Preparation of Silicon Carbide from Organosilicon Gels: II, Gel Pyrolysis and SiC Characterization

Abstract

The controlled pyrolysis of polymeric organosilicon gels has been investigated as a means of preparing high-purity, high-surface-area SiC powders. The preparation of the gels, which have the ideal formula (RSiO{sub 1.5}){sub n}, has been summarized in Part I. Part II will examine the decomposition behavior of the gels under an inert atmosphere. The pyrolysis products are best described as a partially crystalline, partially amorphous mixture of {beta}-SiC, SiO{sub 2}, and C. Surface area in excess of 600 m{sup 2}/g have been obtained for the as-fired products and in excess of 800 m{sup 2}/g for residues purified to remove excess C and/or SiO{sub 2}. The effect of the degree of unsaturation and the carbon chain length of the R group as well as the effect of crosslinking in the starting gel on the composition and the surface area of the products has been determined. The origin of the high surface area of the products has been identified and its implication on potential uses of these materials is discussed.