Synthesis of Titanium Oxycarbide from Titanium Slag by Methane-Containing Gas
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, PETRUS CHRISTIAAN PISTORIUS
,
In this study, reaction steps of a process for synthesis of titanium oxycarbide from titanium slag were demonstrated. This process involves the reduction of titanium slag by a methane-hydrogen-argon mixture at 1473 K (1200 C) and the leaching of the reduced products by hydrofluoric acid near room temperature to remove the main impurity (Fe3Si). Some iron was formed by disproportionation of the main M3O5 phase before gaseous reduction started. Upon reduction, more iron formed first, followed by reduction of titanium dioxide to suboxides and eventually oxycarbide. DOI: 10.1007/s11663-017-1123-5 The Minerals, Metals & Materials Society and ASM International 2017
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INTRODUCTION
TITANIUM is the ninth most abundant element and fourth among common metals in the Earth’s crust. Owing to its high specific strength, good corrosion resistance, and biocompatibility, titanium would be an ideal metal for many applications. Currently, the relatively high price of titanium largely limits its use to demanding and high-value applications,[1,2] but with lower prices many more applications would be feasible. There has been a considerable increase in interest in developing a better method which can replace the Kroll process. As a result, many processes have been developed: examples include the FFC process,[3] Ono and Suzuki process,[4] Armstrong process,[5] preform reduction process,[6] and EMR process.[7] The anode used in the electrolytic MER process (and the related Chinuka[8] and USTB[9] processes) is titanium oxycarbide, produced from titania-rich feedstocks and a carbon source.[10] Titanium oxycarbide (TiOxCy) is a continuous solid solution of TiC-TiO and has the NaCl face-centered cubic (FCC) structure with a high melting point and high conductivity.[11] The preferred
JIE DANG is with the State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing, Beijing 100083, P.R. China and also with the Department of Materials Science and Engineering, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15213. FARZIN FATOLLAHI-FARD and PETRUS CHRISTIAAN PISTORIUS are with the Department of Materials Science and Engineering, Carnegie Mellon University. Contact e-mail: [email protected] KUO-CHIH CHOU is with the State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing. Manuscript submitted January 15, 2016.
METALLURGICAL AND MATERIALS TRANSACTIONS B
oxycarbide composition is Ti2OC since this would allow the carbon and oxygen to be released as CO gas at the anode when titanium ions dissolve in the molten salt of the electrolytic process. The required impurity content depends on the titanium product specification. Metallic impurities such as Fe, Mn, and Si would be readily reduced from the salt at the potential required to plate titanium. This implies that the concentrations of these elements in oxycarbide (relative to titanium) must meet the titanium metal specification. As an example, the maximum allowable mass percentage of iron in
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