CARBONITRIDING OF ANDALUSITE - PHASES INVOLVED AND REACTION-MECHANISM

Carbonitriding reactions of natural aluminosilicates produce phases of the Si-Al-O-N system and polytypes of beta'-sialons. The products obt ained in the carbonitriding reactions depend not only on the raw mater ial but also on the reaction conditions, in this work the carbonitridi ng of andalusite (Al2O3 . SiO2) was studied. The reactions were carrie d out on a mixture of andalusite and carbon black at 1623-1923 K. The reaction time ranged from zero to 180 min under N-2 flow. The evolutio n of crystalline phases was followed through X-ray diffraction analysi s. Silicon carbide and X-phase appeared as intermediate phases. beta'- sialon, polytype sialons and alpha-Al2O3 were the final phases of the reaction. A reaction mechanism is proposed. Crystalline phases depend on the temperature and on the weight loss in the reacted samples.