| 研究実績の概要 |
TiFe is an excellent candidate for stationary hydrogen storage applications. However, TiFe does not absorb hydrogen easily because of surface oxidation. We showed that TiFe processed by HPT absorb hydrogen at room temperature. We showed that the activation of sample is due to (i) enhanced diffusion of hydrogen, (ii) segregation of catalytically active Fe-rich phase and (iii) formation of large fraction of grain boundaries as pathways to transport hydrogen through the oxide layer.
In order to investigate the importance of grain boundaries, TiFe was processed by four different routes and the activation was investigated. The annealed sample, with micrometer grain sizes, did not absorb hydrogen. The cold-rolled sample, with submicrometer-micrometer grain sizes, was partially activated. The HPT-processed sample, with nanometer-submicrometer grain sizes, was fully activated under 2 MPa. The ball-milled sample, with nanometer grain sizes, was fully activated under 1 MPa. Therefore, the activation becomes easier when the grain size is smaller.
In order to investigate the effect of grain boundaries on activation, two other intermetallics, TiFeMn and Mg2Ni, were used. TiFeMn was used to reduce the hydrogenation pressure, but TiFeMn also suffered from difficult activation. While TiFeMn after annealing did not absorb hydrogen, the HPT-processed sample absorbed hydrogen at room temperature under 0.7 MPa. Similar mechanism was observed in activation of Mg2Ni using HPT. The current part of study also confirms that the large fractions of grain boundaries are responsible for activation.
|
