Microstructural evolution of Cu-1 at% Ti alloy aged in a hydrogen atmosphere and its relation with the electrical conductivity

Copper alloys with titanium additions between 1 and 6 at% Ti emerge currently as attractive conductive materials for electrical and electronic commercial products, since they exhibit superior mechanical and electrical properties. However, their electrical conductivity is reduced owing to the residual amount of Ti solutes in the Cu solid solution (Cu_ss) phase. Since Cu shows only poor reactivity with hydrogen (H), while Ti exhibits high affinity to it, we were inspired by the idea that hydrogenation of Cu–Ti alloys would influence their microstructure, resulting in a significant change of their properties. In this contribution, the influence of aging under a deuterium (D₂) atmosphere of Cu-1 at% Ti alloys on their microstructure is investigated to explore the effects on the electrical conductivity. The specimens were investigated by means of transmission electron microscopy (TEM), field ion microscopy (FIM), computer-aided field ion image tomography (cFIIT), and atom probe tomography (APT).     

Hydrogen isotope permeation through yttria coatings on Eurofer in the diffusion limited regime

In fusion power plants a tritium permeation barrier is required in order to prevent the loss of the fuel. Moreover, the tritium permeation barrier is necessary to avoid that the radioactive tritium accumulates in the first wall, the cooling system, and other parts of the power plant. Oxide thin films, e.g. Al₂O₃, Er₂O₃ and Y₂O₃, are promising candidates as tritium permeation barrier layers. With regard to the application, this is especially true for yttrium due to its favorably short decay time after neutron activation compared to the other candidates. The Y₂O₃ layers with thicknesses from 100 nm to 500 nm are deposited on both sides of Eurofer substrates by RF magnetron sputter deposition. Some of the samples are additionally deposited with palladium thin films to analyse the limited regime. During the annealing in the experiments the palladium layers do not show any crack formation or delamination, verified by scanning electron microscopy. After annealing the cubic crystal structure of the Y₂O₃ layers is verified by X-ray diffraction. The cubic phase contains a small amount of a monoclinic phase, which is eliminated after the permeation measurements. The permeation reduction factors of the samples are determined in gas-driven deuterium permeation experiments. A permeation reduction of 5000 of the yttria thin film is verified. The diffusion limited regime is identified by the pressure dependence of the permeation measurement and by permeation experiments with the palladium top layers on the Y₂O₃ thin films. Furthermore, the activation energy of the permeation through the yttria thin films is determined. Pre-annealing times for more than 70 h of the Y₂O₃ thin films and permeation measurements with temperature cycles for 20 days are performed to show the stability of the permeation flux and hence the microstructure of the barrier layers. Measurement times at each constant temperature level of more than 25 h are required for the stabilization of each permeation flux to a constant value. The permeation measurement setup is enhanced to enable a continuously running equipment for these measurement times.     

Deuterium retention and surface morphology modification in oxidized tungsten exposed to D plasma

Tungsten (W) is the most promising plasma facing material in future fusion reactor. However, oxidation occurs readily on W and might influence the hydrogen isotopes retention behavior in W. To explore the mechanism of oxidation on the hydrogen isotopes retention behavior in W, oxidized W samples have been exposed to D plasma (32.3 eV, 2 × 10²⁰ Dm⁻²s⁻¹) in a linear plasma device. Surface morphology and deuterium (D) retention behavior in W have been characterized after exposure to D plasma with fluence of 10²³ D/m². After D plasma exposure, a porous layer has been found on the surface of oxidized W. The main chemical content of the porous layer is pure W. The existence of pre-oxide layer contributes the increase of retention amount of D in the form of D₂O and may contribute to the decrease of the retention amount of D in the form of HD/D₂.     

Analysis of reactor experiments to study the transfer processes of generated tritium in lithium cps (capillary-porous system)

To date, there have been many studies on the possibility of using lithium CPS as a plasma-facing material in fusion reactors. For use such liquid-lithium systems in fusion reactors, it is necessary to determine the interaction parameters of the surface facing the plasma with the working gases under conditions simulating the real operation of the facility, i.e. under conditions of neutron and gamma radiation. Therefore, this paper is devoted to the study of the processes of hydrogen isotopes interaction with lithium CPS under reactor irradiation. The experiments presented in work were carried out at the IVG1.M research reactor by using dynamic sorption method with the presence of deuterium under the lithium CPS sample.The results of reactor experiments simulation, in particular, the distribution of tritium concentration in lithium volume and traps, and the flows of tritium released through the inner surface of the CPS into the experimental chamber at different temperatures are presented.Based on the simulation results, the following interaction parameters of tritium with lithium were determined: temperature dependences of tritium capture constant by lithium and the dissociation constant of LiT. The obtained model can be applied for analysis of tritium generation and release from different lithium-containing materials used as a filling of CPS structure (for example, lithium and tin-lithium eutectics).     

Field ion source development for neutron generators

An ion source based on the principles of electrostatic field desorption is being developed to improve the performance of existing compact neutron generators. The ion source is an array of gated metal tips derived from field electron emitter array microfabrication technology. A comprehensive summary of development and experimental activities is presented. Many structural modifications to the arrays have been incorporated to achieve higher tip operating fields, while lowering fields at the gate electrode to prevent gate field electron emission which initiates electrical breakdown in the array. The latest focus of fabrication activities has been on rounding the gate electrode edge and surrounding the gate electrode with dielectric material. Array testing results have indicated a steady progression of increased array tip operating fields with each new design tested. The latest arrays have consistently achieved fields beyond those required for the onset of deuterium desorption (∼20 V/nm), and have demonstrated the desorption of deuterium at fields up to 36 V/nm. The number of ions desorbed from an array has been quantified, and field desorption of metal tip substrate material from array tips has been observed for the first time. Gas-phase field ionization studies with ∼10,000 tip arrays have achieved deuterium ion currents of ∼50 nA. Neutron production by field ionization has yielded ∼10² n/s from ∼1 mm² of array area using the deuterium-deuterium fusion reaction at 90 kV.     

Effects of Deuterium Oxide on the Oxidative Stability and Change of Headspace Volatiles of Corn Oil

Effects of deuterium oxide and deuterium oxide-free water on the oxidative stability and formation of headspace volatiles were determined for corn oils to evaluate the role of moisture as an active influential factors during lipid oxidation. Mixtures of corn oil and water with different ratios of deuterium oxide were prepared, and the mixtures were stored at 60 °C for 2 days. Headspace oxygen contents, conjugated dienoic acid (CDA) values, and p-anisidine values (p-AV) were analyzed as a measure of oxidative stability, and headspace volatiles were analyzed by solid phase microextraction and a gas chromatography mass selective detector to determine the involvement of deuterium in volatiles. Deuterium oxide accelerated the rate of lipid oxidation in corn oil compared to oils with deuterium-free water based on the results of headspace oxygen content, CDA, p-AV, and total volatile content. Fragmented mass to charge ratios (m/z) of 73.1/72.1 for d ₁-pentane/pentane and 57.0/56.0 for d ₁-2-propenal/2-propenal from samples containing deuterium oxide were significantly higher than those from deuterium oxide-free water, implying that moisture participated to form volatiles in corn oil oxidation under air-tight condition. Deuterium oxide appeared to accelerate the rate of lipid oxidation in corn oils and participated to form volatiles from oils during oxidation.     

Deuterium permeation and isotope effects in nickel in an elevated temperature range of 450–850 °C

A series of deuterium permeation experiments were carried out using a nickel membrane in an elevated temperature range of 450–850 °C for application to nuclear fusion and nuclear hydrogen technologies. A complete set of permeability, diffusivity, and solubility data for deuterium in nickel was successfully determined. The results of this study were compared with results previously reported by other authors. The results for deuterium were also compared with the results for hydrogen to estimate the isotope effect. The results for and a discussion of deuterium permeation and the isotope effects in nickel are presented.     

Fuel retention study in fusion reactor walls by micro-NRA deuterium mapping

Nuclear Reaction Analysis (NRA) with a ³He ion beam is a powerful analytical technique for analysis of light elements in thin films. The main motivation for ³He focused beam applications is lateral mapping of deuterium using the nuclear reaction D(³He,p)⁴He in surfaces exposed to a tokamak plasma, where a lateral resolution in the μm-range provides unique information for fuel retention studies.At the microprobe at the Jo?ef Stefan Institute typical helium ion currents of 300 pA and beam dimensions of 4 × 4 μm² can be obtained. This work is focused on micro-NRA studies of plasma-facing materials using a set-up consisting of a silicon partially depleted charge particle detector for NRA spectroscopy applied in parallel with a permanently installed X-ray detector, an RBS detector and a beam chopper for ion dose monitoring. A method for absolute deuterium quantification is described. In addition, plasma-deposited amorphous deuterated carbon thin films (a-C:D) with known D content were used as a reference.The method was used to study deuterium fuel retention in carbon fibre composite materials exposed to a deuterium plasma in the Tore Supra and TEXTOR tokamaks. The high lateral resolution of micro-NRA allowed us to make a detailed study of the influence of topography on the fuel retention process. We demonstrated that the surface topography plays a dominant role in the retention of deuterium. The deep surfaces inside the castellation gaps showed approximately two orders of magnitude lower deuterium concentrations than in areas close to the exposed surface.     

Deuterium storage of Ti40Zr40Ni20 icosahedral quasicrystal

Ti₄₀Zr₄₀Ni₂₀ icosashedral quasicrystal was observed to load hydrogen in a much lower capacity than similar Ti–Zr–Ni alloys. To verify the result, the alloy is further studied by using deuterium instead of hydrogen in this work. With a home-made gas–solid reaction system, XRD and XPS techniques, the investigation was conducted on deuterium absorption and desorption properties of Ti₄₀Zr₄₀Ni₂₀ alloy and its phase stability during the deuteration course. It is shown that the quasicrystal can load deuterium rapidly in an elevated volume of 11.5 mmol·D₂/g·M (D₂ denotes deuterium molecular and M the metal). After the full storage of deuterium, the quasicrystal phase remained, however the quasilattice expanded at a rate of 6.28%, revealing the occurrence of severe quasilattice stress. The solution of deuterium in the alloy caused the increase of binding energy of the metal elements, as much as 0.4 eV for Ti, 0.6 eV for Zr and 0.1 eV for Ni, which reflects the location of deuterium near Ti and Zr. The deuterium release was very slow at low temperature and could be complete at least above 610 °C. Based on the gained results, the quasilattice shrink would be more reasonable to explain the big difficulty of the desorption.