Role of Phase Composition of PEO Coatings on AA2024 for In-Situ LDH Growth

Abstract

Plasma electrolytic oxidation (PEO) is an environmentally friendly anodizing technique leading to the formation of a ceramic-like coatings under high-voltage discharges. Layered double hydroxides (LDHs) were grown directly on γ, α, and amorphous Al 2 O 3 powders, respectively, in order to investigate the phase responsible for in-situ LDH growth on PEO coating. Furthermore, it is shown that LDH growth is limited by the high tortuosity of the PEO layer and the accessibility of Al(OH) − 4 anions from the substrate covered with thin amorphous aluminum oxide, through the pores.

Chelating agent-assisted in situ LDH growth on the surface of magnesium alloy

“…The chelating agents (salicylic acid, EDTA, and NTA) were separately dissolved in deionized water (different concentrations of chelating agents were prepared, as will be indicated later in the description of each experiment) and pH of the solution was adjusted to 7.0–7.4 using 0.1 M and 1 M NaOH solution, where necessary. Al(NO 3 ) 3 (0.05 M) and NaNO 3 (0.25 M) were added to individual chelating agent solutions for the LDH formation (following the standard ratio of inorganic compounds previously adopted for LDH synthesis on aluminium alloys) 41 – 45 . The pH of the resultant solutions was adjusted to 8.0 ± 0.1, 9.0 ± 0.1, 10.0 ± 0.1, and 11.0 ± 0.1 using NaOH (0.1 M and 1 M).…”

Formation of Anticorrosive Film for Suppressing Pitting Corrosion on Al-Mg-Si Alloy by Steam Coating

“…Electroplating [12], anodization [13][14][15], and chemical conversion treatment [16] are representative surface treatments used industrially for many types of Al alloy. Recently, several new coating techniques have been developed for these alloys, including plasma electrolytic oxidation coating (PEO-coating) although, strictly speaking, this is an anodizing technique [17][18][19]. A major disadvantage of these methods is that the liquid waste that they produce requires treatment prior to its disposal, and incurs a risk of environmental pollution due to the heavy metal ions that are involved.…”

Layered Double Hydroxide Protective Films Developed on Aluminum and Aluminum Alloys: Synthetic Methods and Anti-Corrosion Mechanisms

“…The anodization of substrates is found to promote higher, denser growth of LDHs with additional underlying protection. But the formation of LDH growth in such cases depends upon the PEO tortuosity and the pores which are responsible for the accessibility of the Al(OH) − 4 [66]. Plasma electrolysis modification is found to develop highly stable in situ growth LDH structure and dense LDH geometry [66,67].…”

“…But the formation of LDH growth in such cases depends upon the PEO tortuosity and the pores which are responsible for the accessibility of the Al(OH) − 4 [66]. Plasma electrolysis modification is found to develop highly stable in situ growth LDH structure and dense LDH geometry [66,67]. Meanwhile, the electrochemical deposition approach is another way to develop LDHs directly on the substrate with the advantage of controlled deposition rate and higher growth rate, but the synthetic procedure is complex and not completely discussed yet.…”