A Study On The Hydrogen Absorption Properties Of Slurry Systems Composed Of Hydrogen Storage Alloys And Benzene

The hydrogen storage properties of the slurry systems made by mixing benzene with MINis, Mg-Ni, La-Ca-Mg-Ni and Mg2Ni respectively were investigated. By means of XRD/XPS analyses, SEM investigations, TEM observations and P-C-T measurements, the phase and surface structures of the treated and untreated alloys and the influences to the hydrogen absorption properties produced by organic solvent treatment were studied in detail.It is discovered that only the alloy absorbs hydrogen in the slurry system formed by MlNi5 and benzene below 60"C. The hydrogen absorption rate of the alloy suspended in benzene is only limited by the mass transfer coefficient. The AH?and AS0 of the hydrogen absorption of the alloy in slurry system and gas-solid system are respectively -27.1kJ/molH2, - 83.6J/Kmol and -27.2kJ/molH2, -85.7J/Kmol which confirms that the absorption thermodynamics of the alloy in two systems are similar.After 40h milling, the Lai.gCao.aMgieNi alloy transformed from crystalline to amorphous. The shape of the alloy particles changed sharply. The edges and corners disappeared and the surface became much smoother. The activation properties of the alloy are deteriorated by the mechanical milling treatment but the hydrogen desorption properties of the amorphous alloy is improved. At 275 "C and under O.lMPa H2, the milled Lai.8Cao.2Mg16Ni desorbed ~1.0wt% H2 in Ihr but no hydrogen desorption of cast alloy is observed at the same condition. Some Mg2Ni powders were added into the Lai.gCao^Mg]6Ni alloy and milled together. After 20hr, the composite transformed from crystalline to amorphous, too. The shape of the composite particles changed greatly, but the edges and corners still existed. The incubation period of the milled composite is far shorter than that of the milled Laj.gCao^MgieNi.The slurry formed by benzene and Mg-Ni alloy is a bi-phase hydrogen storage system. There are two portions in the hydriding curves of the slurry formed by Mg-Ni and benzene. The hydriding rate in the former portion is slower than that in the later. The results from the hydrogen absorption measurements of the slurry formed by mixing benzene with Mg-Ni alloy and metal hydride respectively show that the metal hydride is the main catalyst to the hydrogenation of the benzene.Both the alloy and benzene absorb hydrogen in the slurry systems formed by mixing benzene with untreated and treated Lai.8Cao.2Mgi7_xNix and Mg2Ni respectively. When the untreated alloys are used the hydriding rate of the slurry is slow. After organic solvent solution treated, many featheriness microstructures are formed on the surface of Lai gCao^MguNis and Mg2Ni. The XPS analysis resultsshow that some new magnesium compound formed and the content of nickel atoms increased on the top layer. The hydrogen absorption rate of the slurry formed by the treated alloy and benzene increased sharply. In the best treatment condition, the slurry absorbs 6.56wt% hydrogen in 3~4min at 483K and under a hydrogen pressure of 4.5MPa.