An Innovative Process for Production of Ti Metal Powder via TiS x from TiN
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INTRODUCTION
PROCESSING of metallic Ti has been primarily performed through the discontinuous Kroll process, which requires a high carbochlorination temperature of about 1273 K (1000 C) to synthesize TiCl4, distill it at 473 K (200 C), and convert it at 1273 K (1000 C) to sponge Ti by Mg.[1] In addition, molten salt electrolysis of MgCl2 takes a long time at 923 K (650 C) for recycling of reductant Mg.[2–4] Thus, Ti communities are persistently working to innovate feasible and economically viable pyro- or hydrometallurgical processes to remarkably drive down the cost of Ti metal powder processing. The environmental regulations have been also considered in the newly developed methods such as innovative electrochemical reduction methods and a low-temperature chlorination process (LTCP).[2] For example, TiO2 feedstocks have been used for production of metallic Ti in the electro-deoxidation and calciothermic reduction routes called the Fray, Farthing, and Chen (FFC) Cambridge and Ono and Suzuki (OS) processes.[5,6] On the other hand, ilmenite (FeTiO3) can be converted to titanium oxycarbonitride (TiOxCyNz)
ELTEFAT AHMADI and RYOSUKE O. SUZUKI are with the Division of Materials Science and Engineering, Faculty of Engineering, Hokkaido University, N13W8, Sapporo 060-8628, Japan. Contact email: [email protected] Manuscript submitted June 8, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS B
via the carbothermal reduction and nitridation (CTRN) process and subsequent iron removal step in an ammonium chloride (NH4Cl) solution.[7–9] The TiN and TiOxCyNz prepared from FeTiO3 can be easily chlorinated at very low temperatures, such as about 400 C,[2] which could be an alternative route to carbochlorination at high temperatures taken in the Kroll process. Especially, this method has the merit of less contamination of Fe derived from FeTiO3 with low operating costs.[2,7,8,10] Figure 1 illustrates the main processing steps in the present concept in comparison with various methods developed for production of Ti metal from FeTiO3. High-quality TiN or TiOxCyNz can be processed from Ti ores and used in chlorination or sulfurization processes. It is worth noting that TiCl4, synthesized by high-temperature carbochlorination of TiO2, has been employed for production of Ti metal by CSIRO method[11,12] and TiH2 powders by the ADMA non-Kroll process by Mg reduction.[13,14] In addition, iron-free TiN may be refined also and converted to Ti metal powder by the electrochemical USTB method.[15] Moreover, it has been stated that titanium oxycarbides can be readily converted to Ti metal by the electrochemical MER[16,17] and Chinuka[18] processes. Ti(C, O) pellets in these processes were prepared by partial carbothermal reduction of TiO2 under vacuum or in an inert atmosphere and used as anodes in the successive refining process.
of titanium oxysulfides prior to the electrolysis should be avoided also to obtain high-quality Ti powders, because the oxygen removal is more difficult than sulfur from the obtained Ti metal. Recently, the O
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