Solubility, reactivity and nucleation effect of Cr2O3 in the CaO-MgO-Al2O3-SiO2 glassy system

The effect of Cr2O3 in amounts up to 5 mol% on some anorthite-diopside glass-ceramics has been investigated. The solubility in the glassy compositions analysed is for the total oxide, but for amounts higher than 0.5 mol%, an insoluble spinel form, MgCr2O4, precipitates. UV spectroscopy has proved to be the technique most sensitive to the presence of Cr(III) in a crystalline spinel site, followed by XRD and SEM observations. ESR and XPS techniques excluded any oxidation state, other than Cr3+. The influence of the transition cation on glass nucleation is that of an increasing bulk effect with chromium, and thus chromium-spinel, content. The magnesium content affects spinel formation, while heat treatments up to 1100 C do not. The spinel formation influences the anorthite-diopside ratio in the glass-ceramic, favouring pyroxene formation. 23 refs.