Crystallization properties of magnesium aluminosilicate glass-ceramics with and without rare-earth oxides

Abstract

Transparent glass-ceramics were prepared in MgO–Al2O3–SiO2 (MAS) glass by two-step heat-treatments, and the effect of CeO2 and La2O3 on crystallization mechanism of MAS glass-ceramics was investigated. The micro-structure of the transparent glass-ceramic samples was studied by FE-SEM. Crystallization activation energy, E, and Avrami constants, n, were determined by DSC through Kissinger and Augis–Bennett methods. The crystallization mechanism of specimens without rare-earth oxides represents two-dimensional crystallization, and with the addition of CeO2 and La2O3, the mechanism tends to three-dimensional crystallization. After nucleation at 800°C for 4h and crystallized at 950°C for 1.5h, spinel crystals with the mean diameter ~20nm precipitated from matrix glass without rare-earth oxides, and the sample maintained the transparency over ~80% in visible light. The glass without rare-earth oxides showed the highest value of E (362.74kJ/mol) and the lowest value of n (2.09), which is corresponding to the precipitation of spinel. With the addition of CeO2 and La2O3, though the spinel is still the dominate crystal phase, the sizes increased and distributions turned to be broad. The over-growth of crystals leads the transmittance to decrease to ~30%.