Deoxidation of Ti using Ho in HoCl3 flux and determination of thermodynamic data of HoOCl

A novel method for removing the oxygen (O) in titanium (Ti) is proposed and developed, wherein holmium (Ho) and holmium chloride (HoCl3) are used as a deoxidant and flux, respectively. The reduction of O concentration in Ti to a level of below 200 mass ppm O (even reaching 110 mass ppm O) through the formation reaction of holmium oxychloride (HoOCl), i.e., O (in Ti) + 2/3 Ho + 1/3 HoCl3 -> HoOCl, was confirmed. This result reveals that deoxidation of Ti using Ho in HoCl3 flux is effective, and low-O Ti can be obtained under Ho/HoOCl/HoCl3 equilibrium. This new deoxidation technique using Ho as a deoxidant can be applied to the refining of Ti scraps and the production of low-O content Ti powder in the future. The standard Gibbs energy of formation of HoOCl (DG degrees(f,HoOCl)) at 1300 K was experimentally determined to be - 744 +/- 10 kJ mol(-1). In addition, the value of DG degrees(f,Ho2O3) was determined to be - 1503 +/- 10 kJ mol(-1), which is in good agreement with the reported data (-1510 kJ mol(-1)). A potential diagram of the Ho-Cl-O system at 1300 K was newly drawn using the thermodynamic data determined through this study. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

A novel method using holmium and holmium chloride as deoxidizer and flux respectively has been developed to efficiently remove oxygen in titanium, resulting in low-oxygen titanium materials that can potentially be used for titanium scrap recycling and low-oxygen titanium powder production.