Hiroji Katsuta

A zirconium-cobalt compound as the material for a reversible tritium getter

An intermetallic compound of zirconium-cobalt was prepared, and the pressure-composition isotherms for the ZrCo-H system were measured in the pressure range from 10 Pa (0.1 Torr) to approx. =130 kPa (1000 Torr) and in the temperature range from 130 to 400/sup 0/C. The equilibrium hydrogen pressures of plateaus under the the experimental conditions were one or two orders of magnitude higher than that of a uranium-hydrogen system. A pronounced hysteresis between hydrogenating isotherms and dehydrogenating ones was observed. Based on the results, ZrCo is proposed as a substitute for uranium for the purpose of recovering, storing, and supplying gaseous tritium.

Correlation behavior of lithium and tritium in some solid breeder materials

Abstract Tritium behavior in candidate solid breeder materials such as Li 2 O, Li 2 SiO 3 or γ-LiAlO 2 has been clarified to have a close relation with the diffusion of lithium by the analysis of spin-lattice relaxation with nuclear magnetic resonance and ionic conductivity. The conductivity measurement is a simple and brief technique and can be performed even in a in situ condition under irradiation.

Diffusivity and permeability of hydrogen in molybdenum

Abstract The permeability and diffusivity of hydrogen in molybdenum was measured by the time-lag method using molybdenum membranes prepared by electron beam melting and cleaned by argon ion etching. Measurements were also made on membranes prepared in this manner and subsequently coated with palladium. The inconsistencies in the previous data, a consequence of surface effects, have been clarified. The activation energy for H-diffusion in Mo is 10.6 KJ/mol.

Hydrogen and Deuterium Transport through Type 304 Stainless Steel at Elevated Temperatures

The permeation time-lag method have been used to determine the permeabilities, diffusion coefficients and solubilities of hydrogen and deuterium in type 304 stainless steel of three kinds of surface treated specimens; with oxide film, reduced by H2 gas and Pd coated. For the specimen with a thin oxide film the permeability increased abruptly at the temperature higher than 1,050 K owing to reduction of the oxide film by H2 gas introduced. The permeability and diffusion coefficient for hydrogen-reduced specimens agreed with those for Pd-coated specimens showing the data of bulk diffusion limited. The isotope effects for permeability ΦH/ΦD, diffusion coefficient D H/D D and solubility were about 1.4, 1.2 and 1.1, respectively. From these values θ(=hν/k)=1,530±50K and θ′(=hν/k)=2,740±20K were obtained by the quantum effect of a harmonic approximation.

Electrical conductivity of a sintered pellet of octalithium zirconate

Abstract The conductivity of a sintered pellet of Li 8 ZrO 6 was measured in dry or wet argon atmosphere by the two-terminal technique with an AC Wheatstone bridge in the temperature range 350–1050 K. The temperature dependence of conductivity multiplied by temperature (σT) of Li 8 ZrO 6 in a dry environment had two transition points at 426 and 833 K. The activation energies of conductivity in high, middle and low temperature regions were 103.2, 52.1 and 37.4 kJ/mol, respectively. The activation energies of conductivity agreed well with those obtained by temperature dependence of spin-lattice relaxation time T 1 of 7 Li with pulsed nuclear magnetic resonance.

Simultaneous ion and gas driven permeation of deuterium through nickel

Abstract The permeation rate of deuterium through nickel exposed to a deuterium ion beam has been measured as a function of temperature (100–1000°C), incident ion flux ( 0.2−1.1 × 10 15 D-atom cm −2 s −1 ), incident ion energy (1–2.5 keV/D-atom) , and deuterium partial pressure. The results are analyzed with a model which is developed to describe ion driven permeation when gas driven permeation coexists; the rate-limiting process of recycling during ion implantation is identified as surface recombination above 400°C and as bulk diffusion below 300°C, and the recombination coefficient is estimated. The model predicts the whole parameter dependence observed. The permeation spike is also investigated.

Diffusivity and permeability of hydrogen in neutron irradiated molybdenum and platinum

Hydrogen permeability and diffusivity were measured in neutron irradiated (3.0 × 1015 or 1.2 × 1017n/cm2) metals of pure molybdenum of bcc structure and platinum of fcc. Although hydrogen permeability in molybdenum was decreased by 10% to 20% by the irradiation, in platinum it was increased by about 10%. X-ray diffraction analysis of the irradiated metals was also performed to study the relation between hydrogen behaviour in the metals and its neutron irradiated structures.

Damage structure in Al2O3 single crystal irradiated with He-ions

Abstract The microstructures of single crystal alumina irradiated with He-ions at 1023 to 1223 K to a dose of 1 × 10 20 He/m 2 were examined in an electron microscope. In as-irradiated samples, high densities of defect clusters with 6–7 nm in an average size were formed and these were almost independent of the irradiation temperatures. The clusters were revealed to he dislocation loops of interstitial type. In the sample annealed for 1 h at 1223 K after the He-irradiation at 1023 K, five distinguishable features appeared: high density of small cavities with 7 nm in an average size, highly coalesced cavity channels, small sized spherical precipitates of aluminium, large size aluminium islands, and dislocation loops with an average size of 70 nm. These features were revealed to be strongly dependent on the helium irradiation damage and also on the distances of damaged layers from foil surface during annealing.

Electrical properties and phase stabilities of some ceramics irradiated by neutrons and ions

Abstract The electrical properties of silicon nitride (Si 3 N 4 ) and tetragonal zirconia polycrystals (TZP) were measured as a function of temperature in the frequency range 5 Hz to 13 MHz. Dielectric properties at 9.1 GHz were also measured by the standing-wave method. The dielectric loss tangent tan δ at 9.1 GHz of unirradiated hot-pressed Si 3 N 4 with small amounts of MgO was lower than 2 × 10 −3 up to 500°C. On the other hand, TZP with 3 mol% Y 2 O 3 (3Y-TZP) had about 10 times higher values of tan δ than Si 3 N 4 .

Hydrogen permeation through niobium membrane contacting with liquid lithium

Abstract Hydrogen permeation through niobium membrane contacting with liquid lithium was experimented using natural convection type loop containing about one kilogram of lithium. Disk type niobium membrane (0.02 cm thick and 5.8 cm 2 in area) which was welded to a tube was inserted into liquid lithium and permeation constant was obtained from the hydrogen pressure change in the tube after it was disconnected from a vacuum line. Hydrogen permeation constant was smaller by about two orders of magnitude than in the ideal case when diffusion in metal is rate-determining. This is considered to be caused by the layer of niobium nitride (Nb 2 N) which formed on the lithium side surface of the niobium membrane. Changes of hydrogen permeation constants with hydrogen concentration in lithium were studied and hydrogen permeation rate was considered to have a linear relationship with hydrogen pressure. In the next step of our experiments, nitrogen in lithium was gettered by titanium in which case the hydrogen permeation constant became several times larger than in not gettered lithium. Nitrogen transport from niobium surface was however a slow reaction and there would be a limitation of the reaction as well as permeation resistance of oxide film at the gas side.