Abstract
Silicon carbide (SiC) ceramic exhibits several outstanding properties, such as superior chemical and thermal stabilities, high radiation resistance and low thermal expansion, that qualify it as a prime candidate for space applications. Optical quality with surface figure accuracy of the order of 60 nm peak-to-valley (PV) and micro-roughness (root-mean-square, RMS) less than 2 nm is necessary for space optical applications. Sintered SiC (α-HCP) is inherently porous and challenging to make high-grade optics. Hence, it calls for a surface modification of the sintered SiC by means of a clad layer that has superior adhesion to the substrate and facilitates optical polishing. This paper describes a typical method of synthesis and characterization of a thick silicon coating on sintered SiC substrate, directly machinable to aspheric for optical telescope applications. Present approach describes the quantitative opto-mechanical characterization of silicon film over SiC by thermal spray coatings, eventually leading to its space flight-worthiness.
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