Microstructure and Hydrogen Permeability of Duplex Phase M-ZrNi (M=V, Nb, Ta) Alloys
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0980-II05-53
Microstructure and Hydrogen Permeability of Duplex Phase M-ZrNi (M=V, Nb, Ta) Alloys Kazuhiro Ishikawa1, Naoshi Kasagami2, Tomoyuki Takano2, and Kiyoshi Aoki1 1 Materials Science, Kitami Institute of Technology, 165 Koen-cho, Kitami, 090-8507, Japan 2 Graduate student, Kitami Institute of Technology, 165 Koen-cho, Kitami, 090-8507, Japan
ABSTRACT In order to develop non-Pd based high performance hydrogen permeation alloys, microstructure, crystal structure and hydrogen permeability (Φ) of duplex phase M-ZrNi (M=V and Ta) alloys were investigated using a scanning electron microscope, an X-ray diffractometer and a gas flow meter. These results were compared with those of Nb-ZrNi ones which have been previously published. The hydrogen permeation was impossible in the V-ZrNi alloys, because they were brittle in the as-cast state. On the other hand, duplex phase alloys consisting of the bcc-(Ta, Zr) solid solution and the orthorhombic ZrNi (Cmcm) intermetallic compound were formed and hydrogen permeable in the Ta-ZrNi system. The Ta40Zr30Ni30 alloy shows the highest value of hydrogen permeability of 4.1 × 10 −8 [molH2m-1s-1Pa-0.5] at 673 K, which is three times higher than that of pure Pd.
INTRODUCTION The steam reformed hydrogen gas includes impurities such as CO and CO2. Such hydrogen gas must be purified by some methods, because CO degrades severely the catalytic effect of Pt electrodes of fuel cells. Pd alloys are commercially used for a separation and purification of hydrogen, but Pd is too expensive and scare in resources. Therefore, the low cost and high performance alloys other than Pd based ones are strongly desired. Although many researchers try to develop non-Pd based alloys such as V-based alloys [1] or amorphous alloys [2], it is difficult for high hydrogen permeability and large resistance to the hydrogen embrittlement to be compatible in these alloys. The present authors have demonstrated that the hydrogen embrittlement is prominently suppressed in duplex phase Nb-TiNi alloys [3]. These alloys consist of the primary bcc-(Nb, Ti) solid solution, which contributes mainly to hydrogen permeation, and the eutectic {B2-TiNi + (Nb, Ti)} phase, which mainly does to the suppression of the hydrogen embrittlement [4]. Their hydrogen permeability (Φ) is higher than that of pure Pd, and these alloys are not broken down by the hydrogen embrittlement between 673K and 523 K [3]. On the other hand, it is known that both V and Ta show high Φ equivalent to that of Nb [5]. Therefore, it is expected that both Ta-TiNi and V-TiNi alloys show high Φ. This estimation has been recently supported by the present authors [6]. On the other hand, the Nb-ZrNi alloys show two times higher Φ than that of Nb-TiNi ones [7, 8]. These experimental results strongly
suggest that Φ of the V-ZrNi and the Ta-ZrNi alloys are high in the same way as Nb-ZrNi. In the present work, microstructure, crystal structure and Φ of duplex-phase V-ZrNi and Ta-ZrNi alloys are investigated and their characteristics are compared with those of Nb-Z
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