Ultrafine SiC for Optical Mirrors

SiC has exceptionally high thermal conductivity and low linear expansion coefficient to resist thermal distortion, high elastic modulus to resist pressure and bowing distortion. It is lightweight and wear resistant. It also has excellent corrosion resistance and outstanding load bearing characteristics at elevated temperatures. Its hardness is only surpassed by diamond, CBN and boron carbide. As a result, SiC becomes a very attractive material in mirror optics applications. Commercially available SiC mirrors and substrates are produced either by chemical vapor deposition (CVD) or hot pressing technique. Although CVD SiC gives high optical performance, the primary limitation has been the unavailability of large monolithic pieces. In addition, CVD SiC mirrors are very expensive. The hot pressed SiC are relatively cheap, but it suffers from the problem of residual porosity which hinders its optical performance. In this Phase I SBIR program, MMI proposes to synthesize a high quality ultrafine SiC powder, with good sinterability, through a synergistic approach combining sol-gel technology and carbothermal reduction process. The SiC powder will be consolidated to full density by a UHPC system and the compact will then be polished to optical finish with surface roughness of less than 1 nm.