Synthesis of Sialon and Ferrosilicon Multiphase Materials from Coal Gasification Slag and Iron Ore Tailing via Carbothermal Reduction Nitridation
摘要
Sialon ceramics have been widely used in high-temperature industrial fields such as thermocouple protective casing pipes, impellers, bearings, and degassing shafts and rotors for molten aluminum liquids due to its excellent mechanical, thermal, chemical stability, and low coefficient of thermal expansion. Aiming to achieve the goal of “zero waste” and the resource utilization of two kinds of solid waste, the coal gasification slag and iron ore tailing are used to synthesize O′/β/Ca-α-Sialon and ferrosilicon multiphase materials via carbothermal reduction nitridation (CRN). Controlling the content of Fe2O3 and nitridation temperature is an effective way to tailor the phase composition of synthesized Sialon and the ratio of Sialon to ferrosilicon. When Fe2O3 is less than 13.2 wt pct, it is more favorable for the synthesis of high-content β-Sialon or Ca-α-Sialon multiphase materials. The transformation of O′-Sialon to β-Sialon is accelerated at 1450 °C in the presence of Fe (iron), and the conversion from O′/β-Sialon to Ca-α-Sialon at 1500 °C is promoted as well. During CRN process, catalyst Fe initially forms Fe–Si liquid phase, which will promote the continuous diffusion of Al, O, and N to the surface of the spheres. It is observed that O′-Sialon firstly forms rod-like and plate-like grains on the surface of the raw grain, then transforms into nitrogen-rich columnar β-Sialon, and finally develops into the typical hexagonal prismatic Ca-α-Sialon.