Abstract: A process of producing relatively large, dense, free-standing silicon carbide articles by chemical vapor deposition is enabled by the provision of specially designed isolation devices. These devices segregate silicon carbide deposits on the intended portions of substrates, thereby alleviating the need to fracture heavy silicon carbide deposits in order to remove, or otherwise move, the substrate, with the heavy deposit thereon, from the deposition furnace. The isolation devices enable the use of more efficient vertically extended vacuum furnaces. The isolation devices also enable the commercial production of relatively dense, large, thin-walled, silicon carbide shells.

Abstract: An improved chemical vapor deposition (CVD) process which is capable of providing low-scatter water-clear zinc sulfide bulk material is described. The improved method also minimizes bowing, or induced curvature, in the product bulk material. The product zinc sulfide material can be processed into thicker windows and optical devices than was possible with the articles produced by the previous CVD process. The improved process provides for a controlled gradual initial ramping up of the deposition rate and a controlled initial ramping down of the substrate temperature.

Abstract: Articles having at least one precision replicated surface are formed by chemical vapor deposition on a substrate surface which has been precision shaped and finished as the converse of the desired precision surface of the article. The substrate surface is provided with a thin release coating which adheres to the substrate when the article is removed thereby allowing the substrate to be reused. The method is particularly advantageous for forming the interior surfaces of domes and asymmetrical optical surfaces of zinc sulfide.