Hydrogen absorption properties of ZrNi5−xCox alloys

The structural and hydrogen sorption properties of the ZrNi5−xCox (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 AuBe5 type structure, whereas the ZrNi2Co3 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 ZrNi2Co3 alloy (1.3 hydrogen atoms per formula unit).