Naslov
Crystal structure and hydride formation of the HoNi5-xGax alloys

Autori
Miletić, Goran ; Šorgić, Božica ; Drašner, Antun ; Blažina, Želimir

Izvornik
Journal of Materials Scielce Letters (0261-8028) 20 (2001), 13; 1217-1219

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, članak, znanstveni

Ključne riječi
intermetallic compounds; metals and alloys

Sažetak
Alloys of the composition HoNi5-xGax were prepared and studied by means of x-ray powder diffraction. It was found that nickel in HoNi5 can be replaced by gallium up to the composition HoNi2Ga3. The hexagonal structure of the prototype compound (CaCu5 type ; space group P6/mmm) is preserved in all as-cast alloys for xó2. Another hexagonal structure (YCo3Ga2 type ; space group P6/mmm) closely related to the structure of HoNi5 was observed in alloys for xň2.5. However, after annealing HoNi3Ga2 also adopts the unit cell of the YCo3Ga2 type, while HoNi2Ga3 could not be prepared as a good single phase material regardless to heat treatment. All single phase alloys have been exposed to hydrogen and were found to absorb up to 3.8 hydrogen atoms per alloy formula unit at room temperature. The hydrogen uptake depends on the structure and the composition of the alloy. HoNi5, HoNi4.5Ga0.5 and alloys with the unit cell of the YCo3Ga2 type are inert to hydrogen at pressures up to 10 MPa. For the alloys which react with hydrogen the equilibrium pressure and the hydrogen capacity decrease with increasing gallium content. The pressure-composition desorption isotherms were measured, and the thermodynamic parameters have been extracted for the alloy - hydrogen systems that exhibit an equilibrium pressure plateau.

Izvorni jezik
Engleski

Znanstvena područja
Kemija

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