NTSIC (new technology silicon carbide): evaluation of microstructure of high-strength reaction-sintered silicon carbide for optical mirror

Abstract

Silicon carbide (SiC) is the most advantageous as the material of various telescope mirrors, because of high stiffness, low thermal expansion, high thermal conductivity, low density and excellent environmental stability. Newly developed high-strength reaction-sintered SiC, which has two to three times higher strength than a conventional sintered SiC, is one of the most promising candidates in applications such as lightweight substrates of optical mirrors, due to being fully dense and having small sintering shrinkage (±1 %), and low sintering temperature. In this study, in order to improve nano-scale homogeneity of the high-strength reaction-sintered SiC, the microstructure of high-strength reaction-sintered SiC was investigated using scanning electron microscopy (SEM) and microscope type interferometer in comparison with the conventional sintered SiC. And also, the microstructure was investigated by focusing on the crystal structures and the interface of each crystal through transmission electron microscopy and X-ray diffraction analysis. As a result, it was the confirmed that the high-strength reaction-sintered SiC was fully dense in comparison with the conventional sintered SiC, and the finer-scale microstructure consisted of large particles (~1 μm in diameter) of α-SiC starting powder and small particles (<1 μm in diameter) of β-SiC synthesized during the reaction-sintering (Si+C→SiC) with residual silicon (Si) filling the remaining pores. In addition, the β-SiC synthesized during the reaction-sintering was identified as the cubic type (3C), and the α-SiC of the starting powder was identified as the hexagonal type (6H).