Effect of Mechanical Activation on the Synthesis of Ba-Celsian and Sr-Celsian using Precursor Mixtures Containing Coal Fly Ash

摘要

BaAl_2Si_2O_8 and SrAl_2Si_2O_8 were synthesized by solid-state reaction of stoichiometric mixtures of either BaCO_3 or SrCO_3 with coal fly ash and Al_2O_3. The mixtures were mechanically activated in an attrition mill for up to 12 h and then reaction-sintered at 900-1300 °C, aiming to promote the formation of BaAl_2Si_2O_8 and SrAl_2Si_2O_8 as well as the conversion from their hexagonal (Hexacelsian) into their monoclinic (Celsian) forms, which is associated with improved mechanical properties in the sintered materials. Especially in the case of SrAl_2Si_2O_8, the formation of Celsian was favored at relatively low sintering temperatures by increasing milling time. Although only the SrAl_2Si_2O_8 composition was fully converted into Celsian, the Hexacelsian to Celsian conversions obtained for the mechanically-activated BaAl_2Si_2O_8 composition were significantly higher than those previously reported in the literature for this compound. This could be attributed to the use of coal fly ash as raw material, which contains mineralizers that promote the mentioned conversion.