Enhanced Corrosion Resistance of Superhydrophobic Layered Double Hydroxide Films with Long-Term Stability on Al Substrate

Abstract

A superhydrophobic ZnAl-layered double hydroxide (LDH)-La film was prepared by a hydrothermal method and further modification by laurate anions in this work. Comprehensive characterizations of this film were performed in terms of morphology, composition, structure, roughness, and wettability by scanning electronic microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, three-dimensional laser scanning confocal microscopy. The long-term corrosion protection effect of this superhydrophobic film was investigated deeply by monitoring the changes of the electrochemical impedance spectra for a long time of up to a month in 3.5 wt % NaCl solution. In the meantime, the changes of the contact angle were also recorded with the evolution of the immersion time. The result indicated that the stable superhydrophobic ZnAl-LDH-La film was able to provide efficient protection for the underlying Al substrate for a long time. In addition, the capability of the superhydrophobic surface against harsh conditions, including chemical damages and physical damages, was emphatically investigated. It was found that the superhydrophobic surface was chemically stable toward acid (pH ≥ 3), alkali, and heating, and it also exhibited high ultraviolet (UV) radiation resistance. This superhydrophobic coating maintained superhydrophobicity for 7 days of radiation in an UV chamber equipped with a 40 W UV lamp (λ = 254 nm), indicating superior ability of adapting to outdoor environment. This comprehensive investigation of the superhydrophobic ZnAl-LDH-La film is considerably helpful for researchers and engineers to get deep insight into its potential for practical applications in the field of corrosion and protection.

LDH Post-Treatment of Flash PEO Coatings

“…According to Figure 5a, the LDH structure carried out in the presence of NH4NO3 is in good agreement with the XRD patterns that showed broadened peaks and, consequently, a highly open LDH structure. Additionally, Figure 5b clearly shows (also consistent with the XRD pattern) a nondefined LDH structure, which is usually attributed to the incorporation of carbonate ions into the LDH gallery [48]. However, LDH developed in NaNO3 showed typical curved plate-like LDH microcrystals at long exposure times, and a non-defined structure at short exposure times (Figure 5c,d).…”

“…PEO coatings based on aluminate and silicate electrolytes showed the typical peaks at 9.6° and 19.9°, which corresponded to the characteristic (003) and (006) reflections of LDH intercalated with NO3 − [32,48,49]. Additionally, the presence of ZnO and Al2Si2O5(OH)4 characteristic peaks in the S4-LDH XRD pattern came from LDH chemical composition (Table 2) and silicate electrolytes, respectively (Table 1).…”

“…Figure 4 depicts the XRD patterns of the different LDH treatments (Table 2) grown on the bulk material. The presence of peaks at 9.6° and 19.9° corresponding to the characteristic (003) and (006) reflections of LDHs intercalated with NO 3− [32,48,49] indicates the formation of LDH under the different conditions. It was revealed that treatments containing NaNO3 in the solution led to more defined and intense peaks, probably due to the presence of sodium ions in the LDH gallery [50].…”

“…Figure 6 depicts the Bode and Nyquist plots for AA1050 alloy with studied LDH coatings. From the point of view of coating structure, the presence of spheroidal particles in flake-like LDH 1 and LDH 4 ( Figure 5) [14] was associated with the presence of secondary phases [35][36][37] that favored aluminium cation dissolution due to their highly cathodic behavior [48]. In addition, the porous structure of these spheroidal particles also favored Cl − anion penetration into the LDH gallery, and for this reason these coatings showed the lowest corrosion protection among the studied LDH coatings (Figure 6) [53][54][55].…”

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

“…on aluminum substrate and with various type of anions intercalated between the LDH interlayers. 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].…”