Hari Bala

Hydrogenation equilibria characteristics of LaNi5−xZnx intermetallics

Abstract A series of metal hydride alloys were prepared based on the LaNi 5 formula, by substituting 0, 5, 10, 15 and 20 at.% of Zn for Ni. The obtained pseudobinary LaNi 5− x Zn x alloys have been characterized by X-ray diffraction patterns and hydrogen pressure–composition–temperature ( PCT ) diagrams at temperatures ranging from 293 to 353 K. The P – C isotherms were used to determine thermodynamic functions (enthalpy and entropy) for the hydrogen desorption process. Increasing Zn substitution causes the unit cell volume to increase and the plateau pressures to decrease. The maximum concentration of hydrogen in the tested La(Ni,Zn) 5 alloys slightly decreases with increasing Zn content.

Hydrogen absorption properties of ZrNi5−xCox alloys

Abstract The structural and hydrogen sorption properties of the ZrNi 5− x Co x ( x =0,1,2 and 3) system have been studied. The alloys were characterized by X-ray diffraction patterns and by pressure-composition-temperature (PCT) diagrams at temperatures ranging from 448 to 523 K. It was found that compositions with 0≤ x ≤2 were solid solutions of AuBe 5 type structure, whereas the ZrNi 2 Co 3 alloy showed a two-phase structure. Substitution of Ni by Co increases the unit cell volume of the monophase alloys by 0.84% per one substituted atom in formula unit. Hydrogen uptake increases the cell volume of the host alloy by up to 2.3%. In the studied conditions of temperature (448 to 523 K) and pressure (0.05 to 2.5 MPa) the PCT diagrams do not exhibit any plateau of hydrogen equilibrium pressure. The hydrogen capacity increases with increasing Co substitution. The largest hydrogen solubility has been found for the ZrNi 2 Co 3 alloy (1.3 hydrogen atoms per formula unit).