Crystallisation of cu-containing K-fluor-richterite (KNaCa(Mg,Cu)(5)Si8O22F2 glasses

Gradual substitutions of Cu for Mg in K-fluor-richterite glass-ceramics were investigated. Crystallisation of Cu free or Cu containing glasses gave K-fluor-richterite, enstatite, diopside forsterite, rodderite, tenorite, cuprite, fluorite and crystalline silica. Colour changes in the crystallised glasses, from blue to orange or dark brown with increasing copper indicates change of either valency or the position of copper in the glass-ceramic structure. Although the base and low Cu containing glass-ceramic samples had ultrafine microstructures, the high Cu containing ones had pronounced crystals in a cryptocrystalline matrix. Rounded long crystals were thought to be K-fluor-richterite whilst euhedral crystals were thought to be Cu oxide phases. EDS analysis showsed a gradual replacement of Cu2+ for Mg2+ in addition to, Cu+ and Ca2+ for Na+ in the crystallised K-fluor-richterite phase. The coefficient of thermal expansion was low in base or low Cu content glasses and was high in high Cu content ones. The coefficients of thermal expansion of the corresponding glass-ceramic samples were higher than their parent glasses. The Vicker's microhardness values of the glass-ceramic samples are higher than those of the corresponding glasses. The Vicker's microhardness values decrease as the Cu content increases in the glasses or as the Cu oxide phases increase in the glass-ceramic samples. The densities of both glass and glass-ceramic increase with increasing the Cu content or Cu oxide phases, respectively