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Search Results: 1 - 10 of 97 matches for " Zenji Horita "
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Stress-Corrosion Cracking Property of Aluminum-Magnesium Alloy Processed by Equal-Channel Angular Pressing
Hiroaki Nakano,Satoshi Oue,Seiji Taguchi,Shigeo Kobayashi,Zenji Horita
International Journal of Corrosion , 2012, DOI: 10.1155/2012/543212
Abstract: Stress-corrosion cracking property of an aluminum-magnesium alloy processed by equal-channel angular pressing (ECAP) was investigated by a slow strain-rate tensile technique in a 3% NaCl solution of pH?4.2 at 303?K. The maximum stress and elongation of the Al-Mg alloy were lower in the NaCl solution than in air. The stress-corrosion cracking property was evaluated by the decrease ratio of maximum stress and elongation of the Al-Mg alloy with NaCl solution, and , respectively. and were lower with ECAP than without it, showing that the susceptibility of stress-corrosion cracking decreased with ECAP. The polarization curve and time dependence of the anodic current density at constant potential of the Al-Mg alloy in the NaCl solution revealed that the anodic current density was lower with ECAP than without it, or the corrosion resistance of the Al-Mg alloy was improved by ECAP. The decrease in stress-corrosion crack susceptibility of the Al-Mg alloy with ECAP is attributed to an improvement in corrosion resistance afforded by ECAP. 1. Introduction Although aluminum is an inherently active metal, it shows excellent corrosion resistance over a neutral range of pH 4–8 owing to its superficial oxide film. However, in solutions containing Cl?, pitting corrosion occurs locally where the oxide film is attacked by Cl? [1, 2]. When additional stress is applied, stress-corrosion cracking also occurs along the crystal grain boundary, resulting in serious damage [3–5]. On the other hand, reducing the grain size of metallic materials to the submicrometer or even the nanometer range by equal-channel angular pressing (ECAP), high-pressure torsion (HPT), or a severe torsion-straining process (STSP) is being studied increasingly with the aim of improving mechanical properties such as strength and ductility [6–11]. The effect of severe plastic deformation on the pitting corrosion resistance of Al alloys has been reported [12–15]; however, reports on the effect of stress-corrosion cracking are rare. In this study, the stress-corrosion cracking property of an alloy of Al-3%Mg (by mass) processed by ECAP was investigated. Stress-corrosion cracking property was evaluated by a slow strain-rate tensile technique in a 3% NaCl solution. Since the stress-corrosion cracking property of the Al-Mg alloy was expected to depend on corrosion resistance, the effect of ECAP on the corrosion resistance of the Al-Mg alloy was investigated by polarization curves and the anodic current density at constant potential in the NaCl solution. The fracture area after the slow strain-rate tensile test
Application of three-dimensional electron tomography using bright-field imaging—Two types of Si-phases in Al–Si alloy
Kenji Kaneko, Ryo Nagayama, Koji Inoke, Etsuko Noguchi and Zenji Horita
Science and Technology of Advanced Materials , 2006,
Abstract: When a dilute amount of Si is added to Al, it results in the precipitation of Si-phases, either planar- and/or rod-type, depending on the ageing conditions. Observation of these phases had been carried out by TEM two dimensionally so far; nevertheless information of the thickness as well as the distribution had been neglected in the past. In this paper, a combination of electron diffraction, high-resolution transmission electron microscopy, and three-dimensional electron tomography was applied to characterize the morphologies and the orientation relationship of the Si-phases in an Al–Si alloy.
Grain boundaries in ultrafine grained materials processed by severe plastic deformation and related phenomena
Xavier Sauvage,Gerhard Wilde,Sergiy Divinski,Zenji Horita,Ruslan Valiev
Physics , 2012, DOI: 10.1016/j.msea.2012.01.080
Abstract: Grain boundaries in ultrafine grained (UFG) materials processed by severe plastic deformation (SPD) are often called "non-equilibrium" grain boundaries. Such boundaries are characterized by excess grain boundary energy, presence of long range elastic stresses and enhanced free volumes. These features and related phenomena (diffusion, segregation, etc.) have been the object of intense studies and the obtained results provide convincing evidence of the importance of a non-equilibrium state of high angle grain boundaries for UFG materials with unusual properties. The aims of the present paper are first to give a short overview of this research field and then to consider tangled, yet unclear issues and outline the ways of oncoming studies. A special emphasis is given on the specific structure of grain boundaries in ultrafine grained materials processed by SPD, on grain boundary segregation, on interfacial mixing linked to heterophase boundaries and on grain boundary diffusion. The connection between these unique features and the mechanical properties or the thermal stability of the ultrafine grained alloys is also discussed.
Effect of Equal-Channel Angular Pressing on Pitting Corrosion of Pure Aluminum
Injoon Son,Hiroaki Nakano,Satoshi Oue,Shigeo Kobayashi,Hisaaki Fukushima,Zenji Horita
International Journal of Corrosion , 2012, DOI: 10.1155/2012/450854
Abstract: The effect of equal-channel angular pressing (ECAP) on the pitting corrosion of pure Al was investigated using electrochemical techniques in solutions containing 0.1?m?mol·dm?3 of Na2SO4 and 8.46?mol·dm?3 of NaCl (300?ppm?Cl?) and followed by surface analysis. The potential for pitting corrosion of pure Al was clearly shifted in the noble direction by the ECAP process indicating that this process improves resistance to pitting corrosion. The time dependence of corrosion potential and the anodic potential at 1?A·m?2 revealed that the rate of formation of Al oxide films increased due to a decrease in the grain size of the Al after ECAP. Since there exists a negligible amount of impurity precipitates in pure Al, the improvement in pitting corrosion resistance of pure Al by ECAP appears to be attributable to an increase in the rate of formation of Al oxide films. 1. Introduction Although aluminum is inherently an active metal, it shows excellent corrosion resistance over a neutral pH range of 4–8 due to its superficial oxide film. In solutions containing Cl?, however, pitting corrosion occurs locally where the oxide film is attacked by Cl? [1–7]. On the other hand, reducing the grain size of metallic materials to the submicron range or even the nanometer range using equal-channel angular pressing (ECAP), high pressure torsion (HPT), or severe torsion straining processing (STSP) is increasingly being studied with the aim of improving mechanical properties such as strength and ductility [8–13]. Although the literature is reasonably scarce with investigations reporting the effects of severe plastic deformation upon the pitting and general corrosion behaviour [14–20] of Al-based alloys, mainly AA1100 and AA5052 (Al-Mg), those reported their majority suggests that corrosion resistance decreases with decreasing the grain size [14, 15]. It should also be remarked that chloride content, pH and other characteristics and nature of solution significantly affect the corrosion behaviour. Considering the ECAP, it has been reported both increase and decrease on the corrosion resistance [15, 17, 18]. Ralston et al. [15] recently reported that finer grains of commercially pure (c.p.) grade Al samples provide significant gains into the corrosion resistance in acidic and alkaline sodium chloride media whilst having lesser, but noticeable, impact in near neutral electrolytes [15]. It was also reported [15] that ECAP has provided low corrosion rates by using a single cast ingot of ultrahigh purity Al. Precipitate compounds of Fe-Al and Si were found around the pitting area.
Structural instability of the rutile compounds and its relevance to the metal-insulator transition of VO2
Zenji Hiroi
Physics , 2015, DOI: 10.1016/j.progsolidstchem.2015.02.001
Abstract: The metal-insulator transition (MIT) of VO2 is discussed with particular emphasis on the structural instability of the rutile compounds toward dimerization. Ti substitution experiments reveal that the MIT is robust up to 20% Ti substitutions and occurs even in extremely thin V-rich lamellas in spinodally decomposed TiO2-VO2 composites, indicating that the MIT is insensitive to hole doping and essentially takes on a local character. These observations suggest that either electron correlation in the Mott-Hubbard sense or Peierls (Fermi-surface) instability plays a minor role on the MIT. Through a broad perspective of crystal chemistry on the rutile-related compounds, it is noted that VO2 and another MIT compound NbO2 in the family eventually lie just near the borderline between the two structural groups with the regular rutile structure and the distorted structures characterized by the formation of dimers with direct metal-metal bonding. The MITs of VO2 and NbO2 are natural consequences of structural transitions between the two groups, as all the d electrons are trapped in the bonding molecular orbitals of dimers at low temperatures. Such dimer crystals are ubiquitously found in early transition metal compounds having chain-like structures, such as MoBr3, NbCl4, Ti4O7, and V4O7, the latter two of which also exhibit MITs probably of the same origin. In a broader sense, the dimer crystal is a kind of molecular orbital crystals in which virtual molecules made of transition metal atoms with partially-filled t2g shells, such as dimers, trimers or larger ones, are generated by metal-metal bonding and are embedded into edge- or face-sharing octahedron networks of various kinds. The molecular orbital crystallization opens a natural route to stabilization of unpaired t2g electrons in crystals.
Direct Deposition of a Crystallized Si Thin Film on a YSZ/Glass Substrate at 430 Degree Celsius
Sukreen Hana,Susumu Horita
Lecture Notes in Engineering and Computer Science , 2010,
Abstract:
$C1$-Genericity of Symplectic Diffeomorphisms and Lower Bounds for Topological Entropy
Thiago Catalan,Vanderlei Horita
Mathematics , 2013,
Abstract: We show that there is a $C^1$-generic (Baire second class) subset $\mathcal{R}$ of symplectic diffeomorphism on 2d-dimensional manifold, $d\ge 1$ such that every $f$ in $\mathcal{R}$ satisfies a trichotomy: or $f$ is Anosov or $f$ is robustly transitive partially hyperbolic with unbreakable center of dimension $2m$, $1 \le m < d$ or $f$ has totally elliptic periodic points dense on $M$. In the second case, we also show the existence of a sequence of $m$-elliptic periodic points converging to $M$. Moreover, we provide lower bounds for non-Anosov diffeomorphisms in $\mathcal{R}$ by means of theirs largest central Lyapunov exponent.
Partial Hyperbolicity for Symplectic Diffeomorphisms
Ali Tahzibi,Vanderlei Horita
Mathematics , 2004,
Abstract: We prove that every robustly transitive and every stably ergodic symplectic diffeomorphism on a compact manifold admits a dominated splitting. In fact, these diffeomorphisms are partially hyperbolic.
Anomalous Flux Pinning in ?-Pyrochlore Oxide Superconductor KOs2O6
Zenji Hiroi,Shigeki Yonezawa
Physics , 2006, DOI: 10.1143/JPSJ.75.043701
Abstract: The superconducting transition of the ?-pyrochlore oxide KOs2O6 with Tc = 9.60 K is studied by resistivity measurements under various magnetic fields using a high-quality single crystal. The reentrant behavior of superconductivity is observed near Tc in low magnetic fields below 2 T. The recovered resistance probably due to flux flow exhibits an anomalous angle dependence, indicating that flux pinning is enhanced in magnetic fields along certain crystallographic directions such as [110], [001] and [112]. It is suggested that there is an intrinsic pinning mechanism coming from the specific crystal structure of the ?-pyrochlore oxide.
The Effects of Insulin Resistance and Inflammation on Renal Proximal Tubule Sodium Transport and Hypertension  [PDF]
Shoko Horita, Motonobu Nakamura, Masashi Suzuki, Hideomi Yamada, George Seki
Open Journal of Endocrine and Metabolic Diseases (OJEMD) , 2013, DOI: 10.4236/ojemd.2013.35A003
Abstract:

Insulin resistance, closely linked to inflammation, is recognized as a key factor in the onset and aggravation of diabetes, cardio-renal syndrome, hypertension, and obesity. In the renal proximal tubule, insulin resistance may increase renal sodium reabsorption, leading to hypertension, edema and sometimes heart failure. Recently some anti-diabetic agents have been shown to have effects on the transporters in renal proximal tubule. Because renal proximal tubule mediates about 70% of sodium reabsorption, it is quite important to clarify the function of renal proximal tubule under insulin resistance and inflammation.

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