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.