Effect of CaF 2 , B 2 O 3 and the CaO/SiO 2 mass ratio on the viscosity and structure of B 2 O 3 ‐containing calcium‐silicate‐based melts

The relationship between the viscosity and structure of B 2 O 3 ‐containing calcium‐silicate‐based mold fluxes and the effects of fluidizers including CaF 2 , CaO, and B 2 O 3 on the viscosity and their correlation with the structural aspects were studied using a rheometer with Fourier transformation infrared and Raman spectroscopy. The viscosity decreased with increasing CaF 2 addition up to 28 wt% at a fixed CaO/SiO 2 ratio of 0.3, which was related to depolymerization. Furthermore, CaF 2 addition also affected the apparent activation energy for viscous flow, which decreased with increasing CaF 2 content to 105.1 from 151.1 kJ/mol. At higher C/S ratios, the viscosity decreased in the presence of greater Ca 2+ and O 2− supplied from CaO, which subsequently increased the activation energy to 149.7 from 122.0 kJ/mol. With regard to the B 2 O 3 ‐melt, polymerization of the network structure was observed by comparing the B 2 O 3 ‐free to 4.4 wt% B 2 O 3 content. However, the viscosity was relatively constant with increasing B 2 O 3 addition. However, the viscosity decreased due to greater simplification of the network structure above 4.4 wt% B 2 O 3 . The break temperature decreased with greater B 2 O 3 addition as the crystallization was inhibited. Furthermore, the apparent activation energy decreased as depolymerization of the network structures occurred above 4.4 wt% B 2 O 3 .