Mechanism of Corrosion Inhibition of AA2024 by Rare-Earth Compounds

Abstract

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.

Effect of Nd3+ Ion Concentration on the Corrosion Resistance of API X70 Steel in Chloride‐Rich Environments

“…e increase in pH of the cathodic sites causes the precipitation of compounds of the type Me(OH) 3 , which subsequently are transformed to more stable metal oxides (Me 2 O 3 ). e mechanism of precipitation of both rare earth oxides and hydroxides has been cited in the literature previously [7,[27][28][29][30]. In general, the hydrolysis reaction of lanthanide cations (Ln) can occur according to the following reactions:…”

Study of the effect of cerium nitrate on AA2024-T3 by means of electrochemical micro-cell technique

“…It was hypothesized that the process continues in the surrounding regions via island growth involving small active regions which have not been covered yet [35]. Yasakau et al [36] proved that, in case of the AA2024-T3 aluminum alloy, cerium precipitation preferentially occurs on Al-Cu-Mg-based intermetallic particles modified by the local magnesium and aluminum dissolution which leads to the overall copper-enrichment of the intermetallic particles. Despite the fact that many studies have focused on the comprehension of cerium precipitation mechanisms, there are some aspects which still need clarification such as the precipitation of cerium compounds on the matrix.…”

Multidimensional electrochemical imaging in materials science

“…In the past decade many KFM studies have also been conducted on a broad range of topics in corrosion science, including research on the corrosion behavior of steel [136][137][138][139][140][141][142][143][144], Al [143], Cu [145][146][147][148], Zn [143,144,[149][150][151][152], alloys based on Al-Mg [153][154][155][156][157][158][159][160][161][162][163][164] and Ti [165], on corrosion protection with rare-earth elements [166] and other inhibitors [167][168][169][170], the effect of conversion coatings [171][172][173][174][175][176], and the effects of heat treatment on material properties [177][178][179]. Yamawaki et al …”