Abstract: The invention is concerned with preparation of dense ceramics, in particular silicon carbide.Silicon carbide is a useful structural material but difficulties of densifying by sintering have in the past created problems in the production of silicon carbide components. It is however known to use boron and carbon as additives to assist densification by sintering. In this invention a further improvement in densification is effected by carrying out such sintering in a carbon-containing reducing atmosphere such as a methane containing atmosphere. Surface silica which inhibits densification is thereby removed but without removing fine carbon.

Abstract: The open pores of a porous silicon nitride body are partly or wholly filled with and adherent, refractory filler comprising cordierite or a borosilicate glass, thereby to reduce the gas-permeability of the body. A body, so treated, may, for example, have application as a recuperator.