Synthèse de l'andradite par réaction à l'état solide à la pression atmosphérique. Transformation pseudowollastonite → wollastonite

The garnet andradite, Ca₃Fe₂Si₃O₁₂, was obtained at 1 020° C and atmospheric pressure by sintering a mixture of calcium silicate, CaSiO₃. and hematite. In the range 1 100°-1 140° C, less garnet was formed, and at temperatures higher than 1 140°C the presence of andradite was not observed. As andradite decomposes at 1 157° C, the phenomenon was explained by the non-reactivity of the high form of CaSiO₃ (pseudowollastonite) with Fe₂O₃. The promoting effect of Fe₂O₃ on the transformation of pseudowollastonite into wollastonite was observed during this study.