CA1189080A - Process for the preparation of poly(disilyl)silazane polymers and the polymers therefrom - Google Patents
Process for the preparation of poly(disilyl)silazane polymers and the polymers therefromInfo
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- CA1189080A CA1189080A CA000425922A CA425922A CA1189080A CA 1189080 A CA1189080 A CA 1189080A CA 000425922 A CA000425922 A CA 000425922A CA 425922 A CA425922 A CA 425922A CA 1189080 A CA1189080 A CA 1189080A
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Abstract
Abstract What is disclosed is a process for preparing R'3SiNH- containing silazane polymers by contacting and reacting chlorine-containing disilanes with (R'3Si)2NH
where R' is vinyl, hydrogen, an alkyl radical of 1-3 carbon atoms or the phenyl group. The silazane polymers are useful as chemical intermediates to produce silicon-containing chemical compounds. They are also useful in the formation of silicon carbide-containing ceramic materials.
where R' is vinyl, hydrogen, an alkyl radical of 1-3 carbon atoms or the phenyl group. The silazane polymers are useful as chemical intermediates to produce silicon-containing chemical compounds. They are also useful in the formation of silicon carbide-containing ceramic materials.
Description
TITLE: A PROCESS FOR T~E PREPARATION OF
P3LY(DISILYL)SILAZANE POLYMERS AND THE PO~YMERS THEREFROM
Background of the Invention This invention relates to the preparation of silazane polymers. These polymers are useful as chemical intermediates to synthesize organosilicon compounds. They are also useful, when fired at high temperatures, to form silicon carbide and silicon carbide containing ceramic materials.
What i5 disclosed herein is a novel process to obtain novel silazane polymers. ~he process con~ists of contacting and reacting chlorine-containlng di~ilane with disilazanes in an inert, essentially anhydrous atmosphere while distilling volatile by-products.
As is well-known in the art, halosilane monomers will react with ammonia and most organic compounds containing a primary or secondary amino group ~o give a variety of silazanes. For example, the reaction of trim~thylchlorosilane and ammonia produces hexamethyldisilazane, a silazane monomer, while dimethyldichlorosilane and ammonia produce dimethylcyclic silazanes. These two reactions probably constitute the majority of commercial ~ses of the silazane chemistry.
Silazanes in general have been academic curiosities for ~any years and a variety of such silazanes, including monomers, oligomers, cyclics and even low molecular weight resins and linear polymers have been prepar~d by a varie~y of methods. For example, L. W. ~reed et al., ln the Journal of Organic Ghemistry, 27, 1114(1962) report the ~ormation of silazanes from the polymerization o sterically hindered silazane oligomers, while in the Journal of Polymer Science, A 2 45(1964~, cyclic trimer and ~etramer silazanes are reported to be thermally cracked using catalysts to give linear polymers.
In contrast, fluids, rubbery polymers and resins prepared from C~3SiC13, (C~3)2SiC12 and excess ammonia have been reported by Kruger et al. in the Journal of Polymer Science, A 2 3179~1964) and Redl, Silazane Polymer, ARPA-19, Advanced Research Projects Agency, October, 1965.
The patent literature also contains disclo~ures of the preparation of silazanes. Cheronis, in U.S. Patent
P3LY(DISILYL)SILAZANE POLYMERS AND THE PO~YMERS THEREFROM
Background of the Invention This invention relates to the preparation of silazane polymers. These polymers are useful as chemical intermediates to synthesize organosilicon compounds. They are also useful, when fired at high temperatures, to form silicon carbide and silicon carbide containing ceramic materials.
What i5 disclosed herein is a novel process to obtain novel silazane polymers. ~he process con~ists of contacting and reacting chlorine-containlng di~ilane with disilazanes in an inert, essentially anhydrous atmosphere while distilling volatile by-products.
As is well-known in the art, halosilane monomers will react with ammonia and most organic compounds containing a primary or secondary amino group ~o give a variety of silazanes. For example, the reaction of trim~thylchlorosilane and ammonia produces hexamethyldisilazane, a silazane monomer, while dimethyldichlorosilane and ammonia produce dimethylcyclic silazanes. These two reactions probably constitute the majority of commercial ~ses of the silazane chemistry.
Silazanes in general have been academic curiosities for ~any years and a variety of such silazanes, including monomers, oligomers, cyclics and even low molecular weight resins and linear polymers have been prepar~d by a varie~y of methods. For example, L. W. ~reed et al., ln the Journal of Organic Ghemistry, 27, 1114(1962) report the ~ormation of silazanes from the polymerization o sterically hindered silazane oligomers, while in the Journal of Polymer Science, A 2 45(1964~, cyclic trimer and ~etramer silazanes are reported to be thermally cracked using catalysts to give linear polymers.
In contrast, fluids, rubbery polymers and resins prepared from C~3SiC13, (C~3)2SiC12 and excess ammonia have been reported by Kruger et al. in the Journal of Polymer Science, A 2 3179~1964) and Redl, Silazane Polymer, ARPA-19, Advanced Research Projects Agency, October, 1965.
The patent literature also contains disclo~ures of the preparation of silazanes. Cheronis, in U.S. Patent
2,564,674, issued August 21, 1951 discloses the preparation of low molecular weight linear silazane polymers by the reaction of halosilanes with excess ammonia in`a solvent solution. Bausma, et al., in U.S. Patent 3,809,713 issued May 7, 1974, discloses a similar reaction scheme with the added modifica~ion of removing the by-produced solid ammonium halide using ethylene diamine.
More recently, Verbeek, et al., in U.S. Patents
More recently, Verbeek, et al., in U.S. Patents
3,853,567 issued December 10, 1974, and U.S. Patent 3,892,583 issued July 1, 1975, disclosed that mixtures of CH3SiC13 and (C~3)2SiC12 can be treated with ammonia or organoamines to form materials that can be pyrolyzed to yield SiC/Si3N4 ceramics.
~18~8~
As should ~e recognized by those skilled in the art, the present invention differs in at least one respect from all of the above art in that the present invention is based on chlorine-containing disilanes as opposed to the use of chlorine containing monosilanes.
In another segment of the prior art, the ~se of disilanes in the preparation of silazane polymers has been limited to the formation of relatively low molecular weight materials. In one example, Wannagat et al., Ang. Chem.
75~7) 345(1963~, reported the reaction of tetramethyldichlorodisilane with gaseous ammonia to give a six-membered cyclic silazane, {(CH3)2SiSi(CH3)2N~}2, rather than the expected linear silazane polymer and Hengge et al., Montash. Chem. lOlI(2)325(1970), prepared dime~hylamino substituted mixtures o disilanes from dimethylamine and the chlorine-containing disilane mixture obtained from the Direc~ Process ~or the preparation o chlorosilanes.
What has been newly discovered is the coreaction between chlorine-containing disilanes and disilazanes to give high molecular weight silazane polymers.
The Invention The instan~ invention c~ncerns a new class o~
silazane polymers pr~pared from chlorodisilanes. In essence, a single chlorine-containing disilane or a specified mixture of chlorine-containing disilanes is treated with a disilazane, as the nitrogen source, in sufficient amounts to react with all o the chlorine on the chlorine-containing disilanes. This is usually an e~uimolar amount of disilazane based on the chlorine content of the disilane. The inventor does not wish to be he}d to such a theory but it is believed that when the mixture is heated, usually in the absence of solvent and in an essentially anhydrous atmosphere, the reactions -Si-SiCl ~ R'35iNHSiR13~ Si-Si-NHSiR'3 ~ R'3SiCl, ~ ' . . . . .
-Si-Si-Cl + -Si Si-N~SiR'3 ~ ~Si-Si-NH-Si-Si- ~ R'3SiCl and 2-Si-Si-NHSiR'3 ~ -Si-Si-N~-Si-Si * R'3SiNHSiR'3 take place.
The advantage of this process is the ability to stop the reaction at any point by cool ing the reaction mass thus giving polymers with any desirable viscosity, hence any desirable molecular weight. The silazane polymers range in physical appearance from liquids, to high viscosi~y liquids, to hard glassy materials. The m~terials are therefore very easy to handle. They are essentially hydrolytically stable.
~ hus, this invention consists of a process ~or preparing an R' 3SiN~- containing silazane polymer which consists of contacting and reacting in an inert, essentially anhydrous, atmosphere, a chlorine-containing disilane or a mixture of chlorine-containing disilanes, of the general formula (ClaRbSi)2 with a disilazane having the general formula (R~3si)~NH
at a temperature in the range of 25C to 300C while distilling by-produced volatile products~ wherein R is vinyl, an alkyl group of 1-3 carbon atoms or the phenyl group; R' is vinyl, hydrogen, an alkyl group of 1-3 carbon atoms or the phenyl group; a has a value of 0.5-3; b has a value of 0-2.5 and the sum ~f a I b is equal to three.
This invention also deals with a new and novel composition of matter which is an R'3SiNH- containing silazane polymer which is prepared by contacting and reacting in an inert, essentially anhydrous, atmosphere, a chlorine containing disilane or a mixture o chlorine-containing disilanes, of the general formula ( ClaRbS i ) 2 with a disilazane having the general formula (R'35i)2NH
at a temperature in ~he range of 25C to 300C while distilling by-produced volatile products, wherein R is vinyl, an alkyl group o~ 1-3 carbon atoms or the phenyl group; R' is vinyl, hydrogen, an alkyl group of 1-3 carbon atoms or the phenyl group, a has a value of 0.5-3; b has a value of 0-2.5 and the sum of a ~ b is equal to three.
This invention further deals with a process ~or preparing an R'35iNH- containiny silazane polymer which consists of contacting and reacting in an ine~t, essentially anhydrous, atmosphere, a chlorine-containing disilane or a mixture of chlorine-containing disilanes, wherein the number of diorgano-substituted silicon atoms does not exceed the number of monoorgano substituted silicon atoms, of the general formula (ClaRbSi)2 with a disilazane having the genera} formula (~l3Si)2NH
at a temperature in the range of 2SC to 300C while distilling by-produced volatile products wherein R is vinyl, an alkyl group of 1-3 carbon atoms or the phenyl group; R' is vinyl, hydrosen, an alkyl group of 1~3 carbon atoms or the phenyl group; a has a value of 0.5-3; b has a value o~ 0-2.5 and the sum of a ~ ~ is equal to three.
This invention also deals with a new and novel composition of matter which is an R'3SiNH- cont~ining silazane polymer which is prepared by contac~ing and reacting in an inert, essentially anhydrous ~ atmosphere, a chlorine-containing disilane or a mixture o~
chlorine-containing disilanes wherein the number of diorgano-substituted silicon a~oms does not exceed the number of monoorgano-substitu~ed silicon atoms of the general formula (ClaRbSi32 wi~h a disilazane having the general formula (Rl3si)2NH
at a temperature in the range of 125C to 300C while distilling by-produced volatile products, wherein R i5 vinyl, an alkyl group of 1-3 carbon atoms or the phenyl group; R' is vinyl, hydrogen, an alkyl group of 1-3 carbon atoms or the phenyl group; a has a value of 0.5-3; b has a value of 0-2.5 and the sum of a ~ b is equal to three, Still further, this invention deals with a method of preparing a silicon carbide containing ceramic material which consists of heating a silazane polymer in an inert aumosphere or in ~ vacuum to at least a temperature of 750C until the silazane polymer is converted to silicon carbide ceramic material, which silazane pol~mer is obtained by a process which consists of contacting ancl reacting in an inert, essentially anhydrous, atmosphere, a chlorine-containing disilane or a mixture of ~L~L~8~
chlorine-containing disilanes, wherein the number of diorgano-substituted silicon atoms does not exceed the number of monoorgano-substituted silicon atoms, of the general formula ~ ClaR~Si32 with a disilazane having ~he general formula ~ R'3Si)2NH
at a temperature in the range of 125C to 300C while distilling by-produced volatile products, wherein R is vinyl, an alkyl group of 1-3 carbon atoms or the phenyl group; R' is vinyl, hydrogen, an alkyl group of 1-3 carbon atoms or the phenyl group; a has a value of 0.5-3; b has a value of 0-2.5 and the swm of a ~ b is equal to three.
Yet another object of this invention is a method o~ preparing a silicon carbide containing ceramic article which consists of (A) forming an ~rticle of the desired shape from a silazane polymer; (B) heating the article formed in (A) in an inert atmosphere or in a vacuu~ to an elevated temperature of at least 750C until the silazane polymer is converted to silicon carbide containing ceramic, which silazane polymer is obtained by a process which consists of contacting and reacting in an inert, essentially anhydrous, atmosphere, a chlorine-containing disilane or a mixture of chlorine-containing disilanes, wherein the number of diorgano-substituted sil.icon atoms does not exceed ~he number of monoorgano-substituted silicon atoms, of the general formula (~laRbSi)2 with a disilazane having the general formula (R'3~i)2N~
at a te~perature in the range of 125C to 300C while dist:illing by-produced volatile products, wherein R is vinyl, an alkyl group of 1-3 carbon atoms or the phenyl group; R' is vinyl, hydrogen, an alkyl group of 1-3 carbon atoms or th~ phenyl group; a has a value of 0.5-3; b has a value of 0-2.5 and the sum of a ~ b is equal to three.
Still another object of this invention is a method for preparing a filled ceramic article which consist of (A) mixing a silazane polymer with at least one conventional ceramic filler, ~B) orming an a~icle o~ the desired shape from the mixture of silazane polymer and filler and ~C~ heating the article formed in (~) in an inert atmosphere or in a vacuum to an elevated temperature of at least 750C until the silazane polymer is converted to a silicon carbide containing ceramic, which silazane polymer is obtained by a process which consists of contacting and reacting in an inert, essentially anhydrous, ab~osphere, a chlorine-containing disilane or a mix~ure of chlorine-containing disilanes, wherein the number of diorgano-substituted silicon atoms does not exceed the number of monoorgano-substituted silicon atoms, of the general formula . . . . . . .
_ . . .
(ClaRbSi~2 with a disilazane having the gencral ormula (R'3Si)2NH
at a temperature in the range of 125C to 300C while distilling by-produced volatile products wherein R is vinyl, an alkyl group of 1-3 carbon atoms or the phenyl yroup; R' is vinyl, hydrogen, an alkyl group of 1 3 carbon atoms or the phenyl sroup; a has a value of 0.5-3; b has a value of 0-2.5 and the sum of a ~ b is equal to three.
Still ~urther, it is an object of this invention to prepare an article coated with a silicon carbide ceramic material which method consists of (A) mixing a silazane polymer with at least one conventional ceramlc iller, tB) coating a substrate with the mlxture o~ silazane pol~ner and filler and, (C) heating the coa~ed su~strate in an inert atmosphere or in a vacuum to an elevated temperature of at least 75QC until ~he coating is converted to a silicon carbide ceramic material, whereby a silicon carbide containing ceramic coated article is obtained, which ~ilazane polymer is obtained by a process which consists o~
contacting and reacting in an inert, essentially anhydrous, atmosphere, a chlorine-containing disilane or a mixture of chlorine-containing disilanes, wherein the number of diorgano-substituted silicon atoms does no~ exceed the number o monooryano~substituted silicon atomæ, of the general formula ~ClaRbSi)2 with a disilazane having the general formula ~ R13Si)2N~I
at a temperature in the range of 125C to 3~0C while distilling by-producPd volatile products, wherein R is vinyl, an alkyl group of 1-3 carbon atoms or the phenyl group; R' is vinyl, hydrogen, an alkyl group of 1-3 carbon atoms or the phenyl group; a has a value of 0.5-3; b has a value of 0 2.5 and the sum of a ~ b is equal to three.
A further object of this invention is a process for preparing an article coated with a silicon carbide ceramic material which consists of (A) coating a substrate with a silazane polymer, (B) heating the coated substrate in an inert atmosphere or in a vacuum to an elevated temperature o~ at least 750C until the coating is converted to a silicon carbide ceramic material, whereby a silicon carbide containing ceramic coated article is obtained, which silazane polymer is obtained by a process which consists of contacting and reacting in an inert, essentially anhydrous, atmosphere, a chlorine-~ontaining disilane or a mixture of chlorine-containing disilanes, wherein the number of diorgano-substituted silicon atoms does not exceed the number of monoorgano-substituted silicon atoms, of the general formula ~ ClaRbSi)2 with a disilazane having the general formula .
.
( ~2 (R'3Sij2NH
at a temperature in the range of 125C to 30~C while distilling by;produced volatile produc~s wherein R is vinyl, an alkyl group of 1-3 carbon atoms or the phenyl group; R' is vinyl, hydrogen, an alkyl group of 1-3 car~on atoms or the phenyl group; a has a value of 0.5 3; b has a value of 0~2.5 and the sum of a + b is equal to three.
A final object of this invention is a process for preparing an R'3SiNH- containing silazane polymer which consists of contacting and reacting in an inert, essentially anhydrous atmosphere, a disilazane having the general formula (R~3Si)2NH
with (i) a mixture of a chlorine-containing disilane having the general formula (ClaRbSi) ;2 and a chlorine-containing monosilane having the gen~ral formula R'nSicl4-n;
~ii) a mixture of chlorine-containing disilanes having the general formula (ClaRbSi)2 mixed with a chlorine-con~aining monosilane having the general formula R'nSlcl4-n or (iii) a mixture of chlorine-con~aining disilanes having the general formula Cl aRbs i 2 mixed with a mixture of chlorine-containing monosilanes having ~he general formula R'nSicl4-n at a temperature in the range of 25C to 300C while distilling by-produced volatile products, wherein R is vinyl, an alkyl radical of 1-3 carbon atoms or the phenyl group; R' is vinyl, hydrogen, an alkyl group of 1-3 carbon atoms or the phenyl group; a has a value of 0.5-3; b has a value of 0-2.5; n has a value of 0, 1, 2 or 3 and the sum of a ~ b is equal to three.
The inventions described herein result in new compositions of matter which are an improvement in ~he art, in that, essentially hydrolytically stable, easy to handle silazane polymers can be prepared. Further, the silaæane polymers lead to an improvement in the art of formation o~
silicon carbide and they can be used as binders in ceramic materials.
The invention results from reacting disilazanes ~ith chlorine-containing disilanes or mixtures of disilanes with monosilanes in an inert, essentially anhydrous atmosphere and then firing the resulting si~azane polymer to get silicon carbide or silicon carbide containing ceramic materials.
The chlorine-containing disilanes of this invention are those disilanes having the yeneral formula (ClaRbSi)2-In this formula, R is vinyl, an alkyl radical containing 1-3 carbon atoms or the phenyl group. Thus, those groups which are contemplated as being useful in this invention are methyl, ethyl, propyl, vinyl and phenyl. For purposes of this invention, the R groups can all be the same or they can be different. The chlorine-containing disilanes can be those found in the residue from the Direct Process for producing halosilanes (Eaborn, C., ~Organosilicon Compounds", Butterworth Scientific Publications, London, 1960, pg. 1). Whenever the symbols 0, Me, Et and Vi are used herein, their meaning is phenyl, methyl, ethyl and vinyl, respectively.
For purposes of this invention, the value of a and b is f~om 0.5-3 and 0-2.5 respectively and the sum of a + b is equal to three. Examples of chlorine-containing disilanes useful in this invention are {Cl(CH3~2Si}2, {C12CH3si}2r {cl2c2H5si}2r {Cl(C6Hs)2Si}2 and {cl2cH2=c~si}2-Monosilanes useful in admixture with the disilanesof this invention can be for example CH3SiC13, (CH3)2SiC12, ~(CH3)2SiCl, (CH3)3SiCl, (CH2=CH)(CH3)2SiCl, (C2Hs)2SiCl~, C6H5siC13~ (c6H5)2sicl2 and (C6Hs)3SiCl.
Also considered within the scope of this invention is the use of mixtures of chlorine-containlng disilanes.
One aspect of ~-his invention requires that whenevPr certain chlorine-con~aining disilane mixtures are required, the n~ber of units of diorgano-substituted silicon atoms should not exceed the number of units of monoorgano-substituted silicon atoms. Even though silazane polymers can be formed from chlorine-containing disilane mixtures wherein the number of diorgano-substituted units does exceed the number of monoorgano-substituted units, it has been found that these polymers do not have the handling properties for formability because of low viscosities.
The second reactant in this invention is a disilazane of the general formula ~R'3Si)2NH. For purpo~es of this invention, R' is vinyl, hydrogen or has the same meaning as R above. Thus, R' in this ~ormula i5 vinyl, hydrogen or an alkyl radical of 1-3 carbon atoms or the phenyl group. Therefore, R', for purposes of this formula is represented by hydrogen, methyl, ethyl, propyl, vinyl and phenyl. As set forth above, each Rl group in this formula can be the same or they can be different. Examples of compounds contemplated within the scope of this invention include: {(CH3~3Si}2NH, tC6H5(CH3)2si}2~
l'l~OB'O
{(c6H5)2cH3si}2NH~ {C~2-CH(CH3)2si}2NH' {C~ H5C~3)C6~5si}2~ (CH2=CH~tC6H5)2Si}2N~, {CE~25C~(C2H5)2si};~N~I~ {(C~2-C~)C6H51C2H5)5i} 2NH~
{~(CH3)2si}2N~t {~2(c~3)si}2NH and lHc6~scH3si}2N~.
These reactants are brou~ht together in an inert, essentially anhydrous atmosphere. For purposes of this invention what we mean by n iner~" is that the reaction is carried out under a blanket of inert gas, such as, argon or nitrogen or helium. What we mean by ~essentially anhydrous~ is that the reaction is preferably carried out in an abso}utely anhydrou~ atmosphere but minute amounts of moisture can be tolerated.
When the reactants are contacted with each other, the reaction begins which forms an intermediate disilane amino compound i.e.
-Si-Si-Cl ~ (R'3Si)2NH ~ -Si-Si-NH5iR'3 + R'3SiCl.
Upon heating, additional disilane amino compound is formed and upon continued heating, R'3SiC1 is disti}led from the reaction mixture and a disilylsilazane polymer is formed i.e.
~BO
Si-Si-Cl ~ -Si-Si-NH5iR'3~ -Si-Si-~H-Si-Si- ~ R13SiCl .
.. ~, .. ..
2-Si-Si NHSiR'3~ Si-SiNH-Si-Si + R'3SiNHSiR'3.
The order of addition of the materials does not appear to be critical. AS the temperature is raised higher, more condensation takes place and crosslinking occurs, with residual R'3Si- that is not distilled from the mixture, acting as a chain-stopper. This control allows one to stop the reaction at any point to obtain almost any desired viscosi~y. The desirable temperature range for this reaction is 25C to 300C. The most preferred range :is 125C to 300C. The length of time ~hat the reaction requires depends on the temperature and the viscosity one wishes to achieve.
What is meant by "volatile products" are the distillable by-produced products that are formed by the reactions set forth above. These materials can be represented by (CH3)3SiCl, (CH2-CH~(C6Hs)2SiCl, 3(C6H5)2siCl~ (cH3~2c6~ssiu ~ HtcH3)25icl and (CH2=C~)(C~3)2SiCl. Sometimes, these materials require the use of a vacuwm along with the heat in order to remove them from the reaction mixture.
The sila~ane polymers are then essential}y ready to use. The silazane polymers are pyrolyzed in an inert atmosphere or in a vacuum at temperatures o:f at least 750C
to give a silicon carbide containing materi,al. If the polymer is of sufficient viscosity, it can be shaped first (such as an extruded fiber) and then pyrolyzed to give a silicon carbide containing fiber or the silazane polymers can be filled with ceramic type fillers (if desired) and then fired to at least 750C to obtain silicon carbide ceramic materials or silicon carbide ceramic material GOntaining ceramic articles.
When mixtures of chlorine-containing disilanes are to be used, it is best if the chlorine-containing disilanes are mixed prior to contacting and reacting with the disilazanes.
As mentioned above, some of the resulting polymers can be extruded to give various shapes such as fibers. It has been found that the polymers of this invention that have the handleability that enables one to extrude or form them are those polymers in which the number of diorgano-substitu~ed silicon atoms do not exceed the number of monoorgano-substituted silicon atoms. Thus, if the polymer is to be extruded or otherwise formed, it should be prepared from disilanes and disilazanes wherein the diorgano-substituted silicon atoms do not exceed the nu~ber of monoorgano-substituted silicon atoms.
As mentioned above, the polymers of this invention can be used in both the filled and unfilled state, depen~ing on the application. Thus, it is contemplated wi~hin the scope of this invention ~o coat substrates with ~illed and unfilled polymers and heat the s~bstrates to pr~duce silicon carbide containing ceramic ~oated artic}es.
Fillers and adjuvants can be milled on 3 roll mills by simply mixing the polymers of this invention with the fillers and making several passes on the mill. In the alternative, the polymers can be plac~d in solvents and the fillers and adjuvants can be added thereto and after mixing the solvent can be removed to give the filled polymer.
The coating can be carried out by conventional means. The means used depends on the polymer and substrates used and the application one has in mind. ~hus, these materials can be brushed, rolled, dipped or sprayed.
In the filled stated, it is sometimes necessary to trowel the polymer onto the substrate.
Whenever the polymers are converted to the ceramic state, it i5 done by pyrolyzing the polymer to a temperature of at least 750C in an inert atmosphere or in a vacuum.
Attempts to pyrolyze at or above 750C without an inert atmosphere lead to undes:irable side reactions and therefore, caution should be exercised ~o be ~ure to exclude moisture and other potential reactants.
. . . _ , Now so that those skilled in the art can better appreciate and understand the invention, the following examples are given. The examples are for purposes of illustration only and are not to be regard~ed as limitations.
In ~he following examples, the analytical methods used were as follows:
Thermogravimetric analyses (TGA) were carried out on a Netzsch STA 429* (2400C) TGA instrument manufactured by Netzsch Instruments, Selb, West Germany. Sample sizes averayed 11 mg., program rate was 10C/min., gas flow rate was 200 cc/min. The scale setting was 50C/in. ~ 0.5C/in~
Differential Thermal Analyses (DTA) were carried out on the Netzsch instrument using samples averaging 13.S
mg., a flow rate of 200 cc/min., a program rate of lO~C/min and a scale setting of 50C/in + 0.5C/in.
Percent Silicon was determined by a fusion technique which consis~ed of converting the silicon material to soluble forms of silicon and the soluble material is quantitatively determined as total silicon by atomic absorption spec~rometry. Solubilization takes place by weighing the sample into a Parr-type* fusion cup (about 0.3 gm), adding 15.0 gms of Na peroxide, heating for about 90 sec. and ~uenching in cold water. The material is placed in a nickel beaker containing 150-200 ml. of distilled water. 55 ml. of reagent grade acetic acid is added and diluted with water to 500 ml. volume.
Trademark ( Percent Chlorine tresidual) was cletermined ~y Na peroxide decomposition and titration with silver nitrate.
Fusion of ~he halides with Na peroxide is followed by potentiometric titration with standard silver nitrate by weighing a sample into a gelation capsule~ placing about 1.5 gm. of Na2O~, about 0.7 gm of ~NO3 and about 0.15 gm of sug~r into a clean, dry reaction cup and burying the capsule in the mixture. The cup is filled with Na2O2 and placed in a reaction vessel. It is heated for 1-1 1/2 minO
and quenched in cold water. The cup and vessel are washed and ~he washings are collected. The washings are heated to dissolve any solids. 15 ml. of cold 50~ aqueous H2SO4 is added and allowed to stand 15-20 sec. This solution is neutralized with additional H2SO4 and titrated.
Carbon and hydrogen were determined by microcombustion by weighing 10 to 20 mg. of sample into a micro platinum boat and treating it in an A. H. Thomas co~bustion apparatus, Catalog No. 6447-E, Philadelphia, PA.
In the reactions carried out below, the reaction apparatus was essentially the same in each case and consisted of a 500 ml., glass, round-bottomed flask equipped with a mechanical stirrer, gas inle~ tube, distillation apparatus and a thermocouple to record temperature. The distillation apparatus was equipped to use a vacuum if needed.
., 8~
A mixture of 50 gms of chlorine-cont:aining di~ilanes consis~ing of 57.6 wPight percent of tetrachlorodimethyldisilane; 32 weight percerlt of trichlorotrimethyldisilane and 10.4 weight percent of dichlorotetramethyldisilane were added dropwise to a reaction vessel described above which contained 120 gms of hexamethyldisilazane. The reaction vessel was then slowly heated to 275C under argon and held at that ~emperature ~or two hours. The distillate that was collected during ~he heating pariod was found ts contain ~CH3)3SiCl, some hexamethyldisilazane and a small amount of NH4Cl. The polymer residue in the flas~ weighed 29.6 gms and when cooled was a hard, colorless, glassy solid. The material was fired in an Astro Industries Furnace lOOOA water cooled graphi~e heated model 1000.3060-FP-12 to 1200C under Argon for a yield of 46.29%. The material contained 29% carbon, 7-8% hydrogen, 45% silicon and 8.1% nitrogen. Infra red analysis showed the presence of -Si-NH-Si- but no -Si-O-Si-. X-ray analysis of samples fired at various temperatures showed the following:
tem~ type of material 1200C Amorphous ~aterial 1400C Amorphous material 1600C beta-SiC l~oA and Moissanite SiC
18~0C beta-SiC o ~2000~ and Moissanite SiC
2000C beta-SiC of > 2000~ but no Moissanite Ebulliometry gave 3125 gm/mole.
~ examethyldisilazane (214 gms) and S9.90 gms of Si~C16 were placed in a reaction vessel described above.
Upon mixing, the reaction exothermed to 57GC and the mixture turned cloudy white. Distillation began at about 77~C and the reaction mass cleared and turned a faint yellow color when the flask reached 110C.
The reaction mass proceeded to foam and the foam level was controlled by increasing stirrer speed and maintaining the temperature at 160-165C for 1 hour. The temperature was raised to 170C with rapid stirring and then to 265C where the reaction mass foamed excessively.
The temperature was decreased to about ~15C ~or a short while and then the pot was allowed to cool. When cooled the material was a glassy, clear solid which was easily removed from the inside surface of the reaction flask. A
small amount of gummy liquid was also removed from the flask. Infra red analysis showed the presence of NH and Si(CH3)3 with some -SiCH3 and -Si-N-Si. %Si was 42.3%.
X-ray diffraction on a sample fired to 1600C showed the major phase to be beta-silicon car~ide with a minor phase of beta-Si3N4. The average crystallite size of the beta-silicon carbide was 130A.
~.~8$~
~4 ~e~
Tetrachlorodimethyldisilane (32.7 gms) and 17.3 gms of trichlorotrlmethyldisilane were mixed with 168.3 gms of hexamethyldisilazane in a reaction vessel equipped as des~ribed above. This mixture was gradually heated to ~65C under argon and held there for about 10 min.
Distillate was removed during this period of time. ~hen cooled~ the residue was a polymer which was a hard, colorless resin. The yièld was 65.7%. Thermal gravimetric analy~is to 1000~C yielded 54% silicon carbide.
Differen~ial thermal analysis in air to 500C gave an exotherm at 93C. ~TA in argon to 500C showed no ~hermal break. Residual chlorine content was 1.44 weight % and %Si was 47.4. Infra-red analysis showed the presence of NH, NH4Cl, SiC~3, Si-N-Si. X-ray diffraction studies on a sample fired at 1600C showed beta-silicon carbide having a particle size of 120~ and a small amount of alpha-silicon carbide. The polymer was analyzed by derivatization gas chromatography and found to contain 7.5 weight % (C~13)3Si-, 15.0 weight ~ (CH3)2SiS and 68.5 weight ~ of CH3Si~.
Derivatization gas chromatography is an analysis wherein the polymer is treated with tetraethoxysilane and KOH to give the organoethoxysilane derivatives of the individual polymeric units~ Gas chromatography is then used to determine ~he content and relative ratios o~ the various units present in the mixture. This procedure is carried out by weighing about 0.3 gm of the polymer sample into a 50 ml. round-bottomed flask. To this flask is added 8O0 ml. of Si(OC2~s)4. One pellet of XO~ is added and the flask is heated to initiate the reaction and it is then reflllxed for 45 min. to one hour. An additional 2.0 ml. of Si(OC2Hs)4 is added and then about 1/2 teaspoon of pulverized CO2 is added to neutralize the KO~. The sample i5 centrifuged to separate the phases. The silane layer is then analyzed by gas chromatcgraphy which has been standardized.
}~
Tetrachlorodimethyldisilane (45.6 gms) was mi.xed with 129.1 yms of hexamethyldisilazane under argon. The reaction vessel was equipped as in Example 1. This reaction mass was heated to 240C and held for a few minutes and then cooled to room temperature. The resulting material was a solid whit~ powder and 26.6 gms were obtained. The % yield was 58~3%o TGA to 1000C in argon gave 27~ weight loss. DTA in air to 500C gave an exotherm at 140C and DTA in argon to 500C gave no thermal break.
% residual chlorine was 4~83 weight ~ and weight % Si was 44.4, Infra-red analysis showed the presence of ~H4Cl, Si-N-Si and -SiCH3. A yield of 62.6 weight ~ was obtained when the material was fired to 1200C and 78.1 weight % was obtained on firing from 1200C up to 1600C.
Deriva~ization using Si(OC2Hs)4 gave the following: 6.4 weight % (C~3)3Si-, 2.0~ of (CH3)2Si= and 68.0% of CH3Si3.
Exam~le S
Trichlorotrimethyldisilane (45.8 gms) was mixed wi~h 196~84 gms of hexamethyldisilazane in a reaction lask equipped as described above. This mixture was hea~ed under argon to 280 The material was maintained at this temperature for a few minutes and then cooled to room temperature. The polymer obtained was 33.4 gms of a gummy, white solid in a yield of 72.9 weight %. A TGA in argon to lOOO~C gave 87.5% weight loss. DTA in air to 500C gave ,an exotherm at ~5C and a DTA in argon to 500C showed an endotherm from room temperature to 140C. The residual chlorine was 2.29 weight %. ~Si was 45.2. Infra-red analysis showed the presence of -NH, NH4Cl, SiCH3, Si N-Si and a small amount of Si-O-Si. Astro firing gave a ~0.2~
weight loss at 1~00C and 16.2% weight loss on firing from 1200-1600C. X-ray dif~raction studies on the 1600C fired sample showed beta-silicon carbide of 120~ particle size plus a small amount of alpha-silicon carbide.
Derivatization analysis showed 4.0% (CH3)3Si-, 31~0%
(CH3~2Si= a~d 32% C~3Si-.
ExamE~e 6 A mixture of 25 mole % te~rachlorodimethyldisilane and 75 mole % tetramethyldichlorodisilane totaling 55.3 gms was mixed with 113.0 gms of hexamethyldisilazane under argon and heated to 275C in a reaction vessel equipped as described above. The temperature was held for 1/2 hour and then the reaction mass was allowed to cool. Thirty-one and seven tenths grams of a clear yellow liquid were obtained for a yield o~ 57.3~ of the ceramic materia]L. TGA in argon to :1000C gave a 7.0% yield. DTA in air to 500C gave an exothenm at 90C and a DTA in argon at 500C showed no thermal break. ~ residual chlorine was 3.06% and the %si was 43Ø Firing in the ~stro furnace at 1200C gave a 7~6 weigh~ % yield o~ the ceramic material and firing at 1200-1600C gave a 75.8 weight ~ yield. Gas chromatography of the material from derivatization gave 3.5% of (CH3)3Si, 44.1~ (CH3)2Si= and 25.4% of CH3SiYo Example 7 Tetramethyldichlorodisilane (56.3 gms) was mixed with 113.3 gms of hexamethyldisilazane under argon and heated over 1 1/2 hours to 250C and held there for 1 hour.
The reaction vessel was equipped as described above. The bulk of the material distilled from the reaction vessel leaving only 16.1 gms of a light yellow oil which turned colorless on cooling. $he % yield of ceramic materi~1 was 28.6. TGA to 10~0C in argon gave 0% yield of ceramic material. DTA in air to 500C gave an exotherm at 85C and DTA in argon to 500C gave an endotherm from room temperature ~o 200C. The % residual chlorine was 7.47%
and % Si was 39. Infra-red showed the presence of NH, SiCl and Si(CH3)3. The inventor was unable to fire this material in the Astro furnace because of it:s high volatility. Deriva~ization ~as chromatography showed 5.6 (C~13)3Si-, 6896 (C~13~2Si- and 9.0~6 CH3Si--.
~.~
A polymer was prepared from a disilane mixture similar in composition to that set forth in Example 1. The material was heated under argon for 1 hour. This material was made into a filled, molded ceramic material by combining 35.0~ gms of 320 mesh silicon carbide powder and 15.06 gms of the above polymer in a toluene solution. The material was then vacuum evaporated to dryness and then ball milled to give a fine powder. The powder was then press molded at 200C at 7500 psi for 30 minutes to make a pellet which was qlassy and very smooth. ~he resulting pellet was fired in the Astro furnace described abov~e at 1200C for 6 hours to a ceramic material with very low porosity. The yield was about 85%.
Example 9 The polymer from Example 8 was mixed in a ratio of 10 weight % with 90 weight % of 500 mesh Norton crystolon powdered silicon carbide. The mixture was prepared in hexane and then vacuum evaporated to dryness and ball milled for 45 min. to give a fine powder. Six grams of the powder was subjected ~o the following conditions to prepare each pellet.
* Trademark O
Pellet Preparation Pressed at a Pressure TLme : (Rsi~_ (min?
A 175 8,05)0 12 B 250 8,000 10 C 250 10 9 0~)0 10 D 17~ 10,000 10 E 300 8,000 10 F 250 8,000 3Q
G 250 10,000 30 All of the samples formed nice, even pellets except Sample E whirh delaminated. When fired in the Astro furnace these materials give ceramic pellets.
Example 10 The polymer of Example 1 was mixed in a 40/60 weight ratio with 320 mesh Norton Crystolon beta-~ilicon carbide powder using a solution-evaporation-grinding technique. Thus, 20.64 gms of polymer was dissolved in 80 ml of hexane to which was added 30.25 gms of 320 mesh silicon carbide. It was then evaporated to dryness to give a soft material which was ground to a powder using a mortar and pestle rather than the ball mill, The fine powder was then molded in a pellet mold at 175C under 7500 psi for 30 minutes. The resulting pellet was a smooth, very nice pellet. When heated in the Astro furnace, this material gave a ceramic material.
Example 11 - Preparation of a polymer from a mixture of disilanes and a monosilane A disilane mix~ure similar in composition to that found in Example 1 (42.0 gms) and 41. 6 gms of C~3SiC13 were mixed in a 500 ml., 3-necked, round-bottomed glass flask equ:ipped as in Example 1. ~examethyldisilaæane (237 gms) was added under an argon blanke~ with stirring. After stirring about 10 minutes at room temperature, the reaction mixture was hea~ed over 1 hour, 15 minutes to 275C and held there for about 30 minutes. The reaction mixture turned cloudy at about 95-100%C but cleared again at 135C. After cooling to room temperaturel there resulted a pale yellow, clear, hard, glassy resin~
This material was fired in the furnace in a graphite crucible to 1200C over a 2 1/2 hour period. The ceramic resulting from this firing was obtained in 53 weiyht % yields. It was a lo~ density foam-like ceramic.
Example 12 - Preparation of an article coated with a filled ceramic A polymer prepared similar to Example 1 was mixed with Norton 1000* mesh beta-silicon carbide in a weight ratio of 10 gms to 10 gms. This material was then mixed with lO0 gms of dry hexane. This slurry was evaporated under vacuum until a paint-like viscosity of the slurry was obtained. A graphite disc was dip coated with the slurry and allowed to air dry. It was then heated in air at 125C
* Trademark for 30 minutes and at 150C for 30 minutes to dry the coating. The coated disc was then heated to 1200C in an ine~t a~mosphere over a 2 1/2 hour period a~ld then allowed to cQol~ The filled ceramic coating had remained intact during the pyrolysis, showing large areas o:E a smooth, uniform continuous coating. In the areas where the coating was thic~er~ it was pock-marked.
- Ceramic fibers from a silazane polym4r A polymer was prepared similar to ~hat ~ound in Example 1. This material, a clear solid hard resin, was melted and extruded into fibers using conventional fiber extruding equipment. The fibers were then fired in the furnace under argon to 1200C after being treated as follows:
treatment result ~ none B heat at 200C solid clear 1 hour iber C 15 min. dist L H2O ~lear fiber turned at 75C then heat opaque-soft 1 hr. at 200C
D 15 min in 0.1 N HCl dissolved in acid at 75C
E 15 min. in dist. clear fiber turned H2O at 25C then opaque-soft 1 hour at 200C.
F 15 min. at 100C heat -~
100~ hu~idity All samples were given mild heat treabment :Eor 18 hours, then fired.
After 1- ~
result A Fibers retained shape/good quality B Fibers retained shape/excellent quality C Fibers rPtained shape/poor quality E Fibers retained shape/poor quality F Fi~ers retained shape/good quality Example 14 A polymer similar to that found in Example 1 was prepared and melt extruded into small diameter fibers of about 12~. These straight fibers were placed on a 6" x 4"
piece of graphite which had been previously baked out at 1500C for three hours in vacuo and the graphite was rolled up in such a manner that the fibers were main~ained straight and held snugly in place. This roll wa~ then placed in a graphite crucible and fired to 1200C under argon to g ive hara, dark colored fibers.
When the polymer was extruded into small diameter fibers and heat treated in air prior to firing at 1200C.according to the schedule below, the resulting fibers were soft and pliable.
Schedule 1 hr/75C
0O5 hr/125C
0.5 hrflS0C
1.~ hr~l75~C
1.0 hr/200C
1.0 hr/225C
1.0 hr/250C
0.33 hr/275C
Exam~le 15 The polymer of Example 1 was mixed in a 30/70 weight ratio with 320 mesh Norton Crystolon beta-silicon carbide using the solution-evaporation-ball mill technique.
The material was then press molded at 10,000 psi and 175C
for 30 min. to give a very ~mooth glassy surfaced pellet.
This pellet was fired to 1200C over a 6 hour period to give a ceramic pellet with a binder char yield of 50~.
~18~8~
As should ~e recognized by those skilled in the art, the present invention differs in at least one respect from all of the above art in that the present invention is based on chlorine-containing disilanes as opposed to the use of chlorine containing monosilanes.
In another segment of the prior art, the ~se of disilanes in the preparation of silazane polymers has been limited to the formation of relatively low molecular weight materials. In one example, Wannagat et al., Ang. Chem.
75~7) 345(1963~, reported the reaction of tetramethyldichlorodisilane with gaseous ammonia to give a six-membered cyclic silazane, {(CH3)2SiSi(CH3)2N~}2, rather than the expected linear silazane polymer and Hengge et al., Montash. Chem. lOlI(2)325(1970), prepared dime~hylamino substituted mixtures o disilanes from dimethylamine and the chlorine-containing disilane mixture obtained from the Direc~ Process ~or the preparation o chlorosilanes.
What has been newly discovered is the coreaction between chlorine-containing disilanes and disilazanes to give high molecular weight silazane polymers.
The Invention The instan~ invention c~ncerns a new class o~
silazane polymers pr~pared from chlorodisilanes. In essence, a single chlorine-containing disilane or a specified mixture of chlorine-containing disilanes is treated with a disilazane, as the nitrogen source, in sufficient amounts to react with all o the chlorine on the chlorine-containing disilanes. This is usually an e~uimolar amount of disilazane based on the chlorine content of the disilane. The inventor does not wish to be he}d to such a theory but it is believed that when the mixture is heated, usually in the absence of solvent and in an essentially anhydrous atmosphere, the reactions -Si-SiCl ~ R'35iNHSiR13~ Si-Si-NHSiR'3 ~ R'3SiCl, ~ ' . . . . .
-Si-Si-Cl + -Si Si-N~SiR'3 ~ ~Si-Si-NH-Si-Si- ~ R'3SiCl and 2-Si-Si-NHSiR'3 ~ -Si-Si-N~-Si-Si * R'3SiNHSiR'3 take place.
The advantage of this process is the ability to stop the reaction at any point by cool ing the reaction mass thus giving polymers with any desirable viscosity, hence any desirable molecular weight. The silazane polymers range in physical appearance from liquids, to high viscosi~y liquids, to hard glassy materials. The m~terials are therefore very easy to handle. They are essentially hydrolytically stable.
~ hus, this invention consists of a process ~or preparing an R' 3SiN~- containing silazane polymer which consists of contacting and reacting in an inert, essentially anhydrous, atmosphere, a chlorine-containing disilane or a mixture of chlorine-containing disilanes, of the general formula (ClaRbSi)2 with a disilazane having the general formula (R~3si)~NH
at a temperature in the range of 25C to 300C while distilling by-produced volatile products~ wherein R is vinyl, an alkyl group of 1-3 carbon atoms or the phenyl group; R' is vinyl, hydrogen, an alkyl group of 1-3 carbon atoms or the phenyl group; a has a value of 0.5-3; b has a value of 0-2.5 and the sum ~f a I b is equal to three.
This invention also deals with a new and novel composition of matter which is an R'3SiNH- containing silazane polymer which is prepared by contacting and reacting in an inert, essentially anhydrous, atmosphere, a chlorine containing disilane or a mixture o chlorine-containing disilanes, of the general formula ( ClaRbS i ) 2 with a disilazane having the general formula (R'35i)2NH
at a temperature in ~he range of 25C to 300C while distilling by-produced volatile products, wherein R is vinyl, an alkyl group o~ 1-3 carbon atoms or the phenyl group; R' is vinyl, hydrogen, an alkyl group of 1-3 carbon atoms or the phenyl group, a has a value of 0.5-3; b has a value of 0-2.5 and the sum of a ~ b is equal to three.
This invention further deals with a process ~or preparing an R'35iNH- containiny silazane polymer which consists of contacting and reacting in an ine~t, essentially anhydrous, atmosphere, a chlorine-containing disilane or a mixture of chlorine-containing disilanes, wherein the number of diorgano-substituted silicon atoms does not exceed the number of monoorgano substituted silicon atoms, of the general formula (ClaRbSi)2 with a disilazane having the genera} formula (~l3Si)2NH
at a temperature in the range of 2SC to 300C while distilling by-produced volatile products wherein R is vinyl, an alkyl group of 1-3 carbon atoms or the phenyl group; R' is vinyl, hydrosen, an alkyl group of 1~3 carbon atoms or the phenyl group; a has a value of 0.5-3; b has a value o~ 0-2.5 and the sum of a ~ ~ is equal to three.
This invention also deals with a new and novel composition of matter which is an R'3SiNH- cont~ining silazane polymer which is prepared by contac~ing and reacting in an inert, essentially anhydrous ~ atmosphere, a chlorine-containing disilane or a mixture o~
chlorine-containing disilanes wherein the number of diorgano-substituted silicon a~oms does not exceed the number of monoorgano-substitu~ed silicon atoms of the general formula (ClaRbSi32 wi~h a disilazane having the general formula (Rl3si)2NH
at a temperature in the range of 125C to 300C while distilling by-produced volatile products, wherein R i5 vinyl, an alkyl group of 1-3 carbon atoms or the phenyl group; R' is vinyl, hydrogen, an alkyl group of 1-3 carbon atoms or the phenyl group; a has a value of 0.5-3; b has a value of 0-2.5 and the sum of a ~ b is equal to three, Still further, this invention deals with a method of preparing a silicon carbide containing ceramic material which consists of heating a silazane polymer in an inert aumosphere or in ~ vacuum to at least a temperature of 750C until the silazane polymer is converted to silicon carbide ceramic material, which silazane pol~mer is obtained by a process which consists of contacting ancl reacting in an inert, essentially anhydrous, atmosphere, a chlorine-containing disilane or a mixture of ~L~L~8~
chlorine-containing disilanes, wherein the number of diorgano-substituted silicon atoms does not exceed the number of monoorgano-substituted silicon atoms, of the general formula ~ ClaR~Si32 with a disilazane having ~he general formula ~ R'3Si)2NH
at a temperature in the range of 125C to 300C while distilling by-produced volatile products, wherein R is vinyl, an alkyl group of 1-3 carbon atoms or the phenyl group; R' is vinyl, hydrogen, an alkyl group of 1-3 carbon atoms or the phenyl group; a has a value of 0.5-3; b has a value of 0-2.5 and the swm of a ~ b is equal to three.
Yet another object of this invention is a method o~ preparing a silicon carbide containing ceramic article which consists of (A) forming an ~rticle of the desired shape from a silazane polymer; (B) heating the article formed in (A) in an inert atmosphere or in a vacuu~ to an elevated temperature of at least 750C until the silazane polymer is converted to silicon carbide containing ceramic, which silazane polymer is obtained by a process which consists of contacting and reacting in an inert, essentially anhydrous, atmosphere, a chlorine-containing disilane or a mixture of chlorine-containing disilanes, wherein the number of diorgano-substituted sil.icon atoms does not exceed ~he number of monoorgano-substituted silicon atoms, of the general formula (~laRbSi)2 with a disilazane having the general formula (R'3~i)2N~
at a te~perature in the range of 125C to 300C while dist:illing by-produced volatile products, wherein R is vinyl, an alkyl group of 1-3 carbon atoms or the phenyl group; R' is vinyl, hydrogen, an alkyl group of 1-3 carbon atoms or th~ phenyl group; a has a value of 0.5-3; b has a value of 0-2.5 and the sum of a ~ b is equal to three.
Still another object of this invention is a method for preparing a filled ceramic article which consist of (A) mixing a silazane polymer with at least one conventional ceramic filler, ~B) orming an a~icle o~ the desired shape from the mixture of silazane polymer and filler and ~C~ heating the article formed in (~) in an inert atmosphere or in a vacuum to an elevated temperature of at least 750C until the silazane polymer is converted to a silicon carbide containing ceramic, which silazane polymer is obtained by a process which consists of contacting and reacting in an inert, essentially anhydrous, ab~osphere, a chlorine-containing disilane or a mix~ure of chlorine-containing disilanes, wherein the number of diorgano-substituted silicon atoms does not exceed the number of monoorgano-substituted silicon atoms, of the general formula . . . . . . .
_ . . .
(ClaRbSi~2 with a disilazane having the gencral ormula (R'3Si)2NH
at a temperature in the range of 125C to 300C while distilling by-produced volatile products wherein R is vinyl, an alkyl group of 1-3 carbon atoms or the phenyl yroup; R' is vinyl, hydrogen, an alkyl group of 1 3 carbon atoms or the phenyl sroup; a has a value of 0.5-3; b has a value of 0-2.5 and the sum of a ~ b is equal to three.
Still ~urther, it is an object of this invention to prepare an article coated with a silicon carbide ceramic material which method consists of (A) mixing a silazane polymer with at least one conventional ceramlc iller, tB) coating a substrate with the mlxture o~ silazane pol~ner and filler and, (C) heating the coa~ed su~strate in an inert atmosphere or in a vacuum to an elevated temperature of at least 75QC until ~he coating is converted to a silicon carbide ceramic material, whereby a silicon carbide containing ceramic coated article is obtained, which ~ilazane polymer is obtained by a process which consists o~
contacting and reacting in an inert, essentially anhydrous, atmosphere, a chlorine-containing disilane or a mixture of chlorine-containing disilanes, wherein the number of diorgano-substituted silicon atoms does no~ exceed the number o monooryano~substituted silicon atomæ, of the general formula ~ClaRbSi)2 with a disilazane having the general formula ~ R13Si)2N~I
at a temperature in the range of 125C to 3~0C while distilling by-producPd volatile products, wherein R is vinyl, an alkyl group of 1-3 carbon atoms or the phenyl group; R' is vinyl, hydrogen, an alkyl group of 1-3 carbon atoms or the phenyl group; a has a value of 0.5-3; b has a value of 0 2.5 and the sum of a ~ b is equal to three.
A further object of this invention is a process for preparing an article coated with a silicon carbide ceramic material which consists of (A) coating a substrate with a silazane polymer, (B) heating the coated substrate in an inert atmosphere or in a vacuum to an elevated temperature o~ at least 750C until the coating is converted to a silicon carbide ceramic material, whereby a silicon carbide containing ceramic coated article is obtained, which silazane polymer is obtained by a process which consists of contacting and reacting in an inert, essentially anhydrous, atmosphere, a chlorine-~ontaining disilane or a mixture of chlorine-containing disilanes, wherein the number of diorgano-substituted silicon atoms does not exceed the number of monoorgano-substituted silicon atoms, of the general formula ~ ClaRbSi)2 with a disilazane having the general formula .
.
( ~2 (R'3Sij2NH
at a temperature in the range of 125C to 30~C while distilling by;produced volatile produc~s wherein R is vinyl, an alkyl group of 1-3 carbon atoms or the phenyl group; R' is vinyl, hydrogen, an alkyl group of 1-3 car~on atoms or the phenyl group; a has a value of 0.5 3; b has a value of 0~2.5 and the sum of a + b is equal to three.
A final object of this invention is a process for preparing an R'3SiNH- containing silazane polymer which consists of contacting and reacting in an inert, essentially anhydrous atmosphere, a disilazane having the general formula (R~3Si)2NH
with (i) a mixture of a chlorine-containing disilane having the general formula (ClaRbSi) ;2 and a chlorine-containing monosilane having the gen~ral formula R'nSicl4-n;
~ii) a mixture of chlorine-containing disilanes having the general formula (ClaRbSi)2 mixed with a chlorine-con~aining monosilane having the general formula R'nSlcl4-n or (iii) a mixture of chlorine-con~aining disilanes having the general formula Cl aRbs i 2 mixed with a mixture of chlorine-containing monosilanes having ~he general formula R'nSicl4-n at a temperature in the range of 25C to 300C while distilling by-produced volatile products, wherein R is vinyl, an alkyl radical of 1-3 carbon atoms or the phenyl group; R' is vinyl, hydrogen, an alkyl group of 1-3 carbon atoms or the phenyl group; a has a value of 0.5-3; b has a value of 0-2.5; n has a value of 0, 1, 2 or 3 and the sum of a ~ b is equal to three.
The inventions described herein result in new compositions of matter which are an improvement in ~he art, in that, essentially hydrolytically stable, easy to handle silazane polymers can be prepared. Further, the silaæane polymers lead to an improvement in the art of formation o~
silicon carbide and they can be used as binders in ceramic materials.
The invention results from reacting disilazanes ~ith chlorine-containing disilanes or mixtures of disilanes with monosilanes in an inert, essentially anhydrous atmosphere and then firing the resulting si~azane polymer to get silicon carbide or silicon carbide containing ceramic materials.
The chlorine-containing disilanes of this invention are those disilanes having the yeneral formula (ClaRbSi)2-In this formula, R is vinyl, an alkyl radical containing 1-3 carbon atoms or the phenyl group. Thus, those groups which are contemplated as being useful in this invention are methyl, ethyl, propyl, vinyl and phenyl. For purposes of this invention, the R groups can all be the same or they can be different. The chlorine-containing disilanes can be those found in the residue from the Direct Process for producing halosilanes (Eaborn, C., ~Organosilicon Compounds", Butterworth Scientific Publications, London, 1960, pg. 1). Whenever the symbols 0, Me, Et and Vi are used herein, their meaning is phenyl, methyl, ethyl and vinyl, respectively.
For purposes of this invention, the value of a and b is f~om 0.5-3 and 0-2.5 respectively and the sum of a + b is equal to three. Examples of chlorine-containing disilanes useful in this invention are {Cl(CH3~2Si}2, {C12CH3si}2r {cl2c2H5si}2r {Cl(C6Hs)2Si}2 and {cl2cH2=c~si}2-Monosilanes useful in admixture with the disilanesof this invention can be for example CH3SiC13, (CH3)2SiC12, ~(CH3)2SiCl, (CH3)3SiCl, (CH2=CH)(CH3)2SiCl, (C2Hs)2SiCl~, C6H5siC13~ (c6H5)2sicl2 and (C6Hs)3SiCl.
Also considered within the scope of this invention is the use of mixtures of chlorine-containlng disilanes.
One aspect of ~-his invention requires that whenevPr certain chlorine-con~aining disilane mixtures are required, the n~ber of units of diorgano-substituted silicon atoms should not exceed the number of units of monoorgano-substituted silicon atoms. Even though silazane polymers can be formed from chlorine-containing disilane mixtures wherein the number of diorgano-substituted units does exceed the number of monoorgano-substituted units, it has been found that these polymers do not have the handling properties for formability because of low viscosities.
The second reactant in this invention is a disilazane of the general formula ~R'3Si)2NH. For purpo~es of this invention, R' is vinyl, hydrogen or has the same meaning as R above. Thus, R' in this ~ormula i5 vinyl, hydrogen or an alkyl radical of 1-3 carbon atoms or the phenyl group. Therefore, R', for purposes of this formula is represented by hydrogen, methyl, ethyl, propyl, vinyl and phenyl. As set forth above, each Rl group in this formula can be the same or they can be different. Examples of compounds contemplated within the scope of this invention include: {(CH3~3Si}2NH, tC6H5(CH3)2si}2~
l'l~OB'O
{(c6H5)2cH3si}2NH~ {C~2-CH(CH3)2si}2NH' {C~ H5C~3)C6~5si}2~ (CH2=CH~tC6H5)2Si}2N~, {CE~25C~(C2H5)2si};~N~I~ {(C~2-C~)C6H51C2H5)5i} 2NH~
{~(CH3)2si}2N~t {~2(c~3)si}2NH and lHc6~scH3si}2N~.
These reactants are brou~ht together in an inert, essentially anhydrous atmosphere. For purposes of this invention what we mean by n iner~" is that the reaction is carried out under a blanket of inert gas, such as, argon or nitrogen or helium. What we mean by ~essentially anhydrous~ is that the reaction is preferably carried out in an abso}utely anhydrou~ atmosphere but minute amounts of moisture can be tolerated.
When the reactants are contacted with each other, the reaction begins which forms an intermediate disilane amino compound i.e.
-Si-Si-Cl ~ (R'3Si)2NH ~ -Si-Si-NH5iR'3 + R'3SiCl.
Upon heating, additional disilane amino compound is formed and upon continued heating, R'3SiC1 is disti}led from the reaction mixture and a disilylsilazane polymer is formed i.e.
~BO
Si-Si-Cl ~ -Si-Si-NH5iR'3~ -Si-Si-~H-Si-Si- ~ R13SiCl .
.. ~, .. ..
2-Si-Si NHSiR'3~ Si-SiNH-Si-Si + R'3SiNHSiR'3.
The order of addition of the materials does not appear to be critical. AS the temperature is raised higher, more condensation takes place and crosslinking occurs, with residual R'3Si- that is not distilled from the mixture, acting as a chain-stopper. This control allows one to stop the reaction at any point to obtain almost any desired viscosi~y. The desirable temperature range for this reaction is 25C to 300C. The most preferred range :is 125C to 300C. The length of time ~hat the reaction requires depends on the temperature and the viscosity one wishes to achieve.
What is meant by "volatile products" are the distillable by-produced products that are formed by the reactions set forth above. These materials can be represented by (CH3)3SiCl, (CH2-CH~(C6Hs)2SiCl, 3(C6H5)2siCl~ (cH3~2c6~ssiu ~ HtcH3)25icl and (CH2=C~)(C~3)2SiCl. Sometimes, these materials require the use of a vacuwm along with the heat in order to remove them from the reaction mixture.
The sila~ane polymers are then essential}y ready to use. The silazane polymers are pyrolyzed in an inert atmosphere or in a vacuum at temperatures o:f at least 750C
to give a silicon carbide containing materi,al. If the polymer is of sufficient viscosity, it can be shaped first (such as an extruded fiber) and then pyrolyzed to give a silicon carbide containing fiber or the silazane polymers can be filled with ceramic type fillers (if desired) and then fired to at least 750C to obtain silicon carbide ceramic materials or silicon carbide ceramic material GOntaining ceramic articles.
When mixtures of chlorine-containing disilanes are to be used, it is best if the chlorine-containing disilanes are mixed prior to contacting and reacting with the disilazanes.
As mentioned above, some of the resulting polymers can be extruded to give various shapes such as fibers. It has been found that the polymers of this invention that have the handleability that enables one to extrude or form them are those polymers in which the number of diorgano-substitu~ed silicon atoms do not exceed the number of monoorgano-substituted silicon atoms. Thus, if the polymer is to be extruded or otherwise formed, it should be prepared from disilanes and disilazanes wherein the diorgano-substituted silicon atoms do not exceed the nu~ber of monoorgano-substituted silicon atoms.
As mentioned above, the polymers of this invention can be used in both the filled and unfilled state, depen~ing on the application. Thus, it is contemplated wi~hin the scope of this invention ~o coat substrates with ~illed and unfilled polymers and heat the s~bstrates to pr~duce silicon carbide containing ceramic ~oated artic}es.
Fillers and adjuvants can be milled on 3 roll mills by simply mixing the polymers of this invention with the fillers and making several passes on the mill. In the alternative, the polymers can be plac~d in solvents and the fillers and adjuvants can be added thereto and after mixing the solvent can be removed to give the filled polymer.
The coating can be carried out by conventional means. The means used depends on the polymer and substrates used and the application one has in mind. ~hus, these materials can be brushed, rolled, dipped or sprayed.
In the filled stated, it is sometimes necessary to trowel the polymer onto the substrate.
Whenever the polymers are converted to the ceramic state, it i5 done by pyrolyzing the polymer to a temperature of at least 750C in an inert atmosphere or in a vacuum.
Attempts to pyrolyze at or above 750C without an inert atmosphere lead to undes:irable side reactions and therefore, caution should be exercised ~o be ~ure to exclude moisture and other potential reactants.
. . . _ , Now so that those skilled in the art can better appreciate and understand the invention, the following examples are given. The examples are for purposes of illustration only and are not to be regard~ed as limitations.
In ~he following examples, the analytical methods used were as follows:
Thermogravimetric analyses (TGA) were carried out on a Netzsch STA 429* (2400C) TGA instrument manufactured by Netzsch Instruments, Selb, West Germany. Sample sizes averayed 11 mg., program rate was 10C/min., gas flow rate was 200 cc/min. The scale setting was 50C/in. ~ 0.5C/in~
Differential Thermal Analyses (DTA) were carried out on the Netzsch instrument using samples averaging 13.S
mg., a flow rate of 200 cc/min., a program rate of lO~C/min and a scale setting of 50C/in + 0.5C/in.
Percent Silicon was determined by a fusion technique which consis~ed of converting the silicon material to soluble forms of silicon and the soluble material is quantitatively determined as total silicon by atomic absorption spec~rometry. Solubilization takes place by weighing the sample into a Parr-type* fusion cup (about 0.3 gm), adding 15.0 gms of Na peroxide, heating for about 90 sec. and ~uenching in cold water. The material is placed in a nickel beaker containing 150-200 ml. of distilled water. 55 ml. of reagent grade acetic acid is added and diluted with water to 500 ml. volume.
Trademark ( Percent Chlorine tresidual) was cletermined ~y Na peroxide decomposition and titration with silver nitrate.
Fusion of ~he halides with Na peroxide is followed by potentiometric titration with standard silver nitrate by weighing a sample into a gelation capsule~ placing about 1.5 gm. of Na2O~, about 0.7 gm of ~NO3 and about 0.15 gm of sug~r into a clean, dry reaction cup and burying the capsule in the mixture. The cup is filled with Na2O2 and placed in a reaction vessel. It is heated for 1-1 1/2 minO
and quenched in cold water. The cup and vessel are washed and ~he washings are collected. The washings are heated to dissolve any solids. 15 ml. of cold 50~ aqueous H2SO4 is added and allowed to stand 15-20 sec. This solution is neutralized with additional H2SO4 and titrated.
Carbon and hydrogen were determined by microcombustion by weighing 10 to 20 mg. of sample into a micro platinum boat and treating it in an A. H. Thomas co~bustion apparatus, Catalog No. 6447-E, Philadelphia, PA.
In the reactions carried out below, the reaction apparatus was essentially the same in each case and consisted of a 500 ml., glass, round-bottomed flask equipped with a mechanical stirrer, gas inle~ tube, distillation apparatus and a thermocouple to record temperature. The distillation apparatus was equipped to use a vacuum if needed.
., 8~
A mixture of 50 gms of chlorine-cont:aining di~ilanes consis~ing of 57.6 wPight percent of tetrachlorodimethyldisilane; 32 weight percerlt of trichlorotrimethyldisilane and 10.4 weight percent of dichlorotetramethyldisilane were added dropwise to a reaction vessel described above which contained 120 gms of hexamethyldisilazane. The reaction vessel was then slowly heated to 275C under argon and held at that ~emperature ~or two hours. The distillate that was collected during ~he heating pariod was found ts contain ~CH3)3SiCl, some hexamethyldisilazane and a small amount of NH4Cl. The polymer residue in the flas~ weighed 29.6 gms and when cooled was a hard, colorless, glassy solid. The material was fired in an Astro Industries Furnace lOOOA water cooled graphi~e heated model 1000.3060-FP-12 to 1200C under Argon for a yield of 46.29%. The material contained 29% carbon, 7-8% hydrogen, 45% silicon and 8.1% nitrogen. Infra red analysis showed the presence of -Si-NH-Si- but no -Si-O-Si-. X-ray analysis of samples fired at various temperatures showed the following:
tem~ type of material 1200C Amorphous ~aterial 1400C Amorphous material 1600C beta-SiC l~oA and Moissanite SiC
18~0C beta-SiC o ~2000~ and Moissanite SiC
2000C beta-SiC of > 2000~ but no Moissanite Ebulliometry gave 3125 gm/mole.
~ examethyldisilazane (214 gms) and S9.90 gms of Si~C16 were placed in a reaction vessel described above.
Upon mixing, the reaction exothermed to 57GC and the mixture turned cloudy white. Distillation began at about 77~C and the reaction mass cleared and turned a faint yellow color when the flask reached 110C.
The reaction mass proceeded to foam and the foam level was controlled by increasing stirrer speed and maintaining the temperature at 160-165C for 1 hour. The temperature was raised to 170C with rapid stirring and then to 265C where the reaction mass foamed excessively.
The temperature was decreased to about ~15C ~or a short while and then the pot was allowed to cool. When cooled the material was a glassy, clear solid which was easily removed from the inside surface of the reaction flask. A
small amount of gummy liquid was also removed from the flask. Infra red analysis showed the presence of NH and Si(CH3)3 with some -SiCH3 and -Si-N-Si. %Si was 42.3%.
X-ray diffraction on a sample fired to 1600C showed the major phase to be beta-silicon car~ide with a minor phase of beta-Si3N4. The average crystallite size of the beta-silicon carbide was 130A.
~.~8$~
~4 ~e~
Tetrachlorodimethyldisilane (32.7 gms) and 17.3 gms of trichlorotrlmethyldisilane were mixed with 168.3 gms of hexamethyldisilazane in a reaction vessel equipped as des~ribed above. This mixture was gradually heated to ~65C under argon and held there for about 10 min.
Distillate was removed during this period of time. ~hen cooled~ the residue was a polymer which was a hard, colorless resin. The yièld was 65.7%. Thermal gravimetric analy~is to 1000~C yielded 54% silicon carbide.
Differen~ial thermal analysis in air to 500C gave an exotherm at 93C. ~TA in argon to 500C showed no ~hermal break. Residual chlorine content was 1.44 weight % and %Si was 47.4. Infra-red analysis showed the presence of NH, NH4Cl, SiC~3, Si-N-Si. X-ray diffraction studies on a sample fired at 1600C showed beta-silicon carbide having a particle size of 120~ and a small amount of alpha-silicon carbide. The polymer was analyzed by derivatization gas chromatography and found to contain 7.5 weight % (C~13)3Si-, 15.0 weight ~ (CH3)2SiS and 68.5 weight ~ of CH3Si~.
Derivatization gas chromatography is an analysis wherein the polymer is treated with tetraethoxysilane and KOH to give the organoethoxysilane derivatives of the individual polymeric units~ Gas chromatography is then used to determine ~he content and relative ratios o~ the various units present in the mixture. This procedure is carried out by weighing about 0.3 gm of the polymer sample into a 50 ml. round-bottomed flask. To this flask is added 8O0 ml. of Si(OC2~s)4. One pellet of XO~ is added and the flask is heated to initiate the reaction and it is then reflllxed for 45 min. to one hour. An additional 2.0 ml. of Si(OC2Hs)4 is added and then about 1/2 teaspoon of pulverized CO2 is added to neutralize the KO~. The sample i5 centrifuged to separate the phases. The silane layer is then analyzed by gas chromatcgraphy which has been standardized.
}~
Tetrachlorodimethyldisilane (45.6 gms) was mi.xed with 129.1 yms of hexamethyldisilazane under argon. The reaction vessel was equipped as in Example 1. This reaction mass was heated to 240C and held for a few minutes and then cooled to room temperature. The resulting material was a solid whit~ powder and 26.6 gms were obtained. The % yield was 58~3%o TGA to 1000C in argon gave 27~ weight loss. DTA in air to 500C gave an exotherm at 140C and DTA in argon to 500C gave no thermal break.
% residual chlorine was 4~83 weight ~ and weight % Si was 44.4, Infra-red analysis showed the presence of ~H4Cl, Si-N-Si and -SiCH3. A yield of 62.6 weight ~ was obtained when the material was fired to 1200C and 78.1 weight % was obtained on firing from 1200C up to 1600C.
Deriva~ization using Si(OC2Hs)4 gave the following: 6.4 weight % (C~3)3Si-, 2.0~ of (CH3)2Si= and 68.0% of CH3Si3.
Exam~le S
Trichlorotrimethyldisilane (45.8 gms) was mixed wi~h 196~84 gms of hexamethyldisilazane in a reaction lask equipped as described above. This mixture was hea~ed under argon to 280 The material was maintained at this temperature for a few minutes and then cooled to room temperature. The polymer obtained was 33.4 gms of a gummy, white solid in a yield of 72.9 weight %. A TGA in argon to lOOO~C gave 87.5% weight loss. DTA in air to 500C gave ,an exotherm at ~5C and a DTA in argon to 500C showed an endotherm from room temperature to 140C. The residual chlorine was 2.29 weight %. ~Si was 45.2. Infra-red analysis showed the presence of -NH, NH4Cl, SiCH3, Si N-Si and a small amount of Si-O-Si. Astro firing gave a ~0.2~
weight loss at 1~00C and 16.2% weight loss on firing from 1200-1600C. X-ray dif~raction studies on the 1600C fired sample showed beta-silicon carbide of 120~ particle size plus a small amount of alpha-silicon carbide.
Derivatization analysis showed 4.0% (CH3)3Si-, 31~0%
(CH3~2Si= a~d 32% C~3Si-.
ExamE~e 6 A mixture of 25 mole % te~rachlorodimethyldisilane and 75 mole % tetramethyldichlorodisilane totaling 55.3 gms was mixed with 113.0 gms of hexamethyldisilazane under argon and heated to 275C in a reaction vessel equipped as described above. The temperature was held for 1/2 hour and then the reaction mass was allowed to cool. Thirty-one and seven tenths grams of a clear yellow liquid were obtained for a yield o~ 57.3~ of the ceramic materia]L. TGA in argon to :1000C gave a 7.0% yield. DTA in air to 500C gave an exothenm at 90C and a DTA in argon at 500C showed no thermal break. ~ residual chlorine was 3.06% and the %si was 43Ø Firing in the ~stro furnace at 1200C gave a 7~6 weigh~ % yield o~ the ceramic material and firing at 1200-1600C gave a 75.8 weight ~ yield. Gas chromatography of the material from derivatization gave 3.5% of (CH3)3Si, 44.1~ (CH3)2Si= and 25.4% of CH3SiYo Example 7 Tetramethyldichlorodisilane (56.3 gms) was mixed with 113.3 gms of hexamethyldisilazane under argon and heated over 1 1/2 hours to 250C and held there for 1 hour.
The reaction vessel was equipped as described above. The bulk of the material distilled from the reaction vessel leaving only 16.1 gms of a light yellow oil which turned colorless on cooling. $he % yield of ceramic materi~1 was 28.6. TGA to 10~0C in argon gave 0% yield of ceramic material. DTA in air to 500C gave an exotherm at 85C and DTA in argon to 500C gave an endotherm from room temperature ~o 200C. The % residual chlorine was 7.47%
and % Si was 39. Infra-red showed the presence of NH, SiCl and Si(CH3)3. The inventor was unable to fire this material in the Astro furnace because of it:s high volatility. Deriva~ization ~as chromatography showed 5.6 (C~13)3Si-, 6896 (C~13~2Si- and 9.0~6 CH3Si--.
~.~
A polymer was prepared from a disilane mixture similar in composition to that set forth in Example 1. The material was heated under argon for 1 hour. This material was made into a filled, molded ceramic material by combining 35.0~ gms of 320 mesh silicon carbide powder and 15.06 gms of the above polymer in a toluene solution. The material was then vacuum evaporated to dryness and then ball milled to give a fine powder. The powder was then press molded at 200C at 7500 psi for 30 minutes to make a pellet which was qlassy and very smooth. ~he resulting pellet was fired in the Astro furnace described abov~e at 1200C for 6 hours to a ceramic material with very low porosity. The yield was about 85%.
Example 9 The polymer from Example 8 was mixed in a ratio of 10 weight % with 90 weight % of 500 mesh Norton crystolon powdered silicon carbide. The mixture was prepared in hexane and then vacuum evaporated to dryness and ball milled for 45 min. to give a fine powder. Six grams of the powder was subjected ~o the following conditions to prepare each pellet.
* Trademark O
Pellet Preparation Pressed at a Pressure TLme : (Rsi~_ (min?
A 175 8,05)0 12 B 250 8,000 10 C 250 10 9 0~)0 10 D 17~ 10,000 10 E 300 8,000 10 F 250 8,000 3Q
G 250 10,000 30 All of the samples formed nice, even pellets except Sample E whirh delaminated. When fired in the Astro furnace these materials give ceramic pellets.
Example 10 The polymer of Example 1 was mixed in a 40/60 weight ratio with 320 mesh Norton Crystolon beta-~ilicon carbide powder using a solution-evaporation-grinding technique. Thus, 20.64 gms of polymer was dissolved in 80 ml of hexane to which was added 30.25 gms of 320 mesh silicon carbide. It was then evaporated to dryness to give a soft material which was ground to a powder using a mortar and pestle rather than the ball mill, The fine powder was then molded in a pellet mold at 175C under 7500 psi for 30 minutes. The resulting pellet was a smooth, very nice pellet. When heated in the Astro furnace, this material gave a ceramic material.
Example 11 - Preparation of a polymer from a mixture of disilanes and a monosilane A disilane mix~ure similar in composition to that found in Example 1 (42.0 gms) and 41. 6 gms of C~3SiC13 were mixed in a 500 ml., 3-necked, round-bottomed glass flask equ:ipped as in Example 1. ~examethyldisilaæane (237 gms) was added under an argon blanke~ with stirring. After stirring about 10 minutes at room temperature, the reaction mixture was hea~ed over 1 hour, 15 minutes to 275C and held there for about 30 minutes. The reaction mixture turned cloudy at about 95-100%C but cleared again at 135C. After cooling to room temperaturel there resulted a pale yellow, clear, hard, glassy resin~
This material was fired in the furnace in a graphite crucible to 1200C over a 2 1/2 hour period. The ceramic resulting from this firing was obtained in 53 weiyht % yields. It was a lo~ density foam-like ceramic.
Example 12 - Preparation of an article coated with a filled ceramic A polymer prepared similar to Example 1 was mixed with Norton 1000* mesh beta-silicon carbide in a weight ratio of 10 gms to 10 gms. This material was then mixed with lO0 gms of dry hexane. This slurry was evaporated under vacuum until a paint-like viscosity of the slurry was obtained. A graphite disc was dip coated with the slurry and allowed to air dry. It was then heated in air at 125C
* Trademark for 30 minutes and at 150C for 30 minutes to dry the coating. The coated disc was then heated to 1200C in an ine~t a~mosphere over a 2 1/2 hour period a~ld then allowed to cQol~ The filled ceramic coating had remained intact during the pyrolysis, showing large areas o:E a smooth, uniform continuous coating. In the areas where the coating was thic~er~ it was pock-marked.
- Ceramic fibers from a silazane polym4r A polymer was prepared similar to ~hat ~ound in Example 1. This material, a clear solid hard resin, was melted and extruded into fibers using conventional fiber extruding equipment. The fibers were then fired in the furnace under argon to 1200C after being treated as follows:
treatment result ~ none B heat at 200C solid clear 1 hour iber C 15 min. dist L H2O ~lear fiber turned at 75C then heat opaque-soft 1 hr. at 200C
D 15 min in 0.1 N HCl dissolved in acid at 75C
E 15 min. in dist. clear fiber turned H2O at 25C then opaque-soft 1 hour at 200C.
F 15 min. at 100C heat -~
100~ hu~idity All samples were given mild heat treabment :Eor 18 hours, then fired.
After 1- ~
result A Fibers retained shape/good quality B Fibers retained shape/excellent quality C Fibers rPtained shape/poor quality E Fibers retained shape/poor quality F Fi~ers retained shape/good quality Example 14 A polymer similar to that found in Example 1 was prepared and melt extruded into small diameter fibers of about 12~. These straight fibers were placed on a 6" x 4"
piece of graphite which had been previously baked out at 1500C for three hours in vacuo and the graphite was rolled up in such a manner that the fibers were main~ained straight and held snugly in place. This roll wa~ then placed in a graphite crucible and fired to 1200C under argon to g ive hara, dark colored fibers.
When the polymer was extruded into small diameter fibers and heat treated in air prior to firing at 1200C.according to the schedule below, the resulting fibers were soft and pliable.
Schedule 1 hr/75C
0O5 hr/125C
0.5 hrflS0C
1.~ hr~l75~C
1.0 hr/200C
1.0 hr/225C
1.0 hr/250C
0.33 hr/275C
Exam~le 15 The polymer of Example 1 was mixed in a 30/70 weight ratio with 320 mesh Norton Crystolon beta-silicon carbide using the solution-evaporation-ball mill technique.
The material was then press molded at 10,000 psi and 175C
for 30 min. to give a very ~mooth glassy surfaced pellet.
This pellet was fired to 1200C over a 6 hour period to give a ceramic pellet with a binder char yield of 50~.
Claims (3)
1. A process for preparing an R'3SiNH-containing silazane polymer which consists of contacting and reacting in an inert, essentially anhydrous atmosphere, a disilazane having the general formula (R'3Si)2NH
with a chlorine-containing disilane or a mixture of chlorine-containing disilanes having the general formula (ClaRbSi)2 and a chlorine-containing monosilane or a mixture of chlorine-containing monosilanes having the general formula R'nSiCl4-n at a temperature in the range of 25°C to 300°C
while distilling by-produced volatile products, wherein R is vinyl, an alkyl radical of 1-3 carbon atoms or the phenyl group;
R' is vinyl, hydrogen, an alkyl group of 1-3 carbon atoms or the phenyl group;
a has a value of 0.5-3;
b has a value of 0-2.5;
n has a value of 0, 1, 2 or 3 and the sum of a +
b is equal to three.
with a chlorine-containing disilane or a mixture of chlorine-containing disilanes having the general formula (ClaRbSi)2 and a chlorine-containing monosilane or a mixture of chlorine-containing monosilanes having the general formula R'nSiCl4-n at a temperature in the range of 25°C to 300°C
while distilling by-produced volatile products, wherein R is vinyl, an alkyl radical of 1-3 carbon atoms or the phenyl group;
R' is vinyl, hydrogen, an alkyl group of 1-3 carbon atoms or the phenyl group;
a has a value of 0.5-3;
b has a value of 0-2.5;
n has a value of 0, 1, 2 or 3 and the sum of a +
b is equal to three.
2. A process as claimed in claim 1 wherein in the mixture of chlorine-containing disilanes and chlorine-containing monosilanes, there is present at least 50 weight percent disilanes, based on the total weight of silanes.
3. As a composition of matter an R'3SiNH-containing silazane polymer characterized in that it is prepared by the process of claim 1.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US225,274 | 1981-01-15 | ||
| US06/225,274 US4340619A (en) | 1981-01-15 | 1981-01-15 | Process for the preparation of poly(disilyl)silazane polymers and the polymers therefrom |
| CA000374461A CA1161986A (en) | 1981-01-15 | 1981-04-02 | Process for the preparation of poly(disilyl)silazane polymers and the polymers therefrom |
Related Parent Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000374461A Division CA1161986A (en) | 1981-01-15 | 1981-04-02 | Process for the preparation of poly(disilyl)silazane polymers and the polymers therefrom |
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|---|---|
| CA1189080A true CA1189080A (en) | 1985-06-18 |
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ID=25669289
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|---|---|---|---|
| CA000425922A Expired CA1189080A (en) | 1981-01-15 | 1983-04-14 | Process for the preparation of poly(disilyl)silazane polymers and the polymers therefrom |
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1983
- 1983-04-14 CA CA000425922A patent/CA1189080A/en not_active Expired
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