The Study On The GSO Transparent Glass Ceramics With Highly Crystallinity

Abstract:Based on the preparation theory and technical method for soda-lime-silica highly crystalline transparent glass ceramics, we made a attempt to prepare the GSO transparent glass ceramics with highly crystallinity. The precipitated targeted crystalline phase is the same or similar as the Gd2Si05(GSO) crystal. We studied the preparation, structure and characterization of the precursor glasses which were used to prepare the GSO transparent glass ceramics with highly crystallinity. Meanwhile, we also probed the devitrification and crystallization behavior of the precursor glasses with optimum formula. These studies will lay the foundation of the success in preparation of GSO transparent glass ceramics with highly crystallinity.The precursor glasses with designed compositions were melted by conventional melt quenching method and the optimum formula was determined. Its main composition is38Gd2O3-38SiO2-22B2O3-2Li2O (mol%),1wt%Sb2O3and CeCl3-7H2O in excess. By means of transmission electron microscopy (TEM) technique, Infrared (IR) and Raman spectroscopic techniques, we investigated the structure of glasses with compositions (100-2x)B2O3-(x)[SiO2-Gd2O3](x=27.5,30,32.5,35,37.5mol%) and the optimum formula belongs to this glass system. The results indicate that this glass system consists of unmixing borate-rich phase and silicate-rich phase with nanoscale and the crystalline phase with nanoscale also occur in these glasses. The glass with high Gd2O3concentration precipitates Gd4.67(SiO4)3O and the glass with high B2O3concentration precipitates GdBO3. The main crystalline phase precipiated from glasses after crystallization is transformed from GdBO3to Gd4.67(SiO4)3O. Gadolinium dissolves in borate-rich phase forming Gd-metalborate-like structure and the surplus gadolinium dissolves in silicate-rich phase creating non-bridging oxygen (NBO), which lead to Q2and Q3silicate units. Meanwhile, gadolinium cation clusters preferentially occur in borate-rich phase. When the content of Gd2O3is high (x≥37.5mol%), cation clusters also occur in silicate-rich phase. The content of NBOs attains maximum value in glass with x=32.5mol%. This glass sample has the lowest network polymerization, which complies well with the results of packing density measurement.The heat-treatment temperature schedules of nucleation and crystallization of precursor glass with the optimum formula were determined by Differential Scanning Calorimetry (DSC) and thermal expansion curve analyses. The devitrification and crystallization behavior of precursor glasses was studied through X-ray diffraction analysis (XRD), scanning electron microscope (SEM) technique, energy-dispersive spectrum (EDS) analysis etc.. The results show that the ladder temperature schedule is superior to isothermal temperature schedule in terms of preventing devitrification and expanding the stable region of glass; The precursor glass with optimum formula that nucleated at840℃for600min is easy to crystallize at lower temperature and hard to be devitrified; The main crystalline phase of precursor glass precipitated after heat treatment are apatite structure gadolinium silicate clusters whose morphology is snowflake or dendritic needle. Its chemical formula is Gd4.67(SiO4)30and some other elements such as B、Ce、Sb can solid solution into the main crystal phase. The distribution of the clusters is very uneven. The devitrification behavior of precursor glass after heat treatment is associated with both macroscopic phase separation and precipitation and growth of crystalline phase.