| Glass ceramics with the characteristers both glass and ceramic has been applied in many fields due to its predominant performances. Lithium aluminum silicate (LAS) glass ceramic is one of the most valuable glass ceramic systems and becomes an indispensable material because of its low expansion, high heat resistance and excellent mechanical properties. At present, the production cost and energy consumption are too high for LAS glass ceramic and enhancing its performance are too difficult, which restrict its application markets. How to resolve these problems has been one of imperative problems.On the basis of present states of glass ceramics, especially LAS glass ceramic, fluoride was added into LAS glass for the required structure and performance of glass ceramic material. The crystallization mechanism, structure and performance of glasses containing fluoride and free fluoride were studied and compared. The suitable heat-treatment parameters were established for improving the structure and preporties of glass ceramics and deceasing the energy comsumption and production cost. The researches were benefical for the actual production of LAS glass ceramic materials.The effect of fluoride on the crystallization mechanism of LAS glass had been analyzed by DTA and crystallinity (fraction crystallized) analyisis. The results showed that free energy of crystallization decreased from 276kJ/mol to 226kJ/mol when fluoride was added into basic glass; on the other hand, the mechanism of crystallization was different during temperature rise, the crystallization was controlled by grain forming during initial phase and by ion diffusion during last high-temperature stage.According to the crystallization mechanism, the phase separation, nucleation and crystallization of LAS glass containing fluoride and free fluoride were analytically studied by TEM (Transmission Electron Microscope), DTA (Differential Thermal Analysis), XRD (X-ray Diffraction), SEM (Scanning Electron Microscope). The results showed that added fluoride could decrease crystallization temperature of LAS glass from 870℃ to 760℃. The suitable heat-treatment parameters of glass containing fluoride were nucleation at 660℃ for 1h and crystallization at 760℃ for 4hrs, and for glass containing free fluoride those werenucleation at 660 for lh and crystallization at 870°C for 4hrs.On aboved suitable parameters, the grain of LAS glass ceramics showed spheric structure, the grain size of glass ceramics containing free fluoride was larger with 200nm of grain size than that of glass ceramics containing fluoride with 50-150nm of grain size. The addition of fluoride weakens the structure of SiCh, which is benefical for tranfering of ions in glass and improving nucleation and growth of grain phase.Physical and chemical performances of LAS glass ceramics containing fluoride and free fluoride were studied. The results showed that mechanical strength of glass ceramic containing fluoride was higher than that of glass ceramic containing free fluoride, and average bending strength of glass ceramic containing fluoride was 137.1MPa and 111.9MPa for glass ceramics containing free fluoride. Resistance to sudden heating or chilling of glass ceramic containing fluoride was better that of glass ceramic containing free fluoride and elastic modulus of glass ceramic containing fluoride (784.4MPa) was lower than that of glass ceramics containing free fluoride (852.0MPa). In the range of 30~500, average thermal expension coefficient of glass ceramic containing fluoride (7.8229x0~7 K-1) was lower than that of glass ceramics containing free fluoride (14.3704X0-7 K-1). Density of glass ceramic containing fluoride was more than that of glass ceramics containing free fluoride, but its water-resisting property was lower that of glass ceramics containing free fluoride. It is obvious that glass ceramics containing fluoride had better comprehensive performances and lower crystallization temperature than those of glass ceramics containing free fluoride, which can decrease the production cost and energy consumpt...
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