Control of Grain Size and Morphology of Fluor-phlogopite Crystals in the Solidification of a Melt

On the basis of a TTT diagram during solidification of a melt in the system SiO2-Al2O3-MgO-MgF2-K2O-B2O3, the effect of heat-treatment conditions on grain size, morphology and crystallization degree of fluor-phlogopite crystallized was discussed. By isothermal heat-treatment in the temperature range of 1253 to 1473 K, fluor-phlogopite as spherical grains was crystallized directly from a super cooled liquid. On the other hand, below 1253 K spinodal decomposition type phase separation occurred as a prelude to the crystallization sequence. Energy dispersive X-ray analysis suggested that the growth rate of fluor-phlogopite crystals was controlled by diffusion of Mg ions. A linear relationship between the spinodal wave length and the plate diameter of fluor-phlogopite platelets was obtained as a result of the crystallization occurred in a Mg-rich phase.