Effect of La2O3 and FexO on the viscosity and structure of CaO–MgO–Al2O3–SiO2 melts

The effect of La2O3 and FexO on the viscosity and structure of CaO–MgO–Al2O3–SiO2 (CMAS) melt was investigated. The viscosity of CaO–MgO–Al2O3–SiO2 melts with La2O3 and FexO was measured by a rotating cylindrical method from 1375 °C to 1550 °C, and the structures of the melts were analyzed via Raman spectroscopy. The results indicated that the viscosity decreased with increasing temperature and the activation energy decreased from 111.53 to 99.25 kJ/mol with the mole ratio of La2O3/FexO decreased from 2/0 to 0/2. The structural analysis revealed that the weaker chemical bonds or non-chemical bonds between the network structures of the glass were broken with the temperature increases, and both La2O3 and FexO acted as network modifiers to simplify the Si–O–Si tetrahedral structural unit. When the mole ratio of La2O3/FexO decreased from 2:0 to 0:2, the relative fraction of QSi3 and QSi4 decreased and the relative fraction of QSi0, QSi1 and QSi2 increased. Therefore, the degree of polymerization (DOP) of CMAS melt decreased, as well as the viscosity decreased with the addition of FexO and La2O3. FexO has more effective on the decrement in CMAS melt viscosity than that of La2O3 due to the structure modification ability of La3+ being smaller than that of Fe2+. Moreover, the number of non-bridging oxygen atoms per tetrahedrally coordinated atom (NBO/T) was used to characterize the melt structure, the quantitative relationship among the viscosity, temperature and microstructure of the melt was given.