide, silicon nitrid~, silica,
alumina, hafnia, titania, and zirconia ko ~treng~hen the
re ulting monolith. Such a filler in the form o~ a powder,
whisker, or fib~r can be mixed into the monom~r using
conventional me~nsO The fllled product produced by the
`
.
'

2~2337~
process of this invention shows not only increased strength
but also exhibits controlled shrinkage upon the pyroly~is
step. Pyroly~is of the precursor polymer~ change~ these
polymers into very hard ceramic bodie~ that can fi~d
application in high temperature, oxidation-resis~ant, high
strength compo~ite matrice~ and castabl~ cerami~s.
It has been discovered that applica~ion of
pressure to the monomer mixture during the pol~mer :Eorming
opera~ion will prevent nucleate bubbling o~ the reactants
and decrease reaction time in that higher temperatures can
be employed. Buhbling i~ to be avoided since it causes
void~ and cracks to form in the incipient polymer and
thereby weakening the fini~hed product. In the reaction o~
thls invention bubbling occurs whenever the filler content
of the monomer mixture is in excess of about 20% by weight.
Therefore, it is preferred to perform the polymeri~ation of
this inVentiQn under a pres~ure in the range of from 14 psi
to about 30,000 p~i ~o as to produce cra~k-free nearly
voidles~ polymer~0 The application of increased pressure
will also ha~ten the reaction time for unfilled polymer
fo~mation. For the purpose~ of thi~ application and~
appended claim~, the term "crack-free~ will be read ~o mean
fre~ o~ vi~ibl~ crack~.
Harada and Tanaka have shown in ~heir con~rol
experiment that ~he cured product obtained from a mixture o~
175 par~s of cyc:lote~ra~iloxane~ and 200 parts of quartz
f lour wa~ ound to have crack3 and to be urlu3able . xn their
invention, 100 part~ of an organopo~ysilo~ane ~ompo~ed of
~he ~rîorgano~iloxy and ~licon dioxide groups wa~ added to
the cyclotetrasiloxanes sol, resulting in a cured produc~
fr~e from crack defect~. Their monomer compu~ition thus
prepared i5 curable a~ a ~emperature in ~hE3 range from room
temp~rature ~o 100C. Our invention of high pre~sure
polymerization of cyclosiloxane~ by hydro~ilylation reaction
.. ..
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;,
. .

13
2~23378
not only can produce cured thick-walled products without
cracking and gas pocke~s, but also allows the use of
polymerization temperatures higher than lO0C and higher
platinum concentr~tion, thus shortening the reaction tima
for polymerization.
Th~ black glass composition of ma~ter has an
empirical formula SiCXOy wherein x range~ from about 0.5 ~o
about 2.0, and y ranges from about 0.5 to about 3.0, whereby
the carbon co~tent ranges from abo~t 10% to about 40%. Mo
other method known in the art can achieve ~uch a high carbon
content black gla s wherein the car~on is r~sistant to
oxidation at high temperatures.
As di~cuss~d hereinbefore, January and Monomann
were able to produce high carbon black gla~s from
precur~ors diff~rent from this invention but their glass
contained low densities around 1.6 and the carbon was easily
oxidized at low temperature. Using the proce~s of our
inYentiOn~ the carbon contained iD the black glass is
resistant to oxidatian and our den~i~ies are abou~ 2.1 grams
per millilit~r., In addition, ~he prlor work utilizing
silicon hydroly~is had ex~.remely slow fabrication times for
monolith~ on the order of week~ ~ wherea3 our invention can
form th~ polym0r monolith~ in the order of minutes with
higher yield ~han those made from hydrolyRi~ reaction~ of
s~llcon. Our monoll~h~ czln be ~ormed in~o larger shapes
than the hydrolysl~ blac:k glas~
Our invention can be used to manufacture non-
porous a~ well as porous blaclc glass. For most purpose~ it
is preferred to u~ neat cyrlosiloxane~ ~o form non-porous
black gla~s, but porou black qlass can ~e fo~ned if so
de~ired by starting with solvent based cyclosiloxan~
monc1mer~. This inven~ion provide~ crack-free po:lymers when
run in the pre~n~ of pressure while the same reaction
.

~2337~
mixture when run at atmospheric mixture provides a polvmer
containing cracks.
The ollowing examples are yiven for purpo~es of
illustration. E~owever, it i5 to be under~tood tha~ these
examples are only illustrative in nature and tha~ this
invention i~ not nec~ssarily limited thereto.
EXAMPI.E I
Ten milliliters of
tetravinyltetramethylcyclotetra~iloxane was mixed with 7~2
millilitexs of a mixture of cyclo~iloxane~ co~taining from 3
to about 6 ~i}icon atom~ and called m~thylhydrocyclosiloxane
and 0~05 milliliters of platinum-
divinyltetramethyldisiloxane complex containing 3~ platinum
in xylene was added to th~ above mixture. After heating to
about 60C for on~ hour a toluene in~olu~le gel polymer was
formed. The re~ul~ant poly~er wa~ then pyrolyzed in
nitrogen at a heating rate of 200C per hour to about 120UC
re~ulting in forma~ion Qf a carbon containing black ~lass.
The weight lo~ wa~ about 17% for the overall procass and
the skeleton density for the ground black glas~ powder was
about 2.10 gra~ per millillter. The carbon-containing
black gl~ lo~t les~ than 0.6~ by weight when heat~d in
flowing air ~o about 11$0C at a heatl~g rate of 10C p~r
minute in a thermogravime~r~c analysi~. X-ray analysls of
this black gla~ indicate~ that thi~ material is largely
amorphou~ and that ~he sample had a few sma~l diffrac~ion
peaks, whic~ wa~ diff2ren~ from crystalline silicon carbide.
Elemental compo-~ition gave the formula
~; iC 1 3 7 1 n 0 3
-
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, ' ' :

~2337~
for the black glass and the black glass contained <n . l
weigh~ ~ hydrogen and <0.3 weight ~ nitrogen.
EXAMPLES II - VI T T
These examples were all parformed as deseribad in
Example I with the excsption that differen~ volume amounts
of tetravinvltetr~methylcyclotetrasiloxane (T) and
methylhydrocyclosiloxane ~M) were utilized ~o make the black
glass. The results of these experiments are presented in
Table 1 below where T/~ is a volume ratio. The data shows
that the silicon bonded carbon content can be varied and
this ~ariation is controllabl0 within + 1~.
Thermogra~imetric analysis in flowlng air showed that powder
samples from Examples II-VIII had less than 0.~% wei~ht loss
when hea~ed to 1150~.
:
"~:
:
.:
; .

~233'~8
TARLE 1
o~ ~ ti~ ~b ~
Pyrolysis Carbon wt. 9~ Empirical
T/~ _ Yieldin bla~k qlas~ Formulae
II 8/2 67%29.8# ~iCl 450.89
III 7/3 7g%28.0~ SiCl 511.17
IV 6/4 829~27~2~ SiCl 360.~8
.,
V 5/5 839~24,6P6 Si~1.300.95
VI 4/6 84~24.1% SiC1 231.16
,~:
~ VII 3/7 77%21.7% ~iCl 081.17
-
~; VIII 2/8 57%~9-4~ SiCl.01O1.39
.
.,
EXAMPLE IX
The pyrolysis mechani~m wa~ vestigated by
:her~nogr2~rime~rlc analysi~ ~T~,A). ~9.93 mg of the gel
polymer obtained from Exa~nple I was heated under flowing
nitrogen at a heating rate oiE 10C per mlnute ~o 1100 C.
The to~al weight los~ wa~ 17~ Re~ul~!3 for ~he controlled
pyroly~i. are ~u~ arized in Table II below.
,
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. .
.~ , . ..

3378
Table_II
TGA Results fo~ rolvsls of Pol~mer ~.el
Temperature Range '~'eight TJOSS
8nc - 430C ;-
430C - 605~ 5.0%
605~ - 690C 5.n~
; 6gO~ - 745C
745C - 785C ~.0
~ 785C - g50C ?.5~ :
Total l6.8~
The ceramic conver~ion occurred in the 430~-~nC
temperature range. The derivatives of th~ T~.A curve
indica~ed three major pyrolysis mechanism~ at 430-7~0C,
650-800C and 780-900C. The third pyrolvsis step ac~ounted
for ca. 15~ of ~he total weight lo~s.
,
~; EX~UPLE X
~:~ 10 ~l of phenyltriethoxysilane was mixed with 10
ml o tetraethoxysilane in a beaker, 2~8 ml of l.0 ~ acetic
acid wa~ added, and ~he solutlon wa3 ad~usted to about p~ 1
by adding ~evexal drop~ of concentrated hydrochloric acid.
The gel Produ~e~ by this m~thod was pvrolvzed in nitro~en to
1200 & at a hea~ing rat~ o~ ~0~ per hour to qive ~6~l~ o~
a foam material with a 2~.6~ carbon oontent hy weight.
Thermossavimetric analysi~ o~ ~he b1ack glas~ ~oam ~a~
p~rformed in flowing air at a hea~ing ra~e of 20C per
. minute to 1150~C and show~d a loss in weight of 2n.~ which
began at around 550C. The ~olor of th~ sampl~ turned
whi~e, indica~ing that the rasidue is silica and the car~on
is not oxidation resi~tan~ as would he expected i~ the
.

~p
~2~78
carbon wa~ bound to the silicon structure rather than ~eing
present as a mixture of graphi~e in silica~
A second example using 20 ml of phenyl
triethoxysilane was reacted with 4 ml of tetraethoxysilane
as in the fir~t ~xample repor~ed above ~o give a 66% yiel~
of a porous product containing 35.0~ carbon by weight.
Thermogravime~ric analysis of this product showed a weight
loss Qf ~4.05%, again demonstratin~ ~hat the carbon presen~
is not resistant to oxidation at high ~emperatures as is the
carbon present in the black glass made in Example~ I~VTII.
EXAMPLE XI
A sol mixture was prepared as des~ribed in Example
I and silicon carbide whis~ex~ ~Tat~ho3 werP su~pended in
said mixture by ultrasonic agitation for from 15 to abou~ 30
seconds re.~ulting in a stable ~uspension of tha whiskers.
Polyme~ization of the sl~spension occurr~d after l20 minutes
heating at 50C affordin~ a rigid 3.5 centlmeter diameter
compo~ite cylind~r with about 13~ ~y weight whicXer content.
Pyroly~i~ of ~hi5 ~ylinder a~ 200C per hour up ~o
te~perature of about 1200C gave a cylinder who~e di~meter
had contracted by about 20%.
:
EX~PLE XII
In like manner a~ de cribed in Example I, a
mixture was prepared and then polymerized at about 90C in
about 10-15 minute~ under a pres~ur~ of 70 psi. Gelation
took abou~ 90 minutes if the tempera~ure i~ lowexed ~o 5~C
and th~ pre~sure ls atmospheric. An increa~ in pressure
then allow~ higher temperatur~ pol~merizatlo~ and affords
much ~horter polym~riæa~ion time~. Under a~mo~pheric
pres~ure, he sol liquid with 90 ppm P~ started ~o foam when
,

19
~23~78
gelation temperature was over 65C.
E ~ MP~E XIII
A mixture was prepared in like manner as described
in Example I and 50 w~ight percant of sili~on carbide powder
was added to said mixture. Polymerization oc~urred at 85C
and 70 p~i in 15 minutes wi~hout bubble formation. In
a~mospheric pressure operation it i~ not po~sible to obtain
bubblo-free sample~ for filler loadings exceeding about 20
by weight ~iller since the filler acts to produce nucleate
bubbling as ~he ~emperature is raised.
EXAMPLE XIV
For purpo~es of this example and for u~e in the
following Example~ ~V and XX, a standard mixture of
cyclosiloxane monomer~ wa.~ prepared from T,
tetravinyltetramethylcyclotetra~iloxane, and ~, a commercial
mixture of methylhydrocyclo~iloxane3 when the ~ilicon atoms
number fro~ 4-6, in the ratlo of S.7 T to 4~3 M in ~he
presence of 90 ppm platinum.
In this example 4 milliliter~ of the s~andard
mixtur~ wa~ plaG~d in a po}ypropylene ~ube and heat~d at
55C in an oven for 90 minu~e~ to form a polym~r which was
sub~eguen~ly hardened a~ 80C for 30 ml~u~e~O The polymer
exhibited a ~mooth ~ura~e and no cxac~s a~ter removal from
~he ~lypropylena kub~. Pyroly~is of th~ polymer in
nitrogen to 1200C at the ratQ o 200C per minu~e a~forded
a black gla~s ~th a bulk density of 2.05 g/ml exhibiting a
diamet~r shrinkag~ of about 21~ and a reduction in volume to
about 49~ of initial volume.

?O
2~2337~
EX~U~T E XV
Twelve milliliters of ~he mixture o~ ~xam~le XIV
wa~ mixed with 3 grams of alpha silicon carbide powder with
ultrasonic agi~ation and heated to 40C~ for 15 minutes. The
resultant mixtura wa~ poured into an 1lm~ x 1lmm x 55mm
copper case and placed in a pressure ves~el under ~0 p~iq.
The pressurized container waq placed in a 60C water bath
for 60 minutes to polymerize the monomers. ~he polrmsr was
heated in a 90C oven for one hour, and then taken out of
the copper case. The filled polvmer had dimension~ of 1.44
cm x 1.44 cm x 4.60 cm and exhibited a smooth surface and no
crack~. Pyrolysis under nitrogen at 200C per hour up to
12~0C produced a 1.14 cm x 1.t4 cm x ~.60 cm bla~k glass
obiect with uniform ~hrinkaye, as to height and width, of
19.0% and a final volume of ~2.9~ 0~ the initlal ~olume.
The black ~lass was ~hen impregna~ed under vacuum
with the starting mixture, polymerized at 55C ~or 80
minutes, cured at 90~ for 60 minutes, and pyrolvzed to
1200C as before. The pyrolyzed black glass ~xhi~ited no
change in d~mensions and weigh~d 10~28 gram~ wi~h a den~ity
of 2~3 g/ml. The ~ilicon carbide wa~ present in the~ black
glass ~t 23~ by weight.
RX~MPL~ XVI
A comparison experlment w~ run a~ de~cri~ed in
Exampl~ XIV but without a pressurlzed ves~ The resultant
polym~r exhibitPd gas poc~ets and cr~c~ af~er curing at
55~C for 90 minutes. A similar non-pre~surized sampl0 was
cured a~ 35C for 1fi hours and ~xhibi~ed crackq and ~a~
pock2ts. rAh~n a similar ~ixtur~ w~ cured at ~C for 48
hour~ t the polymer did not exhibit cracks and ~as pockets
but sedimen~atlon of the alpha silicon carbide pGwder
occurred and r~sulted i~ a clearlv defined boundary laver in
.
~ . ~

21 2~3378
the polymer.
EXAMPLE XVI I
l~leverl grams of a starting mix~ure as describ~d in
Example XIV was mixed with 7 grams of .alpha ~;ilicon carbide
powder ~39.3% by weight) by ultra~onic dispersion, plac~d in
a cylindrical alumi~sum cas~ with an int~xior diam~ r of 18
mm and a height of 74 mm, pres~uri~ed to 1~0 p ig, immersed
in an 85C water bath for 15 minutes, heated in a 105C ov~n
for one hour, and the filled polymer was then removed from
the case and ~xh~bited a smooth surface having no cracks
with a diameter of 18 mm and h~ight of 4 8 nun . Upon
pyrolysis 1:o 1200C at 200C per hour und~r ni~rogen, th~
filled black gla~ exhi}~ited a lS mm diameter with a height
of 41 m~, A weight of 16.34 gram~, a density of 2.2 g/ml~
and contained 43S by weight o~ ilicon caxbid~ powd~r.
EX~PI.IS XVIII
In lilc~ manner a~ in Example XVII, a 61~ alpha
silicon carbids f~ d monomer m:lxture!! ~as pr~pared from 16
grams of alph~ 8ilicon s~arhide powd~r and 10 ml of monomer
mixtur~. Thi~ ~alxtuxe wa~ heated at 40C for 20 minut~s,
the ~lurry w~ th~n poured into an 11 mm interlor diam~er
pe~lypropyl6~n~ ttlb~, th~ tube wa~ pre~3uri~d to 110 E~iy and
heated for 8 m~nut~ at 80C and aged a~ 8SC ~or 30
minu~ës, and the polym~r wa~ r~moved an~ exh~b~ ~ed a smoo~h
sur:Lacs and no cra~k~. Pyroly~is to 1200~C und~r nitrogen
at 200C per hour gave a f~lled bla~:lc glass wl~h a dlameter
of 8.7 mm arld a hei~ht of 45O7 mm, ~ weight of 6 gxam~, a
denslty of 2O23 g/ml, and contained 66% by weight: of silicon
carbide .
. - : ~ ..~ ,:,:
: ,:
.: . .

22 2~2~'37~
FXAMPLE XIX
;
In like mann~r as in Xxample ~VITI, 14.5 ml of
monomer mixture was combined with 5. 5 grams of ~i].icon
carbide whiskers and the whisker~ were dispersed
ultrasonically. The slurry was then poured in~o a ~ mm x
l8 mm x 12 mm rectangular aluminum mold and polymeri~ed at
50C for 3 hours when the polvmer was separated from the
mold and exhibited cracks and ga~ pockets. Pyrolysi~ was
performed at ~00C per hour under ni~rogen to 1~0~C
resulting in a black glas~ with a 1708 gm (86.6~ vield)
having dimensions of 50 mm x 15 mm x ll mm and a final
volume of 67~ of the initial volume. The density was ~.l6
g/ml and 32~ by weight of the fill~d black glas~ was silicon
carbide whisker.
EXAMPLF, XX
As described in Example XIX, the s~andard monom~r
mixture was heated at 40C for 30 minutes and then lO
millilit~rs wa~ mixed with 2.99 grams of silicon carbide
whiskers. This mixture wa~ di~ided into twc parts. ~One
part wa~ polymexized at 55C at atmos~heric pressure for 90
minut~ and produced a polymer exhibiting ga~ pocke~s and
surfac~ cracks. The second p~rt wa~ polYmerized under 7n
psig at 85C for 15 minutes givinq a polymer exhibitin~ a
smooth surfa~e and no cracks~ This experiment show~ the
impor~ance of pre sur~ in s~ortening the r~ac~ion time and
in produ~ing a crack-fre2 product.

~233~
XAMPLE XXI
A sol ~olutlon, prepared as de~cribed in ~xamplP
II was mixed wsth silicon carbid~ fibers (Nicalon - ~
manufactured by Nippon~ in a 1.9 millimeter glass vial. The
mi~ture was polymeri2ed at 52C for about two hour~
resulting in a crack-free fiber-reinfoxced polymer monolith.
Co~trolled pyrolysis, wherein the temperature wa~ raised
20nc per hour until a final temperature of 1200C wa~
reached, resulted in th~ formation of a black gla~s monolith
with the same diameter as the pre-fired polymer monolith, a
result that wa3 not ~hown by the unr~ orced polymer of
~xample II. The black gla~ fiber-reinforced monolith had a
density of 1.0 grams per milliliter and contained about 9.7
by weight silicon ~arbide flberO
The black glass monolith wa~ impre~nated, under
vacuum~ with monomer mixtur~ and pyroly~ed in nitrogen to
1200C at 200C per hour to give a monolith with a density
of 1.4 grams p~r milliliter. A second impregnation with
monomer mixtur~ followed by further pyroly~is gave a bla~k
glas~ monolith w~th a density of 1.6 gram~ per milliliter.