Effect of La2O3 on the viscosity and structure of CaO–SiO2(–Al2O3)–La2O3 melts

Abstract The rotating cylinder method was used to understand the effects of La2O3 and the La2O3/Al2O3 ratios on the melt viscosity of CaO–SiO2(–Al2O3)–La2O3 at high temperatures. The structural characterization of these quenched glass samples were investigated using Raman spectroscopy. The results show that the viscosity of the CaO–SiO2(–Al2O3)–La2O3 melt is significantly reduced due to additions of La2O3. The La2O3 additions simplified the structure of the silicon-oxygen ion groups in the melt, which created a smaller melt viscosity. The critical transition temperature is proportional to the La2O3 content and inversely proportional to the La2O3/Al2O3 ratio. La3+ and Al3+ make the viscosity-temperature curve of CaO–SiO2–Al2O3–La2O3 melt show different characteristics. There is no critical transition temperature when the melt without La2O3, and the critical transition temperature appears after adding La2O3. The La2O3 plays a role like alkaline oxide in the CaO–SiO2–Al2O3–La2O3 melt. In addition, the degree of polymerization of the melt decreased relative to the La2O3 content and La2O3/Al2O3 ratio. Consequently, the La2O3 behaves as a network modifier for the complex silicate anions of CaO–SiO2–La2O3 and CaO–SiO2–Al2O3–La2O3 melts.