• Journal of the Korean Chemical Society
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• v.51 no.4
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• pp.305-311
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• 2007

Based on the cyclic voltammograms, potentiodynamic polarizations, transient and steady state Tafel plots and electrochemical impedence spectroscopy, we proposed the copper redox mechanism of the corrosion and passivation in artificial sea water. The copper redox mechanism showed the dependence of the concentration of oxygen in artificial sea water and electrode potentials.

• Journal of the Korean Ceramic Society
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• v.32 no.11
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• pp.1301-1307
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• 1995

Pitting corrosion of TiN film deposited on Inconel 600 by plasma assisted chemical vapor deposition (PACVD) was investigated. Cyclic potentiodynamic polarization (CPP) tests were conducted in order to determine the pit nucleation potentials, Enp, of the TiN-deposited sample and the bare Inconel 600 in deaerated NaCl solution at 25, 135 and 20$0^{\circ}C$. The effects of the TiN film thickness, the solution temperature and the Cl- concentration on Enp were studied. Enp of the TiN-deposited sample which had the film thickness above 1${\mu}{\textrm}{m}$ were higher than those of the bare Inconel 600 by 300~600mV at all the solution temperatures, implying the pitting resistance improvement of the TiN film. The morphologies of the pits generated after immersion test were examined with a scaning electron microscopy. The higher was the solution temperature, the more corrosion products, mainly composed of Cr and Ni oxides, were formed.

• Structural Engineering and Mechanics
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• v.63 no.6
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• pp.725-734
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• 2017

This paper investigated the effects of rebar corrosion on bond performance between rebar and two different concrete mixes (compressive strengths of 20.7 MPa and 44.4 MPa). The specimen was designed as a rebar centrally embedded in a 200 mm concrete cube, with two stirrups around the rebar to supply confinement. An electrochemical accelerated corrosion technique was applied to corrode the rebar. 120 specimens of two different concrete mixes with various reinforcing steel corrosion levels were manufactured. The corrosion crack opening width and length were recorded in detail during and after the corrosion process. Three different loading schemes: monotonic pull-out load, 10 cycles of constant slip loading followed by pull-out and varied slip loading followed by pull-out, were carried out on the specimens. The effects of rebar corrosion with two different concrete mixes on corrosion crack opening, bond strength and corresponding slip value, initial slope of bond-slip curve, residual bond stress, mechanical interaction stress, and energy dissipation, were discussed in detail. The mean value and coefficient of variation of these parameters were also derived. It was found that the coefficient of variation of the parameters of the corroded specimens was larger than those with intact rebar. There is also obvious difference in the two different concrete mixes for the effects of rebar corrosion on bond-slip parameters.

• Corrosion Science and Technology
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• v.7 no.1
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• pp.45-49
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• 2008

The cyclic polarisation technique was applied to determine the corrosion, primary-passivation, transpassive, and protection potential of AISI 316L stainless steels immersed in 3550-ppm NaCl solution containing sulfate in the content up to 3000 ppm. The solutions were kept constant at $27^{\circ}C$ and saturated by laboratory air. The solution pH was varied from 3 to 11. Each type of potentials was plotted in function of pH and linked as lines to determine the different zones in the constructed potential-pH diagram. The predominant regimes of the immunity, general corrosion, perfect passivation, imperfect passivation, and pitting corrosion were determined based on those lines of potentials. Comparing to the potential-pH diagram of specimens immersed in the aerated and deaerated 3550-ppm NaCl solutions, the addition of 3000-ppm $Na_2SO_4$ to these solutions increased the overall, perfect and imperfect, passivation regime by shifting the transpassive-potential line to the noble direction. However, it also widened the imperfect passivation area. The addition of $Na_2SO_4$ did not significantly affect the corrosion potential. It was found that the dissolved oxygen tends to negatively shift the transpassive-potential and protection-potential lines at all studied pH. The considerable effect of dissolved oxygen on corrosion and primary-passivation potentials could not be observed.

• Journal of Ocean Engineering and Technology
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• v.22 no.3
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• pp.82-88
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• 2008

The diesel engine of the merchant ship has been aperated in severe environments more and more, because the temperature of the exhaust gas of a combustion chamber is getting higher and higher with increasing use of heavy oil of law quality, due to the significant increase in the price of oil in recent some years. As a result, the degree of wear and corrosion between exhaust valve and seat ring is more serious compared to other engine parts. Thus the repair welding of exhaust valve and seat ring is a unique method to prolong the life of the exhaust valve, from an economical point of view. In this study, the corrosion property of both weld metal and base metal was investigated using electrochemical methods such as measurement of corrosion potential, cathodic and anodic polarization curves, cyclic voltammogram, and polarization resistance in 5% H2SO4 solution. The test specimen was a part of an exhaust valve stem being welded as the base metal, using various welding methods. In all cases, the corrosion resistance as well as hardness of the weld metal zone was superior to the base metal. In particular, plasma welding showed relatively good properties for both corrosion resistance and hardness, compared to other welding methods. In the case of DC SMAW (Shielded metal arc welding), corrosion resistance of the weld metal zone was better than that of the base metal, although its hardness was almost same as the base metal.

• Journal of the Korean Electrochemical Society
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• v.4 no.1
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• pp.21-25
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• 2001

This article is concerned with the application of the fractal geometry to interfacial electrochemistry. Especially, we dealt with diffusion kinetics at the fractal electrodes. This article first explained the basic concepts of the Sacral geometry which has proven to be fruitful for modelling rough and irregular surfaces. Finally this article examined the electrochemical responses to various signals under diffusion-limited reactions during diffusion towards the fractal interfaces: The generalised forms, including the fractal dimension of the electrode surfaces, of Cottrell, Sand and Randles-Sevcik equations were theoretically derived and explained in chronoamperomety, chronopotentiometry and linear sweep/cyclic voltammetry, respectively.

• Structural Engineering and Mechanics
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• v.36 no.6
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• pp.715-727
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• 2010

An experimental investigation is conducted here to study the effects of applying frictional sliding fuses (FSF) in concrete infilled steel frames. Firstly, the influences of some parameters on the behavior of the sliding fuse are studied: Methods of adjusting the FSF for a certain sliding strength are explained and influences of time duration, welding and corrosion are investigated as well. Based on the results, time duration does not significantly affect the FSF, however influences of welding and corrosion of the constitutive plates are substantial. Then, the results of testing two 1/3 scale single-storey single-bay concrete infilled steel frames having FSF are presented. The specimens were similar, except for different regulations of their fuses, tested by displacement controlled cyclic loading. The results demonstrate that applying FSF improves infill behaviors in both perpendicular directions. The infilled frames with FSF have more appropriate hysteresis cycles, higher ductility, much lower deteriorations in strength and stiffness in comparison with regular ones. Consequently, the infills, provided with FSF, can be regarded as an engineered element, however, special consideration should be taken into the affecting parameters of their fuses.

• Journal of Technologic Dentistry
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• v.25 no.1
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• pp.9-20
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• 2003

Using a nickel-chrome casting alloy called 'Rexillium V' which is also available as base metal alloy for dental ceramic crown, 4 types of mixtures(A, B, C, D) with old and new metal were prepared for cyclic casting. The results of cyclic casting can be outlined as follows: 1. For Vickers hardness after casting, specimen A and D tended to have lower hardness in the course of cyclic casting, while specimen B and C tended to higher hardness. 2. The results of X-ray diffraction analysis showed that major crystal phase contained nickelchrome compounds and carbide. 3. The observation results of SEM photographs after cyclic casting show that there was a significant tendency to have similar structures among experimental groups. 4. The results of EDX analysis after cyclic casting showed that there were little differences in chemical composition between parent metal and base metal alloy. Although industrial nickel-chrome cast alloy did not show any significant change in material properties even through cyclic casting over several times, it is recommended that more there be more in-depth studies on how to detect any potential corrosion, discoloration and toxication of dental ceramic crown implanted in patient's oral cavity.

• Journal of Advanced Marine Engineering and Technology
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• v.31 no.6
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• pp.744-752
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• 2007

Recently a fuel oil of the diesel engine in the ship is being changed with low quality as the oil price is higher more and more. Therefore the wear and corrosion in all parts of the engine like cylinder liner ring groove of piston crown, spindle and seat ring of exhaust valve are increased with using of heavy oil of low quality In particular the degree of wear and corrosion in between valve spindle and seat ring are more serious compared to the other parts of the engine due to operating in severe environment such as the high temperature of exhaust gas and repeating impact. Thus the repair weld to the valve spindle and seat ring is a unique method to prolong the life of the exhaust valve in an economical point of view In this study. corrosion property of both weld metal zone and base metal was investigated with some electrochemical methods such as measurement of corrosion potential, cathodic and anodic polarization curves, cyclic voltammogram and polarization resistance etc. in 5% $H_2SO_4$ solution. in the case of being welded with some welding methods and welding materials to the exhaust valve specimen as the base metal. In all cases. the values of hardness of the weld metal zone were more high than that of the base metal. And their corrosion resistance were also superior to the base metal. The weld metal of A2F(AC SMAW: 2 pass welding with foreign electrode) showed a relatively good results to the corrosion resistance as well as the hardness compared to the ether welding methods and welding materials. Moreover it indicated that hardness of the weld metal by the domestic electrode was considerably high compared to that of the foreign electrode.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2016.11a
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• pp.105-105
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• 2016

Recently, high power impulse magnetron sputtering (HIPIMS) has attracted considerable attentions due to its high potential for industrial applications. By pulsing the sputtering target with high power density and short duration pulses, a high plasma density and high ionization of the sputtered species can be obtained. HIPIMS has exhibited several merits such as increased coating density, good adhesion, microparticle-free and smooth surface, which make the HIPIMS technique desirable for synthesizing hard coatings. However, hard coatings present intrinsic defects (columnar structures, pinholes, pores, discontinuities) which can affect the corrosion behavior, especially when substrates are active alloys like steel or in a wear-corrosion process. Atomic layer deposition (ALD), a CVD derived method with a broad spectrum of applications, has shown great potential for corrosion protection of high-precision metallic parts or systems. In ALD deposition, the growth proceeds through cyclic repetition of self-limiting surface reactions, which leads to the thin films possess high quality, low defect density, uniformity, low-temperature processing and exquisite thickness control. These merits make ALD an ideal candidate for the fabrication of excellent oxide barrier layer which can block the pinhole and other defects left in the coating structure to improve the corrosion protection of hard coatings. In this work, CrN/Al2O3/CrN multilayered coatings were synthesized by a hybrid process of HIPIMS and ALD techniques, aiming to improve the CrN hard coating properties. The influence of the Al2O3 interlayer addition, the thickness and intercalation position of the Al2O3 layer in the coatings on the microstructure, surface roughness, mechanical properties and corrosion behaviors were investigated. The results indicated that the dense Al2O3 interlayer addition by ALD lead to a significant decrease of the average grain size and surface roughness and greatly improved the mechanical properties and corrosion resistance of the CrN coatings. The thickness increase of the Al2O3 layer and intercalation position change to near the coating surface resulted in improved mechanical properties and corrosion resistance. The mechanism can be explained by that the dense Al2O3 interlayer acted as an excellent barrier for dislocation motion and diffusion of the corrosive substance.