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Journal Articles

Deposition of uranium oxide following the reduction in weak acid solution using Electrochemical Quartz Crystal Microbalance (EQCM)

Ouchi, Kazuki; Otobe, Haruyoshi; Kitatsuji, Yoshihiro; Yamamoto, Masahiro

ECS Transactions, 75(27), p.51 - 57, 2017/01

 Times Cited Count:1 Percentile:39.05

We investigated the deposition of U(IV) following a valence change of U as electrodeposition using an electrochemical quartz crystal microbalance (EQCM). When measurements of the reduction of U(VI) in a weak acid solution were performed, deposits of U(IV) were observed on the electrode surface. From deposition rates, pH dependence of them, and oxidation potentials of deposits, we proposed the following deposition mechanism. The deposition is divided into the three phases; First, in the induction phase, U(IV) produced by the disproportionation forms U(IV) hydroxide nucleus. Next, in the growth phase, U(IV) deposits begin to grow. In this phase, the deposits catalyze the reduction of U(V) to U(IV), resulting an increase of the reduction current. Finally, in the transformation phase, U(IV) hydroxide species transform into U dioxide having more stable state.

Journal Articles

Electronic structure of Pt and Pt-Co nanoparticles with O$$_{2}$$ and O$$_{2}$$/H$$_{2}$$O adsorption revealed by in situ XAFS and hard X-ray photoelectron spectroscopy

Cui, Y.*; Harada, Yoshihisa*; Hatanaka, Tatsuya*; Nakamura, Naoki*; Ando, Masaki*; Yoshida, Toshihiko*; Ikenaga, Eiji*; Ishii, Kenji*; Matsumura, Daiju; Li, R.*; et al.

ECS Transactions, 72(8), p.131 - 136, 2016/10

 Times Cited Count:1 Percentile:49.92

Journal Articles

Pitting potential of zircaloy-2 in artificial seawater under $$gamma$$-ray irradiation

Motooka, Takafumi; Komatsu, Atsushi; Tsukada, Takashi; Yamamoto, Masahiro

ECS Transactions, 53(21), p.25 - 32, 2013/05

 Times Cited Count:3 Percentile:85.19

Journal Articles

Effects of oxidation states of Np on polarization curve of stainless steel in boiling 3M-HNO$$_{3}$$

Kato, Chiaki; Ueno, Fumiyoshi; Yamamoto, Masahiro; Ban, Yasutoshi; Uchiyama, Gunzo; Nojima, Yasuo*; Fujine, Sachio*

ECS Transactions, 53(21), p.45 - 55, 2013/05

 Times Cited Count:2 Percentile:77.18

Neptunium ion contained as one of the fission products in reprocessing solutions is known as a corrosion accelerator of the stainless steel. But it is not clear why remarkable acceleration of corrosion is caused by a slight amount of the Np ion in boiling nitric acid solution. Neptunium has several oxidation states in nitric acid solution. These changeable oxidation states of Np in nitric acid solution are regarded as the cause. Therefore an evaluation of the electrochemical behaviors on stainless steel in nitric acid solution related to the oxidation state of Np is required in order to understand the corrosion acceleration mechanism. A specially designed electrochemical test cell integrated with optical cell for spectroscopic analysis was used for this purpose. From results of electrochemical tests, cathodic reaction on stainless steel was activated by Np ions. Np(VI) ion made the corrosion potential shift nobler than Np(V) and nobler corrosion potential causes increasing corrosion current and accelerating corrosion of stainless steel in nitric acid solution. Np(V) was easily oxidized to Np(VI) in nitric acid solution and Np(VI) was the stable state in boiling 3M-HNO$$_{3}$$. It was considered that role of Np ions was that of mediator to accelerate corrosion due to activating cathodic reaction and re-oxidizing cycle in boiling 3M-HNO$$_{3}$$.

Journal Articles

Effects of tritiated water on passivation behavior of SUS304 stainless steel

Oyaizu, Makoto; Isobe, Kanetsugu; Yamanishi, Toshihiko

ECS Transactions, 50(50), p.63 - 69, 2013/00

 Times Cited Count:3 Percentile:81.46

The effects of tritiated water on the passivation behavior of SUS304 stainless steel were electrochemically studied by anodic polarization measurements and diachronic measurements of open circuit potential with changing tritium concentration and dissolved oxygen concentration as parameters in the electrolyte of 1N sulfuric acid solution, where the passivation inhibitory effects by tritiated water could be clearly observed. As a result, it was found that the passivation would be proceed with two steps. The effects of tritiated water could be observed in both of two steps; delay in the first step and deceleration in the second step. From these results, it was suggested that the passivation inhibitory effect might be promoted by further oxidation and sequential dissolution of Cr$$^{3+}$$ by radiolysis products.

Journal Articles

Alkaline durable anion exchange membranes based on graft-type fluoropolymer films for hydrazine hydrate fuel cell

Yoshimura, Kimio; Koshikawa, Hiroshi; Yamaki, Tetsuya; Maekawa, Yasunari; Yamamoto, Kazuya*; Shishitani, Hideyuki*; Asazawa, Koichiro*; Yamaguchi, Susumu*; Tanaka, Hirohisa*

ECS Transactions, 50(2), p.2075 - 2081, 2012/10

no abstracts in English

Journal Articles

PFG-NMR and SANS studies in cation exchange membranes based on sulfonated polyphenylene multiblock copolymers

Yoshida, Miru*; Zhao, Y.; Fujita, Masahiro*; Ohira, Akihiro*; Takeoka, Yuko*; Koizumi, Satoshi*; Rikukawa, Masahiro*

ECS Transactions, 50(2), p.1045 - 1053, 2012/10

Journal Articles

Proton conduction characteristics in radiation-grafted polymer electrolyte membranes based on perfluorinated and aromatic hydrocarbon polymers

Sawada, Shinichi; Maekawa, Yasunari

ECS Transactions, 41(1), p.2125 - 2133, 2011/10

 Times Cited Count:5 Percentile:75.06

In order to improve the performance of the radiation-grafted polymer electrolyte membranes (PEMs), it is important to characterize the PEMs prepared by various conditions. In this study, we investigated the proton conduction properties of grafted PEMs based on crosslinked poly(tetrafluoroethylene) (cPTFE) (perfluoropolymer) and poly(etheretherketone) (PEEK) (hydrocarbon polymer). For obtaining a deep insight, the self-diffusion coefficient of protons, D$$_{P}$$, was calculated. In the case of PEEK PEMs, the D$$_{P}$$ did not depend on the ion exchange capacity (IEC). On the other hand, for cPTFE PEMs, the D$$_{P}$$ prominently increased with the IEC. The small D$$_{P}$$ at low IEC can be related to the high crystallinity of the base cPTFE film. Due to PTFE crystallites, poly(styrene sulfonic acid) graft chains were not homogeneously introduced. As a result, the ion-channnel network structures should not be well-connected, thereby restricting the proton mobility.

Journal Articles

Conductometric analysis for the formation of poly(vinylidene fluoride)-based ion track membranes

Yamaki, Tetsuya; Nuryanthi, N.*; Koshikawa, Hiroshi; Asano, Masaharu; Sawada, Shinichi; Hasegawa, Shin; Maekawa, Yasunari; Voss, K.-O.*; Trautmann, C.*; Neumann, R.*

ECS Transactions, 35(24), p.1 - 12, 2011/05

 Times Cited Count:7 Percentile:94.31

Our focus has been placed on ion track membranes of poly(vinylidene fluoride) (PVDF), a type of fluoropolymer, because of their superior chemical, mechanical and ferro-electric properties. The aim of this study is to investigate the formation of the PVDF track membranes in more detail by electrolytic conductometry. Interestingly, application of a higher voltage to the conductometry cell as well as irradiation with a higher-LET beam promoted track etching up to breakthrough probably because electrophoretic migration of dissolved products occurred out of each pore.

Journal Articles

Impact of stacked AlON/SiO$$_{2}$$ gate dielectrics for SiC power devices

Watanabe, Heiji*; Kirino, Takashi*; Uenishi, Yusuke*; Chanthaphan, A.*; Yoshigoe, Akitaka; Teraoka, Yuden; Mitani, Shuhei*; Nakano, Yuki*; Nakamura, Takashi*; Hosoi, Takuji*; et al.

ECS Transactions, 35(2), p.265 - 274, 2011/05

 Times Cited Count:8 Percentile:93.43

Journal Articles

Gate stack technologies for SiC power MOSFETs

Watanabe, Heiji*; Hosoi, Takuji*; Kirino, Takashi*; Uenishi, Yusuke*; Chanthaphan, A.*; Ikeguchi, Daisuke*; Yoshigoe, Akitaka; Teraoka, Yuden; Mitani, Shuhei*; Nakano, Yuki*; et al.

ECS Transactions, 41(3), p.77 - 90, 2011/00

 Times Cited Count:5 Percentile:91.12

Journal Articles

Water transport in polymer electrolyte membranes investigated by dissipative particle dynamics simulation

Sawada, Shinichi; Yamaki, Tetsuya; Ozawa, Taku*; Suzuki, Akihiro*; Terai, Takayuki*; Maekawa, Yasunari

ECS Transactions, 33(1), p.1067 - 1078, 2010/10

 Times Cited Count:6 Percentile:87.98

In order to investigate water transport in polymer electrolyte membranes (PEMs), we calculated the self-diffusion coefficient of water, D$$_{W}$$, by dissipative particle dynamics (DPD) simulation. The simulation target materials are Nafion and radiation-grafted PEMs in the fully-hydrated states. D$$_{W}$$ was obtained by the following steps: (1) molecular modeling with the coarse-grained particles representing groups of several atoms; (2) calculation of the water particle diffusivity, D$$_{W}$$$$^{Particle}$$, in the PEMs; (3) determination of the unit time in the DPD simulation; (4) conversion of D$$_{W}$$$$^{Particle}$$ of the PEMs into D$$_{W}$$ in the standard SI unit. Interestingly, D$$_{W}$$ was found to decrease with the diffusion time period, $$Delta$$t, probably owing to the geometrical confinement effect by water-transport hydrophilic regions. Quantitative analysis of this D$$_{W}$$-$$Delta$$t relationship provided us with the size of hydrophilic regions.

Journal Articles

XAFS analysis of unpyrolyzed CoPPyC oxygen reduction catalysts for Anion-Exchange Membrane Fuel Cells (AMFC)

Asazawa, Koichiro*; Yamamoto, Kazuya*; Yamada, Koji*; Tanaka, Hirohisa*; Matsumura, Daiju; Tamura, Kazuhisa; Nishihata, Yasuo; Atanassov, P.*

ECS Transactions, 33(1), p.1751 - 1755, 2010/10

CoPPyC were analyzed with X-ray adsorption fine structure (XAFS) measurements. Acid-treated CoPPyC (CoPPyC-AT) has higher activity than PPyC for oxygen reduction reaction. From the analysis of EXAFS of Co, CoPPyC electrocatalysts as synthesized consist of two peaks. The peak around 1.6 ${AA}$ was assigned to Co-N and/or Co-O shells. The second peak around 2.6 ${AA}$ was assigned to Co-O-Co shells originated from cobalt hydroxide. CoPPyC-AT showed only one peak of assigned to Co-N and/or Co-O, and it indicates that cobalt hydroxide is removed by acid treatment. It is clear that a coexistence of cobalt and nitrogen in CoPPyC-AT shows specific performance, and pyrolysis is not necessary to make correlation of Co-N.

Journal Articles

Re-oxidation behavior of Cr and V ions in the boiling nitric acid solution and acceleration effect on corrosion rate of stainless steel

Yamamoto, Masahiro; Motooka, Takafumi; Ueno, Fumiyoshi; Kato, Chiaki

ECS Transactions, 25(40), p.23 - 30, 2010/00

 Times Cited Count:1 Percentile:36.26

Corrosion rates of stainless steels have been accelerated by existence of oxidizing ions, i.e. Cr(VI) and V(V). However, the mechanism of acceleration effect by these ions was not clear. The results of examination for the effect showed that the acceleration effect of Cr was larger than that of V. But, the effect was rapidly decreased because of the reduction from Cr(VI) to Cr(III). Although, the acceleration effect of V stayed constant. And V(IV) was more rapidly re-oxidized to V(V) than Cr(VI) in boiling nitric acid solution. So, the corrosion rate in the solution containing V ion does not change with time because of high re-oxidation rate of V ion.

Journal Articles

Fuel-cell performance of multiply-crosslinked polymer electrolyte membranes prepared by two-step radiation technique

Yamaki, Tetsuya; Sawada, Shinichi; Asano, Masaharu; Maekawa, Yasunari; Yoshida, Masaru*; Gubler, L.*; Alkan G$"u$rsel, S.*; Scherer, G. G.*

ECS Transactions, 25(1), p.1439 - 1450, 2009/10

 Times Cited Count:4 Percentile:83.58

A multiply-crosslinked polymer electrolyte membrane was prepared by the radiation-induced co-grafting of styrene and a bis(vinyl phenyl)ethane (BVPE) crosslinker into a radiation-crosslinked polytetrafluoroethylene (cPTFE) film. We then investigated its hydrogen/oxygen fuel-cell performance at 60 and 80$$^{circ}$$C in terms of the effect of radiation and chemical crosslinking. At 60$$^{circ}$$C, all the membranes initially exhibited similar performance, but only the cPTFE-based membranes were durable at 80$$^{circ}$$C, indicating the necessity of radiation crosslinking in the PTFE main chains. Importantly, cell performance of the multiply-crosslinked membrane was found high enough to reach that of a Nafion112 membrane. This is probably because the BVPE crosslinks in the graft component improved the membrane-electrode interface in addition to membrane durability. After severe OCV hold tests at 80 and 95$$^{circ}$$C, the performance deteriorated, while no significant change was observed in ohmic resistivity. Accordingly, our membranes seemed so chemically stable that an influence on overall performance loss could be negligible.

Journal Articles

An Electrochemical sensor array for ${it in-situ}$ measurements of oxide film electric resistance in high temperature water

Uchida, Shunsuke; Sato, Tomonori; Kakinuma, Nagao*; Miyazawa, Takahiro*; Sato, Yoshiyuki*; M$"a$kel$"a$, K.*

ECS Transactions, 2(25), p.39 - 50, 2007/00

no abstracts in English

Journal Articles

Bias temperature instability characterization of advanced gate stacks

Fujieda, Shinji*; Terai, Masayuki*; Saito, Motofumi*; Toda, Akio*; Miura, Yoshinao*; Liu, Z.*; Teraoka, Yuden; Yoshigoe, Akitaka; Wilde, M.*; Fukutani, Katsuyuki*

ECS Transactions, 6(3), p.185 - 202, 2007/00

In order to find how bias temperature instability occurs in advanced gate stacks, we will review experimental results of our investigation on SiO$$_{2}$$, plasma-nitrided SiON, HfSiON and HfSiON with Ni-silicide electrodes. It thus seems that we need to clarify and control the chemical and physical influences on the insulator bulk and the insulator/Si interface caused by newly incorporated materials and process technologies, in order to ensure the reliability of bias temperature instability for advanced gate stacks.

Journal Articles

Low-temperature epitaxial growth of [Fe$$_{3}$$Si/SiGe]$$_{n}$$ (n = 1-2) multi-layered structures for spintronics application

Sado, Taizo*; Ueda, Koji*; Ando, Yuichiro*; Kumano, Mamoru*; Narumi, Kazumasa; Maeda, Yoshihito; Miyao, Masanobu*

ECS Transactions, 11(6), p.473 - 479, 2007/00

Our recent progresses in epitaxial growth of Fe$$_{3}$$Si on Ge substrates are reviewed. Single crystalline Fe$$_{3}$$Si layers with atomically flat interfaces were achieved on Ge(111) substrates by optimizing growth conditions at low temperatures (60$$sim$$200 $$^{circ}$$C). Thermal stability of it was guaranteed up to 400 $$^{circ}$$C. In addition, epitaxial growth of mixed layers composed of Fe$$_{3}$$Si, FeGe, and FeSi on Ge substrates at 400 $$^{circ}$$C is reported. Finally, epitaxial growth of Fe$$_{3}$$Si/Ge/Fe$$_{3}$$Si/Ge structures is discussed. These results will be a powerful tool to open up SiGe related spintronics.

Journal Articles

Effect of Fe/Si ratio on epitaxial growth of Fe$$_{3}$$Si on Ge substrate

Kumano, Mamoru*; Ando, Yuichiro*; Ueda, Koji*; Sado, Taizo*; Narumi, Kazumasa; Maeda, Yoshihito; Miyao, Masanobu*

ECS Transactions, 11(6), p.481 - 485, 2007/00

The effects of the Fe/Si ratios on molecular beam epitaxy (MBE) of Fe$$_{3}$$Si on Ge substrate have been investigated in a wide range of growth temperatures (60$$sim$$300 $$^{circ}$$C). From XRD measurements, it was found that Fe$$_{3}$$Si layers were epitaxially grown on Ge(111) substrates at 60$$sim$$200 $$^{circ}$$C under the stoichiometric (Fe:Si = 3:1) and non-stoichiometric (Fe:Si = 4:1) conditions. From RBS measurement, it was found that atomic mixing of Fe and Ge at Fe$$_{3}$$Si/Ge interfaces began at a growth temperature of 300 $$^{circ}$$C. In the case of MBE under the stoichiometric condition, the crystallinity of Fe$$_{3}$$Si is significantly improved compared to the non-stoichiometric condition. As a result, very low $$chi$$$$_{min}$$ was obtained in a wide temperature (60$$sim$$200 $$^{circ}$$C) under the stoichiometric condition. From the transmission electron microscopy measurements, it was shown that high-quality DO3-type Fe$$_{3}$$Si/Ge structures with atomically flat interfaces were realized at a low temperature ($$sim$$200 $$^{circ}$$C) under the stoichiometric condition.

Journal Articles

Real-time observation of initial thermal oxidation on Si(110)-16$$times$$2 surface by photoemission spectroscopy

Suemitsu, Maki*; Kato, Atsushi*; Togashi, Hideaki*; Konno, Atsushi*; Yamamoto, Yoshihisa*; Teraoka, Yuden; Yoshigoe, Akitaka; Enta, Yoshiharu*; Narita, Yuzuru*

ECS Transactions, 3(2), p.311 - 316, 2006/00

Initial thermal oxidation of Si(110) surface has been investigated by using real-time X-ray photoemission spectroscopy with synchrotron radiation. The Si(110) initial oxidation is characterized by presence of a rapid oxidation just after the introduction of gaseous oxygen molecules. Peak separation of the O1s photoemission spectra suggests the presence of at least two distinct oxidation sites on the surface, which may reflect the complicated surface structure of the Si(110)-16$$times$$2 reconstruction.

Journal Articles

Nano-structure controlled polymer electrolyte membranes for fuel cell applications prepared by ion beam irradiation

Yamaki, Tetsuya; Kozone, Yuichi; Hiroki, Akihiro; Asano, Masaharu; Kubota, Hitoshi*; Yoshida, Masaru

ECS Transactions, 3(1), p.103 - 112, 2006/00

Fluoropolymer-based electrolyte membranes for water electrolyzers and fuel cells were prepared by using heavy ion beams from the cyclotron accelerator. The preparation method for these so-called "nano-scale structure-controlled membranes" involves (1) the swift heavy ion irradiation of polyvinylidene fluoride films and subsequent chemical etching to obtain cylindrical pores with a diameter of 100 nm, and (2) the filling of proton-conducting polymer chains into the etched pores by $$gamma$$-ray-induced graft polymerization. The proton transport only in the thickness direction was observed for the resulting membranes with controlled ion exchange capacities, indicating the formation of one-dimensional straight proton-conducting pathways parallel to the ion-beam incident axis. The membranes exhibited a lower water uptake and reduced methanol permeability compared to commercially-available Nafion probably due to the restricted structures.

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