Electrochemical Deoxidation of Titanium Scrap in MgCl2-HoCl3 System

A novel electrochemical deoxidation process for Ti in the magnesium chloride-holmium chloride (MgCl2-HoCl3) system was developed. The reaction mechanism was proposed on the basis of the E-pO(2-) diagram constructed in this study and the experimental results. Metallic Mg was electrodeposited on a Ti cathode to remove O in the form of O2- from Ti via electrolysis conducted in molten MgCl2-HoCl3, with C and Ti as the anode and cathode, respectively. The activity of the generated O-2-(i.e., a(O)2-) in the system was effectively maintained at a very low value by the generation of holmium oxychloride (HoOCl) and/or the effusion of COx gas from the anode. By applying a voltage ranging from 2.1 to 3.0 V between the cathode and anode at 1173 K, the O concentration in Ti was effectively deoxidized to below 1000 mass ppm O. The deoxidation capability of this process was maintained even after the addition of MgO into the system as an additional source of O2-. This novel deoxidation method can be used to recycle large quantities of Ti scrap with high O concentration. (C) The Author(s) 2019. Published by ECS.