K. Hashi

Hydrogen absorption and desorption in the binary Ti–Al system

Abstract Binary Ti 1− x Al x alloys were hydrogenated at 5 MPa H 2 pressure at room temperature for 173 ks. Structures and thermal stability of the hydrogenated alloys were investigated by XRD and DSC. The hydrogen absorption and hydrogen desorption behavior were investigated by means of a hydrogen analyzer, DSC and XRD. An fcc type (CaF 2 type) hydride formed for x =0, 0.20 and 0.25 and an amorphous hydride for x =0.30 and 0.35. That is, off-stoichiometric (Al-rich) Ti 3 Al ( α 2 ) amorphized by hydrogen absorption. The amount of hydrogen absorption under the quoted conditions decreased with increasing Al concentration, but the 50% hydrogen desorption temperature T d increased. The hcp solid solution alloy Ti 0.80 Al 0.20 showed the best hydrogen absorption and desorption properties of the Ti 1− x Al x alloys investigated.

Effect of substitutional elements on the hydrogen absorption–desorption properties of Ti3Al compounds

Abstract Ternary elements M were substituted into Ti 3 Al with the aim of reducing the hydrogen desorption temperature of Ti 3 AlH x . On hydrogenation at room temperature, three different states, i.e. amorphous, bcc and C14 Laves phases, were obtained depending on the alloying elements and their amount. The amorphous hydrides formed in the alloys substituted with Zr or Hf showed a high hydrogen capacity and high hydrogen desorption temperature. In the case of the bcc hydrides, formed in the alloys substituted with V or Cr, the hydrogen capacity was largely reduced, but the hydrogen desorption temperature was unchanged or increased. Therefore, V and Cr are the worst substitutional elements to Ti 3 Al. On the other hand, the hydrides having C14 Laves structure formed in the alloys substituted with Mn, Co or Ni showed a reduced hydrogen desorption temperature, although the hydrogen capacity was decreased to same extent. From the present work, Mn, Co and Ni are considered to be effective elements for improvement of the hydrogen absorption–desorption properties of Ti 3 Al.

Hydrogen absorption and desorption in Ti−Al alloys

Binary Ti1−xAlx and ternary Ti0.75−xAl0.25Mx (M=V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Pd, Hf, Ta and W; x=0.15 and 0.25) alloys reacted slowly with 5.0 MPa H2 at room temperature for different periods. The hydrogen absorption capacity, the 50% hydrogen desorption temperature (Td) and the structures of their hydride were investigated. Amorphous and fcc type hydrides formed by hydrogenation of the binary Ti−Al alloys. As the Al concentration increased in the Ti−Al alloys, the hydrogen absorption capacity decreased, while the hydrogen desorption temperature decreased at once and then increased again. Amorphous, fcc, bcc and C14 Laves type hydrides formed by hydrogenation of the ternary Ti3Al− based alloys. The hydrogen absorption capacity was reduced despite whatever elements were substituted for Ti in Ti3Al. Ni, Co, Mn and Nb have the ability to reduceTd of Ti0.75−xAl0.25Mx.

Hydrogen absorption properties of Ti3Al-based ternary alloys

Abstract The structure, the hydrogen capacity and the hydrogen desorption behavior of hydrogenated Ti 3 Al-based alloys substituted with Nb, Mo, Pd, Ta and W were investigated by XRD and a hydrogen analysis with the aim of selecting effective elements to improve the hydrogen absorption–desorption properties of a binary Ti 3 Al alloy. The relation between the hydrogen capacity and the 50% hydrogen desorption temperature was plotted in the diagram obtained in the previous work. Mn, Co, Ni and Nb were selected to be effective elements to reduce the hydrogen desorption temperature, although they gave rise to reduction in the hydrogen capacity.