Research Of Crystallization And Properties On The Cordierite Based MAS Glass-ceramics

Glass-ceramics is an even material with glass and crystalline phases controlled by heat treatment with the accession of nucleation agents. It is a kind of inorganic mulriple material with a large proportion of tiny crystallites and a little glass phase remainder. The configuration and properties of glass-ceramics are different with ceramics and glass, its properties are decided by the chemical compose of the mineral and glass phases and their amounts, so it is a kind of special material which holds the characteristics of the ceramics and glass.The cordierite based MgO-Al2O3-SiO2 system glass-ceramics 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 system glass-ceramics are very active all along.In this paper, the development, classification, fabrication technology and application of glass-ceramics ( mainly about MgO-Al2O3-SiO2 system ) were systematically reviewed. A brown glass-ceramics of MgO-Al2O3-SiO2 system was prepared, TiO2 as nucleation agent. The major crystalline phases are MAT and a-Cordierite.The phase compositions of the glass-ceramics were analyzed by XRD, and its microstructures were observed by SEM.Cooled glass is even, opaque and brown. Phase separation takes place in the glass when the precipitation began. The precipitation incipient crystalline MAT was important to the crystalline phases later.Experiments showed that the precipitation began from the surface. The surface precipitation would begin when the content of the TiO2 was 6% or below it. The magnesium aluminotianate ( MAT) is precipitated in glass at 850 C, and -quartz solution ( -QSS ), -quartz, -cordierite are precipitated in sequence,-cordierite is precipitated at 950 C. The crazes of materials happened because the inside stress can not be eliminated by the flow of the glass. Because of comparative contents of the crystalline phrases and dimensions of the crystallitesby different heat treatments, different properties could be got.When the glass is heated at 750 C for 1h and then at 1075 C for 1.5h, low thermal coefficient ( 23.535 10-7/ C ) and low dielectric constants (<7, the dielectric loss factor is less than 4.22 10-3 ) can be obtained. It can be used as microwave dielectric materials.