ساخت آلياژ منيزيم - نيكل به عنوان ذخيره كننده هيدروژن و تاثير عناصر آلياژي بر خواص آن

چكيده انگليسي :

Investigation on Mg Ni Alloy as Hydrogen Storage Material and the Effect of Alloy Element on its Properties Forough sadat Dehghani f dehghani@ma iut ac ir Date of Submission 06 04 2011 Department of Material Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language FarsiSupervisor prof Ahmad Saatchi asaatchi@cc iut ac ir Dr Keyvan Raeisi k raeisi@cc iut ac irAdvasor Dr Mohamad hossein Enayati ena78@cc iut ac irAbstractMg and Mg based alloys have been considered as the negative materials in nickel metal hydride Ni MH batteries because of high hydrogen storage capacity light weight and low cost However their poor kineticand low cyclic life makes a wide study necessary Unlike the recent AB5 type and AB2 type hydrogenstorage alloys such as LaNi5 and ZrMn2 nanocrystalline Mg based alloys provide the highest initialdischarge capacity with no need to activation process Initial discharge capacity and kinetic of charge anddischarge can be improved by increasing the lattice defects creating fresh surfaces and refining the grainsfor example through mechanical alloying MA In this paper the effect of substitution of Ni in Mg2Nialloy compound with Co was studied The nominal Mg2Ni1 xCox x 0 0 1 0 2 0 3 alloys were synthesizedby two method of MA The speed of process and the ball to powder weight ratio were selected 500 rpm and20 1 respectively In method 1 adding Co to Ni and Mg powder at the first moments of MA process wasled to the formation of some new phases such as Mg2Co MgCo2 instead of a complete substitution But in method 2 powder of Co was added after formation of Mg2Ni phase and was milled again for 30 hours Inthis way the most of Co atoms dissolved in Mg2Ni lattice Characterization of powder was carried out bySEM TEM and X ray diffractometer Electrochemical measurements were used to evaluate the effects ofCo substitution on storage capacity cyclic life and kinetic of adsorbsion desorption of Mg2Ni The resultsshowed that adding Co by method 1 causes to decrease hydrogen storage capacity but improves cyclic life Because cobalt oxide serves as a protective film on the alloy surface prevents the electrode from furthercorrosion in KOH solution and enhances the cycle performance In contrast adding Co by method 2increase hydrogen storage capacity Dissolved Co atoms in this method led to increase the lattice parameter So the diffusion rate of hydrogen in bulk of alloy improved and discharge capacity increased The surfaceof the alloy particles after 8th charge discharge cycle changes from smooth to rough The kinetic ofreactions was also characterized by electrochemical impedance spectroscopy and anodic polarization Allthe spectra of electrochemical impedance consisted of a semicircle at high frequencies and a linear region atlow frequencies The loop in the high frequency region indicates on the charge transfer process at thealloy electrolyte interface and the linear response in the low frequency region Warburg is related tohydrogen diffusion in a bulk of electrode Adding Co under method 1 retarded the rate of charge transferprocess and had no influence on the slop of linear response Adding Co by method 2 accelerated not onlycharge transfer but also diffusion process The anodic polarization curves of Mg2Ni1 xCox x 0 1 and 0 3 alloys show a critical current density ic which represents the hydrogen diffusion rate in the bulk alloy andalso electrocatalytic activity of alloy Adding Co in method 1 decrease electrocatalytic activity of alloys Incontrast adding Co in method 2 increases electrocatalytic activation of alloys Keywords Electrochemical properties Hydrogen storage Nanostructure Mg2Ni alloy Mechanical alloying

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ساخت آلياژ منيزيم - نيكل به عنوان ذخيره كننده هيدروژن و تاثير عناصر آلياژي بر خواص آن

آلياژ نانو ساختار Mg2Ni , خواص الكتروشيميايي , آلياژ سازي مكانيكي