FORMATION OF ORGANOSILICON COMPOUNDS 115 - THE APPLICABILITY AS PRECURSORS FOR BETA-SIC OF CARBOSILANES RESULTING FROM THE GAS-PHASE PYROLYSIS OF METHYLSILANES

The thermal properties of polycarbosilanes from the gas phase pyrolysi s of SiMe(4), Me(3)SiCl, Me(2)SiCl(2) and the polymeric (Me(2)Si-CH2)( n) has been investigated. They decompose above 400 degrees C to form v olatile methylsilanes, H-2, CH4, viscous carbosilanes and insoluble gl assy products via condensation reactions, The ceramic yield is between 10 and 20 wt.% at about 900 degrees C and falls to only a few weight per cent when heating is continued to 1000 degrees C. The gas phase py rolysis of Me(2)SiH(2) at 650 degrees C produces plastic, meltable pol ycarbosilanes (PCS). Tempering the compounds to 900 degrees C gives a ceramic residue in 85% yield with Si:C:H 1:1.2:0.4, Heating this resid ue under thermal gravimetry (TG) conditions to 1500 degrees C (argon a tmosphere) results in a further weight loss of 0.7% and formation of b eta-SiC. Silicon carbide is also formed when the PCS from Me(2)SiH(2) (Si:C:H 1:1.5:2.5) are heated to 1400 degrees C, with a weight loss of 16.3% under nitrogen and one of 42% in vacuum.