LAUSR

B2O3 and Na2O are key components of fluorine-free mold fluxes for continuous casting, but both are highly volatile, which affects the flux stability. This paper investigated the evaporation of the SiO2-CaO-Al2O3-B2O3-Na2O fluxes (Na2O: 6 to 10 wt pct, CaO/SiO2 ratio: 0.8 to 1.3) in the temperatures ranging from 1573 K to 1673 K (1300 °C to 1400 °C) using thermogravimetric analysis. The weight loss as a result of the flux evaporation increased with the increasing temperature for all fluxes. The rate of evaporation was found to be very small for the Na2O-free flux but significantly increased with the addition of Na2O. The high evaporation rate of fluxes in the presence of B2O3 and Na2O was attributed to the formation of highly volatile NaBO2. Changing the ratio of CaO/SiO2, however, did not affect the rate of evaporation. Kinetic analysis of the evaporation processes demonstrated that external mass transfer contributed to the rate of evaporation.