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Preparation and Properties of Low-melting Bi-systems Sealing Glass-ceramic

Author: ZhangWenWen
Tutor: GuYingYing
School: Central South University
Course: Chemistry
Keywords: sealing glass sol-gel method Bi2O3-B2O3-SiO2system doping glass structure thermal properties
CLC: TQ171.73
Type: Master's thesis
Year: 2013
Downloads: 36
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Abstract


Due to its environmental-friendly compositions and special chemical properties, the low temperature lead-free sealing glass material has been a hot area of research. With advantages in the field of seal, it attracts the masses more and more attention. A series precursor of Bi2O3system, alkaline-earth compounds doped system (MgO, CaO, SrO, BaO) and other compounds doped system (A12O3, ZnO, La2O3) were successfully prepared by sol-gel method, and then by means of heat treating, the low-melting sealing glass-ceramic were obtained. XRD、 were employed to characterize properties of the sealing glass-ceramic, such as, the optimum process conditions, phase composition, crystallinity and characteristic temperature. Results show that:The optimum reaction conditions for synthesing sealing glass precursor powder by sol-gel method are:Glass-ceramics formula design: Bi2O3-B2O3-SiO2-MO with molar ratio Bi2O3:B2O3:SiO2:MO=4:2:3:1; Colloid solution pH<1; Gelation time:about72hours; Dry shrinkage of gel temperature:70℃.In the process of preparing sealing glass, experimental results show that the corrosion situation of corundum crucible gets obvious improvement, basically achieving zera corrosion. After soaking by the aqua regia, crucible can be reused except the doping La2O3system, which is still eroded strongly.As the calcination temperature rising, the development trend of parent glass color goes deeper gradually as a whole. The glass surface has no stripes and defects, which presents a homogeneously translucent glass state. Along with the sintering temperature of micro crystallization increasing, the surface of sample appears obvious glass luster with the increasing glass phase. Because of the growing enhanced internal stress, the sample also gradually begins to deform, changing with the volume shrinkage and the shape more roundness.The sealing glass doping with MgO and AI2O3quaternary systems mainly present noncrystalline type state. Respectively doping with CaO, SrO and BaO quaternary glass systems and ternary systems show a new status of microcrystalline, which is similar to the crystal phase of Pb4Cl204(JCPDS No.75-0943). The optimal temperature as a whole for crystallization process is650℃, and the heat preservation time should be4h or so. Among them, the crystallization quantity is highest with doped BaO glass-ceramics system.Raman spectrum display:with the glass systems studied in this experiment, Bi3+ions were constituted in the glass network with the form of [BiO6] octahedral and [BiO3] triangles as the basic structural unit. Analogously, the boron-oxygon network was composed of [BO3] triangles and [BO4] tetrahedral units. The doped compunds existed as outer body in the glass network.DSC results reveal that the initial transformation and crystallization temperature (Tg, Tx) of most doping systems were much lower than the tertiary system, except the doping CaO system and BaO system. Compared with the other doping systems, BaO has not very apparent function of reducing the Tg of the sealing glass.In different parent glass system, it was the smallest of the doping A12O3system about the thermal expansion coefficient during the temperature range from25℃to400℃. The behavior of doping alkali earth metal compounds might cause the increasing trend of thermal expansion coefficient. As the temperature rising, the thermal expansion coefficient of each doped parent glass system increased in various degrees with an upward trend.

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