• Title/Summary/Keyword: Micro-scale polarization

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Micro-scale Observation of Corrosion of Hot-Dip Aluminized 11% Cr Stainless Steel

  • Cho, Min-Seung;Park, Choong-Nyeon;Park, Chan-Jin
    • Corrosion Science and Technology
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    • v.18 no.3
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    • pp.73-77
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    • 2019
  • Hot-dip aluminized coating has been widely used to protect steel substrate against corrosion. In this study, the corrosion behavior of hot-dip aluminized type 409L (11% Cr) stainless steel (SS) was investigated using macro- and micro-scale polarization tests. An Al-Fe-Si alloy layer that was formed due to inter-diffusion of alloying elements between Al coating and SS substrate was observed between Al coating and 409L SS substrate. In both macro- and micro-scale polarization tests, the corrosion potential ($E_{corr}$) of the 409L SS substrate was much nobler than that of the Al coating and alloy layer. $E_{corr}$ of the alloy layer was between that of Al coating and 409L SS substrate. This indicates that the alloy layer can act as a buffer between the more active Al coating and the nobler SS substrate for pit growth in aluminized SS. The presence of the alloy layer appears to be helpful in hindering pitting corrosion of aluminized SS.

Polarization Selective Blazed Grating Employing Metal-slit Arrays (금속 슬릿 배열로 구성된 편광 선택 가능한 블레이즈드 회절 격자)

  • Jung, Young Jin
    • Korean Journal of Optics and Photonics
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    • v.24 no.2
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    • pp.53-57
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    • 2013
  • A polarization selective blazed grating employing metal-slit arrays was proposed. Nano-scale metal-slits were applied to the micro-scale blazed grating to give the functionality of polarization selection. Case study was carried out for the proposed structure utilizing numerical FDTD (Finite Difference Time Domain method) simulation. Diffraction efficiency of 77.61% and polarization extinction ratio of 8.99 was achieved with arbitrary parameters and diffraction efficiency of 64.22% and polarization extinction ratio of 81.09 was achieved with other parameters to enhance extinction ratio.

Machining of Micro Grooves using Hybrid Electrochemical Processes with Voltage Pulses (펄스 전기화학 복합가공기술을 적용한 미세 그루브 가공)

  • 이은상;박정우;문영훈
    • Journal of the Korean Society for Precision Engineering
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    • v.20 no.9
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    • pp.32-39
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    • 2003
  • Pulse electrochemical machining process with high or low current density may produce a non-lustrous surface on workpiece surface. The usual polishing process to remove a black layer from the surface has been hand polish the part. But the milli-to-micro meter scale structure formed by the electrochemical machining process may be destroyed while polishing process. The application of ultra short voltage pulses based on the analysis of electrical double layer charging process allows high resolution electrochemical machining and polishing. This technique was based on the specific polarization resistance from the comparison of ideal and experimental potential variation during short voltage pulses.

Electrochemical Catalytic Behavior of Cu2O Catalyst for Oxygen Reduction Reaction in Molten Carbonate Fuel Cells

  • Song, Shin Ae;Kim, Kiyoung;Lim, Sung Nam;Han, Jonghee;Yoon, Sung Pil;Kang, Min-Goo;Jang, Seong-Cheol
    • Journal of Electrochemical Science and Technology
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    • v.9 no.3
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    • pp.195-201
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    • 2018
  • To enhance the performance of cathodes at low temperatures, a Cu-coated cathode is prepared, and its electrochemical performance is examined by testing its use in a single cell. At $620^{\circ}C$ and a current density of $150mAcm^{-2}$, a single cell containing the Cu-coated cathode has a significantly higher voltage (0.87 V) during the initial operation than does that with an uncoated cathode (0.79 V). According to EIS analysis, the high voltage of the cell with the Cu-coated cathode is due to the dramatic decrease in the high-frequency resistance related to electrochemical reactions. From XPS analysis, it is confirmed that the Cu is initially in the form of $Cu_2O$ and is converted into CuO after 150 h of operation, without any change in the state of the Ni or Li. Therefore, the high initial cell voltage is confirmed to be due to $Cu_2O$. Because $Cu_2O$ is catalytically active toward $O_2$ adsorption and dissociation, $Cu_2O$ on a NiO cathode enhances cell performance and reduces cathode polarization. However, the cell with the Cu-coated cathode does not maintain its high voltage because $Cu_2O$ is oxidized to CuO, which demonstrates similar catalytic activity toward $O_2$ as NiO.

Micro Machining Characteristics of V-shaped Single Crystal Diamond Tool with Ductile Workpiece (V형 다이아몬드공구에 의한 연질소재의 미세절삭특성 연구)

  • Hong, Sung-Min;Je, Tae-Jin;Lee, Dong-Ju;Lee, Jong-Chan
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.4 no.4
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    • pp.28-33
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    • 2005
  • Recently, trends of TFT-LCD toward larger scale and thinner thickness continue. so, demands of Light Guide Panel (LGP) which is to substitute for prism sheet are appeared. Functions of LGP obtaining polarization of light of the prism sheet as well as the incidence and reflection of light are demanded. This prism type LGP to complete functions of the existing LGP and polarization at once must be supported by micro machining technology of LGP surface. In this research, the machining characteristics of the various materials were analysed by shaping using V-shaped single crystal diamond tool. The characteristics are machined surface, machining force due to the variation of cutting depth. Used specimens are engineering materials, which are 6:4 brass, oxygen-free copper, Al6061, PC, PMMA. The FFT analysis of the measured cutting force was conducted. The cutting characteristics were analyzed and the optimum cutting conditions with materials were established.

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Performance Modeling of Single-Chamber Micro SOFC (단실형 마이크로 고체 산화물 연료전지의 작동특성 전산모사)

  • Cha, Jeong-Hwa;Chung, Chan-Yeup;Chung, Yong-Chae;Kim, Joosun;Lee, Jongho;Lee, Hae-Weon
    • Journal of the Korean Ceramic Society
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    • v.42 no.12 s.283
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    • pp.854-859
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    • 2005
  • Performance of micro scale intermediate temperature solid oxide fuel cell system has been successfully evaluated by computer simulation based on macro modeling. Two systems were studied in this work. The one is designed that the ceria-based electrolyte placed between composite electrodes and the other is designed that electrodes alternately placed on the electrolyte. The injected gas was composed of hydrogen and air. The polarization curve was obtained through a series of calculations for ohmic loss, activation loss and concentration loss. The calculation of each loss was based on the solving of mathematical model of multi physical-phenomena such as ion conduction, fluid dynamics and diffusion and convection by Finite Element Method (FEM). The performance characteristics of SOFC were quantitatively investigated for various structural parameters such as distance between electrodes and thickness of electrolyte.

Studies of Prismless Type Light Guide Panel Mold Machining using Diamond Tool (다이아몬드공구에 의한 프리즘형 도광판 금형 가공기술 연구)

  • Hong S.M.;Jae T.J.;Choi D.S.;Lee E.S.;Lee D.J.
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 2005.06a
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    • pp.1597-1600
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    • 2005
  • Recently, the trends of TFT-LCD are large scale and thin thickness, so, the demands of Light Guide Panel(LGP) which is able to substitute for prism sheets are appeared. Functions of LGP obtaining polarization of light of the prism sheet as well as the incidence and reflection of light are demanded. This prismless type LGP to complete functions of the existing LGP and polarization at once must be supported by micro machining technology of LGP surface. In this research, we have used the STAMPER method for the mass product and In-Line process, and the optimized conditions are established by analyzing the cutting force and conditions according to the material and processing properties when the prismless type LGP mold is fabricated. Parameters of the cutting condition were the workpiece and cutting depth.

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Near-field interaction of atoms, molecules and dielectric particles in laser light

  • Minogin, V.G.
    • Proceedings of the Optical Society of Korea Conference
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    • 2003.02a
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    • pp.198-198
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    • 2003
  • Two microscopic particles irradiated by light field influence each other by the forces coursed by the dipole-dipole interaction. The interaction changes also the resonance frequencies of the particles. We show that the dipole forces between atoms, molecules or dielectric particles irradiated by laser light play an important role at distances between the particles about or less the light wavelength. We discuss the properties of the near-field forces, including their dependence on direction and polarization of the laser light. We conclude that the near-field forces can be responsible for farmation of dimers in dense atomic gases. The near-field forces can be also used for control the motion of dielectric particles on micro and nanometer scale.

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Polarization Precession Effects for Shear Elastic Waves in Rotated Solids

  • Sarapuloff, Sergii A.
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2013.04a
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    • pp.842-848
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    • 2013
  • Developments of Solid-State Gyroscopy during last decades are impressive and were based on thin-walled shell resonators like HRG or CRG made from fused quartz or leuko-sapphire. However, a number of design choices for inertial-grade gyroscopes, which can be used for high-g applications and for mass- or middle-scale production, is still very limited. So, considerations of fundamental physical effects in solids that can be used for development of a miniature, completely solid-state, and lower-cost sensor look urgent. There is a variety of different types of bulk acoustic (elastic) waves (BAW) in anisotropic solids. Shear waves with different variants of their polarization have to be studied especially carefully, because shear sounds in glasses and crystals are sensitive to a turn of the solid as a whole, and, so, they can be used for development of gyroscopic sensors. For an isotropic medium (for a glass or a fine polycrystalline body), classic Lame's theorem (so-called, a general solution of Elasticity Theory or Green-Lame's representation) has been modified for enough general case: an elastic medium rotated about an arbitrary set of axes. Travelling, standing, and mixed shear waves propagating in an infinite isotopic medium (or between a pair of parallel reflecting surfaces) have been considered too. An analogy with classic Foucault's pendulum has been underlined for the effect of a turn of a polarizational plane (i.e., an integration effect for an input angular rate) due to a medium's turn about the axis of the wave propagation. These cases demonstrate a whole-angle regime of gyroscopic operation. Single-crystals are anisotropic media, and, therefore, to reflect influence of the crystal's rotation, classic Christoffel-Green's tensors have been modified. Cases of acoustic axes corresponding to equal velocities for a pair of the pure-transverse (shear) waves have of an evident applied interest. For such a special direction in a crystal, different polarizations of waves are possible, and the gyroscopic effect of "polarizational precession" can be observed like for a glass. Naturally, formation of a wave pattern in a massive elastic body is much more complex due to reflections from its boundaries. Some of these complexities can be eliminated. However, a non-homogeneity has a fundamental nature for any amorphous medium due to its thermodynamically-unstable micro-structure, having fluctuations of the rapidly-frozen liquid. For single-crystalline structures, blockness (walls of dislocations) plays a similar role. Physical nature and kinematic particularities of several typical "drifts" in polarizational BAW gyros (P-BAW) have been considered briefly too. They include irregular precessions ("polarizational beats") due to: non-homogeneity of mass density and elastic moduli, dissymmetry of intrinsic losses, and an angular mismatch between propagation and acoustic axes.

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Micromachining of the Si Wafer Surface Using Femtoseocond Laser Pulses (펨토초 레이저를 이용한 실리콘 웨이퍼 표면 미세가공 특성)

  • Kim, Jae-Gu;Chang, Won-Seok;Cho, Sung-Hak;Whang, Kyung-Hyun;Na, Suck-Joo
    • Journal of the Korean Society for Precision Engineering
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    • v.22 no.12 s.177
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    • pp.184-189
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    • 2005
  • An experimental study of the femtosecond laser machining of Si materials was carried out. Direct laser machining of the materials for the feature size of a few micron scale has the advantage of low cost and simple process comparing to the semiconductor process, E-beam lithography, ECM and other machining process. Further, the femtosecond laser is the better tool to machine the micro parts due to its characteristics of minimizing the heat affected zone(HAZ). As a result of line cutting of Si, the optimal condition had the region of the effective energy of 2mJ/mm-2.5mJ/mm with the power of 0.5mW-1.5mW. The polarization effects of the incident beam existed in the machining qualities, therefore the sample motion should be perpendicular to the projection of the electric vector. We also observed the periodic ripple patterns which come out in condition of the pulse overlap with the threshold energy. Finally, we could machined the groove with the linewidth of below $2{\mu}m$ for the application of MEMS device repairing, scribing and arbitrary patterning.