Thermodynamic Considerations of Direct Oxygen Removal from Titanium by Utilizing the Deoxidation Capability of Rare Earth Metals

• Published in: Metallurgical and materials transactions. B, Process metallurgy and materials processing science Vol. 49; no. 3; pp. 1056 - 1066
• Main Authors: Okabe, Toru H., Zheng, Chenyi, Taninouchi, Yu-ki
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.06.2018; Springer Nature B.V
• Subjects: Characterization and Evaluation of Materials; Chemistry and Materials Science; CONCENTRATION RATIO; Deoxidizing; ELECTROLYSIS; Environmental impact; ENVIRONMENTAL IMPACTS; IMPURITIES; Ingots; KROLL PROCESS; MATERIALS SCIENCE; Metal scrap; Metallic Materials; Metallurgy; MOLTEN SALTS; Nanotechnology; Neodymium; OXYGEN; Rare earth elements; RARE EARTHS; Recycled materials; REDUCTION; SCRAP; Structural Materials; Surfaces and Interfaces; THERMODYNAMICS; Thin Films; TITANIUM; TITANIUM ALLOYS; Titanium base alloys; YTTRIUM; Light Rare Earth Metals; Molten Salt Electrolysis; Kroll Process; Industrial Electrolysis Cells; Oxygen Removal
• ISSN: 1073-5615; 1543-1916
• DOI: 10.1007/s11663-018-1172-4

Oxygen removal from metallic Ti is extremely difficult and, currently, there is no commercial process for effectively deoxidizing Ti or its alloys. The oxygen concentration in Ti scraps is normally higher than that in virgin metals such as in Ti sponges produced by the Kroll process. When scraps are remelted with virgin metals for producing primary ingots of Ti or its alloys, the amount of scrap that can be used is limited owing to the accumulation of oxygen impurities. Future demands of an increase in Ti production and of mitigating environmental impacts require that the amount of scrap recycled as a feed material of Ti ingots should also increase. Therefore, it is important to develop methods for removing oxygen directly from Ti scraps. In this study, we evaluated the deoxidation limit for β-Ti using Y or light rare earth metals (La, Ce, Pr, or Nd) as a deoxidant. Thermodynamic considerations suggest that extra-low-oxygen Ti, with an oxygen concentration of 100 mass ppm or less can be obtained using a molten salt equilibrating with rare earth metals. The results presented herein also indicate that methods based on molten salt electrolysis for producing rare earth metals can be utilized for effectively and directly deoxidizing Ti scraps.