BETA-SiAlON HOLLOW SPHERES PREPARED FROM COAL FLY ASH MICROSPHERES

Beta-SiAlON hollow spheres were prepared by the carbothermal reduction method, using coal fly ash and active carbon in various proportions (20% less than theoretical addition, theoretical addition and 10% excess theoretical addition) as starting materials, placing in an alumina crucible in a high temperature nitriding furnace after mixing well, and holding at 1300, 1350, 1400, 1450 and 1500 C for 6 h. The effect of temperature, particle size of the microspheres, and addition of active carbon on the phase composition and microstructure of the nitrided products were studied by XRD and SEM. The results show that the nitridation reaction starts at 1300 C; excess active carbon is necessary to form beta-SiAlON hollow spheres, and the particle size is the most important factor affecting their formation; at 1500 C, when the active carbon is 10% in excess, the beta-SiAlON hollow spheres, prepared using fly ash with a particle size > 100 micron, have a rough surface, high hollowness and low density.