Corrosion Mechanism

Turkish Journal of Engineering, 2018

Detection and control of galvanic corrosion is a critical aspect of engineering for the chemical processes used in the fabrication of metals, alloys and materials industry. Galvanic corrosion can occur when two metals having different status in the electrochemical ambient are configured in mutual interaction within the galvanic cell structure and are exposed to the ion conducting electrolyte. In this study, ion-containing water was used as an electrolyte, the zinc as the anode electrode, copper as the cathode was used as an electrode, and a galvanic cell was fabricated. The formation of corrosion products with time on zinc anode reduced the voltage and current in galvanic cell considerable and anode film layer of considerable increase. Time-dependent experiments have provided good sources of information about the performance of the zinc anode electrode and the copper cathode electrode in the galvanic cell.

Corrosion Science, 1974

ChemElectroChem, 2018

Zinc electrodes were polarized cathodically at moderate overpotentials in NaCl 0.6 M solutions under potentiostatic conditions for 7 to 17 hours at room temperature. Corrosion products were characterized by optical microscopy, XRD, Raman microscopy, XPS and FIB-SEM. Close to the open circuit potential, the corrosion products were formed by simonkolleite and the electrochemical response exhibits anodic features. At more negative potentials, the current density remains cathodic throughout the polarization and the deposits on the electrode surface consist almost solely of ZnO. The soluble zinc species necessary for ZnO deposition originate from localized dissolution of the substrate in the form of pits. This effect is assigned to the strong alkalinisation of the surface due to oxygen reduction. Despite developing greater surface area than bare zinc substrates, the nanostructured ZnO deposits reduced the cathodic activity.

Corrosion Science 49 (2007) 726-739. , 2007

The work makes use of the scanning vibrating electrode technique (SVET) and the scanning electrochemical microscope (SECM) to investigate microscopic aspects of the electrochemical reactions that occur in an iron–zinc galvanic couple immersed in aqueous sodium chloride solution. Detection of the corrosion processes was made by sensing the phenomena occurring in solution. The SVET provided information on the distribution of ionic currents arising from the metal surface, whereas the SECM measured the concentration of chemical species relevant to the corrosion processes. The two techniques had comparable sensitivity for the corrosion of iron but significant differences were observed concerning the detection of corrosion of zinc.

The experiment is covering the fundamentals of electrochemistry. The major parts of the laboratory work include preparation of electrodes and electrolyte solutions with different concentrations. The theoretical principles applied during the experiment are electrochemical galvanic cell assemble and potential concepts. The relation of cell potential and concentration is analyzed.

Corrosion Science, 2002

Using a simple model cell the susceptibility of the zinc electrode to pitting corrosion by SO 2À 4 , SO 2À 3 , S 2 O 2À 3 and S 2À anions were examined in naturally aerated carbonate solutions. It was found that, pitting started after an induction period, s, which depended on the type and concentration of the aggressive and passivating anions. The pitting corrosion current increased with time until steady state values were attained. These values depended on both the type and the concentration of the passivating and pitting anions. For the same concentration of the passivating anions, the corrosion current varied with the concentration of the aggressive anion according to the relation: log i pit: ¼ a 1 þ b 1 log C agg. At a constant concentration of the aggressive anion, the corrosion current varied with the concentration of the passivating anions according to: log i pit: ¼ a 2 À b 2 log C pass. The constants a 1 (a 2) and b 1 (b 2 Þ were determined for all the systems studied. From the values of a 1 the corrosivity of the sulphur-containing anions is found to decrease in the order SO 2À 4 > SO 2À 3 > S 2 O 2À 3 > S 2À .

Corrosion Science, 2004

The changes in the pitting corrosion current density with time on zinc electrode concerning the concentration of both the passivating borate and the aggressive chloride anions were followed using a simple electrolytic cell. The pitting corrosion currents started to flow after an induction period, s. This period is found to be a function of the concentration of Cl À anion, according to the relation log s ¼ b À c log C Cl À. The pitting corrosion currents finally reached a steady-state value, which depended on the concentration of both B 4 O 2À 7 and Cl À anions. At a constant B 4 O 2À 7 anion concentration, the pitting corrosion current varied with the concentration of Cl À anion according to the relation log i pit ¼ a 1 þ b 1 log C Cl À. It also varies at constant Cl À anion concentration and various B 4 O 2À 7 anion concentration according to the relation log i pit ¼ a 2 À b 2 log C B 4 O 2À 7. The susceptibility of the passivating zinc to pitting corrosion was found to be increasing as the temperature and pH of the solution increases. Results are discussed on the basis of adsorption of the aggressive anion on the passivating film, followed by penetration through the film and incorporation in it. This undermines the oxide film and causes pitting corrosion.

muduku ivan

Is the potential difference between an element and an aqueous solution of its ions, when it is in equilibrium with its ions. Consider a metal dipped into a solution of its ions, e.g. a Zinc rod dipped in a solution of zinc ions such as zinc sulphate. Two processes may occur;  Metal atoms may ionize leaving a buildup of electrons on the metal surface, metal becomes negatively charged. Zn(s) → Zn 2+ (aq) + 2e  Metal ions from a solution may take up electrons from the rod of the metal; discharged as metal atoms; metal becomes positively charged. Zn 2+ (aq) + 2e → Zn(s) Because of different rates at which the above process occur, and the high electro positivity of the zinc metal, tendency to ionize outweigh the tendency to gain electrons; electrons accumulate on its surface, becomes more negative with respect to the solution.