Research on Li_2O-Al_2O_3-SiO_2-B_2O_3 System Low Expansion Glass-ceramics

Abstract: glass-ceramics (LAS) as one of the most important system glass-ceramics has some excellent properties such as low thermal expansion coefficient, transparence, tolerance for high temperature and heat impulsion etc. Therefore, it attracts many attentions recently. In this paper, the influence of heat treatment and composition on structure and properties of the LASB system glass-ceramics were investigated by DTA, XRD and SEM. And relationships among composition, heat-treatments, micro-structure and properties were studied to attain some results about reasonable composition and heat-treatments and high-performance glass-ceramic substrate.Firstly, the influence of various heat treatment temperatures on structure and properties of the glass-ceramics were investigated simultaneously. The results show that the transparency property of glass-ceramics was enhanced with the increasing of A12O3 content. The results also show that the lower temperature of heat treatment takes advantage to form β-quartz solid solution and β-quartz solid solution is transformed into p-spodumene solid solution with the increasing of the heat treatment temperature, which lead to decrease in the property of transparency and increase in the thermal expansion coefficient.Secondly, the influence of heat treatment system on the thermal expansion coefficient of the LASB system glass- ceramics was investigated. The better heat treatment system was achieved by the analysis of cross experiment to each factor of the heat treatment system. The better heat treatment system was nucleation temperature 670 ℃, nucleation time 90 min; crystal temperature 760 ℃, crystal time 120 min. The order of importance of relevant factors is: crystal temperature > nucleation time>nucleation time>crystal time.In succession, the proper composition of base glass was selected. The influence of changing content of B2O3 based on the proper composition and various heat treatment temperatures on structure and properties of the glass-ceramics were investigated. The results show that the forming property of base glass was enhanced with the increase of B2O3 content. But the transparency property of glass-ceramics becomes worse with the increase of B2O3 content. When B2O3 content exceeds 3 %, glass-ceramics begins to appear phenomenon of various crystal phases. Thermal expansion coefficient of glass-ceramics is lower than the base glass. The tolerance bending intensity and the rigidity also were improved.Finally, according to the above experience, the proper composition of base glass was selected. When TiO2+ZrO2 is a constant, the influence of changing rate of TiO2/ZrO2 based on the proper composition and various heat treatment temperatures on structure and properties of theglass-ceramics were investigated. And the results demonstrate that transformation temperature and crystal temperature are smaller when the rate of TiO2/ZrO2 is 1. The temperature that P-quartz solid solution is transformed into p-spodumene solid solution is increased to 910℃. In this experiment, glass-ceramics samples of preparation has rather perfect crystal phase of p-quartz solid solution, which makes tolerance for heat impulsion improve obviously. The optimum temperature of tolerance for heat impulsion is 659.1 ℃ and the thermal expansion coefficient is 1.15×10~(-7) K~(-1) (25—400℃) …
Key words: LASB system glass-ceramics; thermal expansion coefficient; heat treatments

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