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

Abstract

To restrain the serious flux-steel reaction, CaO-Al 2 O 3 -La 2 O 3 -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 Na 2 O or Li 2 O contents from 0 to 10 wt%, the melting temperature of slags decreased, and the fluxing effect of Li 2 O is improved. The addition of Na 2 O within 10 wt% reduces the slag viscosity at the temperature range of 1663-1823 K. While further increasing Na 2 O content to 15 wt%, the viscous behavior of the slag depends on the balance between the strong charge compensation effect of Na þ and the breaking network effect of O 2À . Increasing Li 2 O contents from 0 to 15 wt% greatly reduces the slag viscosity, which is attributed to the reduction of the fraction of high-polymerized Q Al 4 units from 23.55% to 9.70% and the increase of [AlO 6 ] octahedrons from 0 to 9.02% caused by more O 2À . The NBO/Al and NBO fraction is calculated, which is consistent with the viscosity variations. In the melts, the structural roles of Na þ , Li þ , Ca 2þ , and La 3þ are elucidated. Moreover, the relationship between the variations of crystalline phases and slag structure is discussed.

Research Progress of Desulfurization Refining Slag: A Review

“…Wang [ 40 ] found that substituting an equivalent number of CaF 2 with B 2 O 3 significantly enhanced the desulfurization ability of the flux. Fan et al [ 41 ] found that the melting temperature and viscosity of a slag decreased as the Li 2 O content increased from 0 wt% to 10 wt%. This was attributed to a decrease in the Q Al 4 fraction from 25% to 9.7% and an increase in [AlO 6 ] octahedra from 0% to 9.02%.…”