This study has demonstrated the capability of electrochemically assessing the metal–ion concentrations generated from the localised corrosion of nickel–aluminium bronzes (NAB). Prior to investigating NAB crevice corrosion, its electrochemical properties were studied at different pHs and chloride concentrations. At solution pHs higher than 4 NAB exhibited a corrosion behaviour similar to that of unalloyed copper and its oxidation was controlled by the dissolution of the copper–rich α–phase. However, as the pH was decreased below 4 the corrosion mechanism changed and the other κ–phases rich in aluminium, iron and nickel underwent preferential oxidation. The NAB corrosion performance was also investigated in the presence of benzotriazole (inhibitor) by using potentiodynamic polarisation. The excellent corrosion properties showed by NAB when exposed to neutral benzotriazole solution made the studied inhibitor a promising candidate for limiting crevice corrosion. With knowledge of the NAB corrosion behaviour and the relatively high copper– and nickel–ion extents present within the crevice corrosion solutions, a study related to their electrochemical behaviour and detection was undertaken using a boron–doped diamond (BDD) electrode at different pHs and chloride levels in order to establish viable electrochemical protocols for effectively assess these concentrations. Before investigating the copper and nickel electrochemical behaviours on BDD electrode, the diamond substrate was studied using a number of different techniques such as potentiodynamic polarisation, cyclic voltammetry and electrochemical impedance spectroscopy. Results highlighted its excellent performance having a wide potential window (ca. 3 V) and a low capacitive current (20 μF cm–2 in 0.5 M H2SO4) available for electroanalysis purposes. Finally, the NAB crevice corrosion was monitored using a BDD microelectrode array. The employed setup created an artificial crevice and accommodated the BDD microelectrode array for in situ and a real–time monitoring. The electrochemical response showed the only presence of copper(I) during the investigated time, whose concentration increased within the first two hundred hours to a level of ca. 0.4 mM and then remained stable for the following hundred hours. No copper(II), or other metal–ions, were determined in the crevice solutions, thus suggesting that within the investigated time the copper–rich α–phase dominated the NAB corrosion behaviour. Furthermore, results also indicated (ii) the low dissolved oxygen concentration within the crevice (since it promotes the oxidation of copper(I) to copper(II)) and (ii) that the local pH did not decreased below 4, where the NAB corrosion is controlled by the selective dissolution of the aluminium–, iron– and nickel–rich κ–phases.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:581542 |
| Date | January 2013 |
| Creators | Neodo, Stefano |
| Contributors | Wharton, Julian |
| Publisher | University of Southampton |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://eprints.soton.ac.uk/355881/ |
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