Optimization of the nucleating agent content for the obtaining of transparent fluormica glass-ceramics

Abstract

The crystallization behaviours, mechanical and optical properties of fluormica glass-ceramic system without and with P2O5 as nucleating agent are studied. The crystallization mechanism of fluor-phlogopite (KMg3(Si3AlO10)F2) without P2O5 oxide represented one-dimensional surface crystallization with a fixed number of nuclei, and with the addition of P2O5, the mechanism tends to two-dimensional bulk crystallization with a constant nucleation rate being the most predominant phase, forsterite crystals (Mg2SiO4). The base glasses had the spinodal phase separation, which coarsened considerably by increasing P2O5 content. P2O5 had a strong influence on the microstructure and morphology of this type of glass-ceramic. The addition of small amount of P2O5 (1.0 mol%) to these glass-ceramic changed the microstructure from dendritic growth having leaf-like feature to a flower-like morphology of the crystal phase. Glass-ceramic without P2O5 produces yellowish to colourless transparent glass-ceramic, and with the incorporation of the P2O5 (1.0 mol%), which has been found the optimum to obtain transparent glass-ceramics, the transmittance is still about 85%. As the P2O5 content increased to 3.0 mol%, besides fluor-phlogopite mica, forsterite also precipitates, the size of the crystals increase, their distributions turned to be broad due to the change of the crystallization mechanism and the transparency of glass-ceramic consequently decreases.