K. Watanabe¹⁾, W Shu²⁾, M. Matsuyama¹⁾

¹⁾ Hydrogen Isotope Research Center, Toyama University, Gofuku 3190, Toyama 930-8555, Japan
²⁾ Present Affliation: Tritium Process Laboratory, JAERI, Japan

Abstract

　The decomposition of methane over Zr, Zr₄Ni and Zr₂ and Zr₂Ni was investigated to develop highly active materials for capturing tritiated methane inevitably formed in tritium handling systems. The entire decomposition or absorption curves, however, could not been described by any simple kinetic equations appearing in the literature. The present paper describes verification of plausible kinetic equations reproducing the observed absorption curves, assuming a reaction mechanism consisting of a progressive removal of hydrogen atoms according to CH₄(g) →CH₃(a)→ CH₂(a)→ CH(a)→ C(a) and its modification including carbon segregation schemes by solving a set of kinetic equations by means of finite difference method, by taking into account of ab-initio calculations of potential energy surfaces by Gaussian 03.
It was found that a step-by-step H-deletion model could not generate the experimentally observed absorption curves, but they could be reproduced quite well in the whole reaction range by a modified reaction scheme assuming coagulation of a carbon residue like CH₂(a) or CH(a) to carbonaceous deposits, described as CH₄(g)- ^k1 →CH₃(a)-^k2 → CH(a)-^k3 →C-deposits. It was concluded that the final third step (with a rate constant of k₃) governs the overall absorption reactivity (methane consumption beyond 90%) of the materials.

Masanori Hara, Kuniaki Watanabe, Masao Matsuyama

Hydrogen Isotope Research Center, Toyama University, Gofuku 3190, Toyama 930-8555, Japan

Abstract

　To examine the applicability of Cr-Cu alloys for thermal decomposition of hydrocarbons, thermal decomposition of methane by Cr-Cu alloy were carried out. Cr-Cu alloys were prepared by the argon arc melting. The argon arc discharge was maintained until the copper only melted. The prepared alloy was constructed the mixture of chromium grains and the fused copper, because chromium is not miscible with copper and no intermetallic compounds are formed. The alloy ingots prepared were chipped to small needles to use for thermal decomposition of methane. The thermal decomposition of methane by Cr-Cu alloy needles was took place by means of the temperature-programmed method which the ramp rate was 2.28 K/min. By pure chromium, methane was decomposed to hydrogen gas and chromium carbides at 1060 K. On the other hand, the Cr-Cu alloy needles initiated the decomposition of methane at 900 K. The initiation temperature of the methane decomposition was reduced about 160 K on comparison pure chromium with the alloy. The alloying effect on the reduction of the initiation temperature of thermal decomposition was, however, appeared on the virgin alloy needles.

Hiroshi SAIKAWA¹⁾, Masanori HARA²⁾, Kuniaki WATANABE²⁾,Teruo MIZUSHIMA²⁾,Shotaro MOROZUMI³⁾

1) 1 Department of Mechanical Science, Chiba Institute of Technology Tsudanuma 2-17-1, Narashino, Chiba 275-0016, JAPAN
2)Hydrogen Isotope Research Center, University of Toyama, Gofuku 3160, Toyama 930-8555, Japan
3) Tohoku University Emeritus Professor Katahira 2-1-1, Aoba, Sendai, Miyagi 980-8577, JAPAN

Abstract

　A 10mm cubic specimen cut from a chill-cast Mg-30%Ni-5%Y alloy block was vacuum-heated for 4 h at 873 K and was then examined under optical and electron microscopes to determine structural changes and to identify constituents along from the inside to the outside at the vertical section of the deformed specimen. The specimen was then pulverized for measuring X-ray diffraction patterns, following to hydrogen absorption tests at room temperature and 473 K. As a result, it was deduced that an angular ternary compound existed in hardly visible size and number in the as-cast alloy, but newly produced largely by the vacuum heating and identified as MgNi3Y by EPMA might behave as a catalyst to enhance the hydrogen absorption rate at room temperature．A similar experiment was also performed on Mg-30%Ni-10%Ho alloy as a reference．

Y. Hatano, T. Nozaki, H. Homma, M. Matsuyama

Hydrogen Isotope Research Center, Toyama University, Gofuku3190, Toyama 930-8555

Abstract

　The diffusion coefficient of hydrogen in commercially supplied TiC powder was measured at 773, 873 and 973 K by hydrogen absorption experiments. The pre-exponential factor and activation energy were evaluated to be 10^-11 m²• s^-1 and 87±13 kJ•mol^-1, respectively.

Akira Taguchi¹⁾, Chikako Hiromi¹⁾, Masaaki Tanizawa¹⁾, Tomohito Kitami²⁾, Satoshi Akamaru²⁾, Takayuki Abe²⁾

¹⁾ Nippon PillarPacking Co., Ltd. 541-1 Utsuba, Shimo Uchigami, Sanda, Hyogo 669-1333
²⁾ Hydrogen Isotope Research Center, Toyama University, Gofuku3190, Toyama 930-8555

Abstract

　Total sputtering yield, defined as the ratio of the amount of metal deposited on a powdery substrate and the total amount of metal sputter-deposited, was investigated from Au modification of glass plates and PMMA polymer particles by using barrel-sputtering technique. The dependence of the angle distribution of Au deposition on RF input power was studied in the beginning. The amount of Au deposition was found to linearly depend on the distance from the center of the barrel, and the total amount of Au deposition was also found to linearly depend on the bias voltage for sputtering performed. On the basis of the amount of Au deposited on the PMMA polymer particle and the total amount of Au sputter-deposited, it was concluded that the total sputtering yield for Au modification of PMMA polymer particles was ca. 11 %.

Satoshi Akamaru, Shingo Higashide, Akira Taguchi, Takayuki Abe

Hydrogen Isotope Research Center, University of Toyama Gofuku 3190, Toyama 930-8555, Japan

Abstract

　We demonstrated a surface modification of aluminum flakes with SiO2 by using the barrel-sputtering system equipped with a SiO2 target. In order to find suitable sputtering conditions using the system, a SiO2 film was prepared on an Al sheet under various desired oxygen fractions, sputtering gas pressures, and substrate temperatures. XRD analysis and weight of prepared SiO2 film was determined that the suitable sputtering condition for the SiO2 film were 0% oxygen fraction, 3 Pa a total pressure, and 300 K substrate temperature. Surface coating of Al flakes by SiO2 was carried out under these conditions. It was found from SEM and EDS measurements that the surface of Al flakes was coated with a thin uniform SiO2 film.

K. Akaishi, Y. Torikai, D. Murata, Ralf-Dieter Penzhorn, K. Watanabe, M. Matsuyama

Hydrogen Isotope Research Center, University of Toyama Gofuku 3190, Toyama 930-8555, Japan

Abstract

Stainless-steel specimens of 15 mm square and 0.5 mm thickness in which tritium was dissolved with a uniform concentration were prepared. After the specimens had been chemically etched the thickness approximately 70 μm, the amount of tritium trapped within the top surface layer was measured as a function of time by β-ray -induced X-ray spectroscopy technique. When the specimen was immersed in an argon gas flow in atmosphere at ambient temperature, more than 99% of tritium desorbed from the specimen was tritiated water, and the amount of released tritium was measured as a function of time by the liquid-scintillation counting technique. In this paper, a model for hydrogen transport is proposed to evaluate quantitatively the above experimental results, and results of numerical simulation for tritium release are shown. It is demonstrated that the numerical simulation accurately predicts the amount of tritium released from the stainless-steel specimen in the experiment.

M. Matsuyama¹, W.M. Shu², T.Suzuki²

Hydrogen Isotope Research Center, Toyama University, Gofuku 3190, Toyama 930-8555, Japan
Tritium Tecnology Group, Division of Fusion Energy Tecnology Japan Atomic Energy Agency, Ibaraki319-1195, Japan

Abstract

　The bremsstrahlung X-ray counting method is one of the promising methods for in-situ measurements of high-level tritium, and the applicability of this method to a tritium handling system has been examined. In this study, pressure dependence of X-ray intensity in a high pressure region above 1 kPa was mainly examined using mixtures of H₂-,D₂-, He- and Ar-1%T₂. In a low pressure region below 1 kPa, the X-ray intensity was proportional to the partial pressure of tritium in all of the mixtures, while above that pressure it deviated downward from the proportional tendency. The deviation behavior in the mixtures of H₂-, D₂-, He-1% T₂ was similar, but that in the mixture of Ar-1%T₂ was different from that in the other three mixtures: namely, the downward deviation in the three mixtures is mainly caused by the self-absorption of β-rays in the hydrogen isotope and helium gases, whereas in the mixture of Ar-1%T₂ the emission of characteristic X-rays from argon atoms plays a major role in the deviation.