Novel metallurgical process for titanium production
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In this work, a consumable anode composed of a solid solution of titanium carbide and titanium monoxide was prepared via carbothermic reduction of TiO2. Upon electrolysis, the anode fed Ti2+ into solution and carbon monoxide was generated; no excess carbon remained to contaminate the melt. On the cathode, high-purity titanium (>99.9%) was produced. Our results suggest anode and cathode current efficiencies of 93.5% and 89% respectively, indicating that the method is viable and extremely cost-effective, potentially dropping the cost of titanium to near that of aluminum.
Primary titanium metal, sponge titanium, is produced through a process invented by Dr. Kroll in the 1940s.1 The current industrial practice includes multiple steps. Magnesium and chlorine gas are produced through the electrolysis of MgCl2. Titania is then carbochlorinated, and the resulting TiCl4 is thermoreduced by the magnesium to form titanium sponge. The procedure is complex and is a batch process, factors that drive up the production cost substantially. Much research has been focused on developing a technique to produce low-cost and high-purity titanium.2–8 Recently, electrolysis from TiO29–13 and related methods14–17 have been investigated extensively. In the oxide electrolysis process, TiO2, a semiconductor, serves as the cathode and is reduced in a CaCl2 electrolyte. Titania is slowly consumed, solid titanium is produced, and the resulting oxygen diffuses from the cathode into the melt. Unfortunately, very long electrolyzing times are required for significant conversion, and current efficiencies are low. Furthermore, production is still restricted to a batch process. Japanese research groups14–17 proposed a similar method involving a combination of electrolysis and calciothermic reduction. Calcium, electrodeposited on the cathode, is used to reduce the TiO2. Unfortunately, problems remain associated with the high oxygen content of titania and with difficulties in the extraction of the product titanium from its mixture with TiO2, CaO, Ca, and solvent CaCl2. High-purity titanium can be obtained on the cathode through electrorefining when sponge titanium, produced previously via the Kroll process, is used as a consumable anode.18 Titanium carbide can be used in place of the
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2006.0268 2172 J. Mater. Res., Vol. 21, No. 9, Sep 2006 http://journals.cambridge.org Downloaded: 29 May 2014
sponge because it is also an electronic conductor.19 In practice, however, carbon from the anode would collect in the electrolyte during electrolysis. This problem can be eliminated by incorporating an oxide component into the anode; upon electrolysis, carbon would be removed as CO gas. Fortunately, titanium monoxide (TiO), an electronic conductor, has a structure very similar to that of TiC. Therefore, titanium carbide and titanium monoxide can easily form a high-conductivity solid solution. Historically, this type of material has been prepared from TiC and TiO using an a
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