Research on Computer Optimization of Low-Cost Hydrogen Storage Alloy Containing Boron Prepared by Strip Casting and its
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0971-Z07-04
Research on Computer Optimization of Low-Cost Hydrogen Storage Alloy Containing Boron Prepared by Strip Casting and its Microstructure and Performance Guo Hong1, Han Weiping1,2, Zhang Ximin1, and Shi Likai1 1 Beijing General Research Institute for Non-ferrous Metals, Beijing, 100088, China, People's Republic of 2 Beijing University of Science and Technology, Beijing, 100083, China, People's Republic of ABSTRACT: A kind of low-cost hydrogen storage alloy containing boron has been prepared by near rapid solidification strip casting. And computer optimization has been carried out through mode identification and neuro-network. The alloy microstructure, the alloy performance and the battery performance have been evaluated through optical microscope, TEM and X-ray diffraction. The results indicate that the alloy microstructure is fine columnar crystal and there exists the second phase of CeCo4B on the crystal interface, which increases the diffusion channels for hydrogen atoms and improves the alloy activation. The MmNi3.9Co0.37Mn0.4Al0.3B alloy has excellent performance at room, high and low temperatures prepared by strip casting. KEYWORDS: hydrogen storage alloy, low cost, strip casting INTRODUTION Since the commercialization of small size NiMH battery in 1990, it has rapidly grown and gained a good sales share in the rechargeable battery market. But with the development of electric vehicles (EVs), NiMH cells are encountering serious competition from Li-ion cells, thus the cost reduction of NiMH battery is very critical to the realization of EVs. Willems and Buschow have indicated that the AB5 type hydrogen storage alloys had perfect electrochemical cycling stability[1]. A typical composition of commercial hydrogen storage alloy is MmNi3.55Co0.75Mn 0.4Al0.3. Co was the most expensive element among all the elements, 10wt% Co leading to about 30-40% of the total price of the alloy. Now a key problem is how to improve cycle stability of low cobalt alloys. Several possibilities have been proposed in the literatures [2-5]. We prepared alloys (Co 5%) by substituting boron for part of Co and fixing the stoichiometric ratio at 5.2:1, and the alloys were also re-melted by strip casting. EXPERIMENTAL DETAILS 1. Alloy preparation, X-ray diffraction The low Co Mm-based alloys had a general formula, Mm (Ni4.5-x-yCoyMn0.3Al0.4Bx)5.2, in which x=0.03, 0.05, 0.08, 0.1, 0.2, 0.3, y=0.36-0.38(the content of Co is not more than 5%). They were arc-melting in a water cooled copper hearth under argon atmosphere. The ingots were re-melted three times to ensure good homogeneity. For comparison, the ingots were superheated again in vacuum induction furnace, when the temperature reached the desired level, alloy was cooled on a rotating Mo roll. The strip casting alloys were mechanically pulverized under argon atmosphere, respectively. The alloy powder was passed through a 500 mesh with a diameter of less than 25µm. And the alloy powder was determined for crystal structure by X-ray diffraction (XRD) using Cu Kα radiation. 2. Electroc
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