Mass Spectrometric Study of Retarded Vaporization of Silicon Based Fibres: Origin of their Thermal Stability

Free vaporizations of SiO2/Si, SiC/C and Si3N4/Si mixtures are studied by high temperature mass spectrometry in order to understand compositional evolutions due to gas loss. Using a multiple effusion cell technique, evaporation coefficients that relate equilibrium pressures to real evaporation pressures are deduced for the main gaseous species. These coefficients are related to an entropy barrier existing when bonds in the compounds are ruptured at the interfaces SiO2/Si, SiC/C, and Si3N4/Si. (Author)