Solubility, reactivity and nucleation effect of Cr2O3 in the CaO-MgO-Al2O3-SiO2 glassy system
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The effect of Cr2O3 on some anorthite-diopside glass-ceramics has been investigated up to amounts of 5 mol%. The solubility in the glassy compositions analysed is total for the oxide, but for amounts higher than 0.5 mol%, an insoluble spinel form, MgCr2O4, precipitates. Ultraviolet-visible spectroscopy has proved to be the most sensitive technique to the presence of Cr(III) in a crystalline spinel site, followed by X-ray diffraction and scanning electron microscopy observations. Electron spin resonance and X-ray photoelectron spectroscopy 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, with a large favour towards the pyroxene.
KeywordsElectron Spin Resonance Electron Spin Scanning Electron Microscopy Observation Electron Microscopy Observation Spectroscopy Technique
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