| In order to overcome the major drawbacks of the forming thick ceramic film coating by Chemical Vapor Deposition (CVD), e.g., brittleness and severe limitation of deposition rate, an enhanced CVD vapor deposition method (ECVD) is proposed. This method is based on the idea of taking advantage of Chemical Vapor Deposition in a highly loaded aerosol (ultrafine ceramic powers) flow system. Under appropriate physical conditions of deposition and chemistry, the aerosol particles are deposited towards the surface of the susceptor and the CVD process "glues" them in a solid film.; Two sets of chemical vapor deposition instruments, a 500 watts hydrogen-chlorine flame reactor and a 14 kW dc plasma reactor, were designed and developed to produce ultrafine carbides and refractory metal powders. Analysis of X-ray diffraction, TEM, SEM, particle size measurement, element analyzer, and oxygen analyzer showed that the typical size of the particles was 0.03-0.1{dollar}mu m{dollar} with a narrow size distribution and spherical or polygonal shapes. The metal impurities present were less than 500 ppm. Oxygen content was below 8% in the metallic powders, whereas it was below 1.2% in the silicon carbide powder.; A process for fabrication of silicon carbide tubes by thermal deposition of {dollar}CHsb3SiClsb3{dollar} in a hydrogen atmosphere was presented. A method of carbon coating was used to eliminate the cracks induced by the difference in thermal expansion of the SiC coating and the graphite substrate. Silicon carbide tubing with uniform crystallinity and free of microcracks was developed. The results showed that the density of the silicon carbide material was 3.125{dollar}g/cmsp3{dollar} (97% theoretical density), and the fracture toughness and hardness were {dollar}Ksb{lcub}c{rcub} = 1.95MNmsp{lcub}-3/2{rcub}{dollar} and {dollar}Hsb{lcub}v{rcub} = 13.3GNmsp{lcub}-2{rcub}{dollar}, respectively.; In order to transport the ceramic powders into the CVD film reactor, fluidization and entrainment characteristics of nine micron size ceramic powders have been investigated in a small diameter transport column.; Based on the above work, an enhanced CVD system was developed to deposit ceramic powder and silicon carbide film alternatively on a graphite substrate. The deposition rate of silicon carbide film was increased. The silicon carbide matrix composite film produced by the enhanced CVD method exhibited better mechanical properties, namely, more than twice the fracture toughness and hardness as the films produced by the standard CVD method. It was confirmed that the ECVD method is an effective way to improve CVD ceramic film deposition. |
