Synthesis of Al2O3-SiC from kyanite precursor

Carbothermal reduction of kyanite, a natural aluminosilicate with high alum ina content (Al2O3 . SiO2), was used as a way to synthesize SiC-Al2O3 powde r. 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 tempera ture range 1260-1550 degreesC. Completion of the reaction at 1550 degreesC gave beta -SiC-whiskers and alpha -Al2O3 particles as final products. From observations, the impurities contained in the mineral precursor behave as c atalysts for the vapor-liquid-solid whisker growth mechanism. When the spec ific surface area of the starting carbon was increased from 330 to 996 m(2) /g, the carbothermal reaction rate increased but the morphology of the SiC- whiskers became very irregular. This study aimed to identify the main react ion conditions for obtaining a favorable morphology of the synthesized powd er for elaborating Al2O3-SiC-whisker composite materials by using low cost starting materials and a relatively simple in situ synthesis route in compa rison to the conventional way of separately preparing the phases SiC (whisk ers) and Al2O3 before elaborating composites.