Influence of heating rate and mechanical activation on the reaction between kaolin and aluminium powder

Abstract

In this work, the effect of heating rate and mechanical activation on the reaction of kaolin and aluminium powder was investigated. A batch comprised of 89.5 wt% kaolin and 10.5 wt% aluminium powders was mixed and milled in a planetary ball-mill for 1, 5, 10, 20 and 40 h. The mixture powders were heat treated with a heating rate of 5, 10, 15, 20, 30 and 40 °C/min, respectively. After milling for 20 and 40 h, the results showed the formation of free silicon, quartz and nacrite (Al2Si2(OH)4) at room temperature. The kaolinite dehydroxylation, aluminium oxidation and the θ- to α-Al2O3 transformations are highly affected by heating rate and mechanical activation. As compared with the smallest heating rate, the mixtures heated with faster heating rate show the disappearance of the peak corresponding to the oxidation of aluminium and the appearance of a second peak corresponding to the formation of α-Al2O3. The intensity of the last peak increases with increasing of the heating rate and milled at lower milling time. The effects of heating rate in the reaction of kaolin and aluminium powder are attributed to the amorphization of kaolinite, the diffusion of Al3+ to form an amorphous alumina layer on the particle surface and the generation of microcracks at the particle surface of aluminium powder.