Synthesis, improvement and application of mechanically alloyed AB5´s to a two stages hydrogen compression system

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

Reyhavik, Iceland

Conferencia; MH2008-International Symposium on Metal-Hydrogen Systems; 2008

Hannes Jónsson-Svein Ólafsson-University of Iceland

LaNi5 and La0.67Ce0.19Nd0.08Pr0.06Ni5 intermetallics were synthesized by low energy mechanical alloying under Ar atmosphere. The as milled and annealed AB5´s structural properties and hydrogen sorption pressure-composition isotherms (PCI´s) were analizyed by X ray diffractometry (XRD), scanning electron microscopy (SEM), energy dispersive espectroscopy (EDS) and volumetric methods, respectively. A summary of results is shown in Figure 1. The presence of  broad peaks and steeped plateaus of as milled samples were associated to the residual strain and structural inhomogeneites induced by mechanical alloying [1]. These conditions impede the straighforward use of the intermetallic in thermal hydrogen compression systems.  In each case, the as milled materials features were improved by annealing treatments in Ar during 48 h at different temperatures: 200, 400 and 600 ºC. No significative microstructural changes and a slight increment in PCI´s qualities were obtained for samples annealed at 200 ºC as observed for LaNi5. A marked improvement of these properties was obtained at annealing T = 400 ºC. Reduction in strain, crystallite size increment and an appreciable improvement in hydrogen sorption capacity along with a a decrement in hysteresis and PCI´s slope were obtained. The best set of properties were found after annealing at 600 ºC.  A significative reduction of strain values and an appreciable increment in the PCI´s quality were observed. Both intermetallics were treated by this combined low energy mechanical alloying-low temperature annealing process [2]. Since AB5´s are normally obtained by high temperature fusion and high temperature annealing (T > 900 ºC), this is a successful synthesis-improvement two steps method. A two stages compression scheme composed by a potential in-series-tanks containing LaNi5 and La0.67Ce0.19Nd0.08Pr0.06Ni5  with a hydrogen compression ratio of  3.64 was finally obtained. References: 1.  M.R. Esquivel, G. Meyer, J. Alloys Compd., 446-447, (2007) , 212-217. 2. M.R. Esquivel, J.J. Andrade Gamboa, F.C. Gennari, G. Meyer, Sohn International Symposium Advanced processing of metals and materials, Vol. 4, (2006), 517-526.