Investigation on the Kinetics and Mechanism of Aluminothermic Reduction of Molybdenum Trioxide: Non-isothermal Kinetics
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ORIGINAL ARTICLE
Investigation on the Kinetics and Mechanism of Aluminothermic Reduction of Molybdenum Trioxide: Non-isothermal Kinetics K. Sheybani1 • M. H. Paydar1
•
M. H. Shariat1
Received: 18 March 2020 / Accepted: 6 September 2020 Ó The Indian Institute of Metals - IIM 2020
Abstract In this work, effect of milling process and CaO addition on the reaction mechanism and kinetics of aluminothermic reduction of molybdenum trioxide were studied by simultaneous thermal analysis, differential scanning calorimetry, X-ray diffraction analysis and Coats–Redfern method, respectively. For this purpose, molybdenum trioxide was reduced by Al powder under two different conditions of mechanical activation by milling process and as received form mixed by stoichiometric amount of CaO that was required for creation of CaMoO4 intermediate phase. In the case of using milled molybdenum trioxide, 20 wt% of aluminum oxide was used as heat absorber. The results showed that by using mechanically activated MoO3, the reduction reactions proceeded through the formation of intermediate phases of Al2(MoO4)3 and MoO2. In the presence of CaO, the intermediate phase was changed to CaMoO4. In both cases, the reaction temperatures and their activation energies decreased. The kinetic model for the aluminothermic reduction of un-milled and milled molybdenum trioxide was determined as chemical control, where by addition of CaO, mechanism of the reduction reaction was changed to diffusion control. Keywords Kinetic Mechanism Molybdenum trioxide Aluminothermic reduction Mechanical activation Activation energy Non-isothermal
& M. H. Paydar [email protected] 1
Department of Materials Science and Engineering, School of Engineering, Shiraz University, Shiraz, Iran
1 Introduction Molybdenite (MoS2) is the major source for production of molybdenum and its alloys [1]. Recently, many researchers suggested that combustion-based technology known as combustion synthesis (or self-propagation hightemperature synthesis) can be used for producing Mo powder [2–4]. They proposed that, metallothermic reduction of MoO3 by Zn, Mg and Al, and carbothermic reduction of MoO3 is a good method that can solve the problems of hydrogen reduction of MoO3, which is carried out at different temperature steps and need a close system due to solid–gas reaction [5–7]. The conventional method for producing molybdenum and its alloys is based on roasting of molybdenite, followed by the purification of the resultant oxide (MoO3) and finally reduction of the purified molybdenum oxide by high purity H2 gas [2]. Recently, metallothermic reduction process has been suggested by few researchers for producing metallic molybdenum, in which Zn and Mg have been introduced as reducing agents [8–10]. The studies showed that metallothermic reduction of MoO3 can be carried out successfully, and separation of molybdenum metal from zinc or magnesium oxides can be carried out by HCl leaching [11–13]. Recently, Sheybani et al. [14] showed that molybdenum trioxide can also be reduced
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