Hydrogen pressure-composition isotherms for Ti₄₅Zr₃₈Ni₁₇ amorphous and quasicrystal powders produced by mechanical alloying

Pressure-composition isotherms (PCTs) for amorphous and icosahedral (i) quasicrystal powders produced by mechanical alloying of Ti₄₅Zr₃₈Ni₁₇ powder mixtures were measured at temperatures of 473 K and 523K at low-hydrogen pressures, lower than 0.1 MPa. Sloping plateau-like features on PCTs were observed at equilibrium hydrogen pressures lower than 1 kPa, below an H/M (hydrogen to metal atom ratio) ≈ 1.2 and ≈ 1 for the amorphous and i-phase powders respectively. The plateau-like region for the i-phase powder was steeper and narrower than that for the amorphous powder, implying some small differences between the local structures of the i-phase and the amorphous phase. After the PCT measurements, an increase in the nearest-neighbor atom spacing and an expansion of the quasilattice were observed for the amorphous and i-phase powders respectively. Impurities from some unsynthesized elemental material and a Ti₂Ni type phase were also present. These also absorbed hydrogen, shown by an expansion of their crystal lattices. However, no crystal hydride formation was observed in any of the powders.