SOLUBILITY, REACTIVITY AND NUCLEATION EFFECT OF CR2O3 IN THE CAO-MGO-AL2O3-SIO2 GLASSY SYSTEM

The effect of Cr2O3 on some anorthite-diopside glass-ceramics has been investigated up to amounts of 5 mol%. The solubility in the glassy co mpositions analysed is total for the oxide, but for amounts higher tha n 0.5 mol%, an insoluble spinel form, MgCr2O4, precipitates. Ultraviol et-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. Electr on spin resonance and X-ray photoelectron spectroscopy techniques excl uded any oxidation state, other than Cr3+. The influence:of the transi tion cation on glass nucleation is that of an increasing bulk effect w ith chromium, and thus chromium-spinel, content. The magnesium content affects spinel formation, while heat treatments up to 1100 degrees C do not. The spinel formation influences the anorthite-diopside ratio i n the glass-ceramic, with a large favour towards the pyroxene.