Crystallization behaviour of fluorphlogopite glass ceramics

Transparent fluorphlogopite based glasses were prepared using talc, glass s and and phosphate raw material. The effect of TiO2, ZrO2, phosphate or comb inations of either B2O3-phosphate or TiO2-ZrO2 on the crystallization of fl uorphlogopite Base glass was examined. X-ray diffraction analysis showed fo rmation of fluorphlogopite at 765 degreesC in the base glass. Addition of Z rO2 or 5 wt.% phosphate did not affect the monophase crystallization. Howev er when the amount of phosphate was increased to 10 wt. %, fluorapatite was crystallized together with fluorphlogopite. TiO2 and TiO2-ZrO2 addition en hance the formation of enstatite together with fluorphlogopite. Thermal tre atment of ZrO2-containing glasses was found to induce crystallization of fl uorphlogopite as a main phase. The addition of TiO2 alone or mixed with ZrO 2 catalyzed crystallization of enstatite and fluorphlogopite above 1000 deg reesC. SEM analysis showed that glasses containing fluorphlogopite acquired fine-grained microstructure at 650 - 765 degreesC. At higher temperature, 1000 degreesC, the crystal structure of fluorphlogopite was modified into i nterlocked flakes. Vicker's hardness values of the glass-ceramics increased in presence of enstatite (7358 MPa) and decreased in the presence of fluor apatite (4905 MPa). Addition of B2O3 decreased the density of glass to 2.63 4 g/cm(3) and lass-ceramic to 2.780 g/cm(3). Phosphate or ZrO2 additions sh owed a reverse effect (2.864 g/cm3). Thermal expansion coefficients of fluo rphlogopite glass-ceramic samples in temperature range 20 - 500 degreesC ch anged from 7.8 x 10(-6) degreesC(-1) in presence of fluorapatite to 9.2 X 1 0(-6) IC-1 in case of the dominance of enstatite.