A Study on Non-Equilibrium Phase diagrams for Glass Forming Oxide Systems

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CCT(Continuous Cooling Transformation), CHT(Continuous Heating Transformation ) and TTT(Time Temperature Transformation) phase diagrams, which have been established in steel-making processes, are also need for glass-ceramic processings. The non-equilibrium phase diagrams for the crystallization of aluminosilicate glasses and the solidification of Bi-based superconductor melt are proposed. The mu-to alpha-condierite transformation is observed during the isothermal treatments of glasses with compositions of 2MgO・2Al_2O_3・5SiO_2 and MgO・Al_2O_3・2SiO_2. SEM observation suggests that the mu-to alpha-transformation is similar to the isothermal martensite formation. In RO・Al_2O_3・2SiO_2 glasses (R=Ca, Sr, Ba), the formation period of the metastable phases are related to the cation radii affecting their diffusions during the metastable-to stable-phase transformations, e. g., hexagonal-to monoclinic-celsians transformations. The highest-Tc superconductor phase Bi_2Sr_2Ca_2Cu_3O_x (2223) is formed through the isothermal treatment at 850ﾟC for above 150 ks. The analyzes of XRD and scanning electron micrograph (SEM) with energy dispersive X-ray (EDX) suggest that Bi_2Sr_2CuO_x (2201) needles are crystallized at the interface between (Ca, Sr) _2CuO_3 crystals amd melt, and the part of 2201 crystals transforms to Bi_2Sr_2CaCu_2O_x (2212) and 2223 crystals by the diffusions of Ca, Sr, and Cu ions.