• Journal of the Korean Chemical Society
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• v.18 no.6
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• pp.391-399
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• 1974

Corrosion and passivation of metallic cobalt was studied by means of electrochemical experiments including potentiostatic and galvanostatic measurements and cyclic voltammograms. The mechanisms of active dissolution and passivation of cobalt at the metal/borate buffer solution interface are deduced from the Tafel slope, pH dependence of the Flade potential, and dissolution kinetic data. Hydroxyl group adsorbed on cobalt surface seems to participate in surface oxidation and formation of the passive layer. The growth kinetic data as measured by the current density suggests a mechanism in which the growth of the passive layer is determined by field-assisted transport of ions through the layer. Thickness of the passive layer was estimated by coulometry to be about 10${\AA}$ at the lowest passive potential and to grow gradually with anodic potential to about 20${\AA}$.

• Smart Structures and Systems
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• v.5 no.4
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• pp.443-455
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• 2009

The use of fiber reinforced polymer (FRP) reinforcement in concrete structures has been on the rise due to its advantages over conventional steel reinforcement such as corrosion. Reinforcing steel corrosion has been the primary cause of deterioration of reinforced concrete (RC) structures, resulting in tremendous annual repair costs. One application of FRP reinforcement to be further explored is its use in RC frames. Nonetheless, due to FRP's inherently elastic behavior, FRP-reinforced (FRP-RC) members exhibit low ductility and energy dissipation as well as different damage mechanisms. Furthermore, current design standards for FRP-RC structures do not address seismic design in which the beam-column joint is a key issue. During an earthquake, the safety of beam-column joints is essential to the whole structure integrity. Thus, research is needed to gain better understanding of the behavior of FRP-RC structures and their damage mechanisms under seismic loading. In this study, two full-scale beam-column joint specimens reinforced with steel and GFRP configurations were tested under quasi-static loading. The control steel-reinforced specimen was detailed according to current design code provisions. The GFRP-RC specimen was detailed in a similar scheme. The damage in the two specimens is characterized to compare their performance under simulated seismic loading.

• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.6
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• pp.201-211
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• 2011

Many reinforced concrete structures have been constructed at the offshore in Korea and those are exposed in environments for long period. Due to that, the reinforcement of the structure faces possibility of corrosion by the salt damage. Such corrosions are effects on the bond performance between concrete and reinforcing bar as well as the performance of the structure. In this study, the performance of RC structure has been investigated when the reinforcing bars are totally bonded and unbonded in the structure. Through the experimental tests and finite element analyses of beam-column joint with bond and unbonded reinforcing bar, the energy dissipation capacity, strength, and crack distribution are compared and discussed.

• Journal of the Korean institute of surface engineering
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• v.52 no.4
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• pp.233-238
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• 2019

The formation behavior of zinc phosphate conversion coating (ZPCC) on SCM430 alloy was investigated in 25 vol.% of 1M ZnO + 170 ml/L solution containing various $Fe(NO_3)_2$ concentrations, using open-circuit potential(OCP), electrochemical impedance spectroscopy(EIS), cyclic polarization(CP) curve and tape peel test. OCP of SCM430 alloy and corrosion current density increased with increasing $Fe(NO_3)_3$ concentration. Resistance of films formed on SCM430 alloy by chemical conversion treatment decreased with increasing $Fe(NO_3)_3$ concentration. Color and adhesion of chemical conversion coatings became darker and worse, respectively, with increasing $Fe(NO_3)_3$ concentration. It is concluded that addition of $Fe(NO_3)_3$ into a zinc phosphating bath leads to faster reaction to form porous surface coatings with poor adhesion and corrosion resistance.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.9
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• pp.1087-1093
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• 2014

Stainless steels stabilized with Ti or Nb are largely used in offshore and shipbuilding industries due to its excellent corrosion resistance. In this study, carbide stabilizers, Ti and Nb, were added to stainless steel 304 specimens with different concentrations(Ti: 0.26%, 0.71%, Nb: 0.29%, 0.46%, 0.71%), and their mechanical and electrochemical characteristics were evaluated. Micro-Vickers hardness testing was employed to characterize the mechanical characteristics with alloying elements. Electrochemical evaluation techniques including Tafel analysis, cyclic polarization experiment, galvanostatic experiment were utilized to compare the corrosion characteristics of the specimens. The result of hardness tests revealed that Nb containing specimens showed increasing hardness with increasing alloying contents while adding Ti had little effect on increase in hardness. In the case of electrochemical measurements, the electrochemical characteristics of the specimens were enhanced with increasing Nb contents while they were deteriorated with increasing Ti contents. As a result, different stabilizers and their contents may produce significant differences in electrochemical characteristics, and there such effect must be taken account of in development of stainless steels for marine environment.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.101-104
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• 2008

The cost of repairing the deterioration of concrete structures due to corrosion of the reinforcement steel has been the prominent figure in the maintenacne of the reinforced-concrete infrastructures. As an alternative material to steel reinforcement, the use of Fiber Reinforced Polymer (FRP) bar in concrete is being actively studied for the high resistance of chemical environment and high strength to weight ratio properties of FRP. However, there remain various aspects of FRP properties that still need to be studied before the standard design criteria can be established. One of the imminent issues is the bond between FRP and concrete. In this study, the bond-behavior of FRP bars in concrete is investigated via the pullout test with three varying parameters: surface condition of FRP bars, concrete compression strength, and cyclic loading patterns. As a result of experiment, the bond strength of GFRP increased with the concrete compression strength increasing and decreased with applying cyclic load.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.12
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• pp.6098-6105
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• 2013

In the present study, the characteristics of corrosion and thermal conductivity of thermal spray coatings for seawater heat exchangers were examined experimentally. The coating types of theZn and Al thermal spray coatings with additional epoxy and silicone sealers were tested. To examine the corrosion characteristics of the thermal spray coating, the cyclic voltamogram curve was measured followed by SEM imaging for surface characterization. The laser flash method was usedto measure the thermal conductivity of the specimen. The conductivity test results showed that thermal conductivity decreased by3 ~ 4% with the silicone sealer and decreased by 70 ~ 75% with the epoxy sealer.

• Transactions of the Korean hydrogen and new energy society
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• v.9 no.4
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• pp.169-176
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• 1998

An experimental study on effect of vapor-cooled heat stations in a 5.5 liter cryogenic vessel has been performed. The cryogenic vessel is made of stainless steel of thickness of 1mm and insulated by the combined insulation of vacuum, MLI(multi-layer insulation) and vapor-cooled radiation shield. Vapor-cooled heat stations are also constructed based on the 1-dimensional thermal analysis to reduce the heat inleak through a filling tube. Thermal analysis indicates that the vapor-cooled heat stations can substantially enhance the performance of vessel for cryogenic fluids with high $C_p/h_{fg}$ where $C_p$ the specific heat and $h_{fg}$ the heat of vaporization, such as $LH_2$ and LHe. The experimental results for $LN_2$ shows that the total heat inleak into inner vessel consists of 14% radiation and 86% conduction through the filling tube. Therefore, it is expected that the conduction heat in leak of the vessel for high $C_p/h_{fg}$ cryogenic fluids can be significantly reduced. powders. The amount of copper coating was 20wt%. In order to examine corrosion behavior of the electrodes, the corrosion current and the current density, in 6M KOH aqueous solution after removal of oxygen in the solution, were measured by potentiodynamic and cyclic voltamo methods. The results showed that Co in the alloy increased corrosion resistance of the electrode whereas Ni decreased the stability of the electrode during the charge-discharge cycles. The electrode used Si sealant as a binder showed a lower corrosion current density than the electrode used PTFE and the electrode used Cu-coated alloy powders showed the best corrosion resistance.

• Proceedings of the KWS Conference
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• 2006.10a
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• pp.277-279
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• 2006

Due to the numerous environmental factors, cracks and corrosion are frequently occured especially in old steel bridge, which deteriorate the structural integrity; thus bring about the problems of structural safety of the steel bridge. Therefore, repair and reinforcement are required for the damaged structure. the replacement repair welding method is spotlighted for its brilliant features, i.e. it can be achieved without incurring traffic dislocation. the method cuts the damaged parts and replaces them with new steel plate by welding under live loads. However, the mechanical behavior of the welded joints under cyclic loads due to the traffic which passes along bridge is not clarified. In this paper, the fatigue strength of the replacement repair welded joints was investigated in order to improve reliability in the repair welded joints of old steel bridge.

• Computers and Concrete
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• v.3 no.2_3
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• pp.145-161
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• 2006

This article involves architecting prototype-fuzzy expert system for designing the nominal cover thickness by means of fuzzy inference for quantitatively representing the environment affecting factor to reinforced concrete in chloride-induced corrosion environment. In this work, nominal cover thickness to reinforcement in concrete was determined by the sum of minimum cover thickness and tolerance to that defined from skill level, constructability and the significance of member. Several variables defining the quality of concrete and environment affecting factor (EAF) including relative humidity, temperature, cyclic wet and dry, and the distance from coast were treated as fuzzy variables. To qualify EAF the environment conditions of cycle degree of wet-dry, relative humidity, distance from coast and temperature were used as input variables. To determine the nominal cover thickness a qualified EAF, concrete grade, and watercement ratio were used. The membership functions of each fuzzy variable were generated from the engineering knowledge and intuition based on some references as well as some international codes of practice.