1,721,229 research outputs found
Alloy Design to Prevent Intergranular Corrosion of Low-Cr Ferritic Stainless Steel with Weak Carbide Formers
Full text linkEffect of weak carbide formers, Mo, Mn and Si, on intergranular corrosion (IGC) of low-Cr ferritic stainless steel is analyzed after IGC test using TEM and three dimensional atom probe. The co-addition ofMo, Mn and Si to low-Cr ferritic stainless steel effectively prevents IGC by forming along grain boundaries CMn4MoSi intermetallic compounds, which act not only as carbon trap sites but also as diffusion barrier against solute Cr diffusion toward grain boundaries. The low solubility of Cr in the CMn4MoSi intermetallic compound results in replenishing Cr in the Cr-depleted area. (C) The Author(s) 2015. Published by ECS. All rights reserved.114Ysciescopu
Effect of a yttrium coating on the oxidation behavior of Ni3Al (II)
No full textA Y-coated Ni3Al with a postheat treatment shows much better oxidation resistance than a Y-coated Ni3Al without a postheat treatment. In order to explain the effect of postheat treatment at low oxygen pressure, postheat treatment after Y-ion plating was performed in flowing hydrogen as a function of time. During these treatments, the Y-coated layer was modified into a (Y, Al)O-type oxide by reaction between Y2O3 and Al2O3. The thickness of the modified Y-layer was related to oxygen pressure and time. The Y-modified layer formed by postheat treatment acts as a barrier to the transport of oxygen. The fine ( Y, Al)O-type oxide can easily relieve growth stress by permitting easy plastic deformation, and the ( Y, Al) O-type oxide layer can absorb the thermal stress developed in the Al2O3 layer. The tensile stress generated by the difference in thermal-expansion coefficients of the ( Y, Al) O-type oxide and the Al2O3 layer compensates the large compressive stress generated by the difference in thermal-expansion coefficients of the Al2O3 layer and the Ni3Al alloy.X1123sciescopu
AN ELECTROCHEMICAL STUDY ON ZN-SN-ALLOY-COATED STEEL SHEETS DEPOSITED BY VACUUM EVAPORATION .1.
No full textZn-Sn-alloy-coated steel sheets were prepared by a vacuum evaporation method to overcome the shortcomings of the conventional hot-dip-galvanizing and electrogalvanizing processes. The electrochemical behaviours of these alloy-coated steel sheets were evaluated in a neutral 3.5% NaCl solution. Zn-Sn alloy coatings with an Sn content lower than the eutectic composition consist of a simple mixture of Zn and Sn because of the poor solid solubility between them. During the coating process by vacuum evaporation, Sn tends to become enriched at the interface between the coating and the steel substrate by forming an FeSn2 phase. During polarization in a neutral 3.5% NaCl solution, one passive region due to oxidation of Sn is always observed and a second passive region due to formation of zinc hydroxide may be observed at lower potentials if local alkalization by reduction of dissolved oxygen occurs preferentially on the Sn surface. The order of dissolution of the three elements from the Zn-Sn-alloy-coated steel sheet is Zn, Sn and Fe. The electrochemical test data suggest that the optimum composition is close to Zn-69.8wt.%Sn.X114sciescopu
The oxidation behavior of Ni-50%Co alloy electrode in molten Li+K carbonate eutectic
No full textThe oxidation behavior of Ni-50%Co alloy has been investigated in Li + K carbonate melt by electrochemical impedance spectroscopy and cyclic voltammetry. Equivalent circuits have been worked out by simulating the impedance data, and the results are used to explain the oxidation kinetics. In the overall process of oxidation, the slowest step is the diffusion of metal ions through the metal oxide layer. Lithiation reaction is observed at the second potential plateau region as judged from the values of the resistance element of the oxide layer determined from impedance measurement. From the cyclic voltammetry the peak corresponding to this reaction is also observed. In a Ni-50%/Co, the diffusion of Li+ ion from the carbonate melt into the oxide layer causes further oxidation of Coo into LiCoO2. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.X1112sciescopu
Passivities of steels weathered for nine years
No full textA carbon steel (CS) and a weathering steel (WS) were weathered in a temperate urban atmosphere for nine years. Phases of their rust layers were examined. Their corrosion behaviors were probed in aerated, neutral 0.5 M sodium sulfate (Na2SO4) bulk solution or room temperature using the potentiodynamic anodic polarization technique. Passivities by the layers with a corrosion rate of 0.05 mm/y or less at the corrosion potential of -150 mV us saturated calomel electrode (SCE) or higher were observed, but they survived temporarily in the solution for 20 h and 5 h on the WS and CS covered with magnetite plus hematite phases. respectively, and 4 h and I h on the WS and CS with lepidocrocite plus goethite phases, respectively. They degraded with continued immersion in the solution accompanied by decreasing corrosion potential, finally near the active corrosion of bare steels. The passivities are under diffusion control of the iron ion dissolved from the base steels through the water in open pores of the layers but degrade by thinning and pore-opening of the layers under hydration and reductive reactions of the layers. The passivities are strengthened by integration and pore-seating of the layers with corrosion products of alloying elements for the WS and by more compact and less-reductive magnetite-containing phases than lepidocrocite-containing ones in the layers. These findings may be applied in the evaluation and improvement of corrosion resistance for WS.X114sciescopu
Electrochemical study of the oxidation behaviors of Ni and Ni-Co alloy electrodes in molten Li+K carbonate eutectic
No full textThe oxidation behaviors of Ni and Ni-Co alloy electrodes were investigated using simple electrochemical techniques under an O-2 + CO2 gas mixture in the ratio of 9:1 at a total pressure of 1 atm at 650 degrees C. In situ oxidation processes of Ni, Ni-10Co and Ni-25Co as opposed to Ni-50Co demonstrate 3 and 4 potential plateaux, respectively. The final plateau for all electrodes approached the oxygen potential. Nucleation and growth of the oxide were represented by the first and second plateaux, respectively. For Ni-50Co electrode, however, an additional plateau due to the formation of LiCoO2 was observed. The lithiation took place by chemical reaction at the oxide growth step. Between the lithiated NiO and (Ni, Co)O produced by in situ oxidation of porous Ni and Ni-Co alloy plaques, the solubility of(Ni, Co)O was found to be lower than that of NiO. As the Co concentration in the oxide is increased, the solubility is decreased. Extension of cathode life time appears possible if the Ni cathode is modified by the addition of Co. (C) 1998 Elsevier Science Ltd. All rights reserved.X118sciescopu
Preparation and property control of nano-sized indium tin oxide particle
No full textIndium tin oxide (ITO) particles of 20-30 nm in diameter, which would be used as coating material for electromagnetic wave shield, were synthesized by co-precipitation of indium chloride and tin chloride. Size and shape of particles were controlled by pH of co-precipitation solution, thermal oxidation temperature and tin contents. The prepared particles were thermally reduced under hydrogen gas to control electrical properties. When the solution pH was 6.75, plate type of particles with 60 nm size was coexisted with spherical particles of 20 nm size and the part of crystal structure was hexagonal. As pH was increased, plate type of particles was disappeared and 20-30 nm size of spherical particles were formed. Size of ITO particles was increased and particle resistance was decreased with increasing thermal oxidation temperature of indium tin hydroxide in the range of 400-700 degreesC. Particle size was decreased as tin content was increased from 3.18 to 21.11 at.% Sn/In in co-precipitation. The resistance of particles had a minimum point with changing of tin contents. The lowest resistance was shown in the region of about 3-5 at.% Sn in ITO. It was confirmed by Auger electron spectroscopy (AES) that tin ratio of ITO particle was increased with increasing tin contents. (C) 2004 Elsevier B.V. All rights reserved
Electrochemical hydrogen permeation measurement through high-strength steel under uniaxial tensile stress in plastic range
No full textIn the electrochemical hydrogen permeation test for high-strength steels under plastic loading, the failure of palladium coating has raised controversy over the reliability of the permeation data. To avoid rupture of a palladium layer under plastic stress, a new permeation technique was employed. This study clearly proves that the palladium film obtained by the new technique leads to a highly stable background current even under severe stress conditions, ensuring the reliability of the permeation data under both elastic and plastic stress. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.X112124sciescopu
Effect of ternary elements on the oxidation behavior of aluminized TiAl alloys
No full textThe effects of ternary elements added to TiAl on the coating layer formed by the pack-aluminizing process was studied with respect to oxidation resistance and mechanical properties. All the TiAl specimens, with various amounts of Nb, Cr, Fe, and V, were pack aluminized under identical conditions using a high-activity process. Among the ternary alloying elements tested, Nb showed the best property of the TiAl3 coating layer formed on the surface and, consequently, the best oxidation resistance. The TiAl3 coating layer becomes thicker and has a finer grain size as the content of Nb or Cr is increased. Microhardness tests revealed that the addition of Nb or Cr improved the toughness of the coating layer and thus improved the cracking resistance. Cyclic oxidation tests showed that the TiAl3 coating layer formed on the TiAl alloy has better oxidation resistance with increasing Nb content. The ductility and oxidation resistance of the TiAl3 coating layers improved with Nb addition, which contributes to the grain refinement of TiAl3. The Nb present in the TiAl3 coating layer inhibits grain growth by the solute-drag effect and retards inward diffusion of Al to the TiAl matrix by forming (Nb, Ti)Al-3 precipitates during high-temperature oxidation.X1133sciescopu
A new alloy design concept for austenitic stainless steel with tungsten modification for bipolar plate application in PEMFC
No full textThe feasibility of a new alloy design concept utilizing the principle of 'tungsten bronze effect' is critically evaluated for the development of metallic bipolar plates for proton exchange membrane fuel cell (PEMFC). An austenitic stainless steel (ASS) is modified with W and La to improve the stability of the passive film in an acidic environment as well as to reduce the contact resistance by the tungsten bronze effect. The experimental ASS containing W and La was evaluated in a simulated PEMFC environment of H3PO4 and H2SO4 solutions at 80 degrees C, and the electrical property was evaluated by performing a contact resistance test. The test results show that the ASS modified with W and La has good passive film stability for corrosion resistance and low contact resistance. The X-ray photoelectron spectroscopy (XPS) analysis clearly suggests the possibility of the tungsten bronze effect from the change in valency state of W6+ to W5+ in the passive film formed on the modified ASS. The feasibility of a new alloy design concept utilizing the 'tungsten bronze effect' is well demonstrated; however, more study is highly required for the development of metallic bipolar plates of PEMFC. (C) 2007 Elsevier B.V. All fights reserved.X1124sciescopu
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