High-temperature instability of artificial cuprorivaite: a study using thermal analysis, X-ray powder diffractometry and polarized light microscopy

Abstract

CaCuSi${}_4$O${}_{10}$ powder was studied by differential scanning calorimetry and thermogravimetry methods in the range from room temperature to 1450${}^{\circ }$C at heating and cooling rates of 20${}^{\circ }$C/min. The process of decomposition of cuprorivaite, the composition and transformations of its decomposition products during successive heat treatments were also studied by powder X-ray diffraction and polarization optical microscopy techniques. It was found that CaCuSi${}_4$O${}_{10}$ starts to decompose by incongruent melting at a temperature of about 1020${}^{\circ }$C, with the minimum of the endothermic DSC peak associated with this process being at 1064.4${}^{\circ }$C. CaCuSi${}_4$O${}_{10}$ decomposes irreversibly and subsequent cyclic annealings up to a temperature of 1450${}^{\circ }$C at heating and cooling rates of 20${}^{\circ }$C/min do not cause its re-synthesis. CaCuSi${}_4$O${}_{10}$ transforms into a two-phase system consisting of acicular crystals of monoclinic tridymite fused with green glass with the composition CuO$-$Cu${}_2$O$-$CaO$-$SiO${}_2$, with the weight ratio of tridymite to glass being about $12:13$, as a result of two successive annealings up to the temperature of 1450${}^{\circ }$C.

30 pages, 10 figures, 2 tables