Carbothermal reduction of kaolinite under nitrogen atmosphere

Preliminary studies on the carbothermal reduction of kaolinite (Al2O3.2SiO2.2H2O) in a static nitrogen gas pressure of 0.15 MPa are reported. The effect of various reaction parameters, e.g. temperature of the reaction (1550–1700°C), mole ratios of carbon to silica (4.5–9.0) in the reactant mixture and nature and source of carbon, e.g. activated charcoal (sp. surface area, 1000 m2/gm) and carbon black (sp. surface area, 300 m2/gm) on the carbothermal reduction have been investigated. It is observed that mullite, silicon oxy-nitride and X-sialon phases are present at low temperatures, while β′-sialons, β-SiC, Al2O3 and AlN are present at high temperatures. Activated charcoal is more reactive than carbon black and the reaction rate is more for higher mole ratios of carbon.