Effects of processing parameters on in situ synthesis of β-Sialon/ZrN/ZrO2 from fly ash and zircon

Abstract

β-Sialon(Si4Al2O2N6)/ZrN/ZrO2 ceramic powder was synthesised by an in situ carbothermal reduction–nitridation (CRN) process using fly ash, zircon and active carbon as raw materials. The effects of processing parameters on the phase composition and microstructure of the products were investigated by X-ray diffraction and scanning electronic microscope. The formation process of β-Sialon/ZrN/ZrO2 ceramic powder was also discussed. Increasing carbon content in a sample, reaction temperature and soaking time all could promote the CRN reaction and benefit the formation of β-Sialon and ZrN. The β-Sialon/ZrN/ZrO2 ceramic powder could be fabricated successfully at 1450°C for 2 h, then continually at 1550°C for 4 h while heating the sample with the zircon/fly ash/active carbon mass ratio of 49∶100∶100. The as received β-Sialon particles existed as flaky and their average grain sizes were about 2–3 μm, and the average grain size of ZrN and ZrO2 reached 1–2 μm. The formation process of β-Sialon/ZrN/ZrO2 ceramic powder included the decomposition of zircon and mullite, the formation processes of O’-Sialon (Si1·83Al0·17O1·17N1·83), X-Sialon (Si3Al6O12N2), β-Sialon and ZrN as well as the conversion processes of X-Sialon and O’-Sialon to β-Sialon.