Equilibrium Isotope Effects in the Preparation and Isothermal Decomposition of Ternary Hydrides Pd(H_xD_1−x)_y (0 < x < 1 and y > 0.6)

Abstract

A Sieverts' apparatus coupled with a residual gas analysis is used to measure the concentration variations of hydrogen isotopes in the gas and solid phases during exchange and isothermal decomposition of mixed hydrides. beta-phase palladium hydrides with known ratios of H:D, Pd(H x D 1- x ) y (0 < x < 1, y > 0.6), are prepared by H 2 with PdD y or D 2 with PdH y exchange, and their desorption isotherms are reported here at 323 K. A higher equilibrium pressure in isothermal desorption of mixed hydrides is associated with a higher ratio of D/H in the initial mixed hydrides in beta-phase. The composition of the gas desorbed from a mixed hydride varies; i.e., the ratio of D/H in gas decreases with the sum of (H + D) in Pd. The values of the separation factor alpha during desorption at 323 K and during H-D exchange at 248 K are discussed and compared with those in the literature. Desorption isotherms of mixed isotope hydrides are between those of the single isotope hydrides of H-Pd and D-Pd, however, plateaus slope more than those of pure isotope hydrides. The origin of the plateau sloping in the mixed hydrides can be attributed to the compositional variations during desorption, i.e., the equilibrium pressure is greater when D/H ratio in solid is greater. A simple model is proposed in this study that agrees well with experimental results.

Absorption isotherms for H2(D2)–Pd0.8Ag0.2 (198–323K)

“…The separation factor˛has larger values at lower temperatures, which agrees with those for other metal systems reported in the literature [11]. Some˛values calculated from the literature isotherms for H 2 /D 2 -Pd 0.8 Ag 0.2 desorption [2] and H 2 /D 2 -Pd absorption and desorption [6,12,13] are included in this figure for comparison. Experimental˛data calculated from the definition = (D g /D s )/(H g /H s ) for the H-D-Pd system in plateau region at 323 K [14] are included in Fig.…”

“…For some systems the absorption isotherm shows more sloping than that for desorption, such as H-(Pd-Rh) and H-V systems [8,9]. It is not clear if this accounts for the extra sloping for the absorption isotherm for H(D)-Pd 0.8 Ag 0 . [2]), H2/D2-Pd absorption (brown diamonds are from this work and [12], blue circles are from Lasser and Klatt [13]), and H2/D2-Pd desorption (yellow triangles from Lasser and Klatt [13]). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of the article.…”

Semimetal with both Rarita-Schwinger-Weyl and Weyl excitations

“…The massive RS equations in 2+1 dimensions, especially its behavior in an external magnetic field are nontrivial 37 . We will study this in a separated work 38 .…”

Uranium for hydrogen storage applications : a materials science perspective.

“…From Manchester's review, more work could be done to better understand the phase diagram at low hydrogen concentrations; however, such information is not likely to be of much relevance for storage applications. Exchange experiments, similar to those conducted by Luo [40] for the Pd system would likely be quite valuable.…”