In situ growth of a CaAl-NO₃⁻-layered double hydroxide film directly on an aluminum alloy for corrosion resistance

Abstract

In this study, a calcium–aluminum-layered double hydroxide (CaAl-LDH) thin film was grown on an AA6082 aluminum alloy, for the very first time, by using a facile in situ growth method in an effort to investigate the CaAl-LDH structural geometry and corresponding corrosion resistance properties.

Chlorides Entrapment Capability of Various In-Situ Grown NiAl-LDHs: Structural and Corrosion Resistance Properties

“…Coatings 2020, 9, Lastpage; doi: FOR PEER REVIEW www.mdpi.com/journal/coatings aggressive media, and this phenomenon is well correlated with the previous works [10][11][12][13] and for NiAl-LDHd a reduction of about 3-orders of magnitude in corrosion current density was observed compared to the substrate. Furthermore, the open circuit potential (OCP) is switched toward nobler values with structural variation from NiAl-LDHa to NiAl-LDHd, whilst a high corrosion potential of −0.18 V vs Ag/AgCl was observed for NiAl-LDHd, probably due to the formation of well-ordered platelet structure.…”

“…All the synthesized NiAl-LDHs films on AA6082 have shown lower corrosion current density along with a shift of the corrosion potential to higher values as compared to bare AA6082, however, NiAl-LDHd has shown the significantly reduced anodic and cathodic current density compared to the substrate and also from other developed NiAl-LDHs. It is also worthy to note that NiAl-LDHd has shown the relatively higher film thickness of around 35 µm, which may provide a comparatively better barrier film against the aggressive media, and this phenomenon is well correlated with the previous works [10][11][12][13] and for NiAl-LDHd a reduction of about 3-orders of magnitude in corrosion current density was observed compared to the substrate. Furthermore, the open circuit potential (OCP) is switched toward nobler values with structural variation from NiAl-LDHa to NiAl-LDHd, whilst a high corrosion potential of −0.18 V vs Ag/AgCl was observed for NiAl-LDHd, probably due to the formation of well-ordered platelet structure.…”

“…Recently, layered double hydroxides (LDHs) have got prominent attention for potential applications in various fields, including, adsorbents [6], drug delivery systems [7], environmental sciences [8], and biomedical science [9]. LDHs have also be found an efficient system to enhance corrosion resistance due to their ion-exchange capabilities, high surface area, a wide range of cationic salts availability, cost-effectiveness and other lucrative characteristics [10][11][12]. LDH is a class of two-dimensional anionic clays, represented by the general formula [M 2+ 1−x M 3+ x (OH) 2 ]…”

“…x+ (A n− ) x/n , and exhibit a brucite like structure that formed when some of the divalent cations (M 2+ ) are substituted by trivalent cations (M 3+ ), while anions (A n ) stabilize the layered positive charge [12,13]. Generally, co-precipitated [14] and in situ growth methods are used to develop LDHs, while in situ growth approach can be an optimum choice due to strong adhesion with the substrate, caused by the chemical bonding between the two phases, and thus can prolong the service life of the LDH based anti-corrosion coatings, moreover simple synthetic approach also made it an attractive approach to investigate [10][11][12][13].…”

“…The NO 3 − has shown the lowest ion-exchange equilibrium constant among the following; CO 3 − > SO 4 − > OH − > F − > Cl − > Br − > NO 3 [15], Therefore, it is easy choice for nitrate anions support to modify the LDH geometry by making ion-exchange with various corrosion inhibitors [16]. Recently, we succeeded to synthesize novel CaAl-LDH directly on an aluminum substrate and investigated their physical and electrochemical properties [11]. Nickel-based LDH can also be another class of LDH to enhance the metallic substrate corrosion resistance and to further ascribe various multifunctional properties in it.…”