時分割型Ｉｎ‐ｓｉｔｕ ＸＲＤ法によるＬａＮｉ５の速度論的構造評価

Abstract

Although recently there have been many reports on the in-situ structural characterization of hydrogen storage alloys, these studies were all conducted under equilibrium states. In practice, however, hydrogen storage alloys alternate hydrogen absorption and desorption processes ceaselessly. Therefore, in functional situations where hydrogen storage alloys are utilized, their hydrogen absorption properties cannot be evaluated precisely by applying the results of observations made under equilibrium states. We assessed the hydrogen absorption behavior and phase transformation of LaNi5 during the hydrogen absorption process using our newly developed time-resolved in-situ XRD system for vapor-solid phase reaction. This system, which comprises a chamber for performing in-situ XRD measurements, a Sieverts' component for measuring hydrogenation speed, and a PSPC (position-sensitive proportional counter) X-ray detector, enables sequential XRD measurement in an in-situ atmosphere. Over a period of several minutes, we observed the phase transformation of the master alloy of LaNi5 into a hydride of LaNi5H6 during the hydrogen absorption process and evaluated the process sequentially at intervals of a few seconds. Our results showed that the actual phase transformation during the process of hydrogen storage differs from what had been characterized previously under an equilibrium state. It was also made clear that the lattice volume of the hydride produced remains unchanged between the onset of hydride formation and attainment of the equilibrium state.