tailieunhanh - “Soft Chemistry” synthesis of superfine powder alloys AB for Ni-MH batteries

The oxide reduction diffusion (ORD) procedure has recently been applied in synthesizing hydrogen storage materials AB5 for Ni-MH batteries. Starting from metal hydroxides and La oxalat precursor, superfine powder alloys LaNi5, and were obtained by this “soft-chemistry” route. Chemical composition, structure and morphology of alloy phases were examined by different analysis techniques such as AAS, EPMA, X-ray and TEM. The H2-absorption and desorption behavior of crystalline products was determined by Sieverts’ method. Electrochemical properties of alloy samples were characterized by CV, EIS and Battery Test method. | Journal of Chemistry Vol. 42 2 P. 241 - 249 2004 SOFT CHEMISTRy SyNTHESIS OF SUPERFINE POWDER ALLOyS AB5 for Ni-MH BATTERIES Received 25-12-2003 NGO Quoc QUYEN NGUYEN QUÝNH ANH PHAN THI BINH Lab. for Appl. Electrochemistry Vietnamese Academy of Science and Technology SUMMARY The oxide reduction diffusion ORD procedure has recently been applied in synthesizing hydrogen storage materials AB5for Ni-MH batteries. Starting from metal hydroxides and La oxalat precursor superfine powder alloys LaNi5 LaNi45Co05 and LaNi3S7MnL13 were obtained by this soft-chemistry route. Chemical composition structure and morphology of alloy phases were examined by different analysis techniques such as AAS EPMA X-ray and TEM. The H2-absorption and desorption behavior of crystalline products was determined by Sieverts method. Electrochemical properties of alloy samples were characterized by CV EIS and Battery Test method. I - INTRODUCTION Soft-Chemistry synthesis of superfine powder alloys AB5 is based on the reduction of oxides by calciothermic reaction which was carried out by R. E. Cech 1 many years ago however there are only a few reports 2 - 5 dealing with this synthesis route for hydrogen storage electrode materials although nickel-metal hydrid batteries Ni-MH have especially been directed towards practical use recently. This procedure can in case of known LaNi5 be represented by La2O3 10 NiO 13 Ca 1300 K 2 LaNi5 Argon 13CaO 1 The formation mechanism of LaNi5 according to T. Tanabe and Z. Asaki 6 includes two stages The reduction of La2O3 and NiO by Ca Ca La2O3 ------ La 2a _ Ca NiO Ni 2b The simultaneous diffusion of the just-formed rare earth and transition metal Ni in molten calcium leads to initial formation of CaNi5 3 following the substitution of Ca by La to form the more thermodynamically stable alloy LaNi5 4 Ca 5 Ni ------ CaNi5 3 La CaNi5 ------ LaNi5 Ca 4 Single phase crystals of LaNi5 growth in the CaO - Ca slurry as micron-size loose particle of angular shape whose .

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