Reaction kinetics of H2 absorption by lanthanum with and without surface oxide layers

Reactivities of H2, O2 and H2O with the Cr surface between 77K and 298K

“…Using a volumetric method, we have measured the quantitative reactivity of a gas (H 2 , O 2 , H 2 O) on the polycrystalline surface of a metal such as transition metals (Co, Ni [14]), RE metals (La, Ce, Tb, Dy [2][3][4][15][16][17]), and of the RE based hydrogen storage alloys (LaNi 5 [1,18], LaNi 4.5 Al 0.5 [19], LaNi 2.5 Co 2.5 [14]). In this study, using the same method, we aimed to measure quantitatively the reactivity of H 2 , O 2 , or H 2 O with a clean surface of polycrystalline Cr at pressures ranging from 10 −8 Pa to 10 −2 Pa and at temperature of 298 K. For the H 2 reactivity, we measured also at 77 K to obtain kinetic behavior of H 2 on the Cr surface at low temperature.…”

“…However, little information is available for the kinetic feature of the surface of the Ti-Cr alloys. In our previous studies on the mechanisms of the initial activation of LaNi 5 , we investigated systematically the role of compositional elements of the alloy such as La and Ni, and reported quantitative influences of O 2 and H 2 O on the H 2 reactivity of these elements [1][2][3][4]. From those studies, we elucidated that La oxides in the surface region of the LaNi 5 with oxide layers exhibit high reactivities with H 2 even at 298 K, and that this leads to the fast initial activation of the heavily oxidized LaNi 5 [5].…”

Hydrogen absorption kinetics and mechanisms of rare earths (La, Ce, Pr, Nd, Tb, Dy) in the H2O surface reaction at room temperature

“…Careful approach using a clean surface technique should be made in the investigation of the surface property. We have applied the Wagener method [7,8] using ultra high vacuum condition to evaluate the quantitative reactivity of a gas (H 2 , O 2 , N 2 , H 2 O) on the surface of a metal as a function of the amount of reacted gas for many metals such as transition metals (Ti, Ta, W, Fe [9,10], Co, Ni [11]), RE metals (La, Ce, Tb, Dy [12][13][14][15][16][17]), and RE-based alloys (LaNi 5 [11,[18][19][20], Sm 2 Fe 17 [21]). …”