SiHx absorbance bands in Si3N4 powder surfaces analyzed by diffuse reflectance infrared fourier transform spectroscopy

Abstract

The SiHx stretching absorbance region (2300-2000 cm-1) of seven different commercial Si3N4 powders was investigated by diffused reflectance infrared Fourier transform (DRIFT) spectroscopy. The powders evaluated were produced by three different methods: diimide precipitation, carbothermal reduction and nitridation of silicon using different nitriding media and final treatments. SiH groups were detected in all powders. The results show the presence of H-SiXYZ tetrahedral units. XYZ can be different atoms or groups (Si, H, N, O, NH, NH2 or OH) that bond to the same silicon atom. The H-Si bands were classified considering the backboned atoms of the H-Si into four main tetrahedral by fixing the XY atoms and several possibilities for Z as follows: silicon-based; H-SiSiSi (Z=Si, NH, H or O), nitride-based; H-SiSiN (Z=NH2 or O), oxynitride-based; H-SiNO (Z=N, NH or NH2) and silica-based; H-SiOO (Z=NH2, OH, O or H) tetrahedral configurations. The proportions of these tetrahedral units are different for each powder. The powder produced by the carbothermal reduction process using N2 as nitriding media presents the largest fraction of H-Si groups linked to silica-based tetrahedral units. For the other six powders the largest fraction of H-Si groups is linked to silicon-based tetrahedral units.