A comparison of the evolution during the mechanical milling of both a Mm-Ni and MmNi5-Ni mixture: stages of milling and microstructural characterization

M.R. ESQUIVEL; G. MEYER

Lahaina. Mahui. Hawaii

Congreso; International Symposium on Metal-Hydrogen systems. Fundamentals and applications; 2006

University of Hawaii

Many of the advantages attributed to materials synthesized by mechanical milling oriented to interaction with hydrogen are related to the introduction of defects and strain on microstructure which enhances the alloy-H interaction. To asses this argument, a study of the evolution during mechanical milling of both Mm-Ni and MmNi5-Ni mixtures is presented. Milling was performed under Ar using a Uni-Ball Mill II apparatus. Experimental set-up includes sample extraction at different milling time in a glove box. Both stages detected during milling and comparison of the microstructure for finally obtained MmNi5 compound was done. Strain and crystallite size of Ni and MmNi5 in both mixtures are correlated to milling time. These parameters were studied by X-ray diffraction technique (XRD). Particle size and morphology obtained in each case are related to the presence of four typical stages developed during milling: Initial, Intermediate, Final and Completion. This study was performed by combined energy dispersive spectroscopy (EDS) and scanning electron microscopy (SEM) techniques.  Complete formation of MmNi5 was obtained at 40 h by direct mechanical milling. Formation of MmNi5 was detected after only 2 h of milling the Mm-Ni mixture at milling times as low as 2 h in a low energy ball mill by heating resultant mixture at temperatures lower than 600 ºC. It was attributed to the energy supplied by mechanical milling to the system. Optimal milling time was found for each mixture studied. References: [1] L. Lü, M. O Lai, “Mechanical Alloying”, Kluver Academic Publishers, Boston, (1998), 46-54.