Kinetics of the direct synthesis of molycarbide by reduction-carburization of molybdenite in the presence of lime
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MOLYBDENUM carbide is an important material, which finds numerous applications[1–5] such as speciality cutting tools, heat-resistant hard alloys, and high-temperature solders (for specific applications), and as a catalyst in the manufacture of organic chemicals (e.g., alcohols and cyclohexane). Traditionally, it is produced by three routes: (1) hydrogen reduction of its trioxide followed by carburization under hydrogen atmosphere[1,2] (2) carburization of molybdenum powder by CO (g),[1,2] and (3) carbonaceous roasting of high-purity molybdenite in air followed by its treatment under hydrogen.[5,6] These methods suffer from several inherent limitations such as numerous processing steps, expensive pollution abatement measures, low recoveries, and hence the need for residue processing. A few new routes based on molten salt electrowinning from complex baths have been reported[6–9] but none has yet been commercialised. Because of the growing interest in molycarbide, its direct synthesis by a novel lime-scavenged CO (g) reduction of molybdenite was attempted by Prasad and co-workers[10,11] who found that it is indeed feasible to achieve the simultaneous reduction-carburization of MoS2 resulting in the formation of 98 pct purity molycarbide. Moreover, it was noticed that the new approach is basically nonpolluting with respect to sulfur emission. Hence, compared to the P.M. PRASAD, Ex-Director, IT-BHU, and Professor of Metallurgical Engineering, Department of Metallurgical Engineering, and T.R. MANKHAND, Professor of Metallurgical Engineering, Department of Metallurgical Engineering, are with the Institute of Technology, Banaras Hindu University, Varanasi - 221 005, India. Contact e-mail: mankhand@ banaras.ernet.in P. SURYA PRAKASH RAO, Assistant Professor, is with the Department of Metallurgical Engineering, Regional Engineering College, Warangal - 506 004, A.P., India. S.N. SINGH, Lecturer, is with the Department of Chemistry, H.D. Jain College, Veer Kunvar Singh University, Arrah -802 301, Bihar, India. A.J.K. PRASAD, QHF, is with the National Metallurgical Laboratory, Jamshedpur - 831 007, India. Manuscript submitted April 9, 1998. METALLURGICAL AND MATERIALS TRANSACTIONS B
traditional or other proposed routes of producing molybdenum carbide, its direct synthesis from molysulfide looks attractive as it comprises a fewer number of processing steps. The present article deals with kinetic investigations on the MoS2 (s) ⫹ CaO (s) ⫹ CO (g) reaction so as to understand the probable reaction path. II. THERMOCHEMICAL CALCULATIONS A. Thermodynamics of the Concerned Reactions The relevant thermochemical calculations (from the data taken from References 12 and 13) concerning direct synthesis of molycarbide by the reduction of MoS2 (s) by CO (g) in the presence of lime (CaO) are presented in Table I. The overall MoS2 (s) ⫹ CaO (s) ⫹ CO (g) reaction resulting directly in Mo2C formation is represented by 2MoS2 (s) ⫹ 4CaO (s) ⫹ 6CO (g) ⫽ Mo2C (s) ⫹ 4CaS (s) ⫹ 5CO2 (g)
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The preceding reaction appears to be an appropriate su
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