İlyas Dehri

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 Equivcrt 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 (Rct) is redefined in this study.

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

Abstract 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.

The effects of SO2 and NH3 on the atmospheric corrosion of galvanized iron sheet

Abstract The corrosive effects of SO2 and NH3 gases on zinc and galvanized iron sheet have been investigated. For this purpose, analytical and electrochemical methods were used in laboratory conditions with varying relative humidity values (70–100%). Electrochemically, the anodic current-potential curves of zinc have been obtained in solutions of different concentrations of sulphuric acid (0.50, 0.25, 0.10 M) and ammonia (pH = 13.20). The results indicate that, the corrosion rate of zinc and galvanized iron increases as the relative humidity increases in SO2 containing medium but the corrosion rate is not related much to relative humidity in NH3 containing environment. At the same time, it has been observed that zinc does not get passive in H2SO4 containing medium but it does become passive in ammonia solution. This passivation of zinc in NH3 is due to the formation of a complex [Zn(NH3)4(OH)2] on the metal surface by OH− and NH3.

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%.