SiO_2-Al_2O_3-CaO-ZnO系ガラスの構造と二、三の特性

概要

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Some physical properties of 40SiO_2・10Al_2O_3・(50-x)CaO・xZnO glasses and their glass structure were investigated by measuring glass transition temperature, softening temperature, thermal expansion coefficient, density, viscosity, IR absorption and ctystallization behavior. The crystallzation behavior was examined with the aid of DTA an X-ray diffraction. The structure of glass and the role of Zn^<2+> ions, which were elucideted from crystallization behavior and IR adsorption, are as follows. (1) ZnO combines wih SiO_2 to form a willemite (2ZnO・SiO_2)-like structure in which Zn^2+ is in 4-fold coordination. (2) As the ZnO content increases, a wollastonite (CaO・SiO_2)-like and a gehlenite (2CaO・Al_2O_3・SiO_2)-like units transform into a willemite-like and an anorthite (CaO・Al_2O_3・2SiO_2)-like units. (3) The AlO_4 tetrahedra coupled with Ca^2+ are formed. (4) The substitution of ZnO for CaO lowers viscosity and reduces thermal expansion coefficient. This is explained by the lower dissociation energy of ZnO, compared with CaO, and lowering in the average coordination number of oxide ions with the replacement of the 6-fold coordinated Ca^2+ ions by the 4-fold coordinated Zn^2+ ions.
1993-05-15