Crystal formation in modified fluor-miserite Kx(Ca, Ce)5-xSi8O22F2 glasses

Different ratios of K2O/CaO were investigated in a Kx(Ca,Ce)5-xSi8O22F2 fluor-miserite glass composition to find their effect on crystallization process. Xonotlite, tokkoite, fluorite and cristobalite were developed in all crystallized glasses; however, miserite was only identified in Ce-containing samples. Increase of K2O/CaO ratio, in Ce-free sample, enhanced the formation of tokkoite K2Ca4Si7O17(OH,F)2, and reduced the contents of xonotlite Ca6Si6O17(OH,F)2 and fluorite CaF2. Rietveld evaluation on XRD spectra allowed the quantification of phase percentages. On the other hand, in Ce-containing samples, an increase of K2O/CaO ratio promotes the formation of miserite crystallized with or without cerium in the structure. The cerium containing miserite lattice parameter were also evaluated. The microstructure of Ce-free glass–ceramics was relatively coarse and characterized by presence interlocked flakes, rods; however, it became unpronounced in the sample of highest K2O/CaO ratio. In Ce-containing glass-ceramics, irregular fine growths were spread as nano–size in cryptocrystalline groundmass, such fineness increase with increasing K2O/CaO ratio. The CTE values of the present glasses and the corresponding glass-ceramics varied from 10.305 to 11.053 and from 7.524 to 9.840 x 10-6 °C-1 respectively. The CTE of Ce-free glass-ceramics was lower than Ce-containing ones. Densities of the glass-ceramic samples varied from 2.652 to 2.856 g/cm3 and the samples containing miserite show larger densities.