Absorption of water and corrosion performance of a clear and pigmented epoxy coating on Al-2024 alloy

The corrosion performance of Al-2024 substrates coated with an epoxy clear coating and a pigmented epoxy coating was investigated. The absorption of water in the pigmented coating was high compared to the clear coating. The clear coating provided a good barrier which is stable beyond 120 days of immersion in a 0.5 M NaCl solution. The shape of the Nyquist plot of the pigmented coating changed with immersion time and reveals the existence of physico-chemical processes in the coating and/or at the interface. Its impedance magnitude at low frequencies remained very high (~ 109 .cm2) after 72 days of immersion in sodium chloride solution. Both coatings exhibited good dry adhesion on Al-2024. The wet adhesion of the clear coating was poor while the stress (~ 9 MPa) required in a pull off adhesion test of the wet pigmented coating remained high

Reversed micelle synthesis of Ag/polyaniline nanocomposites via an in situ ultraviolet photo-redox mechanism

Silver/polyaniline nanocomposites were synthesized in reversed micellar solution, and the reaction was performed via in situ reduction of silver nitrate in aniline by photolysis. The nanocomposites were characterized by ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, thermo-gravimetric analysis, differential scanning calorimetric analysis, and electrochemical methods. The results showed that the Ag/polyaniline nanocomposites are composed of nano-sized particles of 15–30 nm that contain Ag domains of 10–15 nm. The electrical conductivity of an Ag/polyaniline pellet is 95.89 S cm-1, whereas a polyaniline pellet is found to be 3.1 × 10-2 S cm-1. Ag/polyaniline composites also have a higher degradation temperature and specific capacitance, when compared with pure polyaniline. Potentiodynamic polarization showed the anodic shifting of the zero current potential and a lower exchange current density for the Ag/polyaniline composite. Compared with polyaniline, the Ag/polyaniline nanocomposite is a promising candidate for coatings with improved anticorrosion performance

Polyaniline/Ag nanocomposite synthesized by using aniline as dispersant and stabilizer of nanosilver sol

Polyaniline/silver (PANI/Ag) nanocomposite was successfully prepared by in-situ polymerization from nanosilver sol using aniline (An) as both dispersant and stabilizer and characterized by FT-IR, XRD SEM, TEM and electrochemical methods, respectively. The results showed that core-shelled composite particles of less than 100 nm were synthesized with PANI as shell formed around a core of silver nanoparticles at higher aniline levels. Compared to pure PANI, PANI/Ag nanocomposites have higher electrical conductivity (65.98 S/cm) and current response and capacitance as well. Potentio dynamic polarization showed the anodic shifting of zero current potential and a lower exchange current density for the PANI/Ag composite. Compared with PANI, the PANI/Ag nanocomposite is a promising candidate for coatings with improved anti-corrosion performance. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 201

Polyaniline/Ag nanocomposite synthesized by using aniline as dispersant and stabilizer of nanosilver sol

Polyaniline/silver (PANI/Ag) nanocomposite was successfully prepared by in-situ polymerization from nanosilver sol using aniline (An) as both dispersant and stabilizer and characterized by FT-IR, XRD SEM, TEM and electrochemical methods, respectively. The results showed that core-shelled composite particles of less than 100 nm were synthesized with PANI as shell formed around a core of silver nanoparticles at higher aniline levels. Compared to pure PANI, PANI/Ag nanocomposites have higher electrical conductivity (65.98 S/cm) and current response and capacitance as well. Potentio dynamic polarization showed the anodic shifting of zero current potential and a lower exchange current density for the PANI/Ag composite. Compared with PANI, the PANI/Ag nanocomposite is a promising candidate for coatings with improved anti-corrosion performance. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 201

Impedance evaluation of permeability and corrosion of Al-2024 aluminum alloy coated with a chromate free primer

The corrosion of AA-2024 aluminum alloy protected with a chromate free primer is investigated afterimmersion in a 0.5MNaCl aqueous solution. Thewater uptake by the coating increases continuouslywhenthe film, applied on an aluminum AA-2024 substrate, is placed in the 0.5MNaCl solution. This increase isattributed to corrosion reactions taking place at the alloy/coating interface when water molecules reachthe interface. The maximum water volume fraction absorbed by a similar coating applied on platinumsubstrate is 3.5 vol% and the permeability is 7.6¿0−12m2 s−1. After 72 h immersion in the 0.5M NaClsolution, the Nyquist representation of impedance data shows transmission line behavior that can beassigned to percolation pathway along the filler particles afterwater uptake. Charge transfer and diffusionof corrosion reactants and products occur, but no delamination was observed for immersion longer than172 h. Furthermore, the coating resistance is still close to 108 ??cm−2 after this immersion time. Thisaccounts for the good protective performance of the coating

Corrosion protection and delamination mechanism of epoxy/carbon black nanocomposite coating on AA2024-T3

The barrier property of a nanocomposite epoxy coating containing 1 or 1.25 vol% of carbon black (CB) applied on AA2024-T3 was investigated by using electrochemical impedance spectroscopy. Micro-electrochemical impedance spectroscopy and optical microscopy were also used to investigate the delamination of the nanocomposite coating containing 1.25 vol% carbon black (CB). A defect of about 500 µm in diameter was created in the composite coating as well as in the unfilled reference sample. The polarization resistance of the unfilled coating decreases 10 times faster than that of the composite. The blister size of the nanocomposite coating is also smaller after 200 h of immersion. It was concluded that the composite delaminates by a factor of ten slower compared to a similar unfilled coating. A protective mechanism was proposed in order to explain this observation. The presence of CB conductive pathways in the composite and the electrical contact between the coating and the substrate is helpful to delocalize electrons generated from the metallic part. After oxidation, electrons do not remain localized at the interface as they have the possibility to migrate into the coating through the CB percolation pathway. This reduces the rate of interfacial oxygen reduction and thus the rate of coating delamination

Influence of mixing ratio on the permeability of water and the corrosion performance of epoxy/amine coated un-pretreated Al-2024 evaluated by impedance spectroscopy

Water uptake by epoxy coatings was measured in 0.5 M NaCl soln. using a single frequency (1 kHz) capacitance method. The influence of substrates as well as the epoxy/amine mixing ratio on the water permeation coeff. was studied. Corrosion reactions at the coating/substrate interface affected the results of water uptake when the coating is applied on Al-2024 alloy. Consequently, the permeation coeff. of supported coating can be detd. accurately only if the coating is applied on an inert substrate. Excess of epoxy or amine improves the soly. of water in the coating. A low water permeation coeff. was obtained with an epoxy/amine mixing ratio 1.05/1. But this formulation has a relatively poor corrosion performance when applied on an un-pretreated Al-2024 alloy. Under-film corrosion which is the characteristic of defective coatings was obsd. using electrochem. impedance spectroscopy. [on SciFinder (R)

Wet adhesion of epoxy–amine coatings on 2024-T3 aluminum alloy

To explore the influence of the molar epoxide-to-amine ratio E/NH on the coating adhesion strength, samples with E/NH ratios ranging from 0.6 to 1.4 were prepared and fully cured. Coatings with an E/NH value of 1.0 appeared to have the highest Tg and cross-link density, and the lowest water absorption ability, which was proved to be independent from solubility or free volume effects. Being verified by the classic "cross-hatch" and the more quantitative pull-off tests, the wet adhesion of coatings was found to be significantly influenced by the epoxide content. Excess epoxide groups highly likely to favor the formation of stronger adhesive bonding at coating–metal interface. No clear correlation could be established between the coating adhesion strength and their cross-link density and water-uptake. In addition, the measurements of the thermal expansion coefficients of substrate and coatings revealed the presence of a tensile internal stress, which is more pronounced for stoichiometric samples. The existence of compressive internal stress induced by water uptake was also confirmed by the adhesion tests on samples which were immersed in water for two days. In these samples, a partial recovery of adhesion strength was found, after the samples were dried for two days, indicating that the compressive internal stress deteriorated the load-bearing properties of adhesive bonds and contributed to debonding. This influence becomes larger as the coating thickness increases as well as the E/NH off-stoichiometry increases. Interestingly, for the samples possessing excess epoxide functional groups, a higher degree of recovery was obtained. This was not the case for coatings with excess amine, confirming that specifically the epoxide groups facilitate the formation of strong bonds against water at the polymer–metal interface

Anticorrosion coating for an alloy

The invention relates to a coating comprising a resin and electron-conductive particles dispersed in the resin, wherein the coating is not ion-conductive and the coating has a specific electrical resistivity of from 102 to 1010 Q-cm. The invention further relates to an Al or Al alloy substrate provided with the coating, wherein the resistivity between the substrate and the coating is at most a factor 200 higher than that of the coating