Hydrogenation of titanium-based quasicrystals

Hydrogen Pressure-Composition Isotherms for Ti<SUB>45</SUB>Zr<SUB>38</SUB>Ni<SUB>17</SUB> Amorphous and Quasicrystal Powders Produced by Mechanical Alloying

“…The PCT for alloys containing two or more phases can be generally obtained by superimposing the PCT for each phase, although the total hydrogen concentration (H/M) in the alloy should be adjusted by the amount in each phases of the alloy. Since no PCT data for the (Ti, Zr) 2 Ni phase have been reported, it is difficult to investigate the influence of that phase on the PCT measurements for the i-phase powder. But, Buchner et al 14) reported that the binary Ti 2 Ni phase absorbed great amount of hydrogen interstitially, forming four kinds of hydride phases, Ti 2 NiH 0.5 , Ti 2 NiH, Ti 2 NiH 2 , and Ti 2 NiH 2.5 , showing clear flat plateaus at about 11 kPa (for Ti 2 NiH 0.5 and Ti 2 NiH), 66 kPa, and 0.1 MPa at a temperature of 423 K. Taking these results into account and assuming that the influence of Zr to the PCT is the same as that of Ti (although there is an atomic size difference between them), it is concluded that the amount of the (Ti, Zr) 2 Ni phase in the i-phase powder must be very small, because the equilibrium hydrogen pressures as well as the plateau-like pressures detected in this study are far less than those for the Ti 2 Ni phase.…”

“…Since no PCT data for the (Ti, Zr) 2 Ni phase have been reported, it is difficult to investigate the influence of that phase on the PCT measurements for the i-phase powder. But, Buchner et al 14) reported that the binary Ti 2 Ni phase absorbed great amount of hydrogen interstitially, forming four kinds of hydride phases, Ti 2 NiH 0.5 , Ti 2 NiH, Ti 2 NiH 2 , and Ti 2 NiH 2.5 , showing clear flat plateaus at about 11 kPa (for Ti 2 NiH 0.5 and Ti 2 NiH), 66 kPa, and 0.1 MPa at a temperature of 423 K. Taking these results into account and assuming that the influence of Zr to the PCT is the same as that of Ti (although there is an atomic size difference between them), it is concluded that the amount of the (Ti, Zr) 2 Ni phase in the i-phase powder must be very small, because the equilibrium hydrogen pressures as well as the plateau-like pressures detected in this study are far less than those for the Ti 2 Ni phase. A PCT at 623 K for a Ti 45 Zr 38 Ni 17 i-phase ribbon obtained by melt-spinning, reported by Kim et al, 8) showed that equilibrium hydrogen pressure remained low (less than 0.5 kPa) below H/M ≈ 1, after which it increased sharply with increasing H/M.…”

“…After the PCT measurement, XRD peaks corresponding to the i-phase and the (Ti, Zr) 2 Ni phase shift to the lower angles, indicating exapnsions of the quasilattice and the crystal lattice. As reported previously, 7) the (511) peak of the (Ti, Zr) 2 Ni phase appears on the higher angle side of the (110000) of the i-phase due to a difference in the degree of expansion between the quasilattice and the crystal lattice after the PCT measurement. The quasilattice constants 15) before and after PCT measurement at 523 K (H/M ≈ 1.3) are calculated to be 0.519 nm and 0.550 nm respectively, corresponding to a 6.0% expansion of the quasilattice.…”

“…Ti-Zr-Ni icosahedral (i) quasicrystals, in which Ti and Zr have a strong chemical affinity for hydrogen, produced by melt-spinning or annealing, can store large quantities of hydrogen, almost twice the hydrogen storage capacity of LaNi 5 by weight percent, indicating their potential as new hydrogenstorage materials. [1][2][3][4][5] We have previously reported the formations of amorphous and i-phase powders by mechanical alloying (MA), high-pressure hydrogen loading of the powders, microstructural changes during the early stage of hydrogen cycling, and activation of the powders against hydrogen gas.…”

Dynamic stabilities of icosahedral-like clusters and their ability to form quasicrystals

“…2 Quasicrystals have already been shown to be important in hydrogen storage and as an aeronautical alloy. 3,4 The quasicrystal formed in nature is mainly composed of Al-Cu-Fe 5 (although the Al-Ni-Fe quasicrystal has also recently beendiscovered 6 ), and other quasicrystals have been synthesized. 2 Basically, the Al-based, 1,2,5-10 Zr-based, [11][12][13][14][15] and Ti-based [16][17][18] quasicrystals are of fundamental concern, although the reason why these are indispensable components in such quasicrystals still remains unclear.…”