SILICON OXYCARBIDE GLASSES WITH LOW O/SI RATIO FROM ORGANOSILICON PRECURSORS

Organosilicon precursors with low O/Si ratios were obtained from dichlorovinylsilane, using hydrolysis and hydrosilylation reactions. The order in which these reactions are performed effects the nature of the residual groups and the texture of the precursors. The conversion to silicon oxycarbide glasses of these precursors was investigated using Si-29 solid-state NMR, elemental analysis and thermogravimetric analysis coupled to mass spectrometry. Redistribution reactions involving Si-O and Si-C bonds took place above 600 degrees C, leading to a random mixture of the five possible SiOxC4-x tetrahedra at 900 degrees C. The O/Si ratios in the glasses obtained were 1.14 +/- 0.05 and 1.29 +/- 0.05. These glasses were compositionally stable up to about 1350 degrees C, but NMR indicated that they slowly rearranged to a mixture of SiO2 and SiC. Above 1350-1400 degrees C, carbothermal reduction occured, leading to silicon carbide with loss of CO and SiO.