Formation of organosilicon compounds 115: The applicability as precursors for β-SiC of carbosilanes resulting from the gas phase pyrolysis of methylsilanes

Article abstract of DOI:10.1016/0022-328X(96)06237-7

The thermal properties of polycarbosilanes from the gas phase pyrolysis of SiMe₄, Me₃SiCl, Me₂SiCl₂ and the polymeric (Me₂Si-CH₂)_n has been investigated. They decompose above 400 °C to form volatile methylsilanes, H₂, CH₄, viscous carbosilanes and insoluble glassy products via condensation reactions. The ceramic yield is between 10 and 20 wt.% at about 900 °C and falls to only a few weight per cent when heating is continued to 1000 °C. The gas phase pyrolysis of Me₂SiH₂ at 650 °C produces plastic, meltable polycarbosilanes (PCS). Tempering the compounds to 900 °C gives a ceramic residue in 85% yield with Si:C:H 1:1.2:0.4. Heating this residue under thermal gravimetry (TG) conditions to 1500 °C (argon atmosphere) results in a further weight loss of 0.7% and formation of β-SiC. Silicon carbide is also formed when the PCS from Me₂SiH₂ (Si:C:H 1:1.5:2.5) are heated to 1400 °C, with a weight loss of 16.3% under nitrogen and one of 42% in vacuum.