Deoxidation of Titanium Using Mg as Deoxidant in MgCl2-YCl3 Flux

To reduce the oxygen level in titanium (Ti) to less than 1000 mass ppm O, using magnesium as the deoxidant at 1300 K (1027 degrees C), the activity of the deoxidation product (MgO), i.e., a(MgO), in the system must be reduced to less than 0.04, from a thermodynamic viewpoint. In this study, we developed a new deoxidation technique for Ti, by adding yttrium chloride (YCl3) to magnesium chloride (MgCl2) flux, which effectively decreases and maintains the a(MgO) in the system at a low level, via the formation of yttrium oxychloride (YOCl). Through thermodynamic assessment using a pO2-pCl2 diagram, as well as experiments, the deoxidation of Ti to an oxygen level below 1000 mass ppm O, via the reaction O (in Ti) + Mg + YCl3 MgCl2 + YOCl, was confirmed. Furthermore, using the E-pO(2-) diagram of the M-O-Cl system (M = Y, Mg), the possibility of electrochemical deoxidation is discussed. In the MgCl2-YCl3 flux, Mg deposits on the Ti cathode and simultaneously deoxidizes it. The activity of the deoxidation product, MgO, decreases due to the formation of YOCl and/or the electrochemical oxidation of oxide ions on the carbon anode; thus, the deoxidation of Ti becomes feasible. This new deoxidation technique using rare-earth-containing MgCl2 flux can be applied to the recycling of Ti scraps, in the future.