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Dive into the research topics where Yoshinobu Oshikiri is active.

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Featured researches published by Yoshinobu Oshikiri.


Japanese Journal of Applied Physics | 2004

Gravity field effect on copper-electroless plating: Comparison with the magnetic field effect

Yoshinobu Oshikiri; Makoto Sato; Akifumi Yamada; Ryoichi Aogaki

To compare the gravity field effect on copper-electroless plating with the magnetic field effect on the same reaction, the plating rates were measured under various vertical gravity fields. Consequently, considerably different results from those of the magnetic-field case, where the reaction was suppressed by the magnetic field, were obtained; the reaction was not suppressed but promoted by the gravity field. The total reaction rate increased with increasing gravitational acceleration, and followed the diffusion current equation in a vertical gravity field. The scanning electron microscope (SEM) observation also revealed the promotion by the gravity field, i.e., the increase of crystal sizes with increasing gravitational acceleration. This is because, in the magnetic field, the micro-magnetohydrodynamic (micro-MHD) flows interact with the nonequilibrium fluctuations accompanying the reaction. Therefore, it was concluded that the gravity convection cells occurring under gravity fields do not interact at least up to 170 G with the nonequilibrium fluctuations. At the same time, the density coefficients intrinsic to cathodic and anodic partial reactions were obtained by measuring current responses to sweeping gravitational acceleration, i.e., sweep gravitammetry. By comparing observed data with those calculated from the density coefficients, it was clarified that the autocatalytic process between the cathodic and anodic reactions is more accelerated by gravity convection than the intrinsic autocatalytic process without gravity convection.


Scientific Reports | 2016

Lifetime of Ionic Vacancy Created in Redox Electrode Reaction Measured by Cyclotron MHD Electrode

Atsushi Sugiyama; Ryoichi Morimoto; Tetsuya Osaka; Iwao Mogi; Miki Asanuma; Makoto Miura; Yoshinobu Oshikiri; Yusuke Yamauchi; Ryoichi Aogaki

The lifetimes of ionic vacancies created in ferricyanide-ferrocyanide redox reaction have been first measured by means of cyclotron magnetohydrodynamic electrode, which is composed of coaxial cylinders partly exposed as electrodes and placed vertically in an electrolytic solution under a vertical magnetic field, so that induced Lorentz force makes ionic vacancies circulate together with the solution along the circumferences. At low magnetic fields, due to low velocities, ionic vacancies once created become extinct on the way of returning, whereas at high magnetic fields, in enhanced velocities, they can come back to their initial birthplaces. Detecting the difference between these two states, we can measure the lifetime of ionic vacancy. As a result, the lifetimes of ionic vacancies created in the oxidation and reduction are the same, and the intrinsic lifetime is 1.25 s, and the formation time of nanobubble from the collision of ionic vacancies is 6.5 ms.


Scientific Reports | 2017

Magneto-Dendrite Effect: Copper Electrodeposition under High Magnetic Field

Makoto Miura; Yoshinobu Oshikiri; Atsushi Sugiyama; Ryoichi Morimoto; Iwao Mogi; Miki Miura; Satoshi Takagi; Yusuke Yamauchi; Ryoichi Aogaki

Ionic vacancy is a by-product in electrochemical reaction, composed of polarized free space of the order of 0.1 nm with a 1 s lifetime, and playing key roles in nano-electrochemical processes. However, its chemical nature has not yet been clarified. In copper electrodeposition under a high magnetic field of 15 T, using a new electrode system called cyclotron magnetohydrodynamic (MHD) electrode (CMHDE) composed of a pair of concentric cylindrical electrodes, we have found an extraordinary dendritic growth with a drastic positive potential shift from hydrogen-gas evolution potential. Dendritic deposition is characterized by the co-deposition of hydrogen molecule, but such a positive potential shift makes hydrogen-gas evolution impossible. However, in the high magnetic field, instead of flat deposit, remarkable dendritic growth emerged. By examining the chemical nature of ionic vacancy, it was concluded that ionic vacancy works on the dendrite formation with the extraordinary potential shift.


Scientific Reports | 2016

Origin of Nanobubbles Electrochemically Formed in a Magnetic Field: Ionic Vacancy Production in Electrode Reaction

Ryoichi Aogaki; Atsushi Sugiyama; Makoto Miura; Yoshinobu Oshikiri; Miki Miura; Ryoichi Morimoto; Satoshi Takagi; Iwao Mogi; Yusuke Yamauchi

As a process complementing conventional electrode reactions, ionic vacancy production in electrode reaction was theoretically examined; whether reaction is anodic or cathodic, based on the momentum conservation by Newton’s second law of motion, electron transfer necessarily leads to the emission of original embryo vacancies, and dielectric polarization endows to them the same electric charge as trans- ferred in the reaction. Then, the emitted embryo vacancies immediately receive the thermal relaxation of solution particles to develop steady-state vacancies. After the vacancy production, nanobubbles are created by the collision of the vacancies in a vertical magnetic field.


International journal of electrochemistry | 2013

Buoyancy Effect of Ionic Vacancy on the Change of the Partial Molar Volume in Ferricyanide-Ferrocyanide Redox Reaction under a Vertical Gravity Field

Yoshinobu Oshikiri; Makoto Miura; Ryoichi Aogaki

With a gravity electrode (GE) in a vertical gravity field, the buoyancy effect of ionic vacancy on the change of the partial molar volume in the redox reaction between ferricyanide (FERRI) and ferrocyanide (FERRO) ions was examined. The buoyancy force of ionic vacancy takes a positive or negative value, depending on whether the rate-determining step is the production or extinction of the vacancy. Though the upward convection over an upward electrode in the FERRO ion oxidation suggests the contribution of the positive buoyancy force arising from the vacancy production, the partial molar volume of the vacancy was not measured. On the other hand, for the downward convection under a downward electrode in the FERRI ion reduction, it was not completely but partly measured by the contribution of the negative buoyancy force from the vacancy extinction. Since the lifetime of the vacancy is decreased by the collision between ionic vacancies during the convection, the former result was ascribed to the shortened lifetime due to the increasing collision efficiency in the enhanced upward convection over an upward electrode, whereas the latter was thought to arise from the elongated lifetime due to the decreasing collision efficiency by the stagnation under the downward electrode.


Russian Journal of Electrochemistry | 2012

Measurement of the change in partial molar volume during electrode reaction by gravity electrode—II. Examination of the accuracy of the measurement

Yoshinobu Oshikiri; Makoto Miura; Ryoichi Aogaki

The reliability of the measurement of the change in partial molar volume between product and reactant ions measured by gravity electrode (GE) was examined by the thermodynamic measurement of pycnometer (PM). Since the PM method requires an experimental equation of the apparent molar volume to calculate the partial molar volumes of the individual ions, the most suitable experimental equation must be first determined. As a test reaction for the experiment, oxidation of ferrocyanide (FERO) ion to ferricyanide (FERI) ion was adopted. After fitting several experimental equations to the data of the apparent molar volumes by the PM method, the calculated changes in the partial molar volume were compared with the data of the GM method. Then, it is concluded that the polynomial with a degree of 3 of the logarithm of the molality of the FERO ion suggests the most suitable equation. As a result, the reliability of the GE method was also experimentally validated.


Russian Journal of Electrochemistry | 2012

Measurement of the change in the partial molar volume during electrode reaction by gravity electrode—I. Theoretical examination

Ryoichi Aogaki; Yoshinobu Oshikiri; Makoto Miura

Gravity electrode is an electrode system, which is operated in a high gravity field arising from centrifugal force, and allows us to measure the change in the partial molar volume between product and reactant ions in an electrode reaction. In this paper, in the presence of a large amount of supporting electrolyte, the partial molar volume of each active ion in equilibrium state is first formulated on the basis of thermodynamics. Then, the change in the partial molar volume applicable to gravity electrode is derived. Therefore, it is possible to validate the equation obtained for gravity electrode by the thermodynamic measurement.


Meeting Abstracts | 2009

Origin of Nanobubble - Formation of Stable Vacancy in Electrolyte Solution

Ryoichi Aogaki; Makoto Miura; Yoshinobu Oshikiri


Electrochemistry | 2014

Microbubble Formation from Ionic Vacancies in Copper Electrodeposition under a High Magnetic Field

Makoto Miura; Ryoichi Aogaki; Yoshinobu Oshikiri; Atsushi Sugiyama; Ryoichi Morimoto; Miki Miura; Iwao Mogi; Yusuke Yamauchi


Electrochimica Acta | 2005

Application of gravity electrode to the analysis of iron-pitting corrosion under vertical gravity field

Makoto Sato; Yoshinobu Oshikiri; Akifumi Yamada; Ryoichi Aogaki

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Ryoichi Aogaki

National Institute for Materials Science

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Miki Asanuma

Nagaoka University of Technology

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Akifumi Yamada

Nagaoka University of Technology

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Makoto Sato

Nagaoka University of Technology

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