Production of shaped articles of homogeneous mixtures of silicon carbide and nitride

while foams of silicon carbide can be used very advantageously as a temperature-resistant and corrosionresistant insulating material and filter material or catalyst support. Pipes, crucibles, bricks or the like of these mixtures are suitable for use as high temperature materials because of their good chemical resistance.

Silicon carbide continuous filaments can be manufactured in accordance with a known process by exposing a carbon filament, manufactured according to conventional processes, to a silicon tetrachloride gas atmosphere at 800 1,200C (U.S. Pat. No. 3,433,725). According to a further known process, silicon carbide continuous filaments are obtained by coating a thin tungsten filament with silicon carbide, which is formed on the tungsten surface, kept at 1,200 to 1,300C, by pyrolysis of methyldichlorosilane (F. Galasso, et al., Appl. Phys. Lett. 9 (1966) 37). The disadvantage of these processes is that relatively thick silicon carbide fibers result which are difficult to handle, and their high manufacturing cost prevents a broad application.

Shaped articles such as, for example, pipes, crucibles or bricks can be manufactured according to known processes by sintering pulverulent silicon carbide, with addition of silicon powder, in appropriate molds, in most cases with the use of high pressures and temperatures, in the presence of nitrogen. In these cases, the silicon nitride formed acts as a sintering aid.

It is furthermore known to manufacture silicon carbide coatings on suitable shaped articles by pyrolysis of a mixture of slicon tetrachloride, toluene and hydrogen (K. Moers, Z. anorg. allg. Chem. 198 (1931) 243).

Foams of silicon carbide can be manufactured according to the process of U.S. Pat. No. 3,100,688, by reacting a mixture of finely divided silicon dust and carbon dust with dilute hydrofluoroic acid and heating the foam thereby formed, after drying, to a temperature of between l,400 and 2,200C under an inert gas.

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