| Title of Invention | PROCESS FOR PREPARING SILICON CARBIDE (SIC) FOAM |
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| Abstract | The present invention relates to a process for preparing silicon carbide foam, said process comprising: refluxing a solution of polycarbosilane in an organic solvent; adding an organic resin to the refluxed solution to obtain a reaction mixture; heating the reaction mixture for about 5 to 7 hours; distilling the heated reaction mixture to obtain a residue; and heating the residue at a temperature of about 200 to about 600°C for about 25 to 35 mins to obtain a preceramic foam, followed by further heating the preceramic foam at a temperature of about 900°C to about 1500°C at a heating rate in the range of 2°C to 10°C/min to obtain the siliconcarbide foam. The present invention further relates to silicon carbide foam prepared by the process of the present invention. Silicon carbide foams prepared by the process of the present invention may be used as thermal shock absorber, sound proofing, fire protection, volume burners, and solar receivers. |
| Full Text | FIELD OF THE INVENTION; The present invention relates to a process of preparing silicon carbide foam by using polycarbosilane as precursor material. The present invention provides silicon carbide foam having a bulk density less then one. The silicon carbide foam may be used as thermal shock absorber, sound proofing, fire protection, volume burners, and solar receivers. BACKGROUND: US 4,885,263 disclose that silicon carbide open celled foam can be made of silicon carbide grains that are bound with an aluminosilicate binder phase. The sintering is carried out in air at 1100 °C tol400 °C. US 5,449,654 describes a process for preparing a silicon carbide foam consist of attacking a polyurethane foam with an alkaline solution, impregnating it, after rinsing and drying, with a suspension of silicon powder in an organic resin, heating progressively to polymerize the resin, carbonizing the polyurethane foam and resin and finally carburizing the silicon, contained in the resin suspension, by means of carbon originating from the carbonization of the foam and the resin. US 6,251,819 describes that silicon carbide foam useful as a catalyst support may be prepared by impregnating organic foam with a suspension of silicon in a resin containing crosslinking agent, followed by incompletely crosslinking the resin, carbonizing the foam and resin, and carburizing the silicon. US 6,887,809 discloses that the open celled silicon carbide foam can be produced by mixing coarse and fine silicon carbide powder in a ratio of 20:80 to 80:20 and a suspension is made from this powdered mixture. An open celled network is coated with this suspension and the network material is removed. The remaining green body is sintered at temperature >1800 °C in protective gas or vacuum. FR 2684092 describes silicon carbide foam obtained by carburization reaction starting from a volatile compound of silicon with activated carbon foam. This activated carbon foam may result from polyurethane foam reinforced using a resin, setting up the resin, followed by carbonation and activation. FR 2705340 describes a process for making silicon carbide foam that consist of starting from a polyurethane foam, impregnating it with a silicon suspension in an oxygenated organic resin (usually furfurylic resin), polymerizing the resin up to 250°C, followed by simultaneously carbonizing the foam and the resin between 250-1000°C under inert atmosphere and carbonizing the silicon contained in the resulting carbon foam up to a temperature between 1300-1600°C and maintaining this temperature for 2 hrs under inert atmosphere. SUMMARY: The present invention provides a process for preparing silicon carbide foam, said process comprising: refluxing a solution of polycarbosilane in an organic solvent; adding an organic resin to the refluxed solution to obtain a reaction mixture; heating the reaction mixture for about 5 to 7 hours; distilling the heated reaction mixture to obtain a residue; and heating the residue at a temperature of about 200 to about 600°C for about 25 to 35 minutes to obtain a preceramic foam, followed by further heating the preceramic foam at a temperature of about 900°C to about 1500°C at a heating rate in the range of 2°C to 10°C/min to obtain the silicon carbide foam. The present invention also relates to silicon carbide (SiC) foam prepared by a process of the present invention. The silicon carbide (SiC) foam has a bulk density in the range of 0.01 to 0.5 g/cc. The silicon carbide (SiC) foam may be used as thermal shock absorber, sound proofing, fire protection, volume burners, and solar receivers. These and other features, aspects, and advantages of the present subject matter will become better understood with reference to the following description and appended claims. This summary is provided to introduce a selection of concepts in a simplified form. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. BRIEF DESCRIPTION OF DRAWINGS: The above and other features, aspects, and advantages of the subject matter will become better understood with regard to the following description, appended claims, and accompanying drawings where: Figure 1 is a scanning electron micrograph of close cell silicon carbide ceramic foam. Figure 2 is a scanning electron micrograph of open cell silicon carbide ceramic foam. DETAIL DESCRIPTION OF THE INVENTION: The present invention provides a process for preparing silicon carbide foam, said process comprising: refluxing a solution of polycarbosilane in an organic solvent; adding an organic resin to the refluxed solution to obtain a reaction mixture; heating the reaction mixture for about 2 to 10 hours; distilling the heated reaction mixture to obtain a residue; and heating the residue at a temperature of about 200 to about 600°C for about 25 to 35 minutes to obtain a preceramic foam, followed by further heating the preceramic foam at a temperature of about 900°C to about 1500°C at a heating rate in the range of 2°C to 10°C/min to obtain the silicon carbide foam. An embodiment of the present invention is a process for preparing silicon carbide foam, wherein the polycarbosilane has a molecular weight of 500 to 2000. Still another embodiment of the present invention is a process for preparing silicon carbide foam, wherein the polycarbosilane has a molecular weight of 1000 to 1700. Yet another embodiment of the present invention is a process for preparing silicon carbide foam, wherein the polycarbosilane has a molecular weight of 1300 to 1500. Further embodiment of the present invention is a process for preparing silicon carbide foam, wherein the polycarbosilane is synthesized by the thermal backbone rearrangement of polydimethylsilane which in turn is synthesized by wurtz coupling reaction of dichlorodimethylsilane with sodium metal under refluxing condition. Another embodiment of the present invention is a process for preparing silicon carbide foam, wherein the organic solvent is selected from a group consisting of petroleum ether, benzene, toluene, xylene, dichloromethane, and terahydrofuran. Another embodiment of the present invention is a process for preparing silicon carbide foam, wherein the organic solvent is preferably selected from a group consisting of petroleum ether, benzene and toluene. Still an embodiment of the present invention is a process for preparing silicon carbide foam, wherein the organic resin is selected from epoxy resin and acrylate resin. Further embodiment of the present invention is a process for preparing silicon carbide foam, wherein the acrylate resin is used along with Spiers catalyst (HaPtCU). Another embodiment of the present invention is a process for preparing silicon carbide foam, wherein the reaction mixture is heated for about 3 to 8 hours. Further an embodiment of the present invention is a process for preparing silicon carbide foam, wherein the reaction mixture is heated for about 5 to 6 hours. Yet another embodiment of the present invention is a process for preparing silicon carbide foam, wherein the heating of residue is carried out under inert atmosphere. Further an embodiment of the present invention is a process for preparing silicon carbide foam, wherein the heating of residue is carried out under inert atmosphere of argon. Another embodiment of the present invention is a process for preparing silicon carbide foam, wherein the heating of residue is carried out under inert atmosphere of nitrogen Further an embodiment of the present invention is a process for preparing silicon carbide foam, wherein the heating of residue is carried out under inert atmosphere of helium. Yet another embodiment of the present invention is a process for preparing silicon carbide foam, wherein the heating of residue is carried out at a temperature of about 250°C to 500°C. Still another embodiment of the present invention is a process for preparing silicon carbide foam, wherein the heating of residue is carried out at a temperature of about 350°C to450°C. Another embodiment of the present invention is a process for preparing silicon carbide foam, wherein the heating of residue is carried out at a rate of 2°C to 50°C/min. Yet another embodiment of the present invention is a process for preparing silicon carbide foam, wherein the heating of residue is carried out at a rate of 10°C to 20°C/min. An embodiment of the present invention is a process for preparing silicon carbide foam, said process comprising: refluxing a solution of polycarbosilane in an organic solvent; adding an organic resin to the refluxed solution to obtain a reaction mixture; heating the reaction mixture for about 2 to 10 hours; distilling the heated reaction mixture to obtain a residue; and heating the residue at a temperature of about 200 to about 600°C for about 25 minutes to 35 minutes to obtain a preceramic foam, followed by further heating the preceramic foam at a temperature of about 900°C to about 1500°C at a heating rate in the range of 2°C to 4°C/min for about 40 minutes to about 50 minutes to obtain the open cell silicon carbide foam. An embodiment of the present invention is a process for preparing open cell silicon carbide foam, wherein the polycarbosilane has a molecular weight of 500 to 2000. Still another embodiment of the present invention is a process for open cell preparing silicon carbide foam, wherein the polycarbosilane has a molecular weight of 1000tol700. Yet another embodiment of the present invention is a process for preparing open cell silicon carbide foam, wherein the polycarbosilane has a molecular weight of 1300 to 1500. Further embodiment of the present invention is a process for preparing open cell silicon carbide foam, wherein the polycarbosilane is synthesized by the thermal backbone rearrangement of polydimethylsilane which in turn is synthesized by wurtz coupling reaction of dichlorodimethylsilane with sodium metal under refluxing condition. Another embodiment of the present invention is a process for preparing open cell silicon carbide foam, wherein the organic solvent is selected from a group consisting of petroleum ether, benzene, toluene, xylene, dichloromethane, and terahydrofuran. Another embodiment of the present invention is a process for preparing open cell silicon carbide foam, wherein the organic solvent is preferably selected from a group consisting of petroleum ether, benzene and toluene. Still an embodiment of the present invention is a process for preparing open cell silicon carbide foam, wherein the organic resin is selected from epoxy resin and acrylate resin. Further embodiment of the present invention is a process for preparing open cell silicon carbide foam, wherein the acrylate resin is used along with Spiers catalyst (HzPtCle). Another embodiment of the present invention is a process for preparing open cell silicon carbide foam, wherein the reaction mixture is heated for about 3 to 8 hours. Further an embodiment of the present invention is a process for preparing open cell silicon carbide foam, wherein the reaction mixture is heated for about 5 to 6 hours. Yet another embodiment of the present invention is a process for preparing open cell silicon carbide foam, wherein the heating of residue is carried out under inert atmosphere. Further an embodiment of the present invention is a process for preparing open cell silicon carbide foam, wherein the heating of residue is carried out under inert atmosphere of argon. Another embodiment of the present invention is a process for preparing open cell silicon carbide foam, wherein the heating of residue is carried out under inert atmosphere of nitrogen Further an embodiment of the present invention is a process for preparing open cell silicon carbide foam, wherein the heating of residue is carried out under inert atmosphere of helium. Yet another embodiment of the present invention is a process for preparing open cell silicon carbide foam, wherein the heating of residue is carried out at a temperature of about 250°C to 500°C. Still another embodiment of the present invention is a process for preparing open cell silicon carbide foam, wherein the heating of residue is carried out at a temperature of about 350°C to 450°C. Another embodiment of the present invention is a process for preparing open cell silicon carbide foam, wherein the heating of residue is carried out at a rate of 2°C to 50°C/min. Yet another embodiment of the present invention is a process for preparing open cell silicon carbide foam, wherein the heating of residue is carried out at a rate of 10°C to 20°C/min. An embodiment of the present invention is a process for preparing silicon carbide foam, said process comprising: refluxing a solution of polycarbosilane in an organic solvent; adding an organic resin to the refluxed solution to obtain a reaction mixture; heating the reaction mixture for about 2 to 10 hours; distilling the heated reaction mixture to obtain a residue; and heating the residue at a temperature of about 200 to about 600°C for about 25 to 35 minutes to obtain a preceramic foam, followed by further heating the preceramic foam at a temperature of about 900°C to about 1500°C at a heating rate in the range of 5°C to 7°C/min for about 10 minutes to about 40 minutes to obtain the closed cell silicon carbide foam. An embodiment of the present invention is a process for preparing closed cell silicon carbide foam, wherein the polycarbosilane has a molecular weight of 500 to 2000. Still another embodiment of the present invention is a process for preparing closed cell silicon carbide foam, wherein the polycarbosilane has a molecular weight of 1000 tol700. Yet another embodiment of the present invention is a process for preparing closed cell silicon carbide foam, wherein the polycarbosilane has a molecular weight of 1300 to 1500. Further embodiment of the present invention is a process for preparing closed cell silicon carbide foam, wherein the polycarbosilane is synthesized by the thermal backbone rearrangement of polydimethylsilane which in turn is synthesized by wurtz coupling reaction of dichlorodimethylsilane with sodium metal under refluxing condition. Another embodiment of the present invention is a process for preparing closed cell silicon carbide foam, wherein the organic solvent is selected from a group consisting of petroleum ether, benzene, toluene, xylene, dichloromethane, and terahydroturan. Yet, another embodiment of the present invention is a process for preparing closed cell silicon carbide foam, wherein the organic solvent is preferably selected from a group consisting of petroleum ether, benzene and toluene. Still an embodiment of the present invention is a process for preparing closed cell silicon carbide foam, wherein the organic resin is selected from epoxy resin and acrylate resin. Further embodiment of the present invention is a process for preparing closed cell silicon carbide foam, wherein the acrylate resin is used along with Spiers catalyst (H2PtCl6). Another embodiment of the present invention is a process for preparing closed cell silicon carbide foam, wherein the reaction mixture is heated for about 3 to 8 hours. Further an embodiment of the present invention is a process for preparing closed cell silicon carbide foam, wherein the reaction mixture is heated for about 5 to 6 hours. Yet another embodiment of the present invention is a process for preparing closed cell silicon carbide foam, wherein the heating of residue is carried out under inert atmosphere. Further an embodiment of the present invention is a process for preparing closed cell silicon carbide foam, wherein the heating of residue is carried out under inert atmosphere of argon. Another embodiment of the present invention is a process for preparing closed cell silicon carbide foam, wherein the heating of residue is carried out under inert atmosphere of nitrogen Further an embodiment of the present invention is a process for preparing closed cell silicon carbide foam, wherein the heating of residue is carried out under inert atmosphere of helium. Yet another embodiment of the present invention is a process for preparing closed cell silicon carbide foam, wherein the heating of residue is carried out at a temperature of about 250°C to 500°C. Still another embodiment of the present invention is a process for preparing closed cell silicon carbide foam, wherein the heating of residue is carried out at a temperature of about 350°C to 450°C. Another embodiment of the present invention is a process for preparing closed cell silicon carbide foam, wherein the heating of residue is carried out at a rate of 2°C to 50°C/min. Yet another embodiment of the present invention is a process for preparing closed cell silicon carbide foam, wherein the heating of residue is carried out at a rate of 10°C to 20°C/min. The present invention also provides silicon carbide foam prepared by the process of present invention. An embodiment of the present invention is silicon carbide foam, wherein the silicon carbide ceramic foam has a bulk density in the range of 0.01 to 0.5 g/cc. Another embodiment of the present invention is silicon carbide foam for use as a thermal shock absorber, sound proofing, fire protection, volume burners and solar receivers. Yet another embodiment of the present invention is to prepare different polytype silicon carbide foam from one source. Still another embodiment of the present invention is to prepare varying density silicon carbide foam from one precursor material. Another embodiment of the present invention is to prepare silicon carbide foam of desired shape and size using same precursor material. Further embodiment of the present invention is to prepare Silicon Carbide (SiC) foam of varying mechanical strength using same precursor material. Another embodiment of the present invention is to prepare silicon carbide foam of any shape and size using appropriate mould. Further embodiment of the present invention is to prepare SiC foam of different density, porosity and crushing strength. Yet another embodiment of the present invention is to prepare SiC foam having density less than one. EXAMPLES The following examples are given by way of illustration of the present invention and should not be construed to limit the scope of present disclosure. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are intended to provide further explanation of the claimed subject matter. Example 1 Into a 250 ml three necked flask, fitted with pressure equalizing dropping funnel, condenser and argon gas inlet tube 10 g of polycarbosilane (molecular weight = 1200) in 50 ml of petroleum ether (b.p. 40-60°C) were taken and refluxed in an oil bath. To the refluxing solution 0.3 g of epoxy resin in 20 ml of toluene was added slowly within 15 minutes and the reaction mixture was further heated for 6 hours. Then the solvent was distilled off under reduced pressure (20 mm of Hg). The residue was heated up to 400 °C at a heating rate of 10°C/min in argon atmosphere for 30 minutes to afford preceramic foam which was further pyrolysed at 1100 °C at a heating rate of 5°C /min for 30 minutes yielding closed cell silicon carbide foam. The bulk density of the SiC foam was 0.150 g/cc. Example 2 Into a 250 ml three necked flask, fitted with pressure equalizing dropping funnel, condenser and argon gas inlet tube 10 g of polycarbosilane (molecular weight = 1500) in 50 ml of petroleum ether (b.p. 40-60°C) were taken and refluxed in an oil bath. To the refluxing solution 0.6 g of epoxy resin in 50 ml of toluene was added slowly within 30 minutes and the reaction mixture was further heated for 6 hours. Then the solvent was distilled off under reduced pressure (20 mm of Hg). The residue was heated up to 400 °C at a heating rate of 15°C/min in under argon atmosphere for 30 minutes to afford preceramic foam which was further pyrolysed at 1100°C for at a heating rate of 3°C/min in 45 minutes yielding open cell silicon carbide foam. The bulk density of the SiC foam was 0.175 g/cc. Example 3 Into a 250 ml three necked flask, fitted with pressure equalizing dropping funnel, condenser and argon gas inlet tube 10 g of polycarbosilane (molecular weight = 1350) in 50 ml of petroleum ether (b.p. = 40-60°C) were taken and refluxed in an oil bath. To the refluxing solution 1.0 g of epoxy resin in 50 ml of toluene was added slowly within 40 minutes and the reaction mixture was further heated for 10 hours. Then the solvent was distilled off under reduced pressure (30 mm of Hg). The residue was heated up to 400°C under argon atmosphere and baked for 30 minutes to afford preceramic foam. The rate of heating was 10°C/min. The preceramic foam was further pyrolysed at 1000°C with a heating rate of 5°C/min for 15 minutes yielding closed cell silicon carbide foam. The bulk density of the SiC foam was 0.127 g/cc. Example 4 Into a 250 ml three necked flask, fitted with condenser and argon gas inlet tube 10 g of polycarbosilane (molecular weight ~ 1450) in 50 ml of tetrahydrofuran were taken and 0.5 g methyl methacrylate was added along with catalytic amount of Spiers' catalyst. Reaction mixture was stirred for 24 hrs at room temperature (30 °C) followed by refluxing for 5 hrs. Then the solvent was removed under reduced pressure (20 mm of Hg). The residue was heated up to 400 °C at the rate of 2°C/min under argon atmosphere for 30 minutes to afford preceramic foam which was further pyrolysed at 1100 °C for 45 minutes with rate of heating of 2.5°C/min yielding open cell silicon carbide foam. The bulk density of the SiC foam was 0.15 g/cc. Although the subject matter has been described in considerable detail with reference to certain preferred embodiments thereof, other embodiments are possible. As such, the spirit and scope of the appended claims should not be limited to the description of the preferred embodiment contained therein. CLAIM: 1. A process for preparing silicon carbide foam, said process comprising: refluxing a solution of polycarbosilane in an organic solvent; adding an organic resin to the refluxed solution to obtain a reaction mixture; heating the reaction mixture for about 2 to 10 hours; distilling the heated reaction mixture to obtain a residue; and heating the residue at a temperature of about 200 to about 600°C for about 25 minutes to 35 minutes to obtain a preceramic foam, followed by further heating the preceramic foam at a temperature of about 900°C to about 1500°C at a heating rate in the range of 2°C to 10°C/min to obtain the silicon carbide foam. 2. The process for preparing silicon carbide foam as claimed in claim 1, said process comprising: refluxing a solution of polycarbosilane in an organic solvent; adding an organic resin to the refluxed solution to obtain a reaction mixture; heating the reaction mixture for about 2 to 10 hours; distilling the heated reaction mixture to obtain a residue; and heating the residue at a temperature of about 200 to about 600°C for about 25 minutes to 35 minutes to obtain a preceramic foam, followed by further heating the preceramic foam at a temperature of about 900°C to about 1500°C at a heating rate in the range of 2°C to 4°C/min for about 40 minutes to about 50 minutes to obtain the open cell silicon carbide foam. 3. The process for preparing siliconcarbide foam as claimed in claim 1, said process comprising: refluxing a solution of polycarbosilane in an organic solvent; adding an organic resin to the refluxed solution to obtain a reaction mixture; heating the reaction mixture for about 2 to 10 hours; distilling the heated reaction mixture to obtain a residue; and heating the residue at a temperature of about 200 to about 600°C for about 25 to 35 minutes to obtain a preceramic foam, followed by further heating the preceramic foam at a temperature of about 900°C to about 1500°C at a heating rate in the range of 5°C to 8°C/min for about 10 minutes to about 40 minutes to obtain the closed cell siliconcarbide foam. 4. The process as claimed in any of claim 1 to 3, wherein the polycarbosilane has a molecular weight of 500 to 2000. 5. The process as claimed in any of claim 1 to 3, wherein the organic solvent is selected from a group consisting of petroleum ether, benzene, toluene, xylene, dichloromethane, and terahydrofuran. 6. The process as claimed in any of claim 1 to 3, wherein the organic resin is selected from epoxy resin and acrylate resin. 7. The process as claimed in claim 6, wherein the acrylate resin is used along with Spiers catalyst. 8. The process as claimed in any of claim 1 to 3, wherein the heating of reaction mixture solution is carried out under inert atmosphere. 9. The process as claimed in any of claim 1 to 3, wherein the heating of residue is carried out at a rate of 2°C to 50°C/min. 10. Siliconcarbide foam as prepared from the process of any of claims 1 to 9. 11. The silicon carbide foam as claimed in claim 10, wherein the silicon carbide ceramic foam has a bulk density in the range of 0.01 to 0.5 g/cc. 12. The silicon carbide foam as claimed in claim 10 for use as a thermal shock absorber, sound proofing, fire protection, volume burners and solar receivers. |
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| Patent Number | 279307 | ||||||||||||||||||
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| Indian Patent Application Number | 792/DEL/2010 | ||||||||||||||||||
| PG Journal Number | 03/2017 | ||||||||||||||||||
| Publication Date | 20-Jan-2017 | ||||||||||||||||||
| Grant Date | 18-Jan-2017 | ||||||||||||||||||
| Date of Filing | 31-Mar-2010 | ||||||||||||||||||
| Name of Patentee | DIRECTOR GENERAL, DEFENCE RESEARCH & DEVELOPMENT ORGANISATION | ||||||||||||||||||
| Applicant Address | MINISTRY OF DEFENCE, GOVT. OF INDIA, ROOM NO.348, B-WING, DRDO BHAWAN RAJAJI MARG, NEW DELHI-110011, INDIA | ||||||||||||||||||
Inventors:
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| PCT International Classification Number | B01D39/20; | ||||||||||||||||||
| PCT International Application Number | N/A | ||||||||||||||||||
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