Hierarchically organized Li-Al-LDH nano-flakes: a low-temperature approach to seal porous anodic oxide on aluminum alloys

abstract

This work suggests a low-temperature sealing approach for tartaric-sulfuric acid (TSA) anodized AA2024 based on hierarchically organized Li-Al-layered double hydroxide (LDH) structures. The new proposed sealing is expected to be directly competitive to the standard hot water sealing (HWS) approaches because of its reduced treatment temperature and high protection efficiency. A hierarchical organization of in situ formed LDH nano-flakes across the depth length of the TSA pores, from the macrodown to the nano-size range, was observed with transmission electron microscopy (TEM). Electrochemical impedance spectroscopy (EIS) studies showed that the densely packed LDH arrangement at the porous oxide layer is directly related to the drastically improved barrier properties of TSA. Moreover, LDH flake-like structures worked as "smart" reservoirs for corrosion inhibiting vanadium species (VOx) that are released on demand upon the onset of corrosion. This was confirmed using a scanning vibrating electrode technique (SVET), giving relevant insights into the time-resolved release activity of VOx and the formation of the passivation layer on cathodic intermetallics, corroborated with EDX and analytical Raman spectroscopy. Passive and active corrosion protection was imparted to the anodic layer via new Li-Al-LDH structures with long-term protection exceeding that of standard HWS procedures.

keywords

LAYERED DOUBLE HYDROXIDE; ANION-EXCHANGE INTERCALATION; X-RAY-DIFFRACTION; CORROSION PROTECTION; TARTARIC ACID; FILMS; COATINGS; AA2024-T3; BEHAVIOR; ELECTROLYTES

subject category

Chemistry

authors

Mata, D; Serdechnova, M; Mohedano, M; Mendis, CL; Lamaka, SV; Tedim, J; Hack, T; Nixon, S; Zheludkevich, ML

Groups

G3 - Electrochemical Materials, Interfaces and Coatings

Projects

MULTI-functional metallic SURFaces via active Layered Double Hydroxide treatments (MULTISURF)

CICECO - Aveiro Institute of Materials (UID/CTM/50011/2013)

acknowledgements

This work has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement no. 645676 project MULTISURF. Dr M. Mohedano is grateful to MICINN (Spain) for financial support via Proyecto Retos Jovenes Investigadores MAT2015-73355-JIN. Dr S. V. Lamaka acknowledges the financial support of Alexander von Humboldt Foundation via Experienced Researcher Grant. Dr J. Tedim thanks FCT for the researcher grant IF/00347/2013. This work was developed in the scope of the project CICECO - Aveiro Institute of Materials, POCI-01-0145-FEDER-007679 (Ref. FCT UID/CTM/50011/2013), financed by national funds through the FCT/MEC and when applicable co-financed by FEDER under the PT2020 Partnership Agreement. Dr D. Mata would like to thank Dr Nico Scharnagl for the Raman scientific discussions. Authors acknowledge Mr Maksim Starykevich for carrying out the GDOES analyses.