CA2023378A1 - Carbon-containing black glass monoliths - Google Patents
Carbon-containing black glass monolithsInfo
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- CA2023378A1 CA2023378A1 CA002023378A CA2023378A CA2023378A1 CA 2023378 A1 CA2023378 A1 CA 2023378A1 CA 002023378 A CA002023378 A CA 002023378A CA 2023378 A CA2023378 A CA 2023378A CA 2023378 A1 CA2023378 A1 CA 2023378A1
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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.
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.
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 . . :' : ' ~
' ' ' ' : ' ". ' ' 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 .
,~
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 . . :' : ' ~
' ' ' ' : ' ". ' ' 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 ::; : ~ ' :
:~
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~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 ., ~
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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.
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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 ~'`
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~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 `
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' 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 .. ..
- , ;, . .
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~.
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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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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%.
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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 , ~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.
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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 .
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FXAMPLE XIX
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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.
-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 ::; : ~ ' :
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~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 ., ~
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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.
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~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.
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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 ~'`
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~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 .. ..
- , ;, . .
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~.
:
"~:
:
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~233'~8 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.
, ' . .; :',~
. .
.~ , . ..
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 , ~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 .
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: ,:
.: . .
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.
Claims (30)
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 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.
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.
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, 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.%.
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 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.
(a) mixing a hydrosilylation catalyst with (a) a cyclosiloxane monomer of formula 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 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.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002023378A CA2023378A1 (en) | 1987-01-09 | 1990-08-16 | Carbon-containing black glass monoliths |
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US07/002,049 US5242866A (en) | 1987-01-09 | 1987-01-09 | Carbon-containing black glass monoliths |
| CA002023378A CA2023378A1 (en) | 1987-01-09 | 1990-08-16 | Carbon-containing black glass monoliths |
| FR9107166A FR2692249B1 (en) | 1987-01-09 | 1991-06-12 | CARBON CONTAINING BLACK GLASS MASSES. |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2023378A1 true CA2023378A1 (en) | 1993-10-07 |
Family
ID=27168788
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002023378A Abandoned CA2023378A1 (en) | 1987-01-09 | 1990-08-16 | Carbon-containing black glass monoliths |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2023378A1 (en) |
-
1990
- 1990-08-16 CA CA002023378A patent/CA2023378A1/en not_active Abandoned
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| FZDE | Discontinued |