Direct Deoxidation of Ti by Mg in MgCl₂–HoCl₃ Flux

Abstract

A new method for removing the dissolved oxygen (O) in titanium (Ti) is developed, wherein magnesium chloride–holmium chloride (MgCl₂–HoCl₃) and Mg are used as a flux and a reducing agent, respectively. Through the thermodynamic assessment using a diagram as well as the experimental results, the deoxidation of Ti to a level below 1000 mass ppm O (and even 500 mass ppm O) via the formation reaction of holmium oxychloride (HoOCl), O (in Ti) + Mg + HoCl₃ → HoOCl + MgCl₂, was confirmed. The deoxidation limit decreases with the increase of the activity of HoCl₃ in the MgCl₂–HoCl₃ flux. One advantage of this method is that the activity of the deoxidized product, a_MgO, in the system can be effectively maintained at a low level by the formation of HoOCl. The E–pO²⁻ diagram of the M–O–Cl system (M = Ho, Mg) constructed in this study indicates that the electrochemical deoxidation of Ti scraps in MgCl₂–HoCl₃ system will be more effective because the a_MgO can be further decreased via the formation of HoOCl, and/or the electrochemical oxidation of oxide ions on the carbon anode. This new deoxidation technique using rare-earth-containing MgCl₂ flux can be applied to the recycling of Ti scraps in the future.