Yasakau Kiryl A, Zheludkevich Mikhail L, Lamaka Sviatlana V, Ferreira Mario G S
Department of Ceramics and Glass Engineering, University of Aveiro, CICECO, 3810-193 Aveiro, Portugal.
J Phys Chem B. 2006 Mar 23;110(11):5515-28. doi: 10.1021/jp0560664.
The mechanism of corrosion protection of the widely used 2024-T3 aluminum alloy by cerium and lanthanum inhibitors in chloride media is described in detail in the present work. The corrosion process was investigated by means of scanning Kelvin probe force microscopy (SKPFM), in situ atomic force microscopy, and scanning electron microscopy coupled with energy dispersive spectroscopy. Employment of the high-resolution and in situ techniques results in a deep understanding of the details of the physical chemistry and mechanisms of the corrosion processes. The applicability of the SKPFM for mechanistic analysis of the effect of different corrosion inhibitors is demonstrated for the first time. The inhibitors under study show sufficient hindering of the localized corrosion processes especially in the case of pitting formation located around the intermetallic S-phase particles. The main role of Ce(3+) and La(3+) in the corrosion protection is formation of hydroxide deposits on S-phase inclusions buffering the local increase of pH, which is responsible for the acceleration of the intermetallics dealloying. The formed hydroxide precipitates can also act as a diffusion barrier hindering the corrosion processes in active zones. Cerium nitrate exhibits higher inhibition efficiency in comparison with lanthanum nitrate. The higher effect in the case of cerium is obtained due to lower solubility of the respective hydroxide. A detailed mechanism of the corrosion process and its inhibition is proposed based on thermodynamic analysis.
本文详细描述了在氯化物介质中，铈和镧缓蚀剂对广泛使用的2024-T3铝合金的腐蚀防护机制。通过扫描开尔文探针力显微镜（SKPFM）、原位原子力显微镜以及扫描电子显微镜与能谱仪联用等手段对腐蚀过程进行了研究。高分辨率原位技术的应用使我们对腐蚀过程的物理化学细节和机制有了深入了解。首次证明了SKPFM在不同缓蚀剂作用机理分析中的适用性。所研究的缓蚀剂对局部腐蚀过程有足够的阻碍作用，特别是在金属间S相颗粒周围形成点蚀的情况下。Ce(3+)和La(3+)在腐蚀防护中的主要作用是在S相夹杂物上形成氢氧化物沉淀，缓冲局部pH值的升高，这是导致金属间化合物脱合金加速的原因。形成的氢氧化物沉淀也可作为扩散阻挡层，阻碍活性区的腐蚀过程。与硝酸镧相比，硝酸铈表现出更高的缓蚀效率。铈的效果更好是由于其相应氢氧化物的溶解度较低。基于热力学分析，提出了腐蚀过程及其抑制的详细机制。
