K. Komiya

Synthesis and Decomposition of Pure Ca(AlH4)2

Pure Ca(AlH4)2 is synthesized and its decomposition reactions are investigated in a fundamental manner. The XRD profile observed is in good agreement with the one reported by Fichtner et al. From TDS measurements, Ca(AlH4)2 appears to decompose into CaH2+2Al+3H2 in three steps. The peak temperature of the first reaction is about 470K which is higher than that for Mg(AlH4)2 (about 450K), indicating that Ca(AlH4)2 is more stable hydride than Mg(AlH4)2. In addition, the catalysis of TiCl3 is doped into Ca(AlH4)2 by ball milling under a hydrogen gas atmosphere and catalytic effects on the decomposition properties are investigated.

Alloying Effects on Hydrogen Permeability of Niobium

Niobium metal is one of the promising material for hydrogen purification because of its high hydrogen permeability. In order to design and develop a new palladium-free hydrogen permeable membrane, it is important to understand the effects of alloying elements on the hydrogen permeability through metals. However, to the niobium metal, the alloying effects still remain unclear. In the present study, using a DC-polarization technique under the diffusion limiting condition, the hydrogen permeability of Nb-5mol%M alloys were investigated in high precision at 573K. Here, M’s were 4d transition metals, Zr, Mo, Ru and Pd. The permeability of niobium is found to be varied with the addition of a small amount of alloying element. For example, the hydrogen permeability of niobium increases by the addition of Zr but decreases by the addition of Ru.

Compositional dependence of phase stability of γ phase formed in vanadium alloys

Abstract Alloying effects have been investigated systematically on the stability of the γ phase (VH 2 ) in various binary V–M and ternary V–Ti–M alloys, where M is a 3d transition metal. It was found that Ti and M in ternary V–Ti–M alloys operate almost independently of each other on the stability of the γ phase. It was also shown that the logarithm of the plateau pressure changes almost linearly with the amount of alloying element, M, in dilute binary V–M alloys. Using this linear relationship, the plateau pressures can be estimated quantitatively even in concentrated V–Ti–Ru and V–Ti–Cr alloys.