Dissolution rate of Al₂O₃ into molten CaO–Al₂O₃–CaF₂ flux

Abstract

Dissolution of Al₂O₃ into molten CaO–Al₂O₃–CaF₂, a base system of mould flux for continuous casting of high Al steel, has been investigated by employing a rotating cylinder method. The dissolution rate of an alumina rod into molten CaO–Al₂O₃–CaF₂ flux increased with increase in rotating speed and temperature. The apparent activation energy for mass transport of flux C was calculated to be 255·6 kJ mol⁻¹. The rate controlling step during the dissolution process of the alumina rod into molten CaO–Al₂O₃–CaF₂ flux was found to be the diffusion of the solute in the flux boundary layer. The dissolution rate of alumina into molten CaO–Al₂O₃–CaF₂ flux increased with increasing CaO/Al₂O₃, and it may be caused by the increase in thermodynamic driving force and the decrease in the viscosity of the flux. When the Al₂O₃ rod was immersed into molten flux, an intermediate compound of CaO.2Al₂O₃ formed firstly and then dissolved into molten flux.

Keywords:

• Mould fluxes
• Dissolution rate
• Alumina
• Rotating cylinder

Acknowledgements

Financial supports from the National Natural Science Foundation of China (grant no. 51174018), the Beijing Higher Education Young Elite Teacher Project (grant no. YETP0346) and the State Key Laboratory of Advanced Metallurgy are gratefully acknowledged.