Papers by Keyword: Hydrogen Absorption

Abstract: The influences of hydrogen absorption on the Curie temperature TC and the isothermal magnetic entropy change for La0.5Pr0.5(Fe0.88Si0.12)13 have been investigated, because the magnetocaloric effects have been confirmed to be enhanced after a partial substitution of Pr for La in La(Fe0.88Si0.12)13. The value of TC for La0.5Pr0.5(Fe0.88Si0.12)13Hy increases from 185 to 324 K with increasing y from 0 to 1.6. The maximum value of the isothermal magnetic entropy change ,Sm MAX is slightly decreased by hydrogen absorption. However, ,Sm MAX = -26 J/kg K in a magnetic field change of 5 T for La0.5Pr0.5(Fe0.88Si0.12)13H1.6 is still larger than the value of -23 J / kg K for La(Fe0.88Si0.12)13H1.5 having almost the same value of TC. Consequently, ,Sm MAX of the La0.5Pr0.5(Fe0.88Si0.12)13Hy is larger than that of La(Fe0.88Si0.12)13Hy in a wide temperature range covering room temperature.

Abstract: Microscopic deformation of each crystal of duplex phases of Ni-Ti-Nb alloy due to hydrogen absorption was investigated by X-ray diffraction technique. Ni30Ti30Nb40 which is hydrogen permeation alloy and consists of the primary phase, NbTi, and the eutectic phases, NiTi + NbTi, was used as a specimen. The change of lattice spacing of the specimen during hydrogen absorption was measured by Cu-Kα characteristic X-ray. As a result, the lattice spacing of crystal of NbTi phase increased extremely, while that of NiTi phase increased slightly. It was pointed out that the NbTi phase is responsible for hydrogen absorption in the Ni-Ti-Nb alloy. When hydrogen gas was released from the specimen at high temperature, both lattice spacing returned nearly to those of them before hydrogen absorption, and the specimen kept its original shape. Therefore, it was confirmed that the volume expansion of crystal of the Ni-Ti-Nb alloy due to hydrogen absorption was elastic deformation.

Abstract: Ti-6Al-4V alloy has proven to be technically superior and cost-effective materials for a wide variety of aerospace, industrial, marine and commercial applications. The mechanical properties of Ti-6Al-4V are very sensitive to the microstructure obtained after the thermo-mechanical treatment. The duplex structures provide good tensile ductility, fatigue strength, resistance to microcrack growth and crack initiation, and are often used in demanding fatigue critical tasks. However, although Ti-6A-4V is considered to be reasonably resistance to chemical attack, severe problems can arise when it comes in contact with hydrogen-containing environments due to its susceptibility to hydrogen embrittlement. The objective of this paper is to investigate the absorption and desorption behavior of external hydrogen on a duplex-annealed Ti-6Al-4V alloy. While investigating the desorption profile, we seek to better understand the thermodynamics and the kinetic nature of the interaction between traps and hydrogen atoms, with specific emphasis on the investigation of the impact of these interactions on the microstructure of the studied aerospace applicative titanium alloy. In order to achieve these goals, thermal desorption spectroscopy (TDS) was applied and the data obtained from this analysis was supported by a variety of other experimental techniques, such as LECO hydrogen determinator, XRD and microstructure investigations by means of optic and electronic microscopy. Hydrogen was found to influence significantly the microstructure of the alloy. The process of hydrogen evolution was found to be a very complex process, being affected mainly by the phase transformations that may occur during the thermal analysis.

Abstract: Beta-21S titanium alloy is ranked among the most important advanced materials for a variety of technological applications, due to its combination of a high strength/weight ratio, good corrosion behavior and oxidation resistance. However, in many of these technological applications, this alloy is exposed to environments which can act as sources of hydrogen, and consequently, severe problems may arise. The objective of this paper is to investigate the influence of high fugacity hydrogen on Beta-21S alloy in as-received (mill-annealed and hot-rolled) condition. Hydrogen effects on the microstructure are studied using X-ray diffraction and electron microscopy, while the absorption and desorption characteristics are determined respectively by means of a hydrogen determinator and thermal desorption spectroscopy. Preliminary results at room temperature revealed hydrogen-induced straining and expansion of the lattice parameters. However, neither second phases formation (hydrides), nor hydrogen-induced cracking, were observed after hydrogenation. The main characteristics of hydrogen absorption/desorption behavior, as well as hydrogen-induced microstructural changes in both microstructures are discussed in detail.

Abstract: Latest post-irradiation experiment results of Zry-2 and HiFi alloy (0.4%Fe-Zry2) showed that iron addition reduces the hydrogen pickup by these alloys compared to oxidation amount. In order to clarify the mechanism of reduced hydrogen absorption rate, (1) autoclave test, (2) surface potential measurement and (3) hydrogen absorption test of the intermetallic compound were carried out. Based on these results, a tentative mechanism for hydrogen absorption by zirconium alloys is proposed, taking into account of both the electrical potential gradient over the oxide film as well as the SPP window for hydrogen absorption.

Abstract: The chemical diffusion coefficient (Dc) of hydrogen in the Ni30Ti50Cu20 shape memory alloy has been determined in the temperature range 700 - 1150 K by investigating the kinetics of H2 absorption. The mobility of H has also been deduced between 250 K and 280 K from a Snoek-type internal friction peak. The values of the Einstein diffusion coefficient (DE) derived from the relaxation time of this peak were in keeping with those of Dc obtained at low H contents (nH = H/Me < 0.01 ). The combined Arrhenius plot of DE and Dc gave the following values for the diffusion parameters: W = 0.52 ± 0.02 eV, D0 = (5±2)x10-4 cm2/s.

Abstract: This study reports hydrogen absorption property of newly-synthesized RAP (rubeanic-acid polymer)-protected palladium nanoparticle (RAP-Pd). From powder X-ray diffraction measurements, the lattice constant of Pd nanoparticle was revealed to increase by 0.11 Å under 600 Torr hydrogen gas condition at room temperature, indicating that the hydrogen absorption occurs in the Pd nanoparticle. Solid-state 2H-NMR spectrum under deuterium gas showed that three different components exist in RAP-Pd, which are derived from imino group, terminal amino group in the RAP and absorbed deuterium atom inside the Pd nanoparticle. This result gives an expectation of the hydrogen absorption in RAP itself.

Abstract: The mechanical properties of palladium (Pd) wire absorbed hydrogen were evaluated by the quasi-static tension test and indentation test. The electrolytic method was used for hydrogen absorption. Pd wire with a diameter of 1mm was used. The electrolyte was a sulfuric acid solution and the current density used in the electrolytic method was 200mAcm-2. The hydrogen absorption ratio defined by the molecular ratio (H/Pd) of hydrogen and palladium was controlled by the absorption time. The gauge length for the tension test was 20mm. The ultimate tensile strength increased with the increase of the absorption ratio. On the other hand, the increase of the ratio decreased the strain hardening parameter and fracture strain. A model considering the specimen absorbed hydrogen and a composite material constructed in a concentric configuration was suggested to estimate the hydrogen absorption area and mechanical properties. The indentation test was conducted to clarify the evolution of the embrittlement due to the hydrogen absorption microscopically and determine the absorption area precisely. Vickers hardness clearly increased with the increase of the hydrogen absorption ratio. The hardness distribution was measured to detect the boundary of the absorption and non-absorption area using a Berkovich indenter that is smaller than a Vickers indenter. The hardness boundary of the absorption and non-absorption of the specimen with the hydrogen absorption ratio of 22 percent was observed experimentally at the position around 100-150μm from the outside of the specimen. The position of the boundary estimated using the model was 85μm from the outside of the specimen. When the stress-strain curves of the specimen with the unknown hydrogen absorption ratio were measured, the hydrogen absorption ratio could be estimated using the proposed model.

Abstract: Structural changes in C15 Laves phase DyCo2 on heating using a pressure differential scanning calorimeter (PDSC) in a hydrogen atmosphere between 0.1 and 5.0 MPa were investigated by a powder X-ray diffractometer (XRD), a differential scanning calorimeter under an argon flow atmosphere (Ar-DSC), a transmission electron microscope (TEM) and a hydrogen analyzer. As the temperature of DyCo2 increases, the reactions such as hydrogen absorption in a crystalline state, HIA (hydrogen-induced amorphization), precipitation of DyH3 and decomposition of the remaining amorphous phase into β-Co + DyH3 occurred exothermically for every hydrogen pressure. The mechanism of HIA in DyCo2 is discussed on the basis of the experimental results.