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Monoclinic (Celsian) and hexagonal (Hexacelsian) Ba 1 _ JC Sr JC Al 2 Si 2 0 8 solid solutions, where x = 0,0.25,0.375,0.5,0.75 or 1, were synthesized by using Coal Fly Ash (CFA) as main raw material, employing a simple one-step solid-state reaction process involving thermal treatment for 5 h at 850-1300 °C. Fully monoclinic Celsian was obtained at 1200 °C/5 h, for SrO contents of 0.25 < x < 0.75. However, an optimum SrO level of 0.25 < x < 0.375 was recommended for the stabilization of Celsian. These synthesis conditions represent a significant improvement over the higher temperatures, longer times and/or multi-step processes needed to obtain fully monoclinic Celsian, when other raw materials are used for this purpose, according to previous literature. These results were attributed to the role of the chemical and phase constitution of CFA as well as to a likely mineralizing effect of CaO and Ti0 2 present in it, which enhanced the Hexacelsian to Celsian conversion.

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