Electrochemical noise and impedance study of aluminium in weakly acid chloride solution

Microstructure and Corrosion Resistance of AZ91 Magnesium Alloy after Surface Remelting Treatment

The effect of surface remelting treatment on the microstructure and corrosion resistance of the AZ91 magnesium alloy was studied. The surface layer was remelted by GTAW (gas tungsten arc welding). An original two-burner system with welding torches operating in a tandem configuration was used, allowing the combination of cleaning the surface from oxides with the remelting process. The studies of the corrosion resistance of the alloy included electrochemical tests and measurements of the rate of hydrogen evolution. The results showed that surface remelting treatment leads to favorable microstructural changes, manifested in strong grain refinement and a more uniform arrangement of the β-Mg₁₇Al₁₂ phase. The changes in the microstructure caused by remelting and the accompanying fast crystallization contributed to an increase in the corrosion resistance of the remelted samples in comparison to their non-remelted equivalents. The results obtained on the basis of the polarization curves showed three-fold lower values of the corrosion current density in the case of the remelted material than the value of the corrosion current density determined for the starting material. In turn, in the case of measurements of the electrochemical noise and corrosion rate determined by the method of measuring the rate of hydrogen evolution, this value for the remelted alloy was two times lower. The research also showed that GTAW technology is highly effective and can be a valuable alternative to laser techniques. The complete experimental details, obtained results and their analyses are presented in this paper.

Electrochemical Study on Corrosion Inhibition of Copper in Hydrochloric Acid Medium and the Rotating Ring-Disc Voltammetry for Studying the Dissolution

Dissolution characteristics of copper in hydrochloric acid medium and the effect of 4-amino 1,2,4-triazole (ATA) on the corrosion process have been studied using conventional electrochemical techniques and rotating ring-disc electrodes (RRDEs). Corrosion potential () and corrosion current density () were obtained by Tafel extrapolation methods. Charge transfer resistance () and double-layer capacitance () were obtained from the electrochemical impedance spectroscopy (EIS). ATA was shown to be an effective inhibitor for the copper-corrosion inhibition in acid medium. The corrosion rate was retarded in presence of inhibitors mainly because of the adsorption of the inhibitor on the electrode surface. Adsorption of the inhibitor on the metal surface was found to follow the Langmuir adsorption isotherm. Standard free energy change of the adsorption process () was calculated to be −54.3 kJ mol−1; such a large negative value of suggests the prescence of a chemisorption process.