Gobara Mohamed, Baraka Ahmad, Akid Robert, Zorainy Mahmoud
Chemical Engineering Department, Military Technical College Cairo Egypt
Department of Materials, The University of Manchester Manchester UK.
RSC Adv. 2020 Jan 10;10(4):2227-2240. doi: 10.1039/c9ra09552g. eCollection 2020 Jan 8.
Cerium is a rare earth element that has been widely proposed for the corrosion protection of aluminium alloys (AA). Both cerium salts, Ce and Ce, have been used in combination with other compounds to offer synergistic inhibition, however, the inhibitive corrosion mechanism when using Ce with organic compounds is still not clear. In this study, the synergistic inhibition effect of Ce and melamine (M) on the corrosion of aluminium alloy 2024 (AA2024) in 3.5% NaCl solution was investigated. Potentiodynamic Polarization (PDP) and Electrochemical Impedance Spectroscopy (EIS) techniques were used to study the synergistic effect of different Ce/M ratios on the corrosion behaviour of AA2024. The PDP study showed that a combination of 50% Ce and 50% M leads to the lowest corrosion rates, both acting as cathodic inhibitors. Both PDP and EIS results indicated that M or Ce in isolation did not offer effective corrosion protection, while the combination of M and Ce significantly enhances the corrosion protection with a synergism parameter equal to 3.5. SEM and EDX observations confirm the findings from the electrochemical techniques. XPS was used to investigate the mechanism of protection, revealing that the reduction of Ce to Ce occurs during protection of AA2024. A new mechanism of corrosion synergistic inhibition by Ce and organic compounds is postulated where the role of the organic compounds is to enhance the reduction of Ce.
铈是一种稀土元素，已被广泛提议用于铝合金（AA）的腐蚀防护。铈盐Ce³⁺和Ce⁴⁺已与其他化合物结合使用以提供协同抑制作用，然而，铈与有机化合物一起使用时的缓蚀机理仍不清楚。在本研究中，研究了铈（Ce）和三聚氰胺（M）对2024铝合金（AA2024）在3.5%氯化钠溶液中腐蚀的协同抑制作用。采用动电位极化（PDP）和电化学阻抗谱（EIS）技术研究了不同Ce/M比的协同效应对AA2024腐蚀行为的影响。PDP研究表明，50%Ce和50%M的组合导致最低的腐蚀速率，两者均作为阴极抑制剂。PDP和EIS结果均表明，单独的M或Ce不能提供有效的腐蚀防护，而M和Ce的组合显著增强了腐蚀防护，协同参数等于3.5。扫描电子显微镜（SEM）和能谱分析（EDX）观察结果证实了电化学技术的研究结果。采用X射线光电子能谱（XPS）研究了防护机理，结果表明在AA2024的防护过程中发生了Ce⁴⁺到Ce³⁺的还原。提出了一种铈与有机化合物协同抑制腐蚀的新机制，其中有机化合物的作用是增强Ce⁴⁺的还原。
