EIS investigation of a C e‐based posttreatment step on the corrosion behaviour of Alclad AA2024 anodized in TSA (original) (raw)
Related papers
CORROSION
To protect Al alloys from corrosion, standard procedures in the aerospace industry use chromium-based acid anodizing with subsequent post-treatment steps also containing hexavalent chromium (Cr(VI)) ions. However, environmental and health related concerns associated with Cr(VI) have encouraged the search for new surface treatments providing effective corrosion protection without the drawback of generating toxic residues. In this investigation, a hydrothermal treatment in aqueous solution with cerium ions is proposed as a post-treatment for tartaric-sulfuric acid (TSA) anodizing, and its effects on the AA2524-T3 alloy corrosion resistance investigated. The effect of Ce on the characteristics of the surface film formed, such as morphology and corrosion resistance, is investigated by scanning electron microscopy and electrochemical impedance spectroscopy (EIS). The results show that the hydrothermal treatment in solution containing Ce(III) ions presents a less stable behavior than the treatment in boiling water. However, the results of the EIS experiments show recovery of the protective properties of the system, indicating that some self-healing properties must be imparted to the system.
CORROSION, 2019
To protect Al alloys from corrosion, standard procedures in the aerospace industry use chromium-based acid anodizing with subsequent post-treatment steps also containing hexavalent chromium (Cr(VI)) ions. However, environmental and health related concerns associated with Cr(VI) have encouraged the search for new surface treatments providing effective corrosion protection without the drawback of generating toxic residues. In this investigation, a hydrothermal treatment in aqueous solution with cerium ions is proposed as a post-treatment for tartaric-sulfuric acid (TSA) anodizing, and its effects on the AA2524-T3 alloy corrosion resistance investigated. The effect of Ce on the characteristics of the surface film formed, such as morphology and corrosion resistance, is investigated by scanning electron microscopy and electrochemical impedance spectroscopy (EIS). The results show that the hydrothermal treatment in solution containing Ce(III) ions presents a less stable behavior than the treatment in boiling water. However, the results of the EIS experiments show recovery of the protective properties of the system, indicating that some self-healing properties must be imparted to the system.
Applied Surface Science, 2020
The effect of temperature of a Ce-H 2 O 2 post-treatment on the corrosion resistance of clad AA2024-T3 anodized in tartaric-sulfuric acid as well as the distribution of Ce oxyhydroxides in the anodized layer was investigated. Electrochemical impedance spectroscopy tests showed that samples post-treated at moderate temperatures (up to 50°C) presented more stable and slightly higher impedance modulus than untreated ones. Increasing the posttreatment temperature to 75°C decreased the corrosion resistance, likely due to damaging of the porous and barrier layer protective properties, as indicated by electric equivalent circuit fitting. Scanning electron microscopy characterization showed that Ce oxyhydroxides deposition (3+ and 4+ oxidation states as determined by X-ray photoelectron spectroscopy) was enhanced with increasing post-treatment temperature, and that pores were not blocked. Glow Discharge Optical Emission Spectrometry and Rutherford Backscattering Spectrometry analyses indicated local enrichment of Ce species at the bottom of the pores, whereas scanning transmission electron microscopy confirmed the presence of Ce-containing nanoparticles stuck to the pore's walls. Analyses of corroded samples showed increased amounts of Ce oxyhydroxides on the surface and that Ce species remained inside the pores, indicating that the post-treatment protocol successfully and durably incorporated Ce ions within the structure of the anodized layer.
2016
Many industries use chromium-based anodizing processes with a subsequent sealing post-treatment containing hexavalent chromium ions to protect Al alloys. However, this method of protection causes large environmental and health related problems. This has encouraged the search for new surface treatments for metals with the requirements of effective protection against corrosion and generation of non-toxic residues to the environment. Recent studies are pointing towards chromium free anodizing processes, specifically the tartaric-sulfuric acid (TSA) one, as a viable alternative. Besides, sealing treatments of the Al anodic layer in chromate solutions are another source of toxic residues and their replacement for environmentally friendly alternatives are also of great interest. Surface treatments with cerium ions are being largely studied for the corrosion protection of Al alloys due to their good anticorrosion properties associated to the lack of toxic residues generated. In this invest...
Journal of the Serbian Chemical Society, 2013
Dip-immersion is simple and cost-effective method for the preparation of Ce-based conversion coatings (CeCCs), a promising alternative to the toxic chromate coatings, on the metal substrates. In this work CeCCs were prepared on Al-alloy AA6060 from aqueous solution of cerium chloride at room temperature. Effect of immersion time and post-treatment in phosphate solution on the microstructure and corrosion properties of the coatings was studied. The longer immersion time, the thicker but nonhomogeneous and cracked CeCCs. The post-treatment contributed to the sealing of cracks, as proven by an increase in corrosion resistance compared with as-deposited coatings. CeCCs prepared at longer deposition time and post-treated showed much better corrosion protection than those prepared at short deposition time. A detailed EIS study was undertaken to follow the evolution of corrosion behaviour of CeCCs with time of exposure to aggressive chloride environment (3.5 % NaCl). For the sake of compar...
Evaluation of mechanically treated cerium (IV) oxides as corrosion inhibitors for galvanized steel
Electrochimica Acta, 2011
The use of cerium salts as corrosion inhibitors for hot dip galvanized steel has been object of a numerous studies in the last few years. The role of cerium ions as corrosion inhibitors was proved: cerium is able to block the cathodic sites of the metal, forming insoluble hydroxides and oxides on the zinc surface. This fact leads to a dramatic decrease of the cathodic current densities and, therefore, to a reduction the overall corrosion processes. On the other hand, the potential of cerium oxides as corrosion inhibitors was also proposed. However, the real effectiveness of this kind of anticorrosive pigments has not been clarified yet.
Cerium Compounds Coating as a Single Self-Healing Layer for Corrosion Inhibition on Aluminum 3003
Sustainability
The formation of cerium hydroxide was studied, and its capacity as a corrosion inhibitor on aluminum substrates was evaluated. These particles were deposited by immersing the substrate in a bath with cerium nitrate and hydrogen peroxide. Four different immersion times were used to determine the differences in behavior from low concentrations to an excess of particles on the surface. The coatings were analyzed morphologically by scanning electron microscope (SEM) and optical microscope, and chemically by energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). Electrochemical corrosion analysis was studied using cyclic potentiodynamic polarization (CPP), electrochemical impedance spectroscopy (EIS), and electrochemical noise (EN). The results show that for 2 and 5 min of immersion, there was corrosion inhibition caused by the presence of cerium Ce3+ in the coating, but with excess cerium hydroxide particles, corrosion was favored. The presence of cerium partic...
Transactions of the IMF, 2012
The effects of the anodising potential and of the combined addition of tartaric acid and cerium nitrate to a sulphuric acid anodising bath on the corrosion behaviour of high purity aluminium and on AA2024T3 aerospace aluminium alloy have been systematically investigated. It is found that the anodising potential is critical in determining the anticorrosion performance; lower potential generates finer pores that provide enhanced corrosion protection compared with the larger pores generated at higher potentials. At both anodising potentials, the addition of cerium nitrate alone to the sulphuric acid bath does not increase significantly the anticorrosion performance. Conversely, the addition of tartaric acid alone is generally beneficial. Finally, when cerium nitrate is added in combination with tartaric acid a further improvement of the corrosion resistance is observed.
Journal of The Electrochemical Society, 2016
Chromic acid anodizing has been used for almost a century to enhance corrosion protection of aerospace alloys. For some applications, hydrothermal sealing in hexavalent chromium-containing solution is required to enhance further the corrosion resistance but, due to environmental concerns, the use of hexavalent chromium must be discontinued. Good progress has been made to replace chromates during anodizing but comparatively less effort has focused on the sealing process. In this work, for the first time, electrochemical impedance spectroscopy (EIS) has been used to characterize in-situ the sealing processes occurring during hot water sealing, sodium chromate sealing and cerium sealing. The results suggest that the processes occurring during sodium chromate sealing are significantly different compared to hot water and cerium sealing. In particular, during chromate sealing, the porous skeleton is significantly attacked, suggesting that the anticorrosion performance is likely to arise from the residuals of chromate rather than from the improvement of the barrier properties. In contrast, during hot water sealing, little attack occurs on the porous skeleton, and the improved corrosion protection is due to the enhanced barrier effect. During cerium sealing, precipitation of cerium products occurs, providing an inhibitor reservoir, and little, if any, attack occurs on the pre-existing oxide.
Revista de Chimie
The corrosion protective ability of the electrodeposited mixed nanocrystalline (CeO2)x(Al2O3)1-x layers has been studied in 0.1M HNO3 solution as a function of the changing ratio between CeO2, CeAlO3 and Al2O3 on the modified SS surface. It was ascertained that the mixed layer changes substantially the character of the cathodic corrosion reaction, which leads to changes in the control of the corrosion process and stabilization of the passive state of the SS, the system (CeO2)x(Al2O3)1-x/SS respectively, in case of prolonged corrosion testing.