Properties and Structure Evolution of CaO–Al2O3–La2O3 Slags with Various Alkali Metal Oxide Contents

Abstract

To restrain the serious flux–steel reaction, CaO–Al2O3–La2O3‐based mold flux is designed for continuous casting of La‐bearing FeCrAl alloy. The properties and structure of slags with various alkali metal oxide contents are investigated. Results show that with the increase in Na2O or Li2O contents from 0 to 10 wt%, the melting temperature of slags decreased, and the fluxing effect of Li2O is improved. The addition of Na2O within 10 wt% reduces the slag viscosity at the temperature range of 1663–1823 K. While further increasing Na2O content to 15 wt%, the viscous behavior of the slag depends on the balance between the strong charge compensation effect of Na+ and the breaking network effect of O2−. Increasing Li2O contents from 0 to 15 wt% greatly reduces the slag viscosity, which is attributed to the reduction of the fraction of high‐polymerized QAl 4 units from 23.55% to 9.70% and the increase of [AlO6] octahedrons from 0 to 9.02% caused by more O2−. The NBO/Al and NBO fraction is calculated, which is consistent with the viscosity variations. In the melts, the structural roles of Na+, Li+, Ca2+, and La3+ are elucidated. Moreover, the relationship between the variations of crystalline phases and slag structure is discussed.