Direct Deoxidation of Ti by Mg in MgCl2-HoCl3 Flux

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 p(O2) -p(Cl2) 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-pO(2-) 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.