Towards continuous processes for the synthesis of precursors of amorphous Si/B/N/C ceramics

Abstract

The development of a process for the continuous synthesis of Cl₃SiNMeBCl₂ (DMTA) as a single-source precursor of highly durable Si/B/N/C ceramics is reported. The process is based on a series of gas phase reactions starting from silicon tetrachloride and methylamine. Cl₃SiNHMe (TSMA), which is initially formed, is subsequently reacted with BCl₃ to yield DMTA as a colorless, highly air-sensitive liquid. Amine hydrochloride byproducts are removed by filtration through ceramic filters. DMTA crystallizes in the monoclinic system, space groupP2₁/m, with a = 709.96(13) pm, b = 685.61(12) pm, c = 897.28(16) pm, and Z = 2. Polymerization of DMTA by aminolysis in n-hexane at −78 °C releases a polyborosilazane, SiBN_2.4C_2.5H_8.8, which upon thermolysis releases amorphous SiBN_2.3C_1.7 ceramic in 56% yield. The latter resists thermal degradation by crystallization in Ar atmosphere up to at least 1700 °C.