• Journal of the Korea Institute of Building Construction
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• v.8 no.3
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• pp.93-99
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• 2008

The purpose of this study is to evaluate the bond strength and corrosion resistance of coated reinforcing bar using hybrid-type polymer cement slurry(PCS). PCS coated steels, which is made from two types of polymer dispersions such as St/BA and EVA are prepared, and tested for bond strength and various corrosion resistances such as autoclaved cure, carbonation and H2SO4 solution. From the test results, the bond strength of PCS coated reinforcing bar using ordinary portland cement at 1-5, 2-1 and 4-5 of mixes is higher than that of uncoated regular steel. However, bond strength of almost PCS coated reinforcing bars using ultra rapid high strength cement is higher than that of epoxy coated bar, is also in ranges of 102% to 123% compared to that of uncoated regular steel. In autoclaved accelerating test, the ratio of corrosion of uncoated regular steel is increased with the increase in NaCl content, but the corrosion of PCS coated steel was very small. In the acceleration test for carbonation, increasing the amount of NaCl the corrosion of coated steel did not produce. The corrosion of uncoated regular steel is increased with the increase in the amount of NaCl. It can be seen that the NaCl following the acceleration test for carbonation can lower the corrosion resistance of concrete. As a result, the corrosion of steel largely is affected by the acceleration curing, chloride ion penetration and carbonation and shown more severe corrosion by applying complex factors. These corrosions of steel can be suppressed by the coating of PCS.

• Corrosion Science and Technology
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• v.6 no.2
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• pp.56-61
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• 2007

Carbide dissolution during heating processes can change chemical composition of martensitic stainless steel in its austenitic phase. Although the austenitizing treatments were carried out at a homogeneous austenite region, the amount of carbon atom in the matrix differs. Increase in the amount of carbon contents in the matrix resulted in decreasing MS temperature, which consequently causes the volume fraction of the retained austenite to increase. This study reveals the effects of the austenitizing treatment on the properties of Fe - 0.3C - 14Cr - 3Mo martensitic stainless steel change with different austenitizing temperatures.

• Corrosion Science and Technology
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• v.11 no.6
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• pp.257-262
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• 2012

Flow accelerated corrosion (FAC) of the carbon steel piping in nuclear power plants (NPPs) has been major issue in nuclear industry. Rotating cylinder FAC test facility was designed and fabricated and then performance of the facility was evaluated. The facility is very simple in design and economic in fabrication and can be used in material and chemistry screening test. The facility is equipped with on line monitoring of pH, conductivity, dissolved oxygen(DO), and temperature. Fluid velocity is controlled with rotating speed of the cylinder with a test specimen. FAC test of SA106 Gr. B carbon steel under 4 m/s flow velocity was performed with the rotating cylinder at DO concentration of less than 1 ppb and of 1.3 ppm. Also a corrosion test of the carbon steel at static condition, that is at zero fluid velocity, of test specimen and solution was performed at pH from 8 to 10 for comparison with the FAC data. For corrosion test in static condition, the amount of non adherent corrosion product was almost constant at pH ranging from 8 to 10. But adherent corrosion product decreased with increasing pH. This trend is consistent with decrease of Fe solubility with an increase in pH. For FAC test with rotating cylinder FAC test facility, the amount of non adherent corrosion product was also almost same for both DO concentrations. The rotating cylinder FAC test facility will be further improved by redesigning rotating cylinder and FAC specimen geometry for future work.

• Corrosion Science and Technology
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• v.7 no.2
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• pp.130-133
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• 2008

Corrosion of silver by outgassed sulfur species from rubber has been investigated by means of quartz crystal microbalance technique (QCM) and cathodic reduction technique. Silver specimens were placed together with a rubber of predefined quantity in an enclosed environment. Corrosion progressed linearly with time and silver sulfide was found as the corrosion product during all the tests. No significant dependence on RH was observed, while the corrosion rate increased as temperature rose. Furthermore the corrosion rate increased logarithmically with the quantity of the rubber placed in the exposure environment. It may be suggested that the corrosion rate of silver is determined by the amount of outgassed sulfur species which is a function of temperature and the quantity of rubber contained in the exposure environment.

• Corrosion Science and Technology
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• v.5 no.3
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• pp.94-98
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• 2006

The next generation nuclear power reactor will use Pb-Bi as the cooling material. The steel structure materials such as HT-9 used in the reactor suffer from corrosion when they are exposed to high temperature Pb-Bi. Therefore corrosion should be prevented to use Pb-Bi as the coolant material without any safety problem. One method is to control the oxygen content in Pb-Bi. An appropriate amount of oxygen in Pb-Bi can produce a thin oxide layer on steel, and this layer protects the steel from corrosion attack. Since the required oxygen content in Pb-Bi is in the range of $10^{-5}$ to $10^{-7}$ wt%, this small oxygen content can be controlled by flowing a mixture of hydrogen gas and water vapor. The stagnant corrosion test of HT-9 samples was performed by controlling the oxygen content up to 2,000 hours. The corrosion behavior of HT-9 was analyzed at the temperatures of $500^{\circ}C$ and $650^{\circ}C$ with a reduced condition and a oxygen content of $10^{-6}$ wt%.

• Corrosion Science and Technology
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• v.5 no.4
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• pp.123-128
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• 2006

It was analyzed the causes of boiler tube rupture due to a degradation and corrosion on the boiler tubes in fossil power plant. The experiments were carried out among samples taken from the operating facilities. The result were analyzed based on experimental results from mechanical strength, microstructure observation, and hardness measurement in order to determine the cause of local rupture on boiler tubes. In general, 2.25Cr-1Mo steel generates carbides, it is coarsened, its ductility and strength abruptly decreased as degradation is in progress, In order to confirm this phenomenon, we observed changes of the mount of Cr and Mo of carbide by carrying out EDX chemical composition analysis. The amount of Cr and Mo in the degraded material or service exposed material gradually increased the amount of Mo but initially they were almost maintained at the same amount. Furthermore, we observed that the carbide become coarsened both in the grain and at the grain boundary. Tensile test was carried out to measure a material hardness and to recognize a drop-off of hardness. Overall result for tensile strength and hardness turned out to be lower than new material and mechanical strength and hardness was degraded as the material degradation was in progress.

• Corrosion Science and Technology
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• v.5 no.1
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• pp.27-32
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• 2006

One of the critical issues in the coating specification is the allowable limit of surface contaminant(s) - such as soluble salt(s), grit dust, and rust - after grit blasting. Yet, there is no universally accepted data supporting the relationship between the long-term coating performance and the amount of various surface contaminants allowed after grit blasting. In this study, it was attempted to prepare epoxy coatings applied on grit-blasted steel substrate dosed with controlled amount of surface contaminants - such as soluble salt(s), grit dust, and rust. Then, coating samples were subjected to 4,200 hours of cyclic test(NORSOK M-501), which were then evaluated in terms of resistance to rust creepage, blistering, chalking, rusting, cracking and adhesion strength. Additional investigations on the possible damage at the paint/steel interface were carried out using an Electrochemical Impedance Spectroscopy(EIS) and observations of under-film-corrosion. Test results suggested that the current industrial specifications were well matched with the allowable degree of rust, whereas the allowable amount of soluble salt and grit dust after grit blasting showed a certain deviation from the specifications currently employed for fabrication of marine vessels and offshore facilities.

• Korean Journal of Metals and Materials
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• v.47 no.9
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• pp.558-566
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• 2009

The alloying effect of a small amount of nickel on low alloy steel for application to flue gas desulfurization(FGD) systems was studied. The structural characteristics of the rust layer were investigated by scanning electron microscopy(SEM). The electrochemical properties were examined by means of potentiostatic polarization test, potentiodynamic polarization test, and electrochemical impedance spectroscopy(EIS) in a modified green death solution of 16.9 vol.% $H_2SO_4$+0.35 vol.% HCl at $60^{\circ}C$ and an acid rain solution of $6.25{\times}10^{-5}M\;H_2SO_4+5.5{\times}10^{-3}M\;NaCl$ at room temperature. It was found that as the amount of nickel increased, the corrosion rate increased in the modified green death solution, which seemed to result from micro-galvanic corrosion between NiS and alloy matrix. In acid rain solution, the corrosion rate decreased as the amount of nickel increased due to the repulsive force of $NiFe_2O_4$ rust against $Cl^-$ ions by electronegativity.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.1
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• pp.83-90
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• 2017

The corrosion behavior of a rebar in concrete according to the amount of NaCl and $LiNO_2$ was observed by using Electrochemical Impedance Spectroscopy. The corrosion was accelerated in a short time by using dry/wet cycles method, which is one of the corrosion acceleration methods, and though the value of measured impedance, equivalent circuit can be introduced. It was confirmed that the passive film of a embedded rebar in concrete with NaCl was broken quickly, and when $0.6M\;LiNO_2$ was added, the velocity of ongoing corrosion was declined considerably compared to the amount of NaCl. However, when $1.2M\;LiNO_2$ was added, it was confirmed that the passive film was not broken and its performance remained, compared to the amount of NaCl.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2016.05a
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• pp.145-146
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• 2016

In this study, Corrosion behavior in mortar was observed by the passage of time by using EIS method. As a result of EIS experiment, equivalent circuit and changes of Impedance parameter could be observed. In addition, it was confirmed that impedance of rebar in mortar and corrosion rate according to the amount of NaCl were different.