Deoxidation Mechanism in Reduced Titanium Powder Prepared by Multistage Deep Reduction of TiO 2
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DUE to high production costs, titanium production has not been implemented on a large scale. The Hunter method[1] uses sodium metal and TiCl4 to produce a titanium sponge, which became available for industrial production in the 1950s. Given the prohibitive cost and high residual chlorine in the product, it was eliminated in the 1990s.[2] The Kroll method[3] utilizes magnesium thermal reduction of TiCl4 to prepare metallic titanium, which is the only industrial-scale production method available at present. To achieve continuous production of titanium metal, ITP company developed the Armstrong method[4,5] wherein TiCl4 vapor and sodium vapor were mixed by jet-blown method and reduced in order to obtain metallic titanium. In addition, a molten
SHI-GANG FAN, ZHI-HE DOU, TING-AN ZHANG, YAN LIU, and LI-PING NIU are with the School of Metallurgy, Northeastern University, Shenyang, 110819, P.R. China and also with the Key Laboratory of Ecological Metallurgy of Multimetal Intergrown Ores of Ministry of Education, Shenyang, 110819, P.R. China. Contact e-mail: [email protected] Manuscript submitted June 25, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS B
salt electrolysis method used TiCl4 as a raw material,[6,7] which was once regarded as complementary to the Kroll method. However, the method was unsuccessful because it is occasionally difficult to control reverse reactions between titanium and chlorine and the conversion between different valent titanium ions. The above methods all use TiCl4 as a raw material, and it is difficult to fundamentally resolve the cost and environmental problems posed by the Kroll method. Short and clean preparation methods for titanium and titanium alloys, namely, direct thermal reduction/electrolysis reduction of TiO2 (or TiClx,[8,9] TiCxOy[10]), are hot and challenging research topics in the titanium industry. In 2000, Fray et al. of the Cambridge University have reported on the FFC process[11–14] in Nature. B-Ti in the United Kingdom and TIMET in the United States are dedicated to the industrialization of the FFC process. Todate, the FCC process remains in the laboratory stage. Units, such as the Institute of Process Research of the Chinese Academy of Sciences, also conducted extensive research on the FFC process, and all of these experiments were still performed in the laboratory. Ono and Suzuki of the Kyoto University in Japan proposed the OS method.[15] Metal calcium (which is obtained by electrolyzing CaO in CaCl2 molten salt) directly reduces TiO2 in situ. This
method can help to solve the problem of current efficiency reduction caused by long-distance oxygen diffusion in the FFC method. The University of Tokyo used an electronic mediation reaction (EMR) method[16] for the direct preparation of titanium powder during the TiO2 reduction process, avoiding contamination by impurities in the reducing agent. Shanghai University proposed the SOM method[17,18] of extracting sponge titanium using a solid oxygen-permeable membrane. Zhu Hongmin of the Beijing University of Science and Techno
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