The effect of relative humidity on the atmospheric corrosion of defective organic coating materials: An EIS study with a new approach

The effect of relative humidity on the atmospheric corrosion of defective polyester-coated galvanized mild steel was investigated using electrochemical impedance spectroscopy. Measurements were carried out on samples which had been tested in an accelerated atmospheric corrosion test. The relative humidity was adjusted to the desired value (70, 80 and 100%) by means of water-glycerol mixture in 0.1 M ammonium sulphate solutions. The impedance diagrams (Nyquist plots) were simulated using Equivert program developed by Boukamp using a recognized model electrical analogue and semi-ellipse model developed by Erbil. It has been shown that the defective coating resistance and corrosion rate of metal under the coating changes with relative humidity. A new equivalent circuit model has been suggested and also a differential capacitance definition has been created in this equivalent circuit model and charge transfer resistance (R(ct)) is redefined in this study. (C) 2000 Elsevier Science Ltd. All rights reserved.The effect of relative humidity on the atmospheric corrosion of defective polyester-coated galvanized mild steel was investigated using electrochemical impedance spectroscopy. Measurements were carried out on samples which had been tested in an accelerated atmospheric corrosion test. The relative humidity was adjusted to the desired value (70, 80 and 100%) by means of water-glycerol mixture in 0.1 M ammonium sulphate solutions. The impedance diagrams (Nyquist plots) were simulated using Equivert program developed by Erbil. It has been shown that the defective coating resistance and corrosion rate of metal under the coating changes with relative humidity. A new equivalent circuit model has been suggested and also a differential capacitance definition has been created in this equivalent circuit model and charge transfer resistance (Rct) is redefined in this study

Electrochemical and quantum chemical studies of some sulphur-containing organic compounds as inhibitors for the acid corrosion of mild steel

The influence of thioacetamide (TAcA), thiourea (TU) and thiobenzamide (TBA) on the corrosion of mild steel in 0.1 M H2SO4 solution has been studied in relation to the concentrations. The -CS-NH 2 group is the common main group for these compounds and they differ only having different groups on the other side of the thiocarbonyl group. Electrochemical impedance spectroscopy (EIS) and polarization resistance measurement (Rp) techniques have been used to obtain experimental data. The results showed that these compounds revealed a good corrosion inhibition, thiobenzamide being the most efficient and thioacetamide the least. The correlation between the molecular structures and corrosion inhibition efficiencies of TAcA, TU and TBA has been investigated using ab initio quantum chemical calculations. The structures of these compounds have been optimized, highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO) energy levels, LUMO-HOMO energy gap and molecular orbital densities have been computed. The relations between the inhibition efficiency and quantum chemical parameters have been discussed. It was seen that there is a clear relation between the increase in corrosion inhibition and the increase of HOMO energy level. The highest values of the HOMO densities were found in the vicinity of the sulphur atom indicating it as most probable adsorption center. © 2004 Elsevier B.V. All rights reserved.This study was financially supported by Cukurova University Research Fund. The authors are grateful to Cukurova University Research Fund. We also wish to thank Dr. M. Yurtsever (Istanbul Technical University) for her contributions in computational calculations

Application of semi-ellipse model in impedance studies of corrosion of 63-37 brass in neutral aqueous solutions containing sulphate, ammonium, and chloride ions

The effects of NH4+ and Cl- ions on the corrosion of 63-37 brass have been investigated using the electrochemical impedance spectroscopy (EIS) technique. For this purpose, 10-3, 10-2, and 10-1 M sodium chloride, sodium sulphate, and ammonium sulphate solutions were used. Impedance data have been obtained at the corrosion potential with a two electrode system. The impedance diagrams (Nyquist plots) were evaluated according to the semi-ellipse model. A new equivalent circuit model has been suggested, and a differential capacitance definition has been created within this equivalent circuit model. The polarization resistance has been divided into the diffuse layer resistance (Rd) and the charge transfer resistance (Rt). The Rt values, which have been calculated from impedance diagrams for all solutions, indicated that the ammonium ions are corrosive to 63-37 brass, the corrosive effect depending on the ammonium concentration. However, chloride ions did not show corrosive effects at the corrosion potential

The effect of temperature on the corrosion of mild steel in acidic media in the presence of some sulphur-containing organic compounds

The effects of methylthiourea (MTU), phenylthiourea (PTU) and thiobenzamide (TBA) on the corrosion of mild steel in 0.1 M H2SO4 solution at temperatures of 30 °C, 40 °C and 50 °C have been studied. AC impedance, polarization resistance measurement and polarization curves measurement techniques have been used to obtain experimental data. The percent inhibition efficiency (IE%) and activation energy (Ea) have been determined in the presence and in the absence of these compounds. The results showed that all compounds have good inhibtion properties at all temperatures studied. The value of activation energy (Ea) found in the presence of PTU and TBA is smaller than that in the uninhibited solution while it is greater in the presence of MTU. The reasons that cause the deviation of a Nyquist plot from a semicircle have been investigated. Differential capacitance (Qdl) has been used instead of double layer capacitance (Cdl) to represent the experimental deviations of a Nyquist plot from a semicircle. Whether the difference in real impedance at lower and higher frequencies correspond with the charge transfer resistance (Rt) has been discussed by taking the resistance contribution of diffuse layer into account. The resistance measured with AC impedance technique has been divided into charge transfer resistance (Rt) and diffuse layer resistance (Rd). The corrosion current density (icorr) values have been determined by making use of the variation of corrosion potential with pH. © 2005 Elsevier B.V. All rights reserved

Evaluation of the corrosion behavior of the polyester-coated galvanized steel subjected to SO2 gas under different relative humidities

Evaluation of the corrosion behaviour of the polyester-coated galvanized steels exposed to different relative humidities was utilized using electrochemical impedance spectroscopy (EIS), anodic polarization curves and linear polarization resistance (LPR) measurement techniques. The samples were exposed to SO2 gas in laboratory conditions that was adjusted to various relative humidities. The results obtained from current-potential curves indicate that, corrosion current density of polyester-coated samples increases as the relative humidity increases in SO2 containing medium. The EIS results showed that polyester-coated samples exposed to relative humidity (RH) of 70% experienced defect-free coating, whereas the samples significantly lost their protection behaviour under relative humidities of 80, 90 and 100%. © 2013 Pleiades Publishing, Ltd.FEF2010D10ACKNOWLEDGMENTS This study was supported by Cukurova University Research Found (FEF2010D10)

Electrochemical synthesis of poly-6-amino-m-cresol (poly-AmC)

The electropolymerization of 6-amino-m-cresol (AmC) on a platinum electrode was studied in 0.1 M Na 2 SO 4 solution containing 5 × 10 -3 M 6-amino-m-cresol at different pHs using cyclic voltammetry technique. Voltammetric results showed that oxidation of 6-amino-m-cresol produced a passivating polymeric film on the platinum surface at all pHs studied. Synthesized polymer has bronze color on platinum. To investigate the structure of poly-6-amino-m-cresol (poly-AmC) films FTIR technique was employed. The spectroscopic results indicate that polymer chain consist of ring opened units rather than phenoxazine structure. © 2005 Elsevier B.V. All rights reserved.FEF2004D13This study has been financially supported by Cukurova University research fund (Project number: FEF2004D13). The authors are grateful to Cukurova University research fund

EIS study of the effect of high levels of NH3 on the deformation of polyester-coated galvanised steel at different relative humidities

The effect of NH3 on the deformation of polyester-coated galvanised steel at different relative humidities (RHs) was investigated using electrochemical impedance spectroscopy. Measurements were performed on specimens which had been tested in accelerated gaseous corrosion test. For this purpose the samples were subjected to NH3 gas for 16 and 24 days in atmospheric test cells with adjusted RH from 60 to 100%. Subsequently, the impedance response of the coated material was measured and evaluated. The results indicated that the coating performance varies with RH. At lower RH, remarkably, the coating remained effectively intact with the coating resistance varying inversely with RH. This work is relevant to the application of such organic-coated products adjacent to some plant flues were high levels of NH 3 occur in association with high humidity. © 2003 Elsevier B.V. All rights reserved.FEF.99.15This study [TBAG-1696 (198T029)] was supported by The Scientific and Technical Research Council of Turkey (TUBITAK) and Cukurova University Research Found (FEF.99.15). The authors are grateful to both supporters

EIS study of the effect of high levels of SO2 on the corrosion of polyester-coated galvanised steel at different relative humidities

The effect of SO2 on the degradation of polyester-coated galvanised steel at different relative humidities was investigated using electrochemical impedance spectroscopy. Measurements were performed on specimens which had been tested in an accelerated gaseous corrosion test. For this purpose the samples were subjected to SO2 gas for 16 days in atmospheric test cells with adjusted relative humidity (RH) from 60 to 100%. Subsequently, the impedance response of the coated material was measured and evaluated. The results indicated that the coating performance varies with RH. Thus, under condensing conditions, the organic coating and galvanised layer was totally removed, the impedance response being interpreted as the formation of an iron sulphide film on the surface. At lower RH, remarkably, the coating remained effectively intact with the coating resistance varying inversely with RH. This work is relevant to the application of such organic-coated products adjacent to combustion flues where high levels of SO2 occur in association with high humidity. © 2002 Elsevier Science B.V. All rights reserved.National Council for Scientific ResearchThis study [TBAG-1696 (198T029)] was supported by The Scientific and Technical Research Council of Turkey (TUBITAK). The authors are grateful to TUBITAK

Organic sulphur-containing compounds as corrosion inhibitors for mild steel in acidic media: Correlation between inhibition efficiency and chemical structure

The effects of thiourea (TU), methylthiourea (MTU) and phenylthiourea (PTU) on the corrosion behaviour of mild steel in 0.1M solution of H 2 SO 4 have been investigated in relation to the concentration of thioamides (-CS-NH 2 ). These compounds are all similar on one side of the thiocarbonly group and different on the other. The experimental data obtained using the techniques of R p (polarisation resistance) and EIS (electrochemical impedance spectroscopy). The results showed that these compounds revaled a good corrosion inhibition, phenylthiourea being the most efficient and thiourea the least. The effect of molecular structure on the inhibition efficiency on corrosion has been investigated by ab initio quantum chemical calculations. The electronic properties such as highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO) energy levels, LUMO-HOMO energy gap and molecular orbital densities were calculated. The relations between the inhibition efficiency and some quantum parameters have been discussed and obvious correlations were found. The highest values of the HOMO densities were found in the vicinity of the sulphur atom indicating it as most probable adsorption centre. © 2004 Elsevier B.V. All rights reserved.Çukurova ÜniversitesiThe authors acknowledge the financial support of Çukurova University. We also wish to thanks Dr. M. Yurtsever (Ystanbul Technical University) for her contributions in familiarising with the computational methods

Effects of ammonium chloride salt added to mixing water on concrete and reinforced concrete subject to atmospheric corrosion

Studied in this paper is the effect of SO2 as a pollutant gas on concrete and reinforced concrete specimens at various relative humidity (RH) rates prepared with ideal mixing water (IMW) and IMW + 80 mg NH4+ (NH4Cl) mixing water. The potential values of reinforcing steel were measured throughout 28 days and compressive strength values of concrete specimens in the same medium were determined at the end of the 28th day. SO2 gas was observed to have a harmful effect at higher RHs on compressive strength of concrete and to make more negative the potential values of reinforcing steel. © 2002 Elsevier Science Ltd. All rights reserved