Synthesis of a polycyclic silazane network and its evolution to silicon carbonitride glass

Abstract

Polysilazanes have been described as excellent polymeric precursors to amorphous silicon carbonitride (SiCN) glasses. In this work, the synthesis, thermal cross-linking and pyrolysis of a polycyclic silazane network precursor for a SiCN glass, were studied. This polymeric precursor was prepared by free radical polymerization of 1,3,5-trimethyl-1 ′,3 ′,5 ′-trivinylcyclotrisilazane, using dicumyl peroxide as radical initiator. The polymer-to-ceramic conversion was investigated by 29 Si and 13 C magic angle spinning nuclear magnetic resonance (MAS NMR) and infrared spectroscopies, X-ray diffraction and by simultaneous thermogravimetric and differential thermal analyses. Based on the results the polymeric precursor can be characterized as a polycyclic silazane network, containing aliphatic carbon segments produced by the vinyl polymerization. 29 Si and 13 C NMR data of this polymeric precursor heated at different temperatures indicated the occurrence of side-reactions in addition to the vinyl polymerization. The SiCN glass was obtained as an amorphous solid up to 1400 ° C . Above this temperature, the crystallization process of the ceramic product was promoted by rearrangement of the different Si sites in the amorphous network. Heat treatment at 1600 ° C , under N 2 atmosphere, produced a ceramic containing 85% silicon carbide (SiC) and 15% silicon nitride, determined by 29 Si MAS NMR in relation to the total silicon sites, and under argon atmosphere, SiC.