Powder Carbon Gas - Solid Reaction Preparation Of Silicon Carbide Ceramics

Reaction-bonded silicon carbide (RBSC) has high thermal conductivity, low CTE and high specific stiffness, which make it a promising mirror material, especially for applications such as space-borne optical systems. In the thesis, the SiC ceramic for mirror substrate is fabricated from carbon powder by reactive sintering process, which is molded into raw body previously. The studies are focused on the effects of molding process and the ratio of the powder components upon the microstructure and properties of RBSC.Through the study of effects of the powder components and molding process on microstructure and properties of RBSC, the optimized process is selected. When the ratio of powder components is C:PF:Si=45%:20%:35% and using heat molding process, RBSC has better synthetic properties as follow: volume density 2.999g/cm³, flexural strength 409.6MPa, modulus 259.1GPa and thermal conductivity 120. 9 W ? m^-1 ? K^-1.According to the analysis, the main components of RBSC are β -SiC, Si and a little of C. However, α -SiC will appear when it is added to the initial ingredients. In the process of the formation of the RBSC's microstructure, silicon steam coagulates in the green body by capillary coagulate phenomenon and reacts with carbon powder.The porosity of the green body plays a key role in the reactive sintering process, which determines the components, microstructure and properties of RBSC. In order to obtain RBSC with uniform microstructure and better properties, a best porosity is in existence.