Annual Report - Volume 26 (2006)

Original

1. Kinetics of Methane Decomposition over Zr-Ni Alloys

   K. Watanabe, W Shu, M. Matsuyama

   
   
2. Thermal decomposition of CH₄ by Cr-Cu alloy

   M. Hara, K. Watanabe, M. Matsuyama

   
   
3. Modification of the Structure of Mg-Ni-Y Alloy by Vacuum-Heating

   H.Sakikawa, M.Hara, K.Watanabe, T.Mizushima, S.Morozumi

   
   
4. Diffusion of Hydrogen in TiC

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

   
   
5. Study of the total sputtering yield for Au modification of PMMA polymer particles by barrel-sputtering technique

   A. Taguchi, C. Hiromi, M. Tanizawa, T. Kitami, S. Akamaru, T. Abe

   
   
6. Surface modification of aluminum flakes with SiO2 by using the barrel-sputtering system equipped with oxide target
   

   S.Akamaru, S.Higashide, A.Taguchi, T.Abe

   
   
7. Consideration for the mechanism of tritium desorption in stainless-steel
   

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

Note

8. Measurement of Tritium Partial Pressure by BIXS(II)-Effects of Mixture Gases-
   

   M. Matsuyama, W.M. Shu, T.Suzuki

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Annual Report 26-1
Original

 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 lierature. 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.

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Annual Report 26-2
Original

 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.

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Annual Report 26-3
Original

 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.

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Annual Report 26-4
Original

 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.

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Annual Report 26-5
Original

 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 %.

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Annual Report 26-6
Original

 Elemental tritium of 3.7x10₁₂ Bq (100 Ci) was loaded into the Tritium Experimental System for 100 Ci/run in the Hydrogen Isotope Research Center. Tritium gas loaded a stainless steel cylinder, which was purchased from American Radiolabeled Chemical Inc., was transferred to a tritium storage getter in the system. Tritium leakage in a glove box was not observed during the gas transfer operation, indicating that tritium handling could be carried out in safe. The tritium storage getter almost absorbed the gas in the cylinder. Analysis of the quadrapole mass spectrum showed that the residual gas mainly contained tritiated hydrocarbons, ³He and only a small amount of elemental tritium. Analysis of the gas absorbed into the getter was also performed. The volume of absorbed gas corresponded approximately to that of 100 Ci elemental tritium gas, but radioactivity measured by BIXS was only about 80 Ci.

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Annual Report 26-7
Original

 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.

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Annual Report 26-8
Note

 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.