engleski

On the structural and hydrogen sorption properties of the GdNi5-xAlx syste

The structural and hydrogen sorption properties of the GdNi5-xAlx system have been studied. It was found that nickel in GdNi5 can be replaced by aluminium up to the composition GdNi2Al3, and that the prototype hexagonal crystal structure of the CaCu5 type is preserved in most of the single phase alloys. However, at the composition GdNi2.5Al2.5 a larger unit cell of the YCo3Ga2 type, but closely related to the CaCu5 structure, was observed. All ternary alloys within the composition region GdNi4.75Al0.25 and GdNi3Al2 absorb at room temperature between 4.49 and 2.47 hydrogen atoms per formula unit. Alloys with more aluminium, as well as binary GdNi5, are inert to hydrogen at pressures up to 20 MPa. Hydrogen uptake increases the unit cell volume of the host alloy for about 14 %. The hydrogen equilibrium pressure and the hydrogen capacity decrease with the increased content of aluminium. The entropy and the heat of formation have been calculated for the systems that exhibit a desorption equilibrium plateau.

hydrogen sorption; crystal structure

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