Formation of Al 2O 3–SiC powder from andalusite and carbon

Abstract

Al 2O 3–SiC powder has been formed by carbothermal reduction of andalusite, an aluminosilicate mineral (Al 2O 3·SiO 2). The andalusite precursor was mixed to carbon black in a molar ratio (C/SiO 2)=5.5. Phase evolution was studied in the temperature range 1260–1550°C. SiC grows in-situ mainly in the form of whiskers. Some whiskers have globules at their tip, indicating that impurities present in the mineral precursor are involved in the vapour–liquid–solid (VLS) whisker growth mechanism. Pure oxides mixed with carbon black and doped with known concentrations of metallic impurities were heat treated and the transformations occurring in these systems were compared with those of andalusite-carbon system. The present work is aimed at studying the reaction conditions for obtaining a powder with favourable characteristics to elaborate Al 2O 3–SiC-whisker composites by using raw materials of large availability and a simple in-situ synthesis method.