1,721,016 research outputs found
Characterization and corrosion performance of poly(pyrrole-siloxane) films on commercial Al alloys
No full textAn alternative approach was developed for the surface treatment of as-received commercial aluminium alloys 6082-T6, 5083-H111 and 2024-T3 by using a pyrrole-based silane. One immersion step is sufficient for poly(pyrrole-siloxane) film deposition, with good adhesion and desirable morphological features. The combination in a single coating of polysiloxane linkages, acting as a barrier for aggressive species penetration towards the metal surface, and polypyrrole units manifesting active anodic protection, together with high degree of compactness, explains the significantly improved corrosion protection of the composite film in comparison to simple coatings of polymethylsiloxane and polypyrrole
Pyrrole-based silane primer for corrosion protection of commercial AA 2024 T3
No full textAn alternative approach was developed for surface treatment of as-received commercial AA 2024 T3 by using a pyrrole-based silane (SiPy). For film deposition, just one immersion step is enough, followed by curing. SiPy layer structure contains both polysiloxane bonds and pyrrole oligomers, with some degree of doping, giving a highly coherent layer. The superior film quality with respect to simple polysiloxane, is probably the main reason for the better corrosion performance obtained for SiPy on 2024
Electrochemical approach to repassivation kinetics of Al alloys : gaining insight into environmentally assisted cracking
No full textThis work provides a broad overview of the systematic experimental studies conducted in our group to understand the factors governing the transition to a more occluded corrosion front during the repassivation of Al alloys, manifested by the appearance of an inflection during anodic polarization into the active region in NaCl solutions. The collected data and the derived empirical relationships enabled us to discern the thermodynamic and kinetic aspects controlling the transition to more occluded local damage. From the thermodynamic standpoint, the potential at the inflection, namely, the pit transition potential Eptp, can be considered as the thermodynamic driving force of Al dissolution in the acidified pit-like solution in contact with a freshly created surface. The associated current density iptp and the steepness of the potential decrease with current below Eptp are determined by interfacial electrochemical kinetics. More importantly, all these properties are influenced by electrochemical and metallurgical events, including residual stresses. These findings point to the electrochemical approach in combination with external mechanical load as a promising tool for investigating environmentally assisted cracking, in particular, crack nucleation and non-steady crack tip processes
Study of Al alloy corrosion in neutral NaCl by the pitting scan technique
No full textThe corrosion behavior of commercial Al alloys was studied in neutral 0.6 mol L(-1) NaCl by using single-cycle polarization. Qualitative interpretation of pitting scans in both deaerated and naturally aerated NaCl solution, with the aid of corrosion morphology characterization, allowed for inference of the features of localized corrosion as a function of Al substrate nature. Electrochemical characteristic parameters such as pitting (E(pit)), repassivation or protection (E(prot)) potentials and pit transition potential (E(ptp)) were determined. The validity of the difference Delta E = vertical bar E(pit)-E(prot)vertical bar as criterion for susceptibility to localized corrosion of aluminium alloys is discussed
Pyrrole-based silane primer for corrosion protection of commercial Al alloys. Part 1, Synthesis and characterization
No full textChromate-free. direct-to-metal treatment using a pyrrole-based silane (PySi) was developed for protection against corrosion of as-received commercial wrought Al alloys of the series 1xxx, 2xxx, 5xxx and 6xxx. The metal surface was modified following the simple procedure for silane deposition by immersion in PySi hydrolyzed solution and curing. The spectroscopic characterization indicates that crosslinked composite PPySi network, containing both polysiloxane and polypyrrole units due to co-polymerization of PySi molecules. is produced by self-assembling of PySi soluble macro-oligomers onto the metallic substrates upon adsorption, with three-dimensional crosslink during heat treatment. Highly ordered well-packed and adherent PPySi film of the order of microns is obtained by just one immersion step in PySi primer. Control coatings of polymethylsiloxane (PMeSi) and polypyrrole (Ppy), the latter synthesized electrochemically, were investigated in parallel. (C) 2009 Elsevier B.V. All rights reserved
Pyrrole-based silane primer for corrosion protection of commercial Al alloys. Part 2, Corrosion performance in neutral NaCl solution.
No full textA chromate-free, direct-to-metal treatment using pyrrole-based silane (PySi) was developed for protection against corrosion of as-received commercial Al alloys, following the typical procedure for silane deposition. The protection performance of composite PPySi films, containing polysiloxane linkages and polypyrrole units, was evaluated in near neutral NaCl solution by simple corrosion tests such as single-cycle anodic polarization, corrosion potential monitoring and long-term immersion experiments. Control coatings of polymethylsiloxane (PMeSi) and electrochemically synthesized polypyrrole (Ppy) were also studied. The superior performance of PPySi with respect to PMeSi and Ppy was attributed to highly crosslinked, well-packed and adherent composite films of thickness of the order of microns, manifesting both barrier action and active protection. The use of pyrrole-based silane for corrosion protection of Al alloys constitutes a promising approach for effective replacement of chromium-based treatments in practical applications. Further investigation from the fundamental point of view is deserved
Electrocatalytic activity for hydrogen evolution of polypyrrole films modified with noble metal particles
No full textPolypyrrole (Ppy) films of various thicknesses contg. particles of noble metals such as Pt, Ru and Ir were electrosynthesized on the surface of austenitic stainless steel (Ss). Two different approaches were applied: (i) electrodeposition of a polymer film from a soln. already contg. an anionic metal complex, followed by potentiodynamic or galvanostatic redn.; and (ii) presynthesized Ppy films modified by galvanostatic electrodeposition of noble metals from solns. of the metal complexes. Surface morphol. and compn. of the resulting layers were studied by means of SEM and XPS. The electrocatalytic activity of the modified electrodes for the hydrogen evolution reaction (her) was tested in 0.05 M H2SO4 by means of potentiodynamic techniques (0.5 mV s-1)
Corrosion of Mg alloy in the presence of ammonium ion : evidence of hydride sub-products
No full textCorrosion of AZ31 Mg alloy was systematically investigated by different experimental approaches in the presence and in the absence of NH4+. Remarkable reactivity of Mg/NH4+ system was manifested by copious evolution of hydrogen over a dark corrosion film, associated to active deprotonation of complex Mg hydrides, more likely bridged Mg2+(AlH4-)2Mg2+(H-)2 complexes covered by a skin of MgO. Metastability of hydride phases is favored in the presence of species that alter the equilibrium dissociation of water, such as NH4+ and SO42-. Chemical recombination of hydrogen atoms of oxidic Mg hydrides is proposed as the kinetically determinant process
Effect of chloride concentration, pH and dissolved oxygen, on the repassivation of 6082-T6 Al alloy
No full textThe effect of chloride concentration, pH and dissolved oxygen on the repassivation behaviour of 6082-T6 Al alloy, was investigated using single-cycle anodic polarization. Pitting taking the place of intergranular attack was obtained with increasing Cl- concentration and solution pH, as well as under continuous bubbling of O-2. An inflection in the reverse curve at the pit transition potential E-ptp shows correlation with pit bottom repassivation, leading to concentration gradients for mass transport and promoting further pit nucleation. The close relation between E-pit and E-ptp was confirmed, though the latter is likely characteristic of the acidified pit-like solution in contact with a freshly created new surface. The associated current density i(ptp) is determined by the rate at which hydrolysis equilibrium is reached at a critical concentration of Al3+. The transition onset during repassivation was more marked for conditions favouring formation at the pit bottom of a solid layer, though poorly protective due to aluminium oxychloride intermediates. The steepness of potential decrease after the transition, related to a periodic active/passive sequence, is determined by Al dissolution controlled by proton reduction
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