Si/SiC optical coatings for C/SiC composites via gel-casting and gas silicon infiltration: Effects of carbon black content

The dense Si/SiC coatings are fabricated by means of gel-casting (GC) and gas silicon infiltration (GSI) for the first time, using carbon black and α-SiC as raw materials. The influences of the carbon black content on the properties of the coating samples have been investigated. Results show that, with the increase of the carbon black content, the viscosity of the slurry increase dramatically, the density and the porosity are closer to theoretical results, leading to the higher density after GSI. And the β-SiC content increases as well as the Si content decreases, resulting in the increase of the mechanical and the thermal matching properties. It is also worth noting that the roughness of the coating of φ160 mm comes to 0.57 nm after polished. The study highlights that the combined application of the GC and the GSI processes can produce high-quality Si/SiC coatings that are suitable in the space optical applications.