Study On The Producing Technics And Thermal Properties Of Glass-ceramics In Mgo-al₂o₃-sio₂ System

Glass-ceramic is polycrystalline material with the glass and the crystal coexistent.The cordierite based MgO-Al₂O₃-SiO₂ of glass-ceramic is a kind of fine traditional microwave dielectric material with low dielectric loss factor,excellent thermal stability and high mechanical intension,used in micro-electronic,spaceflight,navigating fields.The research and application of MgO-Al₂O₃-SiO₂ of glass-ceramic are very active all along.If glass-ceramic has a high thermal shock resistance,its coefficient of thermal expansion must be low as much as possible so that the temperature stress of material dropped to minimum.Therefore the study of coefficient of thermal expansion of glass-ceramic is important significance.The main phase of MgO-Al₂O₃-SiO₂ of glass-ceramic is cordierite.Coefficient of thermal expansion of cordierite is anisotropic.With the temperature rising,c-axis direction is expansion but a-axis direction is contraction .If crystal distributed uniformity,expansion of material could obtain zero volume expansion.In this paper,it reviewed the development,preparation technology and application of glass-ceramic.It was studied that how thermal properties,mechanical properties and chemical properties of cordierite based glass-ceramic were influenced by type and quantity of composite nucleus and heat treatment process.DTA had determined characteristic temperature of the glass;the phase compositions of the glass-ceramics were analyzed by XRD,and its microstructures were observed by SEM.In the experiment,MgO-Al₂O₃-SiO₂ of glass-ceramic was prepared by fusing law,TiO₂/ZrO₂ as nucleation agents.Experiments showed that the precipitation began from the surface.The value of TiO₂:ZrO₂ as too big or too small was not advantageous for the glass crystallization;when the value of TiO₂:ZrO₂ was between 1.75 and 24,the glass crystallization was better.By the analysis of the results,the most superior heat treatment was the nuclear temperature for 750℃,the nuclear time for 1h,the crystallization temperature for 1050℃,the crystallization time for 1.5h and heating rate of 10℃/min.At this point ,the coefficient of thermal expansion of the glass-ceramic was much better.