The synthesis of α- and β-sialon from fly-ash

The paper discusses carbothermal production of both ß-sialon or Ca-a-sialon from fly-ash. The progress of the reaction was followed by XRD and electron microscopy. During the formation of ß-sialon the z-value gradually decreases to the final value. Iron impurities in the fly-ash, which catalyse the reaction have a negative influence on the mechanical strength, but can be removed afterwards by electromagnetic separation or chemical leaching. From fly-ash with a high initial calcium concentration one can prepare Ca-a-sialon at 1500 °C. Initially ß-sialon is formed, but this is rapidly converted to the a-phase.