Abstract: A process is disclosed for making vitreous silica crucibles of exceptional high quality for use in the growing of a silicon crystal from molten silicon. The crucibles are formed from fine particles of high purity fused silica by slip casting or other suitable process, are dried and fired to provide a rigid porous body, and are thereafter sintered to a high density, preferably to the transparent state. The invention solves the problem of spalling, blistering and cracking during crystal growing and the resulting contamination of the molten silicon, which has long plagued the industry, by eliminating water from the fused silica particles before the porous body is sintered to the transparent state. Said body is thoroughly dried in a vacuum furnace at a high temperature and at a sub-atmospheric pressure low enough to remove the chemically bound water which cannot be removed by heat alone.

Abstract: Apparatus is disclosed for automated mass production of precision transparent silica glass products in accordance with a unique process in which slip-cast fused silica articles are rapidly heated and sintered in a vacuum or in a helium or hydrogen atmosphere at high temperatures, such as 2950.degree. to 3150.degree.F. A heated graphite susceptor shaped to conform to the outer surface of the fused silica article is automatically moved between a cooling zone and an induction furnace chamber which is opened momentarily to admit the article. The furnace and the graphite susceptor are designed to cause the trapped gases in the article to move radially outwardly and to effect rapid heating so as to avoid substantial devitrification during sintering.