• Title, Summary, Keyword: Passivation

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Effect of Al2O3 Inter-Layer Grown on FeCrAl Alloy Foam to Improve the Dispersion and Stability of NiO Catalysts (NiO 촉매의 분산성 및 안정성 향상을 위하여 FeCrAl 합금 폼 위에 성장된 Al2O3 Inter-Layer 효과)

  • Lee, Yu-Jin;Koo, Bon-Ryul;Baek, Seong-Ho;Park, Man-Ho;Ahn, Hyo-Jin
    • Korean Journal of Materials Research
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    • v.25 no.8
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    • pp.391-397
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    • 2015
  • NiO catalysts/$Al_2O_3$/FeCrAl alloy foam for hydrogen production was prepared using atomic layer deposition (ALD) and subsequent dip-coating methods. FeCrAl alloy foam and $Al_2O_3$ inter-layer were used as catalyst supports. To improve the dispersion and stability of NiO catalysts, an $Al_2O_3$ inter-layer was introduced and their thickness was systematically controlled to 0, 20, 50 and 80 nm using an ALD technique. The structural, chemical bonding and morphological properties (including dispersion) of the NiO catalysts/$Al_2O_3$/FeCrAl alloy foam were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, field-emission scanning electron microscopy and scanning electron microscopy-energy dispersive spectroscopy. In particular, to evaluate the stability of the NiO catalysts grown on $Al_2O_3$/FeCrAl alloy foam, chronoamperometry tests were performed and then the ingredient amounts of electrolytes were analyzed via inductively coupled plasma spectrometer. We found that the introduction of $Al_2O_3$ inter-layer improved the dispersion and stability of the NiO catalysts on the supports. Thus, when an $Al_2O_3$ inter-layer with a 80 nm thickness was grown between the FeCrAl alloy foam and the NiO catalysts, it indicated improved dispersion and stability of the NiO catalysts compared to the other samples. The performance improvement can be explained by optimum thickness of $Al_2O_3$ inter-layer resulting from the role of a passivation layer.

An Electrochemical Evaluation on the Crevice Corrosion of 430 Stainless Steel with Variation of Crevice Wide by Micro Capillary Tubing Method (Micro Capillary Tube 방법을 이용한 430 스테인레스강 틈의 폭변화에 따른 틈부식의 전기화학적 평가)

  • Na, Eun-Young
    • Journal of the Korean Electrochemical Society
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    • v.6 no.4
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    • pp.250-254
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    • 2003
  • In this study, the IR drop theory was adopted to explain the initiation of crevice corrosion in the framework of IR drop in crevice electrolyte. Furthermore, the electrochemical polarization was measured to study the mechanism of crevice corrosion for type STS430 stainless steel. lest method adopts under condition that the size of specimen is $10\times20\times5mm,\;in\;1N\;H_2SO_4+0.1N\;NaCl$ solution, and the artificial crevice gap sizes are three kinds, the Micro capillary tube size is inner diameter 0.04 mm, outer diameter 0.08 mm. Crevice corrosion is measured under the applied voltage of passivation potential -200mV/SCE, resulted from anodic potentio-dynamic polarization to the external surface along the crevice. The potential difference was measured by depth profile by Micro capillary tube which inserted in the crevice. The obtained results of this study showed that 1) As artificial crevice gap size became narrow, the current density was increased, whereas no crevice corrosion was found in the crevice gap size $3\times0.5\times16mm\;in\;1N\;H_2SO_4+0.1N\;NaCl\;solution\;at\;20^{\circ}C$ 2) potential of the crevice was about from -220 to -358mV which is lower than that of external surface potential of -200mV The results so far confirmes that the potential drop(so-called IR drop) in the crevice is one of the major mechanisms the process of crevice corrosion for 430 stainless steel.

A Study on the Electromigration Characteristics in Ag, Cu, Au, Al Thin Films (Ag, Cu, Au, Al 박막에서 엘렉트로마이그레이션 특성에 관한 연구)

  • Kim, Jin-Young
    • Journal of the Korean Vacuum Society
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    • v.15 no.1
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    • pp.89-96
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    • 2006
  • Recent ULSI and multilevel structure trends in microelectronic devices minimize the line width down to less than $0.25{\mu}m$, which results in high current densities in thin film interconnections. Under high current densities, an EM(electromigration) induced failure becomes one of the critical problems in a microelectronic device. This study is to improve thin film interconnection materials by investigating the EM characteristics in Ag, Cu, Au, and Al thin films, etc. EM resistance characteristics of Ag, Cu, Au, and Al thin films with high electrical conductivities were investigated by measuring the activation energies from the TTF (Time-to-Failure) analysis. Optical microscope and XPS (X-ray photoelectron spectroscopy) analysis were used for the failure analysis in thin films. Cu thin films showed relatively high activation energy for the electromigration. Thus Cu thin films may be potentially good candidate for the next choice of advanced thin film interconnection materials where high current density and good EM resitance are required. Passivated Al thin films showed the increased MTF(Mean-time-to-Failure) values, that is, the increased EM resistance characteristics due to the dielectric passivation effects at the interface between the dielectric overlayer and the thin film interconnection materials.

Studies on Improved Carbon Cathode Performance in High Rate $Li/SOCl_2$ Cell (고율 방전용 $Li/SOCl_2$ 전지의 카본 양극 개선에 관한 연구)

  • 최정자;조성백;박희숙
    • Journal of the Korean Ceramic Society
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    • v.34 no.3
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    • pp.225-232
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    • 1997
  • The performance characteristics of high rate discharge LiSOCl2 cells are highly affected by carbon cathode. During the cell discharge, SOCl2 reduction takes place at the porous carbon cathode, resulting in the precipitation of reaction products, mainly LiCl, within the pores of the substrate. This leads to eventual passivation of the cathode surface and resulting cell failure. To improve the cathode performance, we ex-amined discharge reactions of cathodes (half-cell, 50 mA/$\textrm{cm}^2$ constant current) with various surface density and thickness. The carbon cathode with the optimum capacity for our application is surface density 0.04 g/$\textrm{cm}^2$ and thickness 1.4mm carbon. The carbon cathode with surface density 0.04g/$\textrm{cm}^2$ and thickness 1.4 mm exhibits decreased polarization, increased discharge duration time and capacity (Ah/$\textrm{cm}^2$) as compared with that with surface density 0.04g/$\textrm{cm}^2$ and thickness 0.8mm. The porosities analyses on the two carbon cathodes show that total pore volume of the carbon cathode with thickness 1.4 mm is larger than that with thickness 0.8mm. The increased volume of mesopores (0.05$\mu$m~0.5$\mu$m) and macropores(>0.5$\mu$m) is ob-served with the carbon cathode with thickness 1.4mm as compared with that with thickness 0.8mm, which can be related with the observed capacity increase. We observed LiCl crystals, cubic crystallites and fused, plate-like aggregates, and some elemental S as discharge products by EDS and XRD.

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Electronic Structure and Elemental Composition of the Lead Sulfide Colloidal Quantum Dots Depending on the Types of Ligand and Post-Treatment (리간드 종류와 후처리 공정에 따른 황화납 콜로이드 양자점 박막의 전자 구조 및 원소 조성 분석)

  • Kim, Tae Gun;Choi, Hyekyoung;Jeong, Sohee;Kim, Jeong Won
    • Journal of the Korean Chemical Society
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    • v.60 no.6
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    • pp.402-409
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    • 2016
  • Thin films of lead sulfide colloidal quantum dots (CQDs) of 2.8 nm in diameter are fabricated and their surfaces are passivated by 3-mercaptopropionic acid (MPA) ligand or hybrid type ($MPA+CdCl_2$) ligand, respectively. The changes in valence band electronic structure and atomic composition of each PbS CQD film upon post-treatment such as air, N2 annealing or UV/Ozone have been studied by photoelectron spectroscopy. The air annealing makes the CQD fermi level to move toward the valence band leading to "p-type doping" regardless of ligand type. The UV/Ozone post-treatment generates $Pb(OH)_2$, $PbSO_x$ and PbO on both CQD surfaces. But the amount of the PbO has been reduced in hybrid type ligand case, especially. That is probably because the extra Pb cations in (111) surface are additionally passivated by $Cl_2$ ligand, which limits the reaction between the Pb cation and ozone.

Determination of optimum protection potential for cathodic protection of offshore wind-turbine-tower steel substructure by using potentiostatic method (정전위법에 의한 해상풍력 타워 구조물용 강재의 음극방식을 위한 최적방식전위 결정)

  • Lee, Jung-Hyung;Jung, Kwang-hu;Park, Jae-Cheul;Kim, Seong-Jong
    • Journal of Advanced Marine Engineering and Technology
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    • v.41 no.3
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    • pp.230-237
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    • 2017
  • In this study, electrochemical methods were used to determine the optimum protection potential of S355ML steel for the cathodic protection of offshore wind-turbine-tower substructures. The results of potentiodynamic polarization experiments indicated that the anodic polarization curve did not represent a passivation behavior, while under the cathodic polarization concentration, polarization was observed due to the reduction of dissolved oxygen, followed by activation polarization by hydrogen evolution as the potential shifted towards the active direction. The concentration polarization region was found to be located between approximately -0.72 V and -1.0 V, and this potential range is considered to be the potential range for cathodic protection using the impressed current cathodic protection method. The results of the potentiostatic experiments at various potentials revealed that varying current density tended to become stable with time. Surface characterization after the potentiostatic experiment for 1200 s, by using a scanning electron microscope and a 3D analysis microscope confirmed that corrosion damage occurred as a result of anodic dissolution under an anodic polarization potential range of 0 to -0.50 V, which corresponds to anodic polarization. Under potentials corresponding to cathodic polarization, however, a relatively intact surface was observed with the formation of calcareous deposits. As a result, the potential range between -0.8 V and -1.0 V, which corresponds to the concentration polarization region, was determined to be the optimum potential region for impressed current cathodic protection of S355ML steel.

Chemical Effects on Head Loss across Containment Sump Strainer under Post-LOCA Environment (LOCA이후 환경에서 원자로건물집수조 여과기의 수두손실에 대한 화학적 영향)

  • Ku, Hee-Kwon;Jung, Bum-Young;Hong, Kwang;Jeong, Eun-Sun;Jung, Hyun-Jun;Park, Byung-Gi;Rhee, In-Hyoung;Park, Jong-Woon
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.10 no.11
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    • pp.3260-3268
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    • 2009
  • A test apparatus has been fabricated to simulate chemical effect on head loss through a strainer in a pressurized water reactor (PWR) containment water pool after a loss of coolant accident (LOCA). Tests were conducted under condition of same ratio of strainer surface area to water volume between the test appratus and the containment sump. A series of tests have been performed to investigate the effects of spray, existence of calcium-silicate with tri-sodium phosphate (TSP), and composition of materials. The results showed that head loss across the chemical bed with even a small amount of calcium-silicate insulation instantaneously increased as soon as TSP was added to the test solution. Also, the head loss across the test screen is strongly affected by spray duration and is increased rapidly at the early stage, because of high dissolution and precipitation of aluminum and zinc. After passivation of aluminum and zinc by corrosion, the head loss increase is much slowed down and is mainly induced by materials such as calcium, silicon, and magnesium leached from NUKONTM and concrete. Furthermore, it is newly found that the spay buffer agent, tri-sodium phosphate, to form protective coating on the aluminum surface and reduce aluminum leaching is not effective for a large amount of aluminum and a long spray.

Experimental Study of Chemical Effects on Head Loss across Containment Sump Strainer under Post-LOCA Environment (LOCA이후 원자로건물집수조 여과기의 수두손실에 대한 화학적 영향의 실험연구)

  • Ku, Hee-Kwan;Jung, Bum-Young;Hong, Kwang;Jung, Eun-Sun;Jeong, Hyun-Jun;Park, Byung-Gi;Rhee, In-Hyoung;Park, Jong-Woon
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.10 no.12
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    • pp.3748-3754
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    • 2009
  • An integral head loss test in a test apparatus was conducted to simulate chemical effects on a head loss across a strainer in a pressurized water reactor (PWR) containment water pool after a loss of coolant accident (LOCA). The test was conducted during 30 days in the condition of a short spray, a long spray, and no materials with chemical effects. The result exhibited that the head loss was affected on amounts of the exposed materials according to spray conditions. XRD analysis of the collected precipitates showed that the precipitates were phosphate compounds. Comparison of the head loss with dissolved species concentration showed that high increase rate of the head loss resulted from the corrosion of aluminum and zinc but slow increase rate of the head loss resulted from the precipitates induced by Si, Mg, and Ca from leaching reaction at NUKON and concrete after passivation of metal specimens.

Effects of Blasting and Acidic Treatment on the Corrosion Characteristics of Dental Implant Fabricated with Cp-Ti and Ti-6Al-4V Alloy (Cp-Ti와 Ti-6Al-4V 합금으로 제조된 치과용 임플란트의 부식특성에 관한 블라스팅과 산세처리의 영향)

  • Moon, Young-Pil;Choe, Han-Cheol;Park, Su-Jung;Kim, Won-Gi;Ko, Yeong-Mu
    • Journal of the Korean institute of surface engineering
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    • v.39 no.4
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    • pp.190-197
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    • 2006
  • The effects of blasting and acidic treatment on the corrosion characteristics of dental implant fabricated with Cp-Ti and Ti-6Al-4V alloy have been researched by using electrochemical methods. The fabricated implants were cleaned and sandblasted by $Al_2O_3$ powder and then acidic treatment was carried out in nitric acid solution. The surface morphology were observed using scanning electron microscope. The corrosion behaviors were investigated using potentiosat and EIS in 0.9% NaCl solution at $36.5{\pm}1^{\circ}C$. The potentio-dynamic test in 0.9% NaCl indicated that the corrosion potential of blasting and acidic treated implant was lower than that of non treated implant, but current density was higher than that of non treated implant. From the cyclic potentiodynamic test results of Ti implant, the passivation current density of blasting and acidic treated implant slightly higher than that of non treated implant. From A.C. impedance test results in 0.9% NaCl solution, polarization resistance($R_p$) value of blasting and acidic treated implant was lower than that of non treated implant. In case of blasting and acidic treated implant surface, the pits were observed in valley and crest of implant surface.

A Study of Failure Mechanism through abnormal AlXOY Layer after pressure Cooker Test for DRAM device (DRAM 소자의 PCT 신뢰성 측정 후 비정상 AlXOY 층 형성에 의해 발생된 불량 연구)

  • Choi, Deuk-Sung;Jeong, Seung-Hyun;Choi, Chae-Hyoung
    • Journal of the Microelectronics and Packaging Society
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    • v.25 no.3
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    • pp.31-36
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    • 2018
  • This research scrutinizes the reason of failure after pressure cooker test (PCT) for DRAM device. We use the physical inspecting tools, such as microscope, SEM and TEM, and finally find the discolor phenomenon, corrosion of Al and delamination of inter-metal dielectric (IMD) in the failed devices after PCT. Furthermore, we discover the abnormal $Al_XO_Y$ layer on Al through the careful additional measurements. To find the reason, we evaluate the effect of package ball size and pinhole in passivation layer. Unfortunately, those aren't related to the problems. We also estimate halide effect of Al. The halogens such like Cl are contained within EMC material. Those result in the slight improving of PCT characteristics but do not perfectly solve the problems. We make a hypothesis of Galvanic corrosion. We can find the residue of Ti at the edge of pad open area. We can see the improving the PCT characteristics by the time split of repair etch. The possible mechanism of the PCT failure can be deduced as such following sequence of reactions. The remained Ti reacts on the pad Al by Galvanic corrosion. The ionized Al is easily react with the $H_2O$ supplied under PCT environment, and finally transfers to the abnormal $Al_XO_Y$ layer.