Hirohisa Masuda1, Risa Kimura1,Naotaka Sakamoto2 and Kenji Morinaga1
1Department of Applied Science for Electronics and Materials, Graduate School of Engineering Sciences, Kyushu University, Kasuga 816-8580
BaO-B2O3-ZnO glasses have been studied in order to prepare lead-free glasses with a low-melting point. A glassforming region in the system was determined and thermal expansion coefficients, glass transition temperatures, dilatometric softening temperatures, and densities of the glasses were measured. A glass with a low thermal expansion coefficient comparable to that of PYREX glass was obtained. The behavior of ZnO, an amphoteric oxide, in the glasses was discussed on the basis of viscosities of the melts and chemical shifts of ZnKβ1 in the glasses. In the glass system, the behavior of ZnO depending on the basicity of the glass such as ZnO in silicate glasses was not observed. It was revealed that ZnO in the glass system tended to become the four-fold coordination and contributed as network former (NWF) to maintain the stability of the network structure in the glasses. The change in the properties of the glasses in the system BaO-B2O3-ZnO was termed ``the zinc oxide anomaly'' since it was caused by the coordination number change of ZnO as NWF.
(Received June 4, 1998; In Final Form November 12, 1998)
zinc borate glass, thermal expansion coefficient, coordination number, glass structure, zinc oxide anomaly
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