Reaction pathways during the thermal conversion of polysiloxane precursors into oxycarbide ceramics

A detailed evaluation of the events that occur during the heating of organic–inorganic hybrid solids obtained by the sol–gel method has been established. The correlation of many characterization techniques, in particular TG/MS analysis associated with specific alkoxide structural units, has provided some explanations in terms of a set of mechanisms. l be shown that the residual SiOH and SiOEt, arising from incompletely hydrolyzed and condensed alkoxides, play an important part in the degradation of gel precursors. They undergo reactions with SiH in the temperature range 200–700 °C and with SiMe starting around 450 °C. ermal stability of SiMe is strongly linked to the nature and distribution of the other functional substituents (SiOH, SiH) present in the gels. The cleavage of SiMe may thus take place within a large temperature range varying from 450 °C to 1000 °C.