Preparation of Silicon Carbide from Organosilicon Gels: I, Synthesis and Characterization of Precursor Gels

Abstract

Polymeric organosilicon gel precursors to SiC have been prepared using trifunctional chloro and alkoxysilanes that contain both the Si and C necessary for SiC formation. Crosslinked gels having the ideal formula (RSiO{sub 1.5}){sub n} have been synthesized by a hydrolysis/condensation scheme for a series of saturated and unsaturated R groups. The starting gels have been characterized by elemental analysis and by a variety of spectroscopic and physical measurements including Fourier transform infrared spectroscopy, XRD, surface-area and pore-volume determination, and thermal gravimetric analysis. {sup 13}C and {sup 29}Si solid-state NMR analysis proved to be particularly powerful for characterizing these gels by showing the degree of crosslinking and the residual hydroxy/alkoxy content. Under an inert atmosphere, the gels decompose to produce an intimate mixture of C and SiO{sub 2} which can react to form SiC at higher temperatures. The pyrolysis of these gels to produce SiC is described in Part II.