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 d iffraction patterns and by pressure-composition-temperature (PCT) diagrams at temperatures ranging from 448 to 523 K. It was found that compositions w ith 0 less than or equal to x less than or equal to 2 were solid solutions of AuBe5 type structure, whereas the ZrNi2Co3 alloy showed a two-phase stru cture. Substitution of Ni by Co increases the unit cell volume of the monop hase alloys by 0.84% per one substituted atom in formula unit. Hydrogen upt ake increases the cell volume of the host alloy by up to 2.3%. In the studi ed 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 pressur e. The hydrogen capacity increases with increasing Co substitution. The lar gest hydrogen solubility has been found for the ZrNi2Co3 alloy (1.3 hydroge n atoms per formula unit). (C) 2001 Elsevier Science B.V. All rights reserv ed.