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

Radiation-Induced Segregation and Grain Boundary Migration in Fe–Cr–Ni Model Alloy under Irradiation

A Fe–Cr–Ni model alloy was electron-irradiated using a high voltage electron microscopy (1000 kV), and in-situ observations on structural evolution and microchemical analyses were carried out. When the Fe–Cr–Ni alloy was irradiated, the nucleations of dislocation loops followed by voids were observed and at the same time when a grain boundary migration occurred. The compositional analysis after irradiation of an area including a grain boundary indicated nickel enrichment and chromium depletion near the grain boundary. It is suggested that when the radiation-induced point defects flow into the grain boundary, boundary migration and solutes redistribution are induced and the magnitudes depend on net point defects flow, especially that of interstitial atoms

Solution-Plasma-Mediated Synthesis of Si Nanoparticles for Anode Material of Lithium-Ion Batteries

Silicon anodes have attracted considerable attention for their use in lithium-ion batteries because of their extremely high theoretical capacity; however, they are prone to extensive volume expansion during lithiation, which causes disintegration and poor cycling stability. In this article, we use two approaches to address this issue, by reducing the size of the Si particles to nanoscale and incorporating them into a carbon composite to help modulate the volume expansion problems. We improve our previous work on the solution-plasma-mediated synthesis of Si nanoparticles (NPs) by adjusting the electrolyte medium to mild buffer solutions rather than strong acids, successfully generating Si-NPs with <10 nm diameters. We then combined these Si-NPs with carbon using MgO-template-assisted sol-gel combustion synthesis, which afforded porous carbon composite materials. Among the preparations, the composite material obtained from the LiCl 0.2 M + H3BO3 0.15 M solution-based Si-NPs exhibited a high reversible capacity of 537 mAh/g after 30 discharge/charge cycles at a current rate of 0.5 A/g. We attribute this increased reversible capacity to the decreased particle size of the Si-NPs. These results clearly show the applicability of this facile and environmentally friendly solution-plasma technique for producing Si-NPs as an anode material for lithium-ion batteries

Synthesis and oxidation resistance of MoSi2-SiC composites

Synthesis of fully dense MoSi2-SiC composites without Si02-inclusions was performed, and oxidation behavior of the composites was studied. For the fabrication of MoSi2 and MoSi2-SiC composites, the mixed powders consisting of elemental Mo, Si and C were sintered at 1673 or 1873 K with a spark plasma sintering method. Namely, in-situ synthesis of MoSi2 and SiC and sintering of the compounds were simultaneously performed. As the result, fully dense MoSi2 and MoSi2 composites which little contain SiO2 inclusions were fabricated. Oxidation tests of the sintered bodies were carried out in air at 773 K in the accelerated oxidation region and 1773 K in the passive oxidation region. In the composites, occurrence of simultaneous oxidation of Mo and Si in the accelerated oxidation region was remarkably suppressed. In oxidation at 1773 K, the composites show outstanding oxidation resistance by a formation of a protective SiO2 layer

Effect of neutron irradiation on the microstructure of modified SUS316 stainless steels

The microstructures, prior and posterior to volumetrically remarkable swelling, of heavily neutron-irradiated specimens of compositionally-modified SUS316 based steel were carefully studied and characterized by using transmission electron microscope(TEM) and high resolution TEM to make clear an onset mechanism of radiation-induced swelling as well as an effect of neutron irradiation on microstructure. As the results of TEM study, it was demonstrated that the microstructural evolutions, including radiation-induced swelling, depended strongly on the irradiation condition. The relationship between the onset of swelling and microstructural evolution is quite complicated but the effects of irradiation temperature on microstructural changes appear to be relatively large. The onset mechanisms of swelling at a specific temperature or temperature range are discussed from the viewpoint of microstructure in this paper

Preparation and characterization of water-soluble jingle-bell-shaped silica-coated cadmium sulfide nanoparticles

Treatment of surface silanol groups with hydrophilic compounds enabled silica-coated cadmium sulfide (SiO2/CdS) nanoparticles of core−shell morphologies to be dissolved in a water/methanol mixture. Size-selective photoetching of the particles was performed by irradiation with monochromatic light at 458 nm, resulting in a blue shift of its absorption onset because of the decreasing size of the CdS. TEM analyses revealed that the SiO2 shell structure was not shrunken by photoetching and that a void space (ca. 2.3 nm) was formed between the CdS core and the SiO2 shell to give a jingle-bell structure. The emission spectra of photoetched particles showed the development of band-gap emission when cadmium ion (Cd2+) was added and the pH was adjusted to 10, whereas the same treatment of original particles gave no peaks assigned to band-gap emission, indicating that the SiO2 shell was sufficiently porous for small ionic species such as Cd2+ to penetrate through the shell and that the photoetched CdS core incorporated in the SiO2 shell had a bare surface to be covered with a cadmium hydroxide layer. With increasing shell thickness, the rate of CdS photoetching was reduced as a result of decrease in the rate of scavenging of the photogenerated electrons in CdS by electron acceptors such as O2 and methyl viologen (MV2+) in solution. The structure of the SiO2 layer was varied by surface modification of the CdS with both 3-mercaptopropionic acid (MPA) and 3-mercaptopropyltrimethoxysilane (MPTS) followed by hydrolysis of its trimethoxysilyl group. FT-IR spectra showed that MPA molecules, but not MPTS molecules, attached to the CdS core surface were eliminated by photoetching of the particles, resulting in the formation of windows in the SiO2 shell. The behavior of CdS emission quenching suggested that MV2+ is transported through the windows to the void space inside the SiO2 shell to reach the CdS core