Europâisches Patentamt European Patent Office (ÏÏ) Publication number: 0 075 826

Office européen des brevets B1

® EUROPEAN PATENT SPECIFICATION

(§) Date of publication of patent spécification : 30.04.86 © mtci.4: C 08 G 77/62, C 04 B 35/56 (D Application number: 82108675.8 (g) Date offiling: 20.09.82

@ Préparation of polysilazane and the polymers therefrom.

(§) Priority: 21.09.81 US 304446 (73) Proprietor: DOW CORNING CORPORATION 3901 S. Saginaw Road Midland Michigan 48640 (US) (§) Date of publication of application: 06.04.83 Bulletin 83/14 ' (72) Inventor: Gaul, John Henry, Jr. 3212 Lawndale Drive (§) Publication of the grant of the patent: Midland Michigan (US) 30.04.86 Bulletin 86/18

(74) Représentative: Hann, Michael, Dr. (H) Designated Contracting States: Patentanwâlte Dr. Michael Hann Dr. H.-G. BEDEGB IML Sternagel Marburger Strasse 38 D-6300 Giessen (DE) (58) Références cited: DE-A-2 243 527 US-A-2 564 674 US-A-3 311571

CM 00 If) o o Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the Notice of shail a. European patent granted. opposition be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been ui paid. (Art. 99(1 ) European patent convention). Courier Press, Leamington Spa, England. disilanes in the preparation of silazane polymers has been limited to the formation of relatively low This invention relates to the preparation of molecular weight materials. In one example, polysilazane polymers. These polymers are useful Wannagat et aI., Ang. Chem. 75(7) 345(1963), as chemical intermediates to synthesize organo- reported the reaction of tetramethyldichlorodi- compounds. They are also useful, when silane with gaseous to give a six- fired at high temperatures, to form membered cyclic silazane, and silicon carbide containing ceramic materials. What is disclosed herein is a novel process to obtain novel polysilazane polymers which consists of contacting and reacting chlorine- rather than the expected linear silazane containing disilanes with ammonia in an inert, and Hengge et. al., Montach, Chem. essentially anhydrous atmosphere. 101192)325(1970), prepared dimethylamino sub- As is well known in the art, halosilane stituted mixtures of disilanes from dimethylamine monomers will react with ammonia and most and the chlorine-containing disilane mixture organic compounds containing a primary or obtained from the Direct Process for the prepara- secondary amino group to give a variety of tion of chlorosilanes. silazanes. For example, the reaction of trimethyl- What has been discovered now is the co- chlorosilane and ammonia produces hexamethyl- reaction between chlorine-containing disilanes disilazane, a silazane monomer, while dimethyldi- and ammonia to give high molecular weight chlorosilane and ammonia produce dimethyl- silazane polymers. cyclic silazanes. These two reactions probably The instant invention concerns a new class of constitute the majority of commercial uses of the silazane polymers prepared from chlorodisilanes. silazane chemistry. In essence, a single chlorine-containing disilane Silazanes in general have been academic or a specified mixture of chlorine-containing curiosities for many years and a variety of such disilanes is treated with ammonia, as the nitrogen siiazanes, including monomers, oligomers, source, in sufficient amounts to react with all of cyclics and even low molecular weight resins and the chlorine on the chlorine-containing disilanes. linear polymers have been prepared by a variety This is usually an excess amount of ammonia of methods. For example, L. W. Breed et al., in the based on the chlorine content of the disilane. Journal of Organic Chemistry, 27, 1114(1962) When the mixture is heated in an essentially report the formation of silazanes from the poly- anhydrous atmosphere at elevated temperature, merization of sterically hindered silazane oligo- the reactions take place. mers, while in the Journal of Polymer Science, A2 The advantage of this process is the ability to 45(1964), cyclic trimer and tetramer silazanes are stop the reaction at any point by cooling the reported to be thermally cracked using catalysts reaction mass resulting in polymers with any to give linear polymers. desirable viscosity, hence any desirable In contrast fluids, rubbery polymers and resins molecular weight. The silazane polymers range in prepared from CH3SiCI3, (CH3)2SiCI2 and excess physical appearance from liquids, to high ammonia have been reported by Kruger et al. in viscosity liquids, to hard glassy materials. The the Journal of Polymer Science, A 2 3179(1964) materials are therefore very easy to handle. They and Redl, Silazane Polymer, ARPA-19, Advanced are essentially hydrolytically stable. Research Projects Agency, October, 1965. Thus, this invention consists of a process for The patent literature also contains disclosures preparing polysilazane polymers characterized in of the preparation of silazanes. Cheronis, in U.S. that it consists of contacting and reacting in an Patent 2,564,674 discloses the preparation of low inert, essentially anhydrous, atmosphere at a molecular weight linear silazane polymers by the temperature in the range of 25°C to 370°C. reaction of halosilanes with excess ammonia in a (A) ammonia and solvent solution. Bausma, et al., in U.S. Patent (B) chlorine-containing disilanes selected from 3,809,713 discloses a similar reaction scheme the group consisting of with the added modification of removing the by-produced solid ammonium halide using (i) a chlorine-containing disilane having the ethylene diamine. More recently, Verbeek, et al., general formula in U.S. Patent 3,853,567 and U.S. Patent 3,892,583 disclosed that mixtures of CH3SiCI3 and and (CH3)3SiCI3 can be treated with ammonia or (ii) a mixture of chlorine-containing disilanes organoamines to form materials that can be having the general formula pyrolyzed to yield SiC/Si3N4 ceramics. As should be 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 wherein present invention is based on chlorine-containing a has a value of 1.5-2.0; disilanes as opposed to the use of chlorine- b has a value of 1.0-1.5; containing monosilanes. the ratio of c to d is in the range of 1:1 to In another segment of the prior art, the use of 2:1; the sum of a+b is equal to three; stable, easy to handle polysilazane polymers can the sum of c+d is equal to three; and be prepared. Further, the polysilazane polymers R in each case is selected from a group lead to an improvement in the art of formation of consisting of the vinyl group, an alkyl silicon carbide and they can be used as binders in radical of 1-3 carbon atoms and the phenyl ceramic materials. group. The invention results from reacting ammonia with chlorine-containing disilanes, mixtures of This disclosure also deals with a new and novel disilanes or mixture of disilanes with mono- composition of matter which is a polysilazane silanes in an inert, essentially anhydrous atmo- polymer prepared by the method of this sphere and then firing the resulting polysilazane invention. polymer to get silicon carbide or silicon carbide Furthermore, this disclosure also deals with a containing ceramic materials. method of silicon carbide containing preparing a The chlorine-containing disilanes of this ceramic material which consists of heating a invention those disilanes having the general obtained the of are polysilazane polymer by process formulae this invention, in an inert atmosphere or in a vacuum to at least a temperature of 750°C until is converted silicon the polysilazane polymer to and carbide ceramic material. Still another object of this invention is a method of silicon carbide ceramic preparing a containing In these formulae, R is vinyl, an alkyl radical article which consists of (A) article of forming an containing 1-3 carbon atoms or the phenyl the desired from shape a polysilazane polymer Thus, those which are contem- of this (B) group. groups obtained by the process invention; useful in this invention are the article formed in (A) in inert plated as being heating an methyl, ethyl, propyl, vinyl and phenyl. For atmosphere or in a vacuum to an elevated of this invention, the R groups can all be of at least 750°C until the poly- purposes temperature the same or they can be different. The chlorine- silazane is converted to silicon carbide polymer containing disilanes can be those found in the containing ceramic. residue from the Direct Process for producing Still another object of this invention is a method halosilanes (Eaborn, C., " Com- for filled ceramic article which preparing a pounds", Butterworth Scientific Publications, consists of (A) mixing a polysilazane polymer London, 1960, pg. 1). obtained by the process of this invention with at least one conventional ceramic filler, (B) forming It is contemplated in this invention that single an article of the desired shape from the mixture of chlorine-containing disilanes can be used in this polysilazane polymer and filler and (C) heating invention. Such silanes having the formula (i) the article formed in (B) in an inert atmosphere or above require that the values of a and b are from in a vacuum to an elevated temperature of at least 1.5-2.0 and 1.0-1.5 respectively and the sum of 750°C until the polysilazane polymer is converted a+b is equal to three. Examples of chlorine- to a silicon carbide containing ceramic. containing disilanes useful in this invention are Still further, 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 polysilazane polymer obtained by the process of this invention with at least one conven- and tional ceramic filler, (B) coating a substrate with the mixture of polysilazane polymer and filler and, (C) heating the coated substrate in an inert Also contemplated within the scope of this atmosphere or in a vacuum to an elevated invention are mixtures of chlorine-containing di- temperature of at least 750°C until the coating is silanes. When mixtures of disilanes are used in converted to a silicon carbide ceramic material, this invention, such disilanes have the formula (ii) whereby a silicon carbide containing ceramic above wherein the ratio of c to d is in the range of coated article is obtained. 1:1 to 2:1 and the sum of c+d is three. Examples A further object of this invention is a process for of such chlorine-containing disilanes are those set preparing an article coated with a silicon carbide forth above and in addition such disilanes as ceramic material which consists of (A) coating a substrate with a polysilazane polymer obtained by the process of this invention, (B) heating the coated substrate in an inert atmosphere or in a vacuum to an elevated temperature of at least and 750°C until the coating is converted to a silicon carbide ceramic material. The inventions described herein result in new One last object of this invention is a process for compositions of matter which are an improve-' preparing a polysilazane polymer which consists ment in the art because essentially hydrolytically of contacting and reacting in an inert, essentially anhydrous atmosphere at a temperature in the sphere but minute amounts of moisture can be range of 25°C to 370°C, tolerated. (A) ammonia and The inventor believes that when the reactants (B) a mixture of chlorine-containing disilanes are contacted with each other, the reaction begins and monosilanes selected from the group which forms a transient intermediate disilane consisting essentially of amino compound and NH4CI, i.e.

(i) a mixture of a chlorine-containing disilane and a monosilane, (ii) a mixture of a chlorine-containing disilane The order of addition of the materials does not and a mixture of monosilanes and appear to be critical. (iii) a mixture of chlorine-containing disilanes The initial reaction is manifested by the appear- mixed with a mixture of monosilanes, ance of the white flocculent precipitated NH4CI. NH4CI tends to increase the viscosity of the wherein the chlorine-containing disilanes have reaction mass and therefore, it is desirable to add the general formula a low boiling solvent to disperse the NH4CI and allow more uniform stirring of the reaction mixture. The low boiling solvent should be any and dry organic solvent boiling below about 100°C wherein the monosilanes in each case have the such as pentane, heptane, hexane, benzene and general formula the like. The reaction begins when the ingredients are contacted. The reaction can be carried out at room temperature but in order to hasten the reaction, however, it is best to heat the reaction wherein R is a vinyl group, an alkyl radical of mass to a gentle reflux. Occasionally, depending 1-3 carbon atoms or the phenyl group; R' is on the ingredients being used, it may be vinyl, hydrogen, an alkyl group of 1-3 carbon necessary to stop the reaction and filter the NH4CI atoms or the phenyl group; a has a value of from the reaction mixture. This is especially true if 1.5-2.0; b has a value of 1.0-1.5; the sum of no solvent is used. Occasionally, the reaction a+b is equal to three and n has a value of 0,1, or mixture may need to be filtered more than once to 3. obtain a clear filtrate. Also, one may desire to Monosilanes useful in admixture with the di-. filter the reaction mixture, heat the filtrate for a silanes of this invention can be for example continuation of the reaction and then, refilter to obtain a clear filtrate. This interim stage of the reaction scheme results in low molecular weight materials. The reaction is continued until equi- librium is reached. Equilibrium is established when no more NH4CI is formed on continued and heating. The material is then filtered and the filtrate is returned to the reaction vessel and heated to reflux, if desired, for an additional Whenever chlorine-containing disilane period of time. The solvent is removed by distilla- mixtures are required, the number of units of tion and the residue is then heated to higher diorgano-substituted silicon atoms should not temperatures to form the polymeric product. exceed the number of units of monoorgano- As the temperature is raised higher, more substituted silicon atoms. Even though poly- condensation takes place and crosslinking occurs. silazane polymers can be formed from chlorine- When the reaction is cooled, the condensation containing disilane mixtures wherein the number and crosslinking slow down or cease. This control of diorgano-substituted units does exceed the allows one to stop the reaction at any point to number of monoorgano-substituted units, it has obtain almost any desired viscosity. The desirable been found that these polymers do not have the temperature range of this reaction is 25°C to handling properties for formability because of 370°C. The most preferred range is 125°C to 300°C. low viscosities. The length of time that the reaction requires The other reactant in this invention is ammonia depends on the temperature and the viscosity one and because of the anhydrous nature of the wishes to achieve. process herein, it is required that the ammonia Distillable products can be removed by heating used herein be essentially anhydrous. and/or the application of vacuum. These reactants are brought together in an The silazane polymers are then essentially inert, essentially anhydrous atmosphere. For ready to use. The silazane polymers are pyrolyzed purposes of this invention what we mean by in an inert atmosphere or in a vacuum at tem- "inert" is that the reaction is carried out under a peratures of at least 750°C to give a silicon carbide blanket of inert gas, such as, argon or nitrogen or containing material. If the polymer is of sufficient helium. What we mean by "essentially viscosity, it can be shaped first (such as an anhydrous" is that the reaction is preferably extruded fiber) and then pyrolyzed to give a carried out in an absolutely anhydrous atmo- silicon carbide containing fiber or the silazane polymers can be filled with ceramic type fillers (if averaged 11 mg., program rate was 10°C/min., desired) and then fired to at least 750°C to obtain gas flow rate was 200 cc/min. The scale setting silicon carbide ceramic materials or silicon was 50°C/in. ±0.5°C/in. carbide ceramic material containing ceramic Percent Silicon was determined by a fusion articles. technique which consisted of converting the When mixtures of chlorine-containing disilanes silicon material to soluble forms of silicon and are to be used, it is best if the chlorine-containing then the soluble material is quantitatively disilanes are mixed prior to contacting and determined as total silicon by atomic absorption reacting with the ammonia. spectrometry. Solubilization takes place by As mentioned above, some of the resulting weighing the sample into a Parr-type fusion cup polymers can be extruded to give various shapes (about 0.3 gm), adding 15.0 gms of Na peroxide, such as fibers. It has been found that the heating for about 90 sec. and quenching in cold polymers of this invention that have the handle- water. The material is placed in a nickel beaker ability that enables one to extrude or form them containing 150-200 ml. of distilled water. 55 ml. are those polymers in which the number of of reagent grade acetic acid is added and diluted diorgano-substituted silicon atoms do not exceed with water to 500 ml. volume. the number of monoorgano-substituted silicon Percent Chlorine (residual) was determined by atoms. Thus, if the polymer is to be extruded or Na peroxide decomposition and titration with otherwise formed, it should be prepared from silver nitrate. Fusion of the halides with Na disilanes and ammonia wherein the diorgano- peroxide is followed by potentiometric titration substituted silicon atoms do not exceed the - with standard silver nitrate by weighing a sample number of monoorgano-substituted silicon into a gelation capsule, placing about 1.5 gm. of atoms. Na202, about 0.7 gm of KN03 and about 0.15 gm As mentioned above, the polymers of this of sugar into a clean, dry reaction cup and burying invention can be used in both the filled and the capsule in the mixture. The cup is filled with unfilled state, depending on the application. Thus, Na202 and placed in a reaction vessel. It is heated it is contemplated within the scope of this for 1-1 1/2 min. and quenched in cold water. The invention to coat substrates with filled and cup and vessel are washed and the washings are unfilled polymers and heat the substrates to collected. The washings are heated to dissolve produce silicon carbide containing ceramic any solids. 15 ml. of cold 50% aqueous H2S04 is coated articles. Fillers and adjuvants can be added to the washings and allowed to stand milled on 3 roll mills by simply mixing the 15-20 sec. This solution is neutralized with polymers of this invention with the fillers and additional H2SO4 and titrated. making several passes on the mill. In the alterna- Carbon and hydrogen were determined by tive, the polymers can be placed in solvents and microcombustion by weighing 10 to 20 mg. of the fillers and adjuvants can be added thereto and sample into a micro platinum boat and treating it after mixing, the solvent can be removed to give in an A. H. Thomas combustion apparatus, the filled polymer. Catalog No. 6447-E, Philadelphia, PA. The coating can be carried out by conventional Unless otherwise noted in the reactions carried means. The means used depends on the polymer out below, the reaction apparatus was essentially and substrates used and the application one has the same in each case and'consisted of a glass, in mind. Thus, these materials can be brushed, round-bottomed flask equipped with a rolled, dipped or sprayed. In the filled state, it is mechanical stirrer, gas inlet tube, distillation sometimes necessary to trowel the polymer onto apparatus and a thermocouple to record tem- the substrate. perature. The distillation apparatus was equipped Whenever the polymers are converted to the to use a vacuum if needed. ceramic state, it is done by pyrolyzing the polymer to a temperature of at least 750°C in an Example 1 inert atmosphere or in a vacuum. Under an argon blanket, one hundred grams of Attempts to pyrolyze at or above 750°C without a mixture of disilanes containing 56 weight an inert atmosphere lead to undesirable side percent dichlorotetramethyldisilane; 31.5 weight reactions and therefore, caution should be percent of trichlorotrimethyldisilane and 12.5 exercised to be sure to exclude moisture and weight percent of tetrachlorodimethyldisilane other potential reactants. were combined with 900 gms of dry hexane and Now so that those skilled in the art can better anhydrous ammonia was bubbled through the appreciate and understand the invention, the mixture with vigorous stirring. The temperature following examples are given. The examples are of the mixture rose to about 58°C over a 30 minute for purposes of illustration only and are not to be period at which point some reflux was observed. regarded as limitations. The reflux was continued and the ammonia was In the following examples, the analytical added for about one hour. The mixture slowly methods used were as follows: cooled over that period of time to about room Thermogravimetric analysis (TGA) was carried temperature. The reaction mixture was filtered to out on a Netzsch STA 429 (2400°C) TGA remove the NH4CI. The hexane was removed instrument manufactured by Netzsch under vacuum. The filtrate was then heated under Instruments, Selb, West Germany. Sample sizes argon, with stirring to 275°C for 2 hours. When cooled, the product was a hard, glassy, trans- increased to room temperature. The reaction lucent polysilazane polymer. mixture was filtered and the pentane solvent was removed by vacuum and heat. The resultant Example 2 polysilazane polymer residue was a colorless, Under an argon blanket, fifty-one and one- cloudy viscous fluid. The yield was 45.2%. tenths of a mixture of disilanes consisting grams A small portion of this material was pyrolyzed of 12 weight percent of dichlorotetramethyldi- under an ammonia atmosphere to 1200°C to yield silane; 43 weight percent of trichlorotrimethyldi- a black and white material (two layered). The silane and 45 weight of tetrachlorodi- percent black portion was amorphous to X-rays. The methyldisilane were combined with 449.6 grams white portion was amorphous to X-rays and of dry hexane. Ammonia was bubbled gas contained a minor portion of β-Si3N4. through the solution for two hours. NH4CI precipitated and was filtered The filtrate away. Example 4 was returned to the reaction flask and treated Under blanket, hundred five and with ammonia for 2 hours. The an argon one again gas more two-tenths of disilane mixture the reaction mixture then filtered. The filtrate grams a having was that in Example 1 stored under for The hexane approximate composition as was argon two days. combined with 1.38 of distilled di- then removed to distillation was grams was by heating and 1000 of dry The removal of the hexane resulted methylvinylchlorosilane grams temperature. toluene. The flask flushed with dry and in the of solution due was argon appearance a hazy to the reaction flask cooled with ice/ residual The residue also was a dry NH4CI. was slightly bath while ammonia bubbled in color. The residue heated acetone gas was yellow was slowly to the mixture for two hours. The reaction 300°C. the of the it through During course heating, was mixture filtered and the filtrate left under observed that the residue had turned clear was was yellow for about 16 hours. The toluene was when the reached 160°C. The argon temperature residue distilled from the reaction residue and the foamed at about 200°C and and away vigorous stirring a residue heated to 275°C for 1 hour and then slower rate control the was heating was required to cooled. Infra-red showed Si-N-Si, -NH, -NC, foam. The resulting residue at 300°C a liquid was SiCH3 and a slight amount of Si-O-Si. which was orange in color. When cooled, the residue was an orange-yellow, semi-solid. Infra- Example 5 red analysis of the residue showed it to be an A mixture of 45.2 weight percent tetrachlorodi- (CH3)xSiN-containing polymer. TGA @ 1000°C in methyldisilane, 42.8 weight percent of trichlorotri- an 11 % char yield (80% weight loss). argon gave methyldisilane and 12.0 weight percent of di- TGA conditions for this sample were: DuPont 950 chlorotetramethyldisilane (200.8 total) was TGA; 21.3564 sample size; platinum crucible; gms mg combined with 1374.7 of dry hexane in an atmosphere was flow rate was 200 cc/ gms argon; atmosphere in a flask. Ammonia was min.; heating rate was 10°C/min. argon bubbled rapidly through this mixture for 1 hour. This polymer was subjected to pyrolysis by The reaction mixture was suction filtered. placing 2.4 of polymer in graphite boat. The gms a Ammonia bubbled through the filtrate for boat was placed in a tube furnace and flushed gas was an additional hour and the reaction mass was with for 20 minutes. The sample was then argon refiltered after standing for about 16 hours. The fired under to 1000°C. The product was argon filtrate was slightly hazy and in this form was strip shiny and black in A small sample of appearance. distilled to remove the hexane solvent. The this shiny, black material was fired to 1600°C remaining material was heated to 370°C and held under in a graphite crucible. This argon product at that for 30 minutes. The result was when cooled was a dark color. The 1000°C temperature green a milky yellow polysilazane polymer resin. Infra sample was analyzed by X-ray analysis and red analysis showed the of showed no crystalline material. The 1600°C presence sample was (3-Silicon Carbide having an average crystallite size of 770 A units. and -Si-O-Si-thermogravimetric Example 3 some char of 30% when heated to Under an blanket, five hundred milliliters analysis gave a yield argon 1000°C in Helium, % carbon was 17.8; % H was of dry pentane was added to a reaction flask 5.44 and % N 4.74. A portion of this material equipped as indicated above. The reaction flask was was heated to 1200°C in the Astro furnace to give was cooled by means of a dry ice/acetone bath. a char yield of 29.1 %. X-ray analysis of this fired Ammonia was passed through until the 2 gas material showed no crystalline phases. When liter, round-bottomed flash was about 1/2 full. another was heated to 1600°C, the char One hundred of a mixture of disilanes sample grams yield was 17.9% and X-ray analysis showed having approximately the same composition as in (3-silicon carbide with an crystallite size of Example 1 was mixed with 100 of average grams dry >3000 A units. pentane and this mixture was added dropwise over a 15 minute period to the ammonia/pentane. The resin produced in this example was tested The cooling bath was then removed and the as a ceramic binder using powdered silicon ammonia slowly boiled off as the temperature carbide as the filler. The resin, 2.3193 gms was dissolved in 10 ml. of dry hexane and then after it was cooled. The product was a yellow blended with 7.7388 gms of 320 mesh silicon translucent, solid resin. Infra red analysis showed carbide powder (U.S. Standard). The solution was the presence of NH4CI, -SiNHSi-, -SiOSiO-, then evaporated to dryness. The resulting -Si(CH3)3, -Si(CH3)2 and -SiCH3 moieties. A particulate material was ball-milled for 1 hour to TGA gave a char yield of 35% @ 1000°C in Argon. give it uniformity. A sample of this powder was Samples of this resin were fired to 1200°C. The pressed at 200°C in an inert atmosphere. It X-ray analysis of the product showed it to be retained its shape and gave an 86% char yield but essentially amorphous. upon firing to 1600°C, the pellet weakened and When a sample of this resin was heated to crumbled when an attempt was made to remove 1600°C, the char yield was 41.8% and X-ray it from the crucible. analysis showed the material to be essentially The resin produced in this example, 4.7923 β-silicon carbide with an average crystallite size of gms, was blended into 4.8838 gms of dry toluene. greater than 3000 A units. Two graphite bars (9/16" diameterx2" in length) were coated with the solution and dried at 150°C. The bars were then fired to 1200°C in an inert 1. A process of preparing a polysilazane atmosphere. The coatings were pale green in polymer, said process characterized in that it color and were easily scratched. Firing to 1600°C consists of contacting and reacting in an inert, gave essentially the same type of easily scratch- essentially anhydrous atmosphere, at a tempera- able coating. ture in the range of 25°C to 370°C. (A) ammonia and Example 6 (B) chlorine-containing disilane selected from A disilane mixture similar to that used in the group consisting of Example 5 was used herein (300 gms total). This mixture was combined with 1382.1 gms of dry (i) a chlorine-containing disilane having the hexane in a glass flask, under Argon. Ammonia general formula gas was bubbled through the mixture for 1 hour whereupon the mixture was filtered. This bubbling of ammonia and filtration step was and repeated for 1 hour. The hexane was strip distilled (ii) a mixture of chlorine-containing disilanes and residue was heated to 295°C for 1 hour. A having the general formula vacuum was applied for 4 hours. The result was a greyish colored polysilazane polymer resin. Infra red analysis showed the presence of NH4CI, -SiNHSi-, SiOSi, Si(CH3)3, Si(CH3)2 and -SiCH3. wherein TGA gave a 42% char yield to 1000°C in Argon. a has a value of 1.5-2.0; When a sample of this material was heated to b has a value of 1.0-1.5; 1200°C, the char yield was 35.6% of 0-silicon the ratio of c to d is in the range of 1:1 to carbide which was the main constituent. This 2:1, the sum of a+b is equal to three; material has an average crystallite size of >3000 the sum of c+d is equal to three; A. When heated to 1600°C, the char yield was and 23.5%. The product was a-silicon carbide having R in each case is selected from the group an average particle size of >3000 A. consisting of the vinyl group, alkyl radicals of 1-3 carbon atoms and the phenyl group. Example 7 Preparation of a polysilazane polymer using a 2. The polysilazane polymer produced by the chlorine-containing monomer in the presence of process of claim 1. disilanes and ammonia. 3. A method of preparing a silicon carbide A mixture of chlorine-containing disilanes ceramic material which consists of heating a having 44.9 weight percent of tetrachlorodi- polysilazane polymer prepared according to the methyldisilane; 41.4 weight percent of trichloro- process of claim 1, in an inert atmosphere or in a trimethyldisilane and 13.7 weight percent of di- vacuum to at least a temperature of 750°C until chlorotetramethyldisilane (400.2 gms total) was the polysilazane polymer is converted to silicon combined with 1388 gms of dry hexane in a carbide ceramic material. round-bottomed glass flask under an Argon 4. A method of preparing a silicon carbide atmosphere. To this mixture was added 5.1 gms containing ceramic article which consists of (A) of freshly distilled vinyldimethylchlorosilane of forming an article of the desired shape from a 96.7% purity. Ammonia gas was rapidly bubbled polysilazane polymer prepared according to the through the system for 1 hour whereupon the process of claim 1; (B) heating the article formed mixture was filtered. The bubbling for 1 hour and in (A) in an inert atmosphere or in a vacuum to an filtration were repeated once. The filtrate at this elevated temperature of at least 750°C until the point was slightly hazy. Hexane was distilled from polysilazane polymer is converted to silicon the filtrate and the filtrate was then heated to carbide containing ceramic. 300°C for 1 hour. The polysilazane polymer 5. A process for preparing a polysilazane formed was subjected to a vacuum for 5 hours polymer, said process characterized in that it consists of contacting and reacting in an inert, formé par le groupe vinyle, les radicaux essentially anhydrous atmosphere at a alkyles contenant 1 à 3 atomes de carbone temperature in the range of 25°C to 370°C, et le groupe phényle.

(A) ammonia and 2. Le polymère polysilazane obtenu par le (B) a mixture of chlorine-containing disilanes procédé selon la revendication 1. and monosilanes selected from the group consist- 3. Un procédé de préparation d'un matériau ing essentially of céramique au carbure de silicium qui consiste à chauffer un polymère polysilazane préparé con- (i) a mixture of a chlorine-containing disilane formément au procédé selon la revendication 1 and a monosilane, dans une atmosphère inerte ou sous vide à une (ii) a mixture of a chlorine-containing disilane température d'au moins 750°C jusqu'à ce que le and a mixture of monosilanes; polymère polysilazane se trouve converti en and matériau céramique au carbure de silicium. (iii) a mixture of chlorine-containing disilanes 4. Un procédé de préparation d'un objet en mixed with a mixture of monosilanes, céramique contenant du carbure de silicium qui consiste (A) à former un objet de la forme désirée wherein the chlorine-containing disilanes have à partir d'un polymère polysilazane préparé con- the general formula formément au procédé selon la revendication 1; (B) à chauffer l'objet formé en (A) dans une atmosphère inerte ou sous vide à une tempéra- and ture élevée d'au moins 750°C jusqu'à ce que le wherein the monosilanes in each case have the polymère polysilazane se trouve converti en céra- general formula mique contenant du carbure de silicium. 5. Un procédé pour le preparation d'un polymère polysilazane, ledit procédé étant carac- térisé en ce qu'il consiste à mettre en contact et à wherein R is a vinyl group, an alkyl radical of faire réagir dans une atmosphère inerte, essenti- 1-3 carbon atoms or the phenyl group; R' is ellement anhydre, à une température se situant vinyl, hydrogen, an alkyl group of 1-3 carbon dans l'intervalle de 25 à 370°C, atoms or the phenyl group; a has a value of (A) de l'ammoniac et 1.5-2.0; b has a value of 1.0-1.5; the sum of (B) un mélange de disilanes contenant du a+b is equal to three and n has a value of 0, 1, or chlore et de monosilanes choisi dans le groupe 3. formé essentiellement par

(i) un mélange d'un disilane contenant du chlore et d'un monosilane, 1. Un procédé de préparation d'un polymère (ii) un mélange d'un disilane contenant du polysilazane, caractérisé en ce qu'il consiste à chlore et d'un mélange de monosilanes, et mettre en contact et à faire réagir dans une (iii) un mélange de disilanes contenant du atmosphère inerte, essentiellement anhydre, à chlore mélangé à un mélange de mono- une température se situant dans l'intervalle de 25 silanes, où les disilanes contenant du à 370°C: chlore répondent à la formule générale (A) de l'ammoniac et (B) des disilanes contenant du chlore choisis dans le groupe formé par et

(i) un disilane contenant du chlore répondant à où les monosilanes répondent dans chaque cas la formule générale à la formule générale

et de disilanes du (ii) un mélange contenant où R est un groupe vinyle, un radical alkyle chlore à la form-ile répondant générale comportant 1 à 3 atomes de carbone ou le groupe phényle, R' est un groupe vinyle, un atome d'hydrogène, un groupe alkyl comportant 1 à 3 atomes de carbone ou le groupe phényle; a a une où valeur de 1,5 à 2,0; b a une valeur de 1,0 à 1,5; la valeur de à a a une 1,5 2,0; somme a+b est égale à trois et n a pour valeur 0, b a une valeur de 1,0 à 1,5; 1 ou 3. le rapport de c à d se situe dans l'intervalle de 1/1 à 2/1; la somme a+b est égale à trois; la somme c+d est égale à trois; et 1. Verfahren zum Herstellen eines Polysilazan- R est choisi dans chaque cas dans le groupe polymeren, das dadurch gekennzeichnet ist, daß man in einer inerten, im wesentlichen wasser- fahren von Anspruch 1 hergestellten Polysilazan- freien Atmosphäre bei einer Temperatur im polymer, Bereich von 25°C bis 370°C (B) Erwärmen des nach (A) ausgeformten (A) Ammoniak und Gegenstandes in einer inerten Atmosphäre oder (B) Chlor enthaltende Disilane aus der Gruppe im Vakuum auf eine Temperatur von mindestens 750°C bis das Polysilazanpolymer in Silizium- (i) einem Chlor enthaltenden Disilan der allge- karbid enthaltendes keramisches Material umge- meinen Formel wandelt ist. 5. Verfahren zum Herstellen eines Polysilazan- polymeren, das dadurch gekennzeichnet ist, daß und man in einer inerten, im wesentlichen wasser- (ii) einer Mischung von Chlor enthaltenden freien Atmosphäre bei einer Temperatur im Disilanen der allgemeinen Formel Bereich von 25°C bis 370°C (A) Ammoniak und (B) eine Mischung von Chlor enthaltenden Disilanen und Monosilanen aus der Gruppe, die in denen a einen Wert von 1,5 bis 2,0 hat, b im wesentlichen aus einen Wert von 1,0 bis 1,5 hat, das Verhält- nis von c zu d im Bereich von 1:1 zu 2:1 (i) einer Mischung von Chlor enthaltendem liegt, die Summe von a+b gleich 3 ist, die Disilan und einem Monosilan, Summe von c+d gleich 3 ist und R in jedem (ii) einer Mischung von Chlor enthaltendem Fall aus der Gruppe von Vinylresten, Alkyl- Disilan und einer Mischung von Mono- resten mit 1 bis 3 Kohlenstoffatomen und silanen und dem Phenylrest ausgewählt ist, (iii) einer Mischung von Chlor enthaltenden Disilanen, gemischt mit einer Mischung in Berührung bringt und umsetzt. von Monosilanen, besteht,

2. Polysilazanpolymer, hergestellt nach dem auswählt, miteinander in Berührung bringt und Verfahren von Anspruch 1. umsetzt, wobei die Chlor enthaltenden Disilane 3. Verfahren zum Herstellen eines keramischen die allgemeine Formel Siliziumkarbidmaterials durch Erhitzen eines nach dem Verfahren von Anspruch 1 hergestellten Polysilazanpolymeren in einer inerten Atmo- sphäre oder im Vakuum auf eine Temperatur von und die Monosilane jeweils die allgemeine mindestens 750°C, bis das Polysilazanpolymer Formel R"SiC14-" aufweisen, in denen R eine in keramisches Siliziumkarbidmaterial umge- Vlnylgruppe, eine Alkylgruppe mit 1 bit 3 Kohlen- wandelt ist. stoffatomen oder die Phenylgruppe ist, R' ist 4. Verfahren zum Herstellen eines Silizium- Vinyl, Wasserstoff, eine Alkylgruppe mit 1 bis 3 karbid enthaltenden Gegenstandes, gekennzeich- Kohlenstoffatomen oder die Phenylgruppe, a hat net durch einen Wert von 1,5 bis 2,0, b hat einen Wert von (A) Ausformen eines Gegenstandes der 1,0 bis 1,5, die Summe von a+b ist gleich 3 und n gewünschten Form aus einem nach dem Ver- hat einen Wert von 0, 1 oder 3.