The effects of mechanical activation on the sintering of mullite produced from kaolin and aluminum powder

In this work, the effects of mechanical activation on the sintering of mullite produced from kaolin and aluminum metal powder was investigated. Because of the higher content of silica in kaolin it is necessary to add alumina or aluminum oxide in order to obtain the stoichiometric mullite composition. After mechanical treatment for different milling time, the reactions and phase transformations between kaolin and aluminum metal powder were studied using thermal techniques (DTA/TG), X-ray diffraction (XRD) and infrared spectroscopy (FT-IR). The heated samples at different temperatures were studied by XRD, apparent density, open porosity measurements and SEM analysis. The results showed the formation of silicon, quartz and small amount of nacrite after 40 h of milling at room temperature. All mixture powders milled for different time showed the formation of several alumina transitions during heat treatment. The formation of alumina transitions, α-alumina, cristobalite crystallization of and mullite (primary and secondary) formation was affected by ball milling time. The mixture of kaolin and aluminum milled for 40 h show the formation of kyanite (Al2SiO5) at 1300 °C. The mechanical treatment enhances the formation and sintering of mullite.