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Study On The Component, Structure, Properties And Float Mechanism Of Li2O-Al2O3-SiO2 Float Glass-ceramics

Posted on:2011-12-03Degree:DoctorType:Dissertation
Country:ChinaCandidate:J XieFull Text:PDF
GTID:1101330332979055Subject:Materials science
Abstract/Summary:PDF Full Text Request
Glass-ceramics accompany with glass and ceramics has many superior performance, is widely used in many fields. The lithium aluminum silicon (LAS) system is one of glass-ceramics which has low thermal expansion coefficient, high thermal stability and good mechanical properties has become an indispensable synthetic material. At present, LAS glass-ceramics is made of high temperature melting and high viscosity still exist, leads to the high production cost and energy" consumption, high-performance products not easy to attain, influence the market is applied. Therefore,on the basis of nucleation and crystallization, thermal properties and the mechanical properties of LAS glass-ceramics, to reduce the melting temperature and high viscosity of LAS glass-ceramics has great economic benefits and social value.The high viscosity and glass structure has the close relation, and glass structure was largely determined by the composition, so a series of formulas were designed on LAS system glass-ceramics, to study the relation with structure and properties of LAS-float glass-ceramics with'different dopant of MgO,BaO,Na2O/ZnO,P and F, at the same time corresponding LAS-system of glass-ceramics melting temperature and high viscosity to gain lower melting temperature and high viscosity system.In this paper, uing, XRD, SEM, DTA, thermal expansion, the flexural strength, high viscosity and Raman, spectroscopy, etc, to study the interaction and contacts between LAS system glass-ceramics composition,heat treatment technics, microstructure and properties. Based on the different quantity, MgO,BaO, Na2O/ ZnO,P and F to study of the structure and performance, and meet the requirements of molding float optimum proportion and heat treatment system, explore relevant issues of basic theories with practice,and combining production,achieve similar material research and guiding the development and application. Therefore,has the extremely vital significance.Finally, the conclusions are as follows: 1) MgO can reduce the tendency and crystallization rate, the crystallization of glass can effectively reduce the melting temperature, and adjust the molding temperature, glass-ceramics viscosity testing results can be obtained by the different MgO content of LAS:melting temperature of glass-ceramics roughly 1600 degrees Celsius, in actual operation near in 1520 degrees Celsius temperature, and has good melting performance and molding properties. X-ray diffraction analysis that the main crystalling phase are beta quartz, and with the increase of the MgO content, the diffraction peak increased in intensity, crystallization level unceasing enhancement. SEM results showed that with the increase of the content of MgO, the crystallization of glass-ceramics promoted, the main content of beta quartz unceasing increase, crystal size slightly increased. Because the intensity of beta quartz exceed the glass phase in glass-ceramic, when the content of MgO was lower than 2.0wt%, along with the increase of the content of MgO, porosity improved greatly and the flexural strength increases accordingly. When the content of MgO more than 2.0wt%, flexural strength increases first and then decreases. Expansion coefficient test results show:The coefficient of expansion of LAS glass-ceramics increased with the content of MgO increases. By the way, different content of MgO in LAS system glass-ceramics has better chemical stability, from the test results can be obtained with the increase of the content of MgO, resistance to water, acid and alkali have increased.2) With the increasing of BaO, transparency of glass-ceramics shows badly, but can promote LAS glass-ceramics crystal morphology change, the more stable crystal separate out. The thermal expansion coefficient of LAS glass-ceramics increased from 2.98×10-7/K to 6.27×10-7/K with the amount of BaO, and mechanical properties increased first then decreased. At 850℃crystallization of the sample showed better structure and performance. LASB system glass-ceramics structure and performance can be obtained:when BaO was 2.5 (wt)% and nucleation temperature at 750℃, crystallization temperature at 850℃,the LAS glass-ceramics products presents the best structure and properties.3) With the decreasing of Na2O/ZnO, the viscosity of maternal glass and the melting temperature decreasing. Melting temperature around 1500℃has good melting and mechanical properties. At the same time, along with the decrease of Na2O/ZnO, The content of crystal phase increased continuously and grain size minished, the main phase of LAS glass-ceramics change from beta spodumene into beta quartz:As Na2O/ZnO reduce, thermal expansion coefficients of maternal glass significantly reduce from 8.802×10-7K-1 to -0.536-7×10-7K-1,that is inflation into negative inflation. but the softening point temperature increasing. Comprehensive conclusion is:4) When increasing the content of F, P doped with the LAS glass-ceramics,crystal diffraction peaks and quantity of crystal gradually increasing, transparency reducing. Samples containing F on heat treatment system has good crystallization effect. Samples containing P on heat treatment system has good crystallization effect. With the increase of the content of doping, thermal expansion coefficient and softening temperature increased first and then decreased.Especially, the high temperature viscosity marked reduce during 1150-1450℃, which is do benefit for float forming technics.5) The results showed that the equilibrium-thickness of LAS glass containing nucleating agents was about 7.24~7.26mm. The equilibrium thickness of LAS glass excluding nucleating agents, was about 7.12-7.22mm. The equilibrium thickness of LAS glass thickness decreased slightly with temperature increasing.The thickness,of LAS glass containing nucleating agents reaching equilibrium needed 8~10min, about 4min for LAS glass. The surface tension and density of LAS glass, excluding nucleating agents increased linearly as the temperature decreased; which achieved a good polishing effect at 1250℃. The theoretical flatting time of LAS glass shortened with increasing temperature,which was about 31s at 1308.1℃(103.7dPa·s), approximately 101s at 1236.4℃(104.2dPa·s). In order to realize the float forming of LAS glass,the surface tension/viscosity ratio should be controlled within the range of 96 to 108 (10-5Ncm-1/dPa·s).
Keywords/Search Tags:LAS system, glass-ceramics, high temperature viscosity, thermal expansion coefficient, bending strength, float Mechanism
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