CO-PYROLYSIS OF HYDROCARBONS AND SIET4 FOR THE SYNTHESIS OF GRADUATED SIXC1-X CERAMIC THIN-FILMS BY CHEMICAL-VAPOR-DEPOSITION

The thermal decomposition of hydrocarbons has been investigated under particular conditions in a low-pressure chemical vapour deposition reactor in order to select suitable carbon sources for the preparation of carbon-rich or graduated SixC1-x layers. Growth of pyrolitic carbon thin films (pyro-C) starts at ca. 1050 K and only above 1273 K using CH5Pri and CH4, respectively. The microstructure of the pyro-C layers is more dependent on the deposition temperature than on the nature of hydrocarbons. Their co-pyrolysis with SiEt4 used as SiC precursor has been achieved in the temperature range 1050-1250 K. As expected, the film composition does not change significantly at 1173 K using CH4 as an additional C source. By contrast, the C content of the films deposited by co-pyrolysis of SiEt4 and C6H5Pri increases continuously from 0.48 to 1 by increasing the mole fraction ratio x(C6H5Pri)/[x(C6H5Pri) +x(SiEt4)] from 0 to 1. Multilayers and compositional gradient layers can be prepared by discrete or continuous changes of the gas-phase composition, respectively. These films were successfully used as interphase in ceramic-ceramic composite materials to weaken the fibre/matrix bond and to improve their ductility.