Reserches Of Equipment Design And Process Mechanics About CVD(CVI) Silica

Because of the high sintering temperature and resulting in the microstructural degradation of quartz fibers, 3D quartz composite fabricated by traditional method has been not satisfied with the high Mach aircrafts. SiO₂ film fabricated by chemical vapor deposition (CVD) at relatively low temperature has the same structure and performance like quartz. So CVI method is an important candidate to fabricate SiO₂ matrix composite reinforced by continuous quartz fibers.A set of CVD/CVI equipment was successfully designed and fabricated to investigate the mechanism and processs of CVD/CVI amorphous SiO₂. The equipment has four parts: vacuum system, gas supply system, reaction chamber and off gas treatment system. Useing the CVD/CVI equipment, the effects of the temperature and precursor content on the deposition rate of a CVD process and the infiltrative of a CVI process were investigated. Subsequently the appropriate precursors and optimized parameters were determined by analysising the phases, conposition and microstructures of the deposition products via XRD, EDS and SEM. The main results are as follows:(1) The equipment has accurate temperature control and vacuum control. The vacuum pump can work well more than 400 hours. The subsequent experiment indicated the equipment can meet the requirement.(2) Vinyl tirethoxy-silane is the ideal precursors for CVD/CVI of SiO₂. The CVD/CVI process is controlled by mass transport. Amorphous SiO₂ can be obtained in the range of 550⁷50℃ during the CVD/CVI process.(3) The results exhibited that Vinyl tirethoxy-silane has perfect infiltrative than tetraethoxysilane. 2D SiO₂/SiO₂ composite is fabricated by several times deposition, no evidence was found in interphase boundary, in the fracture many fibers was pulled out from the matrix, this is an ideal composite interface.(4) Amorphous SiO₂ prepared by CVI without oxygen gas has tittle carbon, sothe dielectric loss factor is very high. The product's dielectric loss factor reduced to 2 after heat oxidation treatment, which can meet the requirement of radome materials.