Crystallization Behaviors of Mold Fluxes Containing Li<sub>2</sub>O Using Single Hot Thermocouple Technique

Abstract

Minor addition of Li 2 O (<2 mass%) can significantly alter the melting temperature and viscosity of a mold flux. However, the crystallization tendency of mold fluxes containing Li 2 O more than 2 mass% hasn't been understood. In this paper, single hot thermocouple technique, X-ray diffraction, and Back Scattered Electron (BSE) were employed to investigate the crystallization behavior concerned with CCT and TTT diagrams of mold fluxes containing high content of Li 2 O. The critical cooling rate and crystallization rate of samples were increased with the addition of Li 2 O, whether there is Na 2 O or not. But the incubation time was reduced obviously with Li 2 O more than 6 mass% in mold fluxes. The critical cooling rate and incubation time of NL 1.5 sample (Na 2 O=8 mass%, Li 2 O= 1.5 mass%) were close to those of L 7 sample (Na 2 O=0 mass%, Li 2 O=7 mass%). Moreover, there is no difference in the crystal phase of the two samples, and the crystal phases precipitated at high temperature and low temperature were respectively Ca 2 (SiO 4 ) and Ca 4 Si 2 O 7 F 2 . Li-cuspidine was promoted to precipitate when the basicity of the sample was increased. The small, dense grains of cuspidine were observed in NL 1.5 sample, and the thickness of slag film was 0.4 mm more than that of L 7 sample. The heat flux of NL 1.5 sample measured was 10 % less than that of L 7 sample, as expected. Therefore, high content of Li 2 O can be substituted by the combination of Na 2 O and minor of Li 2 O, as is the composition in the commercial mold fluxes.