Mullite formation in the kaolinite-aluminum hydroxide system under different heat treatment regimes

Abstract

It is shown that the stages of formation of the primary mullite and the binding of the excess silica released from kaolinite by the introduction of additional aluminum oxide into the secondary mullite overlap. The effect of the heating rate of a mixture of kaolinite and bayerite Al(OH)3 on the yield of mullite was studied. It has been established that with an increase in the rate of temperature rise, the product yield increases (by ~10%), which may be due to the preservation of a significant number of defects in the lattices of substances. A variable temperature regime is proposed: slow rise (3 o C/min) to 550 °C, then rapid heating (10 o C/min, 550–950 °C) and 3 o C/min above 950 °C, which further increased mullite yield by ~15%. A rapid rise in temperature slowed down the processes of crystallization and defects healing in the structure of components, which means that they maintained their high reactivity.