Synthesis of Al₂O₃–SiC from kyanite precursor

Carbothermal reduction of kyanite, a natural aluminosilicate with high alumina content (Al₂O₃ · SiO₂), was used as a way to synthesize SiC–Al₂O₃ powder. Carbon black was mixed with the mineral precursor in a molar ratio of (C/SiO₂) = 5.5. The Carbothermal reaction sequence was studied in the temperature range 1260–1550 °C. Completion of the reaction at 1550 °C gave β–SiC-whiskers and α–Al₂O₃ particles as final products. From observations, the impurities contained in the mineral precursor behave as catalysts for the vapor–liquid–solid whisker growth mechanism. When the specific surface area of the starting carbon was increased from 330 to 996 m²/g, the carbothermal reaction rate increased but the morphology of the SiC-whiskers became very irregular. This study aimed to identify the main reaction conditions for obtaining a favorable morphology of the synthesized powder for elaborating Al₂O₃–SiC-whisker composite materials by using low cost starting materials and a relatively simple in situ synthesis route in comparison to the conventional way of separately preparing the phases SiC (whiskers) and Al₂O₃ before elaborating composites.