Effect of Oxygen Impurities on Positronium Formation in Voids of Vanadium

To clarify the effect of oxygen impurities on positronium (Ps) formed in irradiation-induced voids, measurements of the angular correlation of two photon annihilation radiation (ACAR) have been done on vanadium samples doped with oxygen impurities and subsequently irradiated with fast neutrons of doses up to 5.5x10^cm^ at about 400℃ in the Japan Materials Testing Reactor (JMTR). It has been shown that slight contamination of voids with oxygen impurity atoms, presumably submonolayer adsorption on the void surface, causes Ps formation. On the other hand, the considerable contamination leads suppression of Ps formation. Energy loss process of Ps in voids is found to be also influenced by the surface contamination

Mechanical Property and Microstructure in Neutron Irradiated Fe-Cr-Mn-Al Alloys

A series of Fe-xCr-yMn-zAl alloys have been examined by tensile test and electron microscopy following irradiation in JMTR to 5x10^ n/m^2 at about 470 K. After the irradiation, 0.2% proof stress, ultimate tensile stress and total elongation were compared with the unirradiated data. From this experiment, it can be assumed that appropriate composition in these alloys is as follows : Fe-10Cr-(20-25)Mn-3Al for ferritic alloys, and Fe-10Cr-30Mn for austenitic alloys

Hydrogen effects on tensile property of pure iron with deformed surface

To study the interaction of hydrogen and surface structure of iron, two types of tensile test are carried out under hydrogen gas environment and cathodic hydrogen charging condition. According to the tensile tests, hydrogen induces reduction of flow stress (softening) for the specimens without deformed surface, but increase of flow stress (hardening) for the one with deformed surface. The results of jump tests signify that hydrogen enhances the dislocation mobility by reducing the thermal activation volume for overcoming barriers, and because of this, in the samples with smooth surface, homogeneously distributed hydrogen leads to the softening effect. On the other hand, the deformed layer just under the surface has larger solubility of H due to trap sites provided by dislocation cell structures. As a result of hydrogen shielding effect, the strong interaction between dislocations in surface layer and multiplication of new defects causes the hardening effect

Onset of plasticity of helium-implanted ferritic/martensitic steels during nanoindentation

The onset of plasticity during nanoindentation is a new method to investigate the irradiation damage of structural materials in fission and fusion reactors. In this paper, nanoindentation experiment was carried out to helium implanted F82H-IEA and nano-sized oxide dispersion strengthened F82H-ODS steels for studying the elastic-plastic transition at a constant loading rate. The onset of plasticity shifted after helium implantation. By a statistical thermal activation model, activation volume was extracted to discuss the strength of barrier for dislocation motion. The results reveal an increase in the pinning force and number density of effective obstacles for dislocation motion in He-implanted F82H-IEA, and a decrease in the local pinning force without changing the density of effective obstacles in He-implanted F82H-ODS

AB–MH (Ammonia Borane–Metal Hydride) composites : systematic understanding of dehydrogenation properties

Dehydrogenation properties of AB–MH (Ammonia Borane–Metal Hydride, M = K, Na, Li, Ca, Mg, Al) composites were systematically investigated by thermal and mass analyses. The results suggest that the Pauling electronegativity of M, χp, is a good indicator to predict the phases of composites, the dehydrogenation temperature and the amount of by-product gases (NH3 and B2H6). The phases of composites were classified by χp as follows. MBH4 was formed for M = K, Na (χp ≤ 0.9), MNH2BH3 was formed for M = Na, Li (0.9 ≤ χp ≤ 1.0) and no new compounds were formed for M = Ca, Mg, Al (1.0 ≤ χp). The 1st dehydrogenation temperatures of the samples (M = Na, Li, Ca, Mg) were 10–20 °C lower than that of AB itself (χp ≤ 1.2). The amount of NH3 was decreased as χp increased. On the other hand, the amount of B2H6 was decreased as χp decreased. The emission of B3H6N3 could occur by the reaction of NH3 and B2H6. Finally, AB–MAlH4 (M = Na, Li) composites, which were prepared based on the indicator, showed superior potential as hydrogen storage materials because they did not desorb any by-products NH3, B2H6 and B3H6N3

Strain field of interstitial hydrogen atom in body-centered cubic iron and its effect on hydrogen-dislocation interaction

Effect of hydrogen in body-centered cubic iron is explored by using the density function theory. Hydrogen atoms increase the concentration of free electrons in the simulation cell and have bonding interaction with Fe atom. Caused by anisotropic strain components of hydrogen atoms in the tetrahedral sites, elastic interaction for hydrogen with screw dislocation has been found. The dependence of hydrogen-screw dislocation interaction on hydrogen concentration is confirmed by repeated stress relaxation tests

Plastic bag method for active sample loading into transmission electron microscope

A plastic bag method was developed to observe air sensitive samples on microstructure and phases distribution without air exposure during holder transfer process into the Transmission Electron Microscope (TEM). As an example, a type of lithium aluminum hydride (Li3AlH6) was observed in TEM to demonstrate the effectiveness of this method. Results show that plastic bag method is a simple and practical TEM transfer method utilized to reduce air contact for a series of air sensitive materials

Ammonia borane-metal alanate composites : hydrogen desorption properties and decomposition processes

Hydrogen desorption properties and decomposition processes of NH3BH3-MAlH4 (M = Na, Li) composites were investigated by using thermogravimetry-differential thermal analysis-mass spectrometry (TG-DTA-MS), powder X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analyses. We prepared the composites by ball-milling and the mixtures by hand-milling. The ball-milled composites desorbed 4-5 wt% hydrogen at three exothermic steps below 260 degrees C. The emissions of by-product gases, NH3, B2H6 and B3H6N3, were effectively suppressed. From XRD analysis, the formation of a mixed-metal (Na(Li), Al) amidoborane phase was suggested. Very different results were obtained using hand-milling. They showed only one exothermic reaction at 80-90 degrees C. The emission of by-product gases was not suppressed. By comparing the differences between ball-milled composites and hand-milled mixtures, the importance of mixed-metal amidoborane in this system was proposed

Physical properties of α-Fe upon the introduction of H, He, C, and N

The effects of impurities of H, He, C, and N in α-Fe are investigated in terms of electronic structures using the density functional theory. Calculations reveal that H and He are stable at the T-site while C and N are stable at the O-site within α-Fe. The local strain field by H, He, C, and N in α-Fe causes structural elongation. Furthermore, the decrease of magnetic moment of Fe upon the introduction of C and N is found where the charge transfer is responsible. H, He, C, and N affect the electronic structure of α-Fe and change the fundamental physical properties of α-Fe

Interaction of electrons with light metal hydrides in the transmission electron microscope

Transmission electron microscope (TEM) observation of light metal hydrides is complicated by the instability of these materials under electron irradiation. In this study, the electron kinetic energy dependences of the interactions of incident electrons with lithium, sodium and magnesium hydrides, as well as the constituting element effect on the interactions, were theoretically discussed, and electron irradiation damage to these hydrides was examined using in situ TEM. The results indicate that high incident electron kinetic energy helps alleviate the irradiation damage resulting from inelastic or elastic scattering of the incident electrons in the TEM. Therefore, observations and characterizations of these materials would benefit from increased, instead decreased, TEM operating voltage