Structural and Thermodynamic Properties of TiC x N y O z Solid Solution: Experimental Study and First-Principles Approac
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TRODUCTION
TITANIUM carbide, nitride, and oxide (TiC, TiN, and TiO) are widely used due to their special properties such as high melting points, conductivity, and excellent wear resistance in coating and thin films.[1–3] Besides, these compounds can form a series of continuous solid solution (TiCxNy, TiCxOz, and TiNyOz, 0 £ x, y, z £ 1) because of structural similarity,[4–7] especially the titanium oxycarbides (TiC1xOx) could be utilized as the consuming anode for USTB titanium electrolysis process,[8, 9] which presents bright prospect and great potential for decreasing the cost of titanium production. High purity titanium deposits in the cathode through the electrolysis in molten salt while the carbon and oxygen component in the solid solution evolve into the carbon oxide (CO, CO2) gases. Generally, TiC1xOx is obtained through carbothermal reduction of TiO2 in Ar atmosphere at temperatures higher than 1473 K (1200 C)[10–13] and can also be produced by carbothermal reduction of titanium-iron ores in consideration of cost reduction.[14] Furthermore, the carbothermal reduction can even be conducted in the JIUSAN XIAO, Graduate Student, and KAI HUANG, Associate Professor, are with the School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, Beijing 100083, China. BO JIANG, formerly Ph.D. Student with the School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, is now Postdoctoral Researcher with Norwegian University of Science and Technology, 7491 Trondheim, Norway. SHUQIANG JIAO, Professor, is with the State Key Lab of Advanced Metallurgy, University of Science and Technology Beijing, Beijing 100083, China. HONGMIN ZHU, Professor, is with the School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, and also with Tohoku University, 6-6-02, Aramaki-Aza-Aoba, Aoba-ku, Sendai, 980-8579, Japan. Contact emails: [email protected] and [email protected] Manuscript submitted September 29, 2015. Article published online June 28, 2016 METALLURGICAL AND MATERIALS TRANSACTIONS A
air at a lower temperature and titanium oxycarbonitride (TiCxNyOz, 0 £ x, y, z £ 1, x + y + z = 1) instead of TiC1xOx is obtained in the products. It is worth to mention that the titanium oxycarbonitride with a certain range of C/N/O component could also be utilized as the consuming anode in the USTB titanium electrolysis process,[15] since the carbon and oxygen component should evolve into CO and CO2 while the nitrogen component in the solid solution liberates to form N2 during the electrolysis process. TiCxNyOz solid solution can be synthesized through carbothermal reduction of TiO2 in N2 atmosphere at a lower temperature than producing TiC1xOx,[16–19] however, the structural and thermodynamic properties of TiCxNyOz solid solution with different C/N/O concentration are still unclear. In this paper, we have synthesized a series of TiCxNyOz solid solutions with different C/N/O concentration through solid-state reaction instead o
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