Comparison of Si/C/N pre-ceramics obtained by laser pyrolysis or furnace thermolysis

This paper reports a comparison between two different methods used for the synthesis of amorphous Si/C/N pre-ceramics: the laser pyrolysis method, coupled with an aerosol generator, and thermolysis in a furnace in an inert gas atmosphere. The same precursor, liquid oligomethylvinylsilazane (OMVS, [−(CH3)Si(HCCH2)NH−]n) has been chosen to establish this comparison. Laser spray pyrolysis of OMVS produces nano-sized powder particles with a specific surface area of about 120 m2/g. The characteristics of the as-formed Si/C/N nanopowders (chemical composition, local order, structural evolution...) are compared to those of pre-ceramic samples obtained by thermolysis in a furnace (at 800 and 1050 °C). The amorphous network of the as-pyrolysed materials mainly consists of SiCxN4−x (x=0,1,2) units and amorphous or sp2-hybridized carbon. The carbon and hydrogen contents are higher in samples obtained by laser spray pyrolysis. Heat-treatment experiments at temperatures up to 1550 °C were performed to investigate the high temperature behaviour of the various samples. Decomposition was observed at about 1500 °C.