2005 Volume 113 Issue 1322 Pages 647-653
Surface structures of seven different commercial Si3N4 powders were investigated by X-ray photoelectron spectroscopy (XPS). The evaluated powders were produced by three different methods: diimide precipitation, carbothermal reduction and nitridation of silicon using different nitriding media with final treatments. The XPS spectra of all as received powders show Si2p, C1s, N1s and O1s signals after 0, 5 and 10 s etching priods. Tetrahedral structures Si-XYZW with different atoms (Si; H; N; O) or groups (NH; NH2; OH) in XYZ and W, from here after substituted by them, were observed for all as received commercial Si3N4 powders. For five out of the seven Si3N4 powders, the two main tetrahedra present on the most outer surface layer are Si-SiSiN(OH), and tetrahedra containing O; Si-O(NNN; SiSiH; SiNN; NNO). The two powders produced by nitridation of silicon with HF acid washing in the final treatment present Si-SiSiN(NH2) and tetrahedra containing OH; Si-SiN(Si; N) (OH). The powder produced by carbothermal reduction process using NH3 (g) presents the highest fraction of O containing tetrahedra. For all powders after 5 and 10 s etching periods, the main structure changed to NH2; Si-SiN(H; Si)(NH2) and NH groups containing configurations Si-SiN(Si; N)(NH), respectively. The surface of Si3N4 powders of any production method does not have structure close to SiO2, Si2N2O or an intermediate between them as commonly accepted.
