بررسي تاثير آهن و كار مكانيكي بر احياي كربوترمي موليبدنيت در حضور آهك

چكيده انگليسي :

Investigation of the Effect of Iron and Mechanical Milling on the Carbothermic Reduction of Molybdenite in the Presence of Lime Noushin Loghmani Devin n loghmani@ma iut ac ir May 11 2011 Department of Materials Engineering Isfahan University of Technology Isfahan 84156 83111 IranDegree M Sc Language FarsiDr Mohammad Hasan Abbasi Prof Supervisor E mail abbasi32@cc iut ac irDr Mehdi Ahmadian Ass Prof Supervisor E mail ahmadian@cc iut ac irAbstractIn this study the effect of iron and mechanical activation on structural evolution and reduction behavior ofmolybdenite with Carbon in the presence of Lime has been investigated Various iron amounts 0 10 wt were added to the powder mixture of molybdenite carbon and lime 1 2 2 Mechanical milling wasperformed on the mixtures in argon atmosphere for different time periods 0 70 hours using a planetary ballmill Phase determination was carried out using a X Ray diffractometer with Cu k radiation 1 5405 Ao The results demonstrated that by 70 hours milling on activated powders with and without iron no chemicalreaction occured in the mixture XRD analysis revealed that carbon peaks completely disappeared indiffraction patterns of samples milled for more than 10 hours due to the annihilation of carbon crystalstructure In addition change in molybdenite crystallite size and structural microstrain were studied based onintegral breadth analysis of obtained XRD patterns However by mechanical activation the grain size andstructural strain of molybdenite were decreased and increased respectively Furthermore iron content had noinfluence on molybdenite carbon and lime mixture activation 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 produsces a compacted composite structure of particles Themechanical activation parameter d was introduced for evaluation of mechanical activation and also as acriterion for the degree of mechanical activation in different mixtures The obtained results from the methodswere in agreement with previous findings The effect of milling time and iron content on the reduction ofdifferent samples were thoroughly investigated by Simultaneous Thermal Analysis STA The samples wereheated in argon atmosphere with the linear heating rates of 10 15 20 oC min The plots of processconversion degrees versus temperature showed that by mechanical activation for 50 hours the starting andfinal reduction temperature of the reduction of samples with no iron and 10 wt iron is decreased 186 oC and327 oC respectively Kinetics of molybdenite carbothermic reduction in non isothermal conditions werestudied by model fitting Coats Redfern and model free Ozawa Kessinger Tang Starink methods It salso obtained that the Boudouard reaction was the controlling step in the carbothermic reduction ofmolybdenite The reduction activation energy and pre exponential factor were about 83 18 kcal mol and1 56 1012 s 1 respectively Milling for 50 hours decreases the activation energy and pre exponential factor to67 08 kcal mol and 1 81 1010 s 1 respectively Due to the catalytic effect of iron the activation energy in thepresence of 7 wt iron reduced to 51 13 kcal mol The reduction reaction pre exponential factor of sampleswith 7 wt iron was1 01 108 s 1 At low temperatures the carbothermic reduction reaction of samples withand without iron progresses in solid state and at higher temperatures the reaction is gas solid type Keywords Kinetic Molybdenite Mechanical activation Carbothermic reduction Iron

لقماني دوين، نوشين

بررسي تاثير آهن و كار مكانيكي بر احياي كربوترمي موليبدنيت در حضور آهك

سينتيك , فعال سازي مكانيكي