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Effect Of Alloying, Heat Treatment And Magnetization Treatment On Microstructure And Electrochemical Properties Of AB5 Type Hydrogen Storage Electrode Alloy

Posted on:2003-07-26Degree:DoctorType:Dissertation
Country:ChinaCandidate:J X MaFull Text:PDF
GTID:1101360062475899Subject:Materials science
Abstract/Summary:PDF Full Text Request
In this thesis, based on the review of the research and development of AB5 type mismetal-based hydrogen storage electrode alloys, some ways to improve the overall properties of AB5 type electrode alloy were proposed as the objects of this study. By the means of XRD analyses, gaseous p-c-T measurements, metallographic observations and electrochemical investigations, the microstructure and electrochemical properties of Co-free ABs type MiNi4 4s,~Mno.4oA1o.IsSn~ alloy, the effect of heat treatment on the microstructure and electrochemical properties of MINi3 60C0085Mn030AJ015 alloy, the effect of magnetization treatment on the electrochemical properties of Lao.9Smo.1Nis.o~Co~ alloy, and rn-situ EIS of AB5 alloy during the first charge were studied in detail, respectively.For Co-free MINI4 4s~Mno4oAlo isSn~ (x=04).5) alloy, it is found that when Sn content x in the alloy is higher than 0.3, the alloy contains the second phases such as LaNiSn besides the LaNi5 main phase, and the amount of the second phase increases with an increasing of Sn content. Absorption.Idesorption p-c-T curves of the alloy studied indicate that both the plateau pressure and the hydrogen storage capacity decrease markedly with increasing Sn content. The electrochemical studies show that the cycling life of the alloy can be improved markedly although the discharge capacity decreases with increasing Sn content. The partial Ni substituted by Sn in the alloy is also found to affect detrimentally the high-rate-dischargeabity (I{RD). and the related mechanism has been studied in detail by means of some electrochernical methods. Among the alloy under studied.the alloy with the chemical composition of M1Ni4.15Mn040A1015Sn03 has the best overall electrochemical properties. This alloy can be activated after two charge/discharge cycles with the discharge capacity of 295.OmAh/g and the capacity retention of 70.45% after 300 cycles. Furthennore, the alloy also shows a high-rate dischargeability (HRD90055. 18%), and the values of some kinetic parameters including exchange current density Jo, limiting current density 'L.transfer coefficient /1 and diffusion coefficient D are 132.5mAIg. 7O7mAig, 0.62 and 3.00x1010 cm2/s~ respectively.The microstructure, p-c-T characteristics and electrochemical properties of as-casted MiNi3 60C0o85Mn030Al01~ alloy and the heat-treated alloy under different conditions have been investigated systematically. The results reveal that the microstructure of as-casted alloy is typical dendrite, and a large number of microcrack are observed at the limb of dendrite. The microstructure of alloys by heat-treatment at 1273K for different holding lime and water-cooling is columnar crystal, and the grain size increases, to some degree, with an increasing of holding time. Compared with as-casted alloy, the plateau pressure of the heat-treated alloy decreases, the p-c-I curves flatten, and the hydrogen storage capacity increases tosome degree. The electrochemical studies show that, for the heat-treated alloy, the cycling life and the high-rate dischareability increases while the discharge capacity decreases when heating temperature increases from 1273K to 1423K; the electrochernical properties of the alloy vary irregularly with cooling rate; and electrochemical properties of the alloy have almost no change when holding time prolong from 2hr to 8hr.Based on the studying on phase structure and the intrinsic magnetic properties of La0 gSm0 ]Ni5OXC0X (x1 .5--3 .0) alloys, the effect of magnetization treatment on the electrochemical properties of the alloy were investigated systematically. The results show that the alloys consist of a single phase of CaCu5 type LaNi5 phase, arid the Curie temperature T~ and the saturation magnetization intensity M~ increase with increasing Co content. It is found that the electrochemical properties of the alloys studied can be improved effectively by magnetization treatment. Firstly, after being magnetized, the discharge capacity of the treated alloys increase markedly. Secondly, the discharge...
Keywords/Search Tags:AB5 type hydrogen storage electrode alloy, Microstructure, Electrochemical propeines, Alloying, Heat treatment, Magnetization treatment, In-situ EIS
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