A particle preform was designed and prepared by conglomerating and cold-pressed process, which was condensed by chemical vapor infiltration （CVI） process to fabricate silicon nitride particles reinforced silicon nit...A particle preform was designed and prepared by conglomerating and cold-pressed process, which was condensed by chemical vapor infiltration （CVI） process to fabricate silicon nitride particles reinforced silicon nitride composites. The conglomerations are of almost sphericity after conglomerated. There are large pores among the conglomerations and small pores within themselves in the preform according to the design and the test of pore size distribution. The pore size of the preform is characterized by a double-peak distribution. The pore size distribution is influenced by conglomeration size. Large pores among the conglomerations still exist after infiltrated Si3N4 matrix. The conglomerations, however, are very compact. The CVI Si3N4 looks like cauliflowershaped structure. 2008 University of Science and Technology Beijing. All rights reserved.展开更多
With liquid petrol gas(LPG)as carbon source,carbon felt as porous perform and hydrogen as diluent,C/C composites were fast fabricated by using a multi-physics field chemical vapor infiltration(MFCVI)process in a self-...With liquid petrol gas(LPG)as carbon source,carbon felt as porous perform and hydrogen as diluent,C/C composites were fast fabricated by using a multi-physics field chemical vapor infiltration(MFCVI)process in a self-made furnace.A set of orthogonal experiments were carried out to optimize parameters in terms of indices of density and graphitization degree.The results show the optimal indices can be achieved under the conditions of temperature 650℃,LPGconcentration 80%,gas flux 60 mL/s, total pressure 20 kPa,infiltration time 15 h.The verification experiment proves the effectiveness of the orthogonal experiments. Under the optimal conditions,the graphitization degree of 75%and bulk density of 1.69 g/cm are achieved with a uniform density distribution.At the same time,a new structure is obtained.展开更多
A finite difference (FD) model is proposed to simulate the chemical vapor infiltration (CVI) processes for fabrication of carbon carbon composites. With iterative operation of many discrete values, the FD based mode...A finite difference (FD) model is proposed to simulate the chemical vapor infiltration (CVI) processes for fabrication of carbon carbon composites. With iterative operation of many discrete values, the FD based model can be used to describe and analyze the real, continuous densification processing quantitatively. Many densification characteristics of carbon carbon composites can be predicated by modeling. The prediction results can be compared with experiment value directly, which shows its good ability for practical application. Special verification experiments are designed with Iso thermal CVI processing and slender cylindroid unidirectional C/C composites are prepared to verify the accuracy of the model. The modeling curve of density versus infiltration time is in good agreement with experiment values. According to modeling analysis, the effects of infiltration temperature and fiber volume fraction on densification are also discussed preliminarily. The conclusion obtained also accords with experiment or results in other literature, further approving the accuracy of the FD based model.展开更多
基金the National Natural Science Foundation of China(No.50672076 and 50642039)the Key Foundation of National Natural Science in China(No.90405015)+1 种基金the National Young Elitist Foundation in China(No.50425208)the Doctorate Foundation of Northwestern Polytechnical University(No.CX200505).
文摘A particle preform was designed and prepared by conglomerating and cold-pressed process, which was condensed by chemical vapor infiltration （CVI） process to fabricate silicon nitride particles reinforced silicon nitride composites. The conglomerations are of almost sphericity after conglomerated. There are large pores among the conglomerations and small pores within themselves in the preform according to the design and the test of pore size distribution. The pore size of the preform is characterized by a double-peak distribution. The pore size distribution is influenced by conglomeration size. Large pores among the conglomerations still exist after infiltrated Si3N4 matrix. The conglomerations, however, are very compact. The CVI Si3N4 looks like cauliflowershaped structure. 2008 University of Science and Technology Beijing. All rights reserved.
基金Projects(5080211550721003)supported by the National Natural Science Foundation of ChinaProject(2006CB600901)supported by the National Basic Research Program of China
文摘With liquid petrol gas(LPG)as carbon source,carbon felt as porous perform and hydrogen as diluent,C/C composites were fast fabricated by using a multi-physics field chemical vapor infiltration(MFCVI)process in a self-made furnace.A set of orthogonal experiments were carried out to optimize parameters in terms of indices of density and graphitization degree.The results show the optimal indices can be achieved under the conditions of temperature 650℃,LPGconcentration 80%,gas flux 60 mL/s, total pressure 20 kPa,infiltration time 15 h.The verification experiment proves the effectiveness of the orthogonal experiments. Under the optimal conditions,the graphitization degree of 75%and bulk density of 1.69 g/cm are achieved with a uniform density distribution.At the same time,a new structure is obtained.
文摘A finite difference (FD) model is proposed to simulate the chemical vapor infiltration (CVI) processes for fabrication of carbon carbon composites. With iterative operation of many discrete values, the FD based model can be used to describe and analyze the real, continuous densification processing quantitatively. Many densification characteristics of carbon carbon composites can be predicated by modeling. The prediction results can be compared with experiment value directly, which shows its good ability for practical application. Special verification experiments are designed with Iso thermal CVI processing and slender cylindroid unidirectional C/C composites are prepared to verify the accuracy of the model. The modeling curve of density versus infiltration time is in good agreement with experiment values. According to modeling analysis, the effects of infiltration temperature and fiber volume fraction on densification are also discussed preliminarily. The conclusion obtained also accords with experiment or results in other literature, further approving the accuracy of the FD based model.
