Chlorination of Titanium Oxycarbide Produced by Carbothermal Reduction of Rutile
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TION
TITANIUM minerals are primarily processed into titanium dioxide white pigment, which is a valuable commodity used in paint, paper, and plastic industries because of its exceptional scattering properties, chemical stability, and lack of toxicity.[1] Usage of metallic titanium is limited because of high production cost, although titanium has superior properties such as high strength, low density, excellent corrosion resistance, extreme mechanical and thermal loading capacity, etc. Processing of titanium minerals to TiO2 pigment or titanium metal involves chlorination process in which titanium dioxide is conventionally converted to titanium tetrachloride. Chlorination of TiO2 occurs at high temperatures in the range 800 C to 1100 C, and it is a stable oxide. At these temperatures impurities are also chlorinated, which requires high-quality materials such as rutile, synthetic rutile, or TiO2-rich slag. Nieberlein[2] investigated the process of low-temperature chlorination of titanium carbide and suboxides produced by carbothermal reduction at 1500 C. He found that a temperature of 250 C was sufficient to ignite the reaction. The chlorination temperature was 400 C to 500 C. Meerson et al.[3] proposed a technology combining carburization and low-temperature chlorination for the production of titanium tetrachloride from titanium-iron concentrates and titanium slags. They found that carbothermal reduction at 1350 C to 1450 C and 150 to 200 mm Hg pressure for 30 to 120 minutes converted titania to titanium oxycarbide with 50 to 60 pct TiC and 50 to 40 pct TiO. The chlorination rate of this material at 600 C to 700 C ANDREW ADIPURI, PhD Student, GUANGQING ZHANG, Lecturer, and OLEG OSTROVSKI, Professor, are with the School of Materials Science and Engineering, University of New South Wales, UNSW Sydney, NSW 2052, Australia. Contact e-mail: G.Zhang@ unsw.edu.au Manuscript submitted December 10, 2006. Article published online January 8, 2008. METALLURGICAL AND MATERIALS TRANSACTIONS B
was greater than that of titanium slag at 700 C to 900 C, but no detailed kinetic examination was reported. Zelikman and Leonova[4] investigated the chlorination of titanium carbide in the form of compact briquettes at 600 C to 900 C. The reaction rate was controlled by the chlorine diffusion in the layer of carbon residue formed in the process of titanium chlorination. An original technology was developed for processing of calcium-containing titanium ores and slags.[5] The materials reacted with solid carbon at high temperature between the melting points of CaC2 and TiC, and formed TiC distributed in the matrix of CaC2. The CaC2 was removed by reaction with water and TiC was chlorinated at a temperature above the boiling point of TiCl4 and below the chlorination temperature for impurities, so high-purity TiCl4 was obtained without distillation. This technology was also applied to titaniferous ores.[6] Brandstatter[7] developed a technology in which titanium in ilmenite ore and slag was carburized at 1700 C to 2000 C. The process
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