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Positron lifetime study on the degradation of LaNi 5 and LaNi 4.8 Sn 0.2 during hydrogen absorption‐desorption cycling

2007; Wiley; Volume: 4; Issue: 10 Linguagem: Inglês

10.1002/pssc.200675827

1862-6351

Hideki Araki, Ryousuke Date, Kouji Sakaki, Masataka Mizuno, Yasuharu Shirai,

Ammonia Synthesis and Nitrogen Reduction

Abstract LaNi 5 and LaNi 4.8 Sn 0.2 alloys have been subjected to pressure‐induced cycling tests at 248 K under a hydriding condition at a hydrogen pressure of 3 MPa and under a dehydriding condition of evacuating by a rotary pump. At the beginning of cycling the hydrogen absorbing capacity of LaNi 5 was larger than that of LaNi 4.8 Sn 0.2 . However, the capacity of LaNi 5 was markedly decreased by the cycling, whereas the capacity of LaNi 4.8 Sn 0.2 was hardly changed. After 100 cycles, the capacity of LaNi 5 became smaller than that of LaNi 4.8 Sn 0.2 . On the other hand, it was also found that the increase in the positron mean lifetime by the cycling for LaNi 4.8 Sn 0.2 was smaller than that for LaNi 5 , revealing that substitution of Sn suppresses the formation of vacancy during the cycling. This result suggests that the degradation in hydrogen absorbing capacity should be attributed at least partly to trapping of hydrogen at excess vacancy formed by hydriding. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)