[en] Cyclic hydrogenation of an LmNi₅-based alloy up to 3000 cycles at room temperature was conducted. Based on the (P-C-T) curve of the activated alloy, the initial charging pressures were set at four different values so that the saturated hydrogen loadings in equilibrium were controlled at H/M=1.0, 0.75, 0.50, and 0.25. The cyclic hydrogenation test was made for each loading. The absorption kinetic curves, hydrogen contents, and (P-C-T) curves after 1000, 2000, and 3000 cycles of testing were collected and compared with those of the activated sample. It is observed that the maximum hydrogenation capacities are reduced to 0.95, 0.92, 0.82, and 0.74 for the loadings of 0.25, 0.50, 0.75, and 1.0, respectively. The plateaus for the loadings of 0.25 and 0.50 do not change much, but are lowered and become more sloped for the loadings of 0.75 and 1.0, indicating that non-homogeneous chemical modification has been induced. The X-ray diffraction patterns show broadening of the peaks for all samples, and even the presence of some second phase for the loading of 1.0. The degradation is explained based on reduction of grain size, phase separation, and accumulation of strain energy in the alloy

[en] 'Full text:' Previously, an LmNi5-based alloy was prepared and its hydrogenation properties were studied. In order to make use of such a type of metal hydride for application in PEMFC, the room-temperature desorption pressure has to be adjusted to 1-2atm and the cyclic stability has to be maintained. In this study, the same alloy was partially substituted with Al and cyclic hydrogenation was conducted with different hydrogen loadings up to 3000 cycles at room temperature. The saturated hydrogen loadings in equilibrium were controlled at H/M = 0.75 and 1.0. The P-C-T curves after 1000, 2000, and 3000 cycles of test were collected at T=30, 50, and 70^oC. After 3000 cycles, it is observed that the maximum hydrogenation capacities of the samples for the loadings of 0.75 and 1.0 are reduced to 0.93 and 0.91, respectively. The plateaus do not change much for T=30 and 50^oC, but become little sloped without observable split at 70^oC. X-ray diffraction analysis shows that the strains associated with repeated hydrogenation are isotropic for all samples. Both unsubstituted and Al-substituted alloys were then used to store hydrogen in a small cylinder with a diameter 10mm and length of 40 mm. The cylinder was connected to a small PEMFC for discharge test at room temperature. More than 540ml H2 was released at below 2atm and discharged to a capacity of 1200mAh. The hydrogenation properties of the alloys and design of the hydrogen storage cylinder for application in small portable PEMFCs for electronic devices are evaluated. The effect of Al substitution and hydrogen loading on cyclic hydrogenation property of the LmNi5-based alloy is also discussed. (author)

[en] Cyclic hydrogenation of an LmNi_4.8Al_0.2 alloy with different hydrogen loadings up to 3000 cycles at room temperature was conducted, and the performance is compared with that of a similar alloy containing no Al. The saturated hydrogen loadings in equilibrium were controlled at H/M = 0.75 and 1.00. The P-C-T curves after 1000, 2000, and 3000 cycles of test were collected at T = 30, 50, and 70 deg. C and were compared with those of the activated sample. After 3000 cycles, it is observed that the maximum hydrogenation capacities for the loadings of 0.75 and 1.00 are reduced to 0.89 and 0.87, respectively. The plateaus do not change much for T = 30 and 50 deg. C, but become little sloped with no observable split at 70 deg. C, indicating that the formation of an intermediate phase β-LmNi₅H₃ may be suppressed by substitution of Al for Ni. The X-ray diffraction patterns indicate that the strains associated with repeated hydrogenation are isotropic for all samples. It is concluded that partial replacement of Ni by Al has substantially improved the cyclic hydrogenation stability of the Lm(NiAl)₅-based alloy. The degradation in cyclic stability for the alloy containing no Al is related to the formation of the β-hydride and phase separation

[en] Coral microatolls allow for the reconstruction of relative sea level (RSL) and the inference of tectonic deformation along tropical coastlines over the Holocene. Microatolls track RSL with unparalleled vertical precision, and their annual banding allows us to count years precisely over an individual coral’s lifetime; however, RSL histories reconstructed from multiple corals depend on accurate and precise radiocarbon (14C) or uranium-thorium (230Th) ages. We collected coral microatoll slabs from sites in Ilocos Region, northwestern Luzon, Philippines, and dated them with 14C and 230Th techniques. Notably, initial RSL reconstructions for some sites disagreed markedly depending on the dating technique used. Attempts to replicate geochronologic analyses have shown that the coral skeletons are susceptible to diagenesis, complicating efforts to accurately determine coral ages. We are developing a strategy to overcome this limitation. We extracted multiple samples from each microatoll slab for paired 14C and 230Th dating. The number of annual bands separating any dated sample was used to further constrain the age of the coral; by subtracting the number of years from each dated sample, samples taken from different parts of the slab can produce independent estimates of the outermost preserved band. After excluding anomalously young replicate 14C ages and samples flagged as partly calcified by x-ray diffraction, we find that 230Th ages from a single coral disagree at 4σ in 4 of 8 cases, whereas calibrated 14C dates overlap at 2σ in 8 of 9 cases for an arbitrary radiocarbon marine reservoir correction, ∆R = 0 yr. Using OxCal and the Marine20 calibration curve, we apply Bayesian statistics to combine 14C and 230Th ages, to estimate ∆R, and to determine the coral ages using the best available data. We further analyze the ∆R value for each coral, and account for overdispersion and underdispersion, whilst generating a ∆R value per site, and an overall ∆R value (inclusive of all sites). We find no statistically significant difference in ∆R for each site, and we calculate an overall ∆R of -155 ± 117 yr for sites in Ilocos Region since the mid-Holocene, though century-scale variability in ∆R may occur. Additionally, to improve the reliability of our dates, our final dating strategy in OxCal is to apply the previously determined ∆R, to a code that places the corals in sequence (based on precise elevation measurements, morphological similarities, and coral die-down events), along with the 14C dates that are dated to the outermost preserved band.

[en] Reversible stepwise phase transformations induced by the addition and removal of hydrogen in pure Ti and Ti-6Al-4V (Ti64) were examined by means of pressure-composition (P-C) isotherm measurement from 550 to 700 deg. C. Both Ti-H and Ti64-H systems exhibit two pressure plateaus in the P-C isotherms which indicate phase transformations. Phase transformations take place at lower hydrogen content and higher hydrogen pressure in Ti64 than in Ti due to the effect of substitutional elements Al and V. Upon hydrogenation, the Ti-H system exhibits the sequence of phase transformation α ↔ α_H ↔ α_H + β_H ↔ β_H ↔ β_H + δ ↔ δ, whereas the Ti64-H system shows a sequence of α + β ↔ α_H + β_H ↔ β_H ↔ β_H + δ ↔ δ because of the presence of the original β phase. Partial phase diagrams for Ti-H and Ti64-H were established based on their P-C isotherms. Modification of microstructure of Ti64 occurs after cyclic hydrogenation. This can be ascribed to hydrogen-induced atomic migration during the sequential phase transformations