Optimization of structural and hydriding properties of (La,Ce,Nd,Pr)Ni5 intermetallics obtained by low energy mechanical alloying

B.A. TALAGAÑIS; M.R. ESQUIVEL; G. MEYER

Ciudad de Guarujá - Brasil

Congreso; VII Encontro SBPMat - 7 th Brasiliam MRS Meeting; 2008

Sociedade Brasileira de Pesquisa de Materiais

The synthesis of AB5´s from different starting materials can be achieved successfully by mechanical alloying (MA).The process leaves the intermetallic with an adequate particle size distribution and highly distorted and reactive surfaces. These characteristics enhance the hydrinding kinetics. But the residual strain and defects present in the structure diminishes the quality of the hydrogen equilibrium properties leading to steeped plateaus on the pressure composition isotherms. In homogeneities can be released by annealing. The best annealing conditions are reached when the lower temperature and shorter time are found. In this work, the structural and equilibrium hydriding properties of (La, Ce, Nd, Pr) Ni5 intermetallics synthesized by MA were studied.  Microstructures, crystallite size, strain and particle size morphology and distribution of as milled samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). PCI´s were measured by volumetry. Structural and hydrogen sorption properties were improved by annealing. Between 200 and 400 º, the sorption properties show and slight increment in PCI´s quality while the structural properties show almost no changes. Between 400 and 600 ºC, both sets of properties are improved mainly because of the recrystallization processes present. Flat PCI´s plateaus and well defined X-ray diffractograms are obtained for samples annealed 24 h at 600 ºC.  An optimization program was followed at this temperature. 1 The best set of annealing parameters were obtained for time and temperature values of 1 h and 600 ºC, respectively. These are mild conditions respect to usual conditions of synthesis and annealing at temperatures higher than 800 ºC as reported in the bibliography.