Toyosaburo Takeuchi

Absorption and desorption of hydrogen, deuterium, and tritium for Zr–V–Fe getter

Nonevaporable getters have wide applicability for developing the tritium handling techniques for thermonuclear fusion devices. From this viewpoint, mechanisms of the absorption and desorption of hydrogen isotopes and the isotope effects were investigated for a Zr–V–Fe alloy (St‐707) by means of the mass analyzed thermal desorption spectroscopy. It was observed that the absorption rate was proportional to the first power of the pressure, indicating that the rate limiting step is the dissociative adsorption of hydrogen isotopes on the surface. The activation energy was very small, in the order of magnitude of a few tens of calories per mole in a temperature range from −196 to 200 °C. The desorption rate was proportional to the square of the amount of absorption, indicating that the rate limiting step is the associative desorption reaction of hydrogen atoms or ions diffused to the surface from the bulk. The rate constants for hydrogen and deuterium were determined as kd(H2)=(5.3+2.6−1.7)exp[−(28.0±0.7)×103/R...

Catalytic inactivities of Ni alloys expressed by surface and bulk compositions

The surface compositions of three kinds of powdered alloys with different structures, CuNi (fcc-fcc), FeNi (bcc-fcc), and CoNi (hcp-fcc), were determined by the penetration of β-rays of 63Ni mixed previously in the alloy, then the effect of the respective alloy structure both of the surface and of the bulk on the catalytic hydrogenation of ethylene was studied. The surfaces of these alloys were found to be Ni-poor for the wide range of alloy composition. The catalytic activity expressed by each surface composition was difficult to explain by the physicochemical properties of the surface. The activity expressed by the bulk composition of CuNi of fcc structure was high in the region of unfilled d-band, and so were that of FeNi and that of CoNi in the region of fcc structure. The activity of FeNi for the dimerization of 14C-ethylene was studied, of whose activity the similar tendency was observed as found in the hydrogenation reaction. These could be interpreted as the results of the positive contribution of the dissolved hydrogen in bulk to the catalytic reactions.

Activation process and absorption/desorption of D2O for Zr-V-Fe getter

Abstract Nonevaporable getters have wide applicability for tritium handling systems. From this view point, the activation process of the Zr-V-Fe getter (St-707) and absorption/desorption of D 2 O on the getter surface were investigated, by means of XPS-SIMS and mass analyzed thermal desorption spectroscopy. XPS-SIMS measurements revealed that the getter surface exposed to air was covered with adsorbed H 2 O, CO and small amounts of hydrocarbons and that the getter components are oxidized. Upon heating of the getter above 500 °C, the adsorbed species disappeared from the surface, partly due to desorption and partly due to migration into the bulk. Consequently, metallic Zr and V appeared on the surface, whereas Fe disappeared. The surface composition was evaluated to be 87 at% Zr-13 at% V. After the activation, water (D 2 O ) was readily absorbed into the getter at 300 °C in the form of deuterium atoms. The absorption rate was proportional to the partial pressure of water, indicating that the rate determining step for the absorption is the dissociation of water molecules on the surface. The absorption rate constant was 0.009 and 0.24 cc/s/cm 2 (net surface area) [or 1.5 and 39 cc/s/cm 2 (projected area)] at 25 and 300°C, respectively. Only D 2 was desorbed from the getter exposed to D 2 O at 25 and 300 °C. The rate determining step for the desorption is association of deuterium atoms on the surface diffused from the bulk.

Gettering of Hydrogen Isotopes by Zr-Ni Alloys

Activation process and absorption/desorption of hydrogen isotopes were studied for Zr-Ni alloys by means of XPS-SIMS and thermal desorption spectroscopy. Alloying of Ni to Zr gave rise to considerable modification of the getter properties: it caused the changes in the activation temperature, the activation energy for hydrogen absorption, the heat of absorption, selective pumping property, and the kinetic isotope effect. The results indicate that one can develop Zr-Ni getters applicable to the various unit processes in the fuel handling systems of thermonuclear reactors.

The reduction mechanism of powdered copper-nickel oxides

Abstract The mechanism of the formation of copper-nickel alloys from copper and nickel nitrates by calcination and by reduction with hydrogen was investigated by means of X-ray diffraction and measurement of the rate of the reduction. X-ray diffraction showed that the unreduced copper-nickel oxides were composed of cupric oxide and miscible oxide of nickel and copper. Cuprous oxide and free nickel did not appear in the process of reduction. The completely reduced copper-nickel was composed of nickel-rich alloy and extremely copper-rich alloy. The rate of reduction of copper-nickel oxide was practically the same as that of cupric oxide. From these results and the change in the BET areas, it was concluded that the alloys are formed by the interdiffusion of nickel into a copper phase which forms earlier than nickel.

Recovery and Storage of Tritium by Zr-V-Fe Getter

The rates of ab/desorption of water vapor for zr-V-Fe getter were investigated by means of mass analyzed thermal desorption spectroscopy. The absorption rate obeyed first order kinetics with respect to the pressure of water vapor. The activation energies for absorption were determined as 1.8 (H/sub 2/O), 2.7 (D/sub 2/O), and 3.2 (T/sub 2/O) kcal/mol. Only hydrogen was desorbed by heating the getter in which water was absorbed. The desorption obeyed second order kinetics with respect to the amount of absorption. The activation energies for desorption were determined as 28.0 (H/sub 2/O), 28.6 (D/sub 2/O), and 29.3 (T/sub 2/O) kcal/mol. It is concluded that the rate determining step for absorption is the dissociation reaction of adsorbed water molecules or hydroxyl groups on the surface. The rate determining step for desorption is the association reaction of hydrogen atoms which diffuse from the bulk to the surface.

Absorption/desorption of hydrogen isotopes and isotopic waters by Zr-alloy getters

Zr‐alloy getters have been applied to tritium handling and vacuum conditioning for fusion devices. Some of their properties, however, should be improved to apply them in future devices. From this viewpoint, we have studied the effects of alloying on the getter properties of Zr alloys. We found that the activation energy of absorption and desorption of hydrogen varied considerably with alloying. The activation energy for hydrogen absorption was 0.74 for Zr61Al39, 0.01 for Zr57V36Fe7, 0.63 for Zr67Ni33, and 2.8 kcal/mol for Zr85Ni15, whereas that for Zr was 2.6 kcal/mol. The heat of hydrogen absorption was 27.8 kcal/mol for Zr: it changed with alloying as 32.0–33.4 (Zr61Al39), 27.8–28.4 (Zr57V36Fe7), 29.0 (Zr67Ni33), and 28.0 (Zr85Ni15). In addition, the ratio of the pumping speed of water vapor to that of hydrogen at room temperature varied with alloying element: for example, 1/40 for Zr57V36Fe7 and 1/4 for Zr67Ni33. The alloying effects mentioned above are considered due to modification of the electronic ...

The catalytic activity and electric resistance of evaporated copper-nickel films

Abstract The dependencies of the hydrogenation catalytic activity and electric resistance of copper-nickel films upon the composition of the film were investigated. The film was prepared by the evaporation of copper and nickel metals or their alloys on a substrate cooled by liquid oxygen. Prior to use, the film was treated in a vacuum at 30 ° or 250 °C. The catalytic activity was tested by the hydrogenation reaction of ethylene. The maximum of activity for the reaction was always found in the alloy region of the film, irrespective of the order of the deposition of the two metals, when the film was treated at 30 °C. However, the maximum activity shifted to the pure nickel, when the treatment temperature was raised to 250 °C. The electric resistance of 50% nickel film was always maximum. It was also noted that an increase in treatment temperature resulted in a marked decrease in electric resistance, especially on 50% nickel film. The catalytic activity is discussed in view of the change of the amount of the especially unstable lattice imperfections in the film.

Autoradiographical studies of the behavior of the tritium produced by 6Li(n,α)3H reaction on nickel

Abstract The behavior of tritium produced on nickel by a 6 Li( n , α ) 3 H reaction in the catalytic hydrogenation of ethylene was investigated by autoradiography using nickel plates which had preliminarily been covered with lithium and irradiated with neutrons. Two autoradiographical methods were used, the ordinary stripping-film method and the electron-microscope autoradiographical method. The autoradiographs given by the stripping-film method indicated that the grain boundaries which were not used in the catalytic reaction exhibited a much stronger radioactivity due to the tritium than did the grain; on the other hand, those which were used in the catalytic reaction behaved in just the opposite way. The electron-microscope autoradiographs indicated that tritium accumulated preferentially on the step-edges of the slip-band of the crystal. These findings enable us to conclude that the tritium in lattice imperfections is highly active in catalytic reactions.

Enrichment of tritium by thermal diffusion column—I. TH-H2 and TD-D2 systems

Abstract Tritium present in H 2 or D 2 , 1.7 × 10 −2 Ci/mol, was enriched using a hot-wire type vertical glass thermal-diffusion column with a gas reservoir on top. Four columns with different diameters (mmφ), 8, 20, 30 and 41, were tested, while the temperature of a DC heated nichrome wire along the axis of each column was changed over a range from 200 to 450°C. The maximum equilibrium separation factors in hydrogen and in deuterium were 17 and 4.5 respectively. The optimum diameters were calculated by a modification of Waldmanns equation which can be used for the separation using parallel plates.