Glass - Back to the Future!

Presenting Author:
Jun Matsuoka

article posted 07 April 2016

Jun Matsuoka is professor of the University of Shiga Prefecture, Japan. He earned B. Eng. and M. Eng. both from Kyoto University, for study about the fracture behaviour of glass. In 1987, he joined the Government Industrial Research Institute, Osaka, and studied chemical durability and optical property of glass. From 1991 to 1995, he belongs to Mie University and studied photonic glasses and sol-gel method. He earned doctoral degree from Kyoto University for study about sol-gel derived photonic materials. Since 1995, he belongs to the University of Shiga Prefecture, and studies thermal and mechanical properties of glass as well as properties of glass-forming melt.

Effect of the partial substitution of calcium to other divalent cations on the viscosity of ternary soda lime silicate glass

Jun Matsuoka*, Takahiro Yoshida, Akihiro Yamada & Satoshi Yoshida
The University of Shiga Prefecture, Hikone, Shiga 522-8533, Japan

Divalent cation of transition metals are widely used as colorants in commercial soda lime silicate glasses. Addition of these cations to glass changes not only its colour but also its viscosity. Therefore, viscosity change has been studied in the last 100 years. However, most of the studies are limited to commercial compositions and the concentration of transition metals varies with the element species. For example, the concentration of Co2+ in cobalt blue glass is much lower than that of Cu2+ in copper blue glass. Understanding the element dependence scientifically from these studies is difficult.
In this study, in order to clarify the effect of partial substitution of divalent cation on the viscosity of soda lime silicate glass, viscosity of 15Na2O-2MO-8CaO-75SiO2 glasses (M = Ca, Mg, Sr, Ba, Mn, Fe, Co, Ni, Cu, Zn, and Pb) was measured. Rotating parallel plate method was adopted and the measured viscosity range was 102.8 to 104.3 Pa.s.
In the substitution to alkaline earth metal ions, element having larger ionic radius gives lower viscosity. Partial substitution of Ca2+ to Mg2+ increases the viscosity, and to Sr2+ or Ba2+ gives the opposite effect. On the other hand, although most of the transition metal ions have smaller radius compared to Ca2+, partial substitution lowers the viscosity. An example is shown in Figure 1 where logarithm of the viscosity is plotted against inverse temperature for M = Ca and Co. This difference between alkaline earth and transition metal ions is found to be explained by the difference of the ionic field strength of cations. We define the field strength of a cation as f Z / r, where f the ionicity fraction calculated from the electronegativity difference of metal and oxygen, Z the formula charge of metal cation (= 2 in this study), and r the ionic radius of the cation. Figure 2 shows the relation between field strength f Z / r and the viscosity at 1423 K. A good relationship is found except for some elements such as barium. The anomaly in the case of barium should be due to its very large ionic radius that would increase the fraction of free volume in glass melt.