Silicon-Nitrogen Polymers and Ceramics Derived from Reactions of Dichlorosilane, H2SiCl2

Abstract

Silicon nitride, Si3N4, is of great current interest as a material of high thermal and oxidative stability and high hardness for ceramics, electronic and other applications. 1 Silicon nitride may be prepared by the reaction of elemental silicon with gaseous nitrogen or ammonia at elevated temperatures. Ceramic bodies may be produced directly (reaction sintering) or, alternatively, Si3N4 powder may be obtained first and converted to solid bodies by subsequent processing. 1 Chemical vapor synthesis also has served in the preparation of Si3N4 (films or powders), using high temperature reactions of ammonia with chlorosilanes (H2SiC2, HSiC3, SiC14) for this purpose. 2 Solution-phase chemistry also has found application in the synthesis of Si3N4. In particular, the reaction of ammonia with silicon tetrachloride, carried out in an inert solvent, has been the subject of investigations by a number of groups of workers.3 This ammonolysis reaction initially produces a solid, insoluble, cross- linked product, [Si(NH)2]x, together with four molar equivalents of ammonium chloride. Pyrolysis of this product at 1250°C gives α-Si3N4, but the fact that [Si(NH)2]x is a nonvolatile, insoluble solid brings some limitations to its practical applications.