The effect of Al2O3 on glass transition temperature Tg and thermal expansion coefficient α is studied for CaO-Al2O3-SiO2 glasses including 45, 50, 55, and 60 mol% SiO2 with a molar ratio of CaO/Al2O3 > 1. Tg increases and α decreases monotonically with increasing Al2O3 concentration. The result of infrared spectra suggests the formation of ring-type mixed anions of SiO4 and AlO4 due to Al2O3 addition. The measured values of α are related to a parameter calculated from the coulomb force between cation and oxide anion based on chemical composition.
