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The corrosion properties of the nickel–aluminium bronze (NAB) in aqueous chloride media were investigated at different pHs by using linear potential sweep voltammetry and scanning electron microscopy. The NAB electrochemical behaviour was dependent on the solution pH, due to the different stabilities of the phases present within its microstructure. In particular, at solution pHs higher than 4.0 the NAB oxidation was driven by the dissolution of the copper-rich ?-phase, whereas at pH values lower than 4.0 its anodic behaviour was controlled by the oxidation of the iron-, nickel- and aluminium-rich ?I-, ?II- and ?IV-phases. Furthermore, a kinetic model for the NAB oxidation, in neutral chloride solutions, was developed on the basis of the observed behaviour, i.e., order of reactions of NAB with respect to protons and chloride. Finally, considering the high affinity of benzotriazole for copper, the corrosion performance of NAB was studied in the presence of the inhibitor in neutral (pH of 6.2) and acidic (pH of 3.5) chloride solutions, where NAB exhibited different anodic behaviours.

This work demonstrates the potential to assess Ni(II) concentration in neutral and acidic chloride environments on a boron-doped diamond electrode, without the introduction into the solution of an external chelating agent or markedly raising the pH. The nickel-ion quantification was achieved in solutions with pH values ranging from 8 to 4 using the electrochemical response associated with the Ni(II)/Ni(III) transition on a bare boron-doped diamond electrode. The associated electrochemical reaction was determined to be sensitive to the pH with a dependence relying on a proton stoichiometric number of 0.5 per mole of electrons. The detection protocol consisted of a reagentless electrodeposition of Ni in neutral or acidic solutions followed by oxidation to Ni(II) using differential pulse anodic voltammetry. This allowed the nickel-ion quantification with a limit of detection of 26.1 μM and a linearity over the concentration interval from 10 to 500 μM in a solution pH of 6.2. The regeneration of the pristine electrode surface was also achieved in the sample solution with an electropolishing treatment by holding the applied potential at +1.3 V vs. Ag/AgCl for 30–240 s, thus allowing a fast and efficient surface recovery.

Corrosion induced structural failures continue to be a costly problem in many industrial situations, and the development of robust corrosion sensing systems for structural health integrity monitoring is still a demanding challenge. The applicability of corrosion monitoring of copper alloys using a boron-doped diamond electrode (BDD) has been performed based on determination of copper ions within localised corrosion microenvironments. The electrochemical behaviour of copper ions on the BDD electrode surface were first reported in details in 0.60 M NaCl aqueous solution, and the results revealed that the electrochemical processes of copper ions on the BDD electrode proceed as two successive single electron transfer steps producing two well-separated pairs of peaks in cyclic voltammograms in the chloride ion containing electrolyte solutions. Compared with perchlorate and sulphate ions, chloride ions were observed with a significant stabilization effect on copper ions via the formation of CuCl2- complex, thus having two well-separated pairs of peaks in the obtained cyclic voltammograms on the BDD electrode in the chloride ion electrolyte solution. The apparent rate constant for the redox couple of Cu2+/Cu+ in chloride ion electrolyte was determined as 0.94 × 10–6 cm s–1 by using quasi-steady polarisation technique, thus indicating a quasi-reversible electron transfer process of Cu2+/Cu+ redox couple. Moreover, differential pulse voltammetric results exhibited the BDD electrode is promising for corrosion monitoring of copper alloys with an excellent relationship between peak current and concentration of copper ions without significant interference from the commonly presented metal ions within the simulated marine corrosion environments.

a b s t r a c t In the present work, the electrolytic process of diluted aqueous chloride solutions was investigated at Ti/RuO2·2SnO2 and Ti/Pt electrodes, at different values of current density, temperature and electroly- sis time. The time evolution of chlorine-related species (i.e., active chlorine (dissolved Cl2, HClO, OCl − ), chlorite, chlorine dioxide, chlorate and perchlorate) was investigated in order to establish whether their formation and consumption was related to either chemical or electrochemical path of reactions. The estimated Faradic efficiencies demonstrated the better catalytic activity of the Ti/RuO2·2SnO2 electrode towards the chlorine evolution reaction with respect to the Ti/Pt anode, and the key-role played by the temperature, which reflects the different activation energies of the two competing electrochemical reac- tions, i.e., chloride and water oxidations. The concentration trends of chlorate and perchlorate indicated that the electrochemical route was responsible for their presence in the bulk solution, instead of a chem- ical path. The low concentration levels assessed for chlorites throughout the tests did not suggest the preponderance of the chemical over the electrochemical depletion process; however, further potentio- dynamic tests suggested their high reactivity towards both anodic and cathodic surfaces, thus suggesting that the electrochemical path of depletion could prevail over the chemical. Conversely, due to a solution pH unfavourable to the stability of chlorine dioxide, its low concentration level was associated with a chemical depletion route.