Sodium Magnesium Aluminate Silicon System Glass Microcrystalline Mechanism,

A quick-crystallized glass-ceramic of sodium-magnesium-alumina-silicate system was prepared at the basis of the glass composed of 20Na2O, 4CaO,12MgO, 22A12O3, 4TiO2, 38SiO2(wt % ). The kinetics, thermodynamics, microstructure morphology and relationship of phase separation, phase separation nucleation and crystallization of glass treated under different conditions had been studied and the effects of compositions on the properties of glass were investigated by differential thermal analysis (DTA), X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), electron probe microanalysis(EPMA) and energy spectrum analysis(EDX) respectively. The size and distribution of phase separation nucleation treated under differential nucleation processing temperature were measured. The crystallization and phase separation activation energy were calculated by modified kissinger method. Results indicated as follow:The effects of chemical compositions indicate: the transformation temperature Tg, the temperature of phase separation peak TS and crystallization peak Tc decreased as the content of sodium increased. The temperature of TC reaches its maximum point when the content of magnesia is 10% and decreases promptly to the lowest point when the content is 14%. In the meantime, the temperature of phase separation peak increased but the temperature of Tg decreased as the content of magnesia increased. The temperature of Tg increased when the content exceed 14%.The maximum temperature ranges of nucleation of phase separation and crystallization are near 923K. The crystallization nucleation related with the phase separation nucleation closely. The thermal treatments in nucleation temperature range have an influence on the exothermic behavior of phase separation and crystallization. The reduction of system free energy caused by nucleation corresponds to the change of phase separation peak area and temperature. It can be expressed as:G = (HC0-HCi)-TN (SC0-SCi)The exothermic effect of phase separation of glass measured by DTA was the process that micro spherical phase separation formed and accumulated around the nuclei quickly, which occurred in the earlier growth stage of phase separation within small temperature range and was the important character of quick phase separation and crystallization. With the result of XRD, we verified that there was no microcrystalline phase during the process of phase separation.The microstructure of initial growth stage of phase separation depends on the number of small nuclei, i.e. the number of growth and accumulation center. When the nuclei were few, the big spherical phases formed (the diameter is five micron), in which a lot of small nuclei accumulated together in a direction towards their center at the temperature of phase separation. When the glass sample was heated through the nucleation temperature range with a slow heating-up speed, a lot of small nuclei can be formed and provide many organic center. The micro spherical phase developed and accumulated quickly during the early stage of phase separation growth, and formed evenly distribution in the fine texture of the glass. But in the middle and final stage of the phase separation, a lot of homogeneous distributed micro spherical phase accumulated again and formed bigger area of phase separation construction (outside diameter of phase separation is 8~25um). Above indicated that, the different nucleation processes have not changed the character of the quick phase separation. The content of the irregular bigger drop phase approached to pyrope.It showed that the crystallization and phase separation mechanics of the glass was the nucleation-and-growth transformation and the crystallization is bulk crystallization. The activation energies of phase separation and crystallization were calculated by the modified Kissinger method, about 310.445 KJ/mol and 249.26 KJ/mol respectively.Using the aluminum hydroxide as the reference, we calibrated the phase separation exothermal enthalpy of the quenched and nucleation treated glass, ca...