Crystallization of Mica from Glasses with Composition of Lead-fluorphlogopite

Abstract

The glass samples having the composition of K_1-2nPb_nMg₃AlSi₃O₁₀F₂ (n=0.1-0.5) were prepared by melting of PbO, SiO₂, MgO, MgF₂, K₂SiF₆ and K₂CO₃ at 1350°-1450°C. Clear and cloudy glasses were obtained from the melts with composition of n>0.3 and of n<0.2, respectively. The crystallization of mica from the glasses at 600°-1100°C was investigated by use of DTA, electron microscopy and X-ray diffraction techniques. In the DTA curves, exothermic peaks due to crystallization of mica phase appeared at about 700°C, and shifted towards slightly higher temperature as the n value increased. From the changes in X-ray diffraction intensity of mica with annealing temperature and time, it is deduced that the growth rate of mica crystals in the direction of c-axis is lower than that in the other directions. Lattice constants of mica crystallized from the glasses with composition of Pb_0.5Mg₃AlSi₃O₁₀F₂ were as follows:
a=5.31₃Å, b=9.18₄Å, c=9.95₁Å, β=101°20′
The c was remarkably decreased with an increase in the n value.