In situ synthesis of Si2N2O/Si3N4 composite ceramics using polysilyloxycarbodiimide precursors

In situ synthesis of Si2N2O/Si3N4 composite ceramics was conducted via thermolysis of novel polysilyloxycarbodiimide ([SiOSi(NCN)3]n) precursors between 1000 and 1500 °C in nitrogen atmosphere. The relative structures of Si2N2O/Si3N4 composite ceramics were explained by the structural evolution observed by electron energy-loss spectroscopy but also by Fourier transform infrared and 29Si-NMR spectrometry. An amorphous single-phase Si2N2O ceramic with porous structure with pore size of 10–20 μm in diameter was obtained via a pyrolyzed process at 1000 °C. After heat-treatment at 1400 °C, a composite ceramic was obtained composed of 53.2 wt.% Si2N2O and 46.8 wt.% Si3N4 phases. The amount of Si2N2O phase in the composite ceramic decreased further after heat-treatment at 1500 °C and a crystalline product containing 12.8 wt.% Si2N2O and 87.2 wt.% Si3N4 phases was obtained. In addition, it is interesting that residual carbon in the ceramic composite nearly disappeared and no SiC phase was observed in the final Si2N2O/Si3N4 composite.