LAUSR

Abstract Thermal and mechanical activation methods for crystallization of amorphous nano silica particles were investigated. Thermal crystallization of amorphous SiO 2(np) was studied by differential scanning calorimetry as well as heating the amorphous particles under argon atmosphere. The results showed that crystallization of amorphous SiO 2(np) started at temperatures above 700 °C and the synthesized crystalline silica had an average size of about 200 nm. Furthermore, 50 wt%Al-50 wt% amorphous SiO 2(np) mixtures were mechanically activated at ambient conditions. The results showed that crystallization of amorphous SiO 2(np) started after about 7.5 h of ball milling and reached its peak at 60 h. Longer milling times resulted in re-amorphization of part of the crystallized silica. The average size of crystalline SiO 2(np) synthesized by mechanical activation was about 30 nm. A diffusion induced mechanism for crystallization of the amorphous nano silica, based on diffusion of aluminum atoms assisted by mechanical activation, was also proposed and discussed.