1993 年 42 巻 476 号 p. 467-472
Some physical properties of 40SiO2·10Al2O3·(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 crystallization behavior. The crystallization behavior was examined with the aid of DTA and X-ray diffraction. The structure of glass and the role of Zn2+ ions, which were elucidated from crystallization behavior and IR absorption, are as follows.
(1) ZnO combines with SiO2 to form a willemite (2ZnO·SiO2)-like structure in which Zn2+ is in 4-fold coordination.
(2) As the ZnO content increases, a wollastonite (CaO·SiO2)-like and a gehlenite (2CaO·Al2O3·SiO2)-like units transform into a willemite-like and an anorthite (CaO·Al2O3·2SiO2)-like units.
(3) The AlO4 tetrahedra coupled with Ca2+ 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 Ca2+ ions by the 4-fold coordinated Zn2+ ions.