Silicon carbide (SiC) is a new type candidate material for large-scale lightweight space mirror. Its low thermal distortion, high stiffness, high optical quality, and its dimensional stability are better than other traditional optical substrate materials such as ULE, Zerodure, Beryllium (Be) and so on. In this paper, the lightweight silicon carbide space mirror blank was fabricated by reaction sintering. As a space born mirror material, silicon carbide must be an optical grade ceramic. So we prepared the silicon carbide green body with gel-casting method. Then some carbon materials were supplemented into the green body which will bring reaction-sintering with silicon in a vacuum furnace during 1500-1600℃, ultimately the reaction bonded silicon carbide was made. The diameter of SiC space mirror blank we have made is 680mm. If expanding the size of the vacuum furnace, bigger mirror blank can be obtained.. The test results show that the mechanical and thermal properties of RB-SiC are excellent with bending strength of 350MPa, fracture toughness of 4.1 MPa·m1/2 and coefficient of thermal expansion(CET) of 2.67×10-6/K. The surface roughness(RMS) could be better than 3nm.

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Curing and sintering of silicon carbide with phenolic resin and carbon produces materials that have the mechanical strength and environmental stability required for the largest telescope mirrors.

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