• Title/Summary/Keyword: Pitting corrosion inhibition

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Corrosion Behavior and Inhibition Studies of AZ31B Magnesium Alloy With and Without Cl- in the Alkaline Electrolytes in Addition with Various Inhibitor Additives

  • Shin, Yoonji;Cho, Kyehyun
    • Corrosion Science and Technology
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    • v.18 no.6
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    • pp.243-252
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    • 2019
  • The pitting corrosion and inhibition studies of AZ31B magnesium alloy were investigated in the alkaline solution (pH12) with chloride and inhibitors. The corrosion behavior of passive film with/without Cl- in the alkaline electrolyte were conducted by polarization curve and immersion tests in the presence of various additives (inhibitors) to clarify the inhibition efficiency of pitting corrosion at higher potential region. Critical concentration of pitting corrosion for Mg alloy was evaluated with 0.005 M NaCl in 0.01 M NaOH on the anodic polarization behavior. Critical pitting of AZ31B Mg alloy in 0.01 M NaOH is a function of chlorides; Epit = - 1.36 - 0.2 log [Cl-]. When the Sodium Benzoate (SB) was only used as an inhibitor, a few metastable pits developed on the Mg surface by an immersion test despite no pitting corrosion on the polarization curve meaning that adsorption of SB on the surface is insufficient protection from pitting corrosion in the presence of chloride. The role of SB and Sodium Dodecylbenzenesulfonate (SDBS) inhibitors for the Mg alloy surface in the presence of chloride was suppressed from pitting corrosion to co-adsorb on the Mg alloy surface with strong formation of passive film preventing pitting corrosion.

Inhibition of Pitting Corrosion of Copper Tubes in Wet Sprinkler Systems by Sodium Sulfite (아황산나트륨을 이용한 스프링클러 동배관 공식 부식 방지)

  • Suh, Sang Hee;Suh, Youngjoon;Kwon, HyukSang
    • Corrosion Science and Technology
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    • v.16 no.5
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    • pp.265-272
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    • 2017
  • Inhibition of pitting corrosion of the copper sprinkler tubes by removing dissolved oxygen in water with sodium sulfite was studied on the wet sprinkler systems operated in 258 household sites. First, air in the sprinkler tubing was removed by vacuum pumping. The tube was then filled with sodium sulfite dissolved in water. Sodium sulfite was very effective in maintaining a very low dissolved oxygen concentration in water in the sprinkler tube for the observation period of six months. Water leakage from the copper sprinkler tube was reduced significantly by using sodium sulfite. Both pitting corrosion process and pitting corrosion inhibition mechanism were investigated by examining microscopical and structural aspects of corrosion pits formed in failed copper sprinkler tube. Pitting corrosion was caused by pressurized air as well as sediments such as sand particles in copper tubes through oxygen concentration cells. It was confirmed microscopically that growth of corrosion pits was stopped by reducing dissolved oxygen concentration to a very level by using sodium sulfite.

Inhibition of Pitting Corrosion Failure of Copper Tubes in Wet Sprinkler Systems (스프링클러 구리배관의 공식 파손 억제)

  • Suh, Sang Hee;Suh, Youngjoon;Lee, Jonghyuk;Kwon, HyukSang
    • Corrosion Science and Technology
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    • v.19 no.2
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    • pp.89-99
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    • 2020
  • The inhibition of pitting corrosion failure of copper sprinkler tubes in wet sprinkler systems was studied. First, an apparatus and technology for removing air in the sprinkler tubes by vacuum pumping and then filling the tubes with water were developed. Using this apparatus and technology, three methods for inhibiting the pitting corrosion of the copper sprinkler tubes installed in several apartment complexes were tested. The first one was filling the sprinkler tubes with water bubbled by high-pressure nitrogen gas to reduce the dissolved oxygen concentration to lower than 2 ppm. In the second method, the dissolved oxygen concentration of water was further reduced to lower than 0.01 ppm by sodium sulfite. In the third method, the sprinkler tubes were filled with benzotriazole (BTAH) dissolved in water. The third method was the most effective, reducing the failure frequency of the sprinkler tubes due to pitting corrosion by more than 80%. X-ray photoelectron spectroscopy analyses confirmed that a Cu-BTA layer was well coated on the inside surface of the corrosion pit, protecting it from corrosion. A potentiodynamic polarization test showed that BTAH should be very effective in reducing the corrosion rate of copper in the acidic environment of the corrosion pit.

Use of Hydrazine for Pitting Corrosion Inhibition of Copper Sprinkler Tubes: Reaction of Hydrazine with Corrosion By-Products

  • Suh, Sang Hee;Kim, Sohee;Suh, Youngjoon
    • Corrosion Science and Technology
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    • v.16 no.5
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    • pp.247-256
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    • 2017
  • The feasibility of using hydrazine for inhibiting pitting corrosion in copper sprinkler tubes was investigated by examining microscopical and structural evolution of corrosion by-products with SEM, EDS, and XRD. Hydrazine removed dissolved oxygen and reduced CuO and $Cu_2O$ as well. The stable phase was changed from CuO to $Cu_2O$ or Cu depending on hydrazine concentration. Hydrazine concentration of 500 ppm could convert all CuO corrosion by-products to $Cu_2O$. In a tightly sealed acryl tube filled with aqueous solution of 500 ppm hydrazine, octahedral $Cu_2O$ particles were formed while plate-like structures with high concentration of Cu, O, N and C were formed near a corrosion pit. The inside structure of a corrosion pit was not altered by hydrazine aqueous solution. Uniform corrosion of copper was almost completely stopped in aqueous solution of 500 ppm hydrazine. Corrosion potential of a copper plate was linearly dependent on log (hydrazine concentration). The concept of stopping pitting corrosion reaction by suppressing oxygen reduction reaction could be verified by applying this method to a reasonable number of real sprinkler systems before full-scale application.

Inhibition of Rebar Corrosion by Carbonate and Molybdate Anions

  • Tan, Y.T.;Wijesinghe, S.L.;Blackwood, D.J.
    • Corrosion Science and Technology
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    • v.16 no.4
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    • pp.167-174
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    • 2017
  • Bicarbonate/carbonate and molybdate anions have been characterized for their inhibitive effect on pitting corrosion of carbon steel in simulated concrete pore solution by using electrochemical tests such as electrochemical impedance (EIS) and linear polarization (LP). It was revealed that bicarbonate/carbonate has a weak inhibitive effect on pitting corrosion that is approximately one order of magnitude lower compared to hydroxide. Molybdate is effective against pitting corrosion induced by the concentration of chloride as low as 113 mM and can increase the pitting potential of a previously pitted sample to the oxygen evolution potential by the concentration of molybdate as much as 14.6 mM only. The formation of a $CaMoO_4$ film on the surface hinders the reduction of dissolved oxygen on the steel surface, reducing corrosion potential and increasing the safety margin between corrosion potential and pitting potential further. In addition, pore-plugging by $FeMoO_4$ as a type of salt film within pits increases the likelihood of repassivation.

Surface Treatment of 304L Stainless Steel for Improving The Pitting Corrosion Resistance by Inhibitor

  • Hue Nguyen Viet;Kwon Sik Chol
    • Journal of the Korean institute of surface engineering
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    • v.36 no.3
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    • pp.277-283
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    • 2003
  • Electrochemical techniques were used to study the surface treatment for improving the pitting corrosion resistance of 304L stainless steel by inhibitors in chloride medium. Sodium molybdate (in concentration range : 0.005-80 g/l) , sodium nitrite (in concentration range : 0.001-50 g/l) and their mixture were used for this study. It was found that, molybdate and nitrite were good passivators for 304L stainless steel, but molybdate was not able to prohibit the pitting ; nitrite prevented pitting corrosion of 304L stainless steel only at the concentration more than 25 g/l. The relationship between pitting potentials and concentrations of inhibitors in the logarithm expression obeyed the linear function. It was found that the surface treatment by mixture of two inhibitors enables stainless steel to have increased the corrosion resistance , the pitting corrosion of 304L stainless steel was completely prohibited by the mixtures of molybdate and nitrite in ratio min, with $m\;\geq\;3\;and\;n\;\geq\;10$. The interesting cases on electrochemical measurement of threshold of inhibitors concentration combination for optimum surface treatment were described.

Pitting Corrosion Inhibition of Sprinkler Copper Tubes via Forming of Cu-BTA Film on the Inner Surface of Corrosion pits

  • Suh, Sang Hee;Suh, Youngjoon;Kim, Sohee;Yang, Jun-Mo;Kim, Gyungtae
    • Corrosion Science and Technology
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    • v.18 no.2
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    • pp.39-48
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    • 2019
  • The feasibility of using benzotriazole (BTAH) to inhibit pitting corrosion in the sprinkler copper tubes was investigated by filling the tubes with BTAH-water solution in 829 households at an eight-year-old apartment complex. The water leakage rate was reduced by approximately 90% following BTAH treatment during 161 days from the previous year. The leakage of one of the two sprinkler copper tubes was investigated with optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction analysis to determine the formation of Cu-BTA film inside the corrosion pits. All the inner components of the corrosion pits were coated with Cu-BTA films suggesting that BTAH molecules penetrated the corrosion products. The Cu-BTA film was about 2 nm in thickness at the bottom of a corrosion pit. A layer of CuCl and $Cu_2O$ phases lies under the Cu-BTA film. This complex structure effectively prevented the propagation of corrosion pits in the sprinkler copper tubes and reduced the water leakage.

Inhibition Effects of Chromate, Phosphate, Sulfate, and Borate on Chloride Pitting Corrosion of Al

  • Lee, Ho-Chun;Isaacs, Hugh S.
    • Journal of the Korean Electrochemical Society
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    • v.11 no.3
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    • pp.184-189
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    • 2008
  • Inhibitive effects of chromate, phosphate, sulfate, and borate on chloride pitting corrosion of Al have been investigated using cyclic voltammetry. During the anodic oxide growth, the critical concentration of chloride for pit initiation decreased in the order: chromate > phosphate > sulfate > borate, and the maximum pitting current density increases in the reverse order: chromate < phosphate < sulfate < borate. The decreasing pitting current density was observed in the successive polarization cycles, which was attributed to the aging of Al oxides and field relaxation at oxide/solution interface.

Pitting Corrosion Behavuor of N2+ ion Implanted AISI 316L Stainless Steel Compacts (질소 이온주입된 AiSi 316L 스테인리스강 소결체의 공식거동)

  • 최한철
    • Journal of the Korean institute of surface engineering
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    • v.31 no.2
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    • pp.73-80
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    • 1998
  • The aim of this study is to develop sintered stainless steels (SSS) with good mechanical strength, wear resistance, and corrosion resistance by nitrogen ion implantation on the Culated SSS surface. Stainless steel compacts containg Cu (2-10 wt%) were prepared by electroless Cu-pating method which results in the increased3 homogenization in alloying powder. Nitrogen ion implantation was carried out by using N2 gas as the ion source. Nitrogen ions were embedded by an acceleratol of 130keV with doese $3.0\times10^{17}\;ions/\textrm{cm}^2$ on the SSS at $25^{\circ}C$ in$2\times10^{-6}$ torr vacuum. The nitrogen ion implanted SSS obtained from anodic ploarization curves revealed higher corrosion potential than that of nitrogen ion unimplante one. And nitrogen ion implanted 316LSSS had good resistance to pitting corrosion due to the synergistic effect of Mo and N, and the inhibition of $NH_4\;^+$<\TEX>, against $CI^-$<\TEX>.

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