Effect of mechanical milling on both the structure and the first hydriding-dehydriding properties of a MmNi5-Ni mixture

M.R. ESQUIVEL; G. MEYER

Lyon - France

Congreso; World Hydrogen Energy Conference 2006; 2006

International Association for Hydrogen Energy

The effects of mechanical milling on both the structure and hydring properties of  MmNi5 synthesized by mechanical alloying has not been studied in detail (1,2). Particularly, it could not be clearly identified the mechanisms that operate during milling and the relationship between time of milling and its effect on the interaction with hydrogen. Mm and Ni were milled 100 h in Ar atmosphere to obtain a MmNi5-Ni mixture. The experimental set up included sample preparation in glove box under low oxygen atmosphere (less than 5 ppm) monitored by traces analyzer and milling of reactants using a Uni-Ball-II apparatus. Alloy was heated at 600 ºC during 3 days to obtain a crystalline compound which served as reference. MmNi5 and Ni mass percentage were determined by Rietveld analysis. During the milling process, aliquots were withdrawn and studied by X-ray diffraction (XRD) , scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). XRD allowed the determination of the change of the crystallite size and strain on both MmNi5 and Ni due to milling. SEM helped to observe the temporal evolution in morphology and size of the particles. From this study, the stages occurring during milling were identified and characterized. DSC was used to determinate the temperature of crystallization of MmNi5 from samples milled at higher times. Selected samples were analyzed and hydrogen absortion-desorption curves were obtained using a modified sievert’s type apparatus designed in our laboratory. The data obtained from room temperature absorption-desorption isotherms was correlated with the defect and strain production on the material during milling.   References (1) M. Jurczyk, W. Rajewski, W.Majchrzycki, G. Wójcik, J. Alloys Compounds, 290, (1999), 262-266. (2) M. Jurczyk, J. Alloys Compounds, 307, (2000), 279-282.