Influence of mechanical activation on the synthesis of Sr-Celsian employing a precursor mixture containing coal fly ash

Abstract

Strontium aluminosilicate, SrAl2Si2O8 (SAS), was synthesized by a solid state reaction using coal fly ash (CFA) as main raw material. A precursor mixture of SrCO3, CFA and Al2O3 was mechanically-activated for times of up to 12 h using an attrition mill, and subsequently sintered at temperatures of 900-1300 °C. The CFA and the mechanical activation were employed with the aim to promote the transformation from the hexagonal (Sr-Hexacelsian) into the monoclinic (Sr-Celsian) polymorphic form of SAS, since the latter phase is associated with better physical and mechanical properties but the former tends to be the first one to appear. The mean particle size, the crystallite size and the temperature at the end of the curve of weight loss (Tf) decreased, while the specific surface area and the degree of amorphization increased, with increasing milling time. Samples milled for at least 4 h and then sintered at 1100 °C achieved full transformation into Sr-Celsian. The same result was obtained for sintering temperatures higher than 1100 °C, independently of milling time. An increment in both the milling time and the sintering temperature allowed us to improve the densification and the mechanical properties of the synthesized materials.