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Study On Sealing Glass-ceramic Of High Thermal Expansion Coefficient

Posted on:2013-08-19Degree:MasterType:Thesis
Country:ChinaCandidate:X L ZhouFull Text:PDF
GTID:2181330467464185Subject:Chemical processes
Abstract/Summary:PDF Full Text Request
Li2O-ZnO-SiO2glass-ceramics find widely applications in hermetic sealing to a variety of metals and alloys, not only because of they have low melting temperature and wide range of thermal expansion coefficients, but also because of some interesting basic properties as good mechanical properties, chemical stability and electrical insulation. These characteristics of the glass-ceramics depend on the properties of crystalline phase and glass phase they contain.Lithium zinc silicate glasses containing Li20-Zn0-SiO2-Na20-B203-BaO-P2O5with different BaO/(BaO+ZnO) ratios (0~0.226) were prepared by conventional melt and quench technique and subsequently converted into glass-ceramics. During the processing, two-step heat-treatments including nucleation and crystallization were adopted. And these parameters were determined by differential thermal analysis (DTA). The glass or glass-ceramics were investigated by means of crystallization ability test, DTA, X-ray diffraction (XRD), coefficient of thermal expansion (CTE), scanning electron microscopy (SEM) and chemical durability test. Results are as follows:all base glasses’ crystallization ability are large, and the glass-ceramics are low-melting glass-ceramics. XRD results were shown that Li3Zn0.5SiO4and Li2OZnSiO4were identified as major crystalline phases along with some cristobalite phase in the samples prepared without BaO, whereas the intensity of cristobalite in the samples with BaO is higher than that of counterpart samples without BaO. Furthermore, the intensity of Li3Zn0.5SiO4and Li2ZnSiO4crystalline phase significantly increased with the BaO/(BaO+ZnO) ratio, while the intensity of cristobalite phase decreased. Particularly for the glass ceramics obtained with BaO/(BaO+ZnO) ratio of0.075, cristobalite was detected as major crystalline phase. The CTE in the temperature range70-400℃increased from107×10-7to141×10-7℃-1, and the glass-ceramic has the largest CTE when BaO/(BaO+ZnO) ratio is0.075. The microstructure and crystalline phases were analyzed by SEM, and the grain size became bigger after the addition of BaO. The chemical durability was measured and the chemical durability increased with increase of BaO/(BaO+ZnO) ratio. was added in the above component, and another six glass-ceramics of different components were prepared and been investigated as means of above. In addition, the mol activation energies for crystallization was calculated by measuring the DTA peak of crystallization at different heating rates. Results shows that all the glass-ceramics are low-melting glass-ceramics, both their crystallization and melting temperature were decreased significantly by Sb2O3addition. XRD results were shown the intensity of cristobalite phase increased gradually with the Sb2O3content and the higher intensity were observed when the doping content was0.5~1.5g/100g. The CTE in the temperature range70~400℃increased from105.93×10-7to177.82×10-7℃-1, and the glass-ceramic has the largest CTE when Sb2O3addition was1g/100g. The mol activation energies for crystallization result was corresponded to the crystalline peak intensity and TEC value, and the values were lower when Sb2O3addition was0.5~1.5g/100g.
Keywords/Search Tags:Lithium zinc silicate glass, glass-ceramics, sealing, high thermal expansioncoefficient, activation energies for crystallization, chemical durability
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