• Corrosion Science and Technology
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• 제7권1호
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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.

• 대한금속재료학회지
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• 제50권3호
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• pp.218-223
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• 2012

Fe-(8.5, 18.5, 28.3, 36.9) wt% Cr alloys were corroded between 600 and $800^{\circ}C$ for up to 70 h in a 1 atm gas mixture that consisted of 0.0242 atm of $H_2S$, 0.031 atm of water vapor, and 0.9448 atm of nitrogen gas. Their corrosion resistance increased with an increment in the Cr content. The Fe-8.5%Cr alloy corroded fast, forming thick, fragile, nonadherent scales that consisted primarily of an outer FeS layer and an inner (Fe, Cr, O, S)-mixed layer. The outer FeS layer grew into the air by the outward diffusion of $Fe^{2+}$ ions, whereas the inner mixed layer grew by the inward diffusion of oxygen and sulfur ions. At the interface of the outer and inner scales, voids developed and cracking occurred. The Fe-(18.5, 28.3, 36.9)% Cr alloys displayed much better corrosion resistance than the Fe-8.5Cr alloy, because thin $Cr_2O_3$ or $Cr_2S_3$ scales formed.

• 한국표면공학회지
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• 제49권4호
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• pp.339-343
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• 2016

ASTM T23 steel with a composition of Fe-2.25%Cr-1.6%W corroded at 600 and $700^{\circ}C$ for 5-70 h in $N_2$/(0.5, 2.5)%$H_2S$-mixed gas at 1 atm. It corroded rapidly, forming the outer FeS scale and the inner (FeS, $FeCr_2O_4$)-mixed scale. The ensuing outward diffusion of $Fe^{2+}$ ions during corrosion led to the protrusion of FeS platelets over the outer FeS scale. The formation of FeS at the surface facilitated the oxidation of Cr to $FeCr_2O_4$ in the inner scale. Since the nonprotective FeS scale existed over the whole scale, T23 steel displayed poor corrosion resistance in the $H_2S$-containing atmosphere.

• 한국표면공학회지
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• 제48권3호
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• pp.110-114
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• 2015

The effect of hot-dip aluminizing on the corrosion of the low carbon steel was studied at $650-850^{\circ}C$ for 20-50 h in $N_2/0.5%\;H_2S$ gas. The aluminized steel consisted primarily of the Al topcoat and the underlying Al-Fe alloy layer. Aluminizing drastically improved the corrosion resistance by forming the ${\alpha}-Al_2O_3$ surface scale. Without aluminizing, the steel formed nonadherent, fragile, thick scales, which consisted of FeS as the major phase and iron oxides such as FeO, $Fe_3O_4$ and $Fe_2O_3$ as minor ones.

• 한국표면공학회지
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• 제50권2호
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• pp.85-90
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• 2017

The carbon steel formed the thick, somewhat porous, loosely adherent iron oxide scale when oxidized at $500-800^{\circ}C$ for 15 h in air. It formed the thicker, more porous, nonadherent scale consisting of FeS plus iron oxides in $Ar/1%SO_2$-mixed gas. It formed the much thicker, more porous, nonadherent scale consisting of FeS plus iron oxides in Ar/0.1% $H_2S$-mixed gas. However, the aluminized carbon steel formed the thin, protective $Al_2O_3$ surface scale even in $Ar/1%SO_2$-, and $Ar/0.1%H_2S$-mixed gas. Aluminizing drastically improved the corrosion resistance in (O, S, H)-containing gas.

• Corrosion Science and Technology
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• 제22권6호
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• pp.399-407
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• 2023

This study investigated the formation of oxide films on 6061 aluminum (Al) alloy and their impacts on corrosion resistance efficiency by regulating anodization voltage. Despite advantageous properties inherent to Al alloys, their susceptibility to corrosion remains a significant limitation. Thus, enhancing corrosion resistance through developing protective oxide films on alloy surfaces is paramount. The first anodization was performed for 6 h with an applied voltage of 30, 50, or 70 V on the 6061 Al alloy. The second anodization was performed for 0.5 h by applying 40 V after removing the existing oxide film. Resulting oxide film's shape and roughness were analyzed using field emission-scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM). Wettability and corrosion resistance were compared before and after a self-assembled monolayer (SAM) using an FDTS (1H, 1H, 2H, 2H-Perfluorodecyltrichlorosilane) solution. As the first anodization voltage increased, the final oxide film's thickness and pore diameter also increased, resulting in higher surface roughness. Consequently, all samples exhibited superhydrophilic behavior before coating. However, contact angle after coating increased as the first anodization voltage increased. Notably, the sample anodized at 70 V with superhydrophobic characteristics after coating demonstrated the highest corrosion resistance performance.

• Corrosion Science and Technology
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• 제5권6호
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• pp.206-212
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• 2006

The effects of sub-ppm levels of $H_2S$ and the adsorbed water on the atmospheric corrosion of silver were studied with In situ weight balance to study the effect of the adsorbed water on the kinetic behavior and to determine the rate-controlling step, with XPS to analyze the tarnish film, and with calculation of phase equilibrium to predict the stable solid phase, the concentrations of dissolved species ($Ag^-$, $H^+$, $S^{2-}$, $HS^-$) and the equilibrium potentials ($E_{Ag^+/Ag}$, $E_{H^+/H_2}$, $E_{O_2/O^{2-}$). The results of weight measurements showed that oxygen was required for the sulfidation of silver in 100 ppb $H_2S$ and humidified environments enhanced the tarnished rate and oxidizing power. In addition, the rate determining step for tarnishing silver was shown to be changed to transport though the tarnish film.

• Corrosion Science and Technology
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• 제2권5호
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• pp.219-224
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• 2003

Crevice corrosion of stainless steels in natural seawater was investigated for several post weld treatments; as-annealed, as-welded, pickled, and ground. The results confirmed the effect of the biofilm on the cathodic reaction leading to an ennoblement of the rest potential. The degree of ennoblement of corrosion potential depends on the surface finish. As-annealed and pickled samples show stable corrosion potential approaching to 200 ~ 300 mV (SCE) while as-welded and ground samples show the fluctuating corrosion potential. This points to a situation where there are conflicting effects determining the trend in free corrosion potential. Crevice corrosion initiation will tend to pull the free corrosion potential in the active direction, whereas the presence of biofilm will tend to ennoble corrosion potential. There was no visible attack on UNS S31803, S32550, and 2205W. Therefore, those stainless steel grades appeared to be resistant to crevice corrosion in natural seawater on condition of weld metal.

• 열처리공학회지
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• 제21권3호
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• pp.150-156
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• 2008

The effects of austenitizing temperature in a range of $1000{\sim}1150^{\circ}C$ on the corrosion resistance in 420J2 stainless steel tempered at $150^{\circ}C$ were investigated by an electrochemical uniform corrosion test in a solution of 0.5M $H_2S0_4$. Pitting test and DL-EPR test for intergranular corrosion were carried out in a solution of 3.5% NaCl and 0.5M $H_2S0_4$ + 0.01 M KSCN respectively. In uniform corrosion test, specimens austenitized below $1100^{\circ}C$ showed similar corrosion current density and passive current density, whereas specimens austenitized at $1150^{\circ}C$ showed a little higher values. Pitting potential slightly increased with an increase of austenitizing temperature. The degree of sensitization, DOS, also slightly increased with an increase of austenitizing temperature, reaching the highest degree at $1150^{\circ}C$. It was expected that the increase of DOS was due to the larger grain size rather than the dissolved precipitates in the matrix.

• Nuclear Engineering and Technology
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• 제55권6호
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• pp.2256-2262
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• 2023

The electrochemical corrosion behaviors of SA106 Grade B (SA106B) carbon steel in H₂SO₄4-N₂H₄ and H₂SO₄-N₂H₄-CuSO₄ solutions at 95 ℃ have been investigated with the addition of commercial corrosion inhibitors (CI#30 and No. 570S), to determine the stability of SA106B in the hydrazine-based reductive metal ion decontamination (HyBRID) process. The potentiodynamic polarization experiment revealed that the corrosion inhibitors were capable of lowering the corrosion rate of SA106B in H₂SO₄-N₂H₄ solution. It was found that the corrosion inhibitors induced formation of fixed surface layer on the carbon steel upon the corrosion. This corrosion inhibition performance was reduced in the presence of CuSO₄ in the solution owing to the chemical reactions between organic compounds in the corrosion inhibitors and CuSO₄. CI#30 showed a better corrosion inhibition effect in the H₂SO₄-N₂H₄-CuSO₄ solution. Although the corrosion inhibitors can provide better stability to SA106B in the HyBRID solution, their application should be carefully considered because it may result in reduced decontamination performance and increased secondary waste generation.