تاثير فعال سازي مكانيكي بر احياي كربوترمي موليبدنيت در حضور اكسيدهاي قليايي

چكيده انگليسي :

Effect of mechanical activation on carbothermic reduction of molybdenite in the presence of alkaline oxides Khadijeh Biralvand Kh biralvand@yahoo com February 2012 Department of Materials Engineering Isfahan University of Technology Isfahan 84156 83111 IranDegree M Sc Language FarsiDr Mohammad Hasan Abbasi Prof Supervisor Email abbasi32@cc iut ac irDr Ali Saidi Prof Supervisor Email a saidi@cc iut ac irAbstractIn this study Carbothermic reduction of Molybdenite in the presence of Magnesium oxide and calcinedDolomite has been thermodynamically studied Also the effect of Mechanical activation on structural evolutionand reduction behavior of Molybdenite with carbon in two mixtures of MoS2 C MgO and MoS2 C CaxMg1 xOhas been investigated It was found that the reaction proceeds through direct oxidation of MoS2 by CaO andMgO to form intermediate molybdenum oxidized species MoO2 MgMoO4 and CaMoO4 The results showedthat the Reduction of oxidized species leads to the formation of Mo Mo2C MoC or MgO and CaO products Also the results showed that the gaseous phase was mainly composed of CO Mechanical activation wasperformed on the mixtures molybdenite Graphite Magnesium oxide 1 2 2 and molybdenite Graphite calcined Dolomite 1 2 2 in argon atmosphere for different time periods 0 50 hours using a planetary ballmill Structural and phase changes in the powder mixtures were investigated by X ray diffraction XRD TheResults showed that no reaction occurred in the mill to produce new phases in the mixtures Changes inMolybdenite crystallite size and structural micro strain were studied based on integral breadth analysis ofobtained XRD patterns However by mechanical activation the grain size and structural strain of Molybdenitewere decreased and increased respectively The Parameters d and tan were introduced for evaluation ofthe degree of mechanical activation in different mixtures The Results showed that the activation inMoS2 C MgO mixture was lower than MoS2 C CaxMg1 xO More over Scanning electron microscopy SEM was carried out in order to investigate the morphological changes in the structure due to milling SEMobservations revealed that mechanical milling produces a compacted composite structure of particles Theeffects of Mechanical activation on the reduction of different samples were thoroughly investigated bysimultaneous Thermal Analysis STA The samples were heated in argon atmosphere with the linear heatingrates of 10 15 20 C min the plots of process conversion degrees versus temperature showed that bymechanical activation for 50 hours the starting reduction temperature of reduction in two mixtures molybdenite Graphite Magnesium oxide and molybdenite Graphite calcined Dolomite decreased 190 Cand 240 C respectively Kinetics of Molybdenite carbothermic reduction in non isothermal conditions werestudied by model fitting Coats Redfern and model free Ozawa Friedman Kessinger methods It s wasfound that the Boudouard reaction was the controlling step in the carbothermic reduction of Molybdenite inpresence of Magnesium oxide The reduction activation energy and pre exponential factor were about 425kJ mol 1 and 7 1010 Sec 1 respectively Milling for 50 hours decreased the activation energy and pre exponential factor to 251 kJ mol 1 and 1 106 Sec 1 respectively The Carbon gasification with CO2 was thecontrolling step in the carbothermic reduction of Molybdenite in presence of Dolomite The reduction activationenergy and pre exponential factor were about 367 kJ mol 1 and 1 1012 Sec 1 respectively Milling for 50 hoursdecreased the activation energy and pre exponential factor to 226 kJ mol 1 and 4 109 Sec 1 respectively Key Words Carbothermic reduction Molybdenite Magnesium oxide thermodynamic Kinetic

بيرالوند، خديجه

تاثير فعال سازي مكانيكي بر احياي كربوترمي موليبدنيت در حضور اكسيدهاي قليايي

اكسيدمنيزيم , دولوميت , سينتيك