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The effect of carbon dioxide ͑CO 2 ͒ on the NaCl-induced atmospheric corrosion of copper was studied using in situ Fourier transform infrared microspectroscopy, in situ scanning Kelvin probe, and scanning electron microscopy/energy-dispersive analysis by X-ray. The copper surface was contaminated with a single NaCl particle and then exposed to 80 ± 2% relative humidity clean humidified air with two concentrations of CO 2 ͑Ͻ5 and 350 ppm͒. After formation of an electrolyte droplet secondary spreading of electrolyte from the peripherical parts of the droplet was observed. The secondary spreading effect, which was much larger at Ͻ5 ppm CO 2 than at 350 ppm, was a consequence of the formation of a galvanic element between a local cathode outside the edge of the droplet and an anode in the droplet. This lead to alkaline conditions in the secondary spreading area and transport of Na + ions to the local cathode. The large secondary spreading at low CO 2 concentration was possible due to lowering of the surface tension of the electrolyte/metal oxide interface at the peripheral parts of the droplet. Carbonate formation lowered the pH when the CO 2 concentration was 350 ppm and resulted in a decrease of the pH and inhibition of the secondary spreading.

Fourier transform infrared microspectroscopy has been used to provide a better understanding of filiform corrosion processes on coated aluminum alloys. Results from scanning Kelvin probe microanalysis are also presented. The investigations were performed on untreated or chromium-free pretreated AA6016 covered with an organic coating. An active head with a Volta potential approximately 400 mV lower than that of the tail of the filament was identified. The head was filled with a partially hydrolyzed aluminum chloride solution, containing monomeric and polymeric cations of aluminum, which are highly soluble and hygroscopic, and contain monomeric and polymeric cations of aluminum. The aluminum ions produced by the anodic reaction in the front of the head are hydrolyzed by the hydroxyl ions generated by the cathodic oxygen reduction, which occurs at the back of the head and the tail. Complete neutralization of the aluminum chloride solution in the back of the head and in the tail leads to the formation of an aluminum hydroxide gel. During the precipitation process, carbonate ions are also incorporated in the gel. A carbonate containing the mineral, dawsonite, was formed in the scratch. © 2002 The Electrochemical Society. All rights reserved.

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The aim of the present work was to study the influence of the stress on the electrode potential of the austenitic stainless steel301LN using Scanning Kelvin Probe (SKP). It was found that elastic deformation reversibly ennobles the potential whereas plasticdeformation decreases the potential in both tensile and compressive deformation mode and this decrease is retained even 24 h afterremoval of the load. To interpret the stress effects, different surface preparations were used and the composition and thickness ofthe passive film were determined by GDOES. Slip steps formed due to plastic deformation were observed using AFM. The effect ofplastic strain on the potential is explained by the formation of dislocations, which creates more a defective passive film.

QC 20160516

The adsorption of different ethoxysilanes on Al was studied. It was established that during polymolecular adsorption of ethoxysilanes from the vapor phase on aluminum the first monolayer is adsorbed irreversibly with adsorption van der Waals bonds between silane molecules and the aluminum surface. The covalent bonding of silanes with the surface (Al-0-Si bonds) occurs in the presence of adsorbed water on the aluminum surface. The presence of a silane monolayer on Al decreases water adsorption on the surface, and inhibits hydration of the oxide metal film. The formation of a negatively charged siloxane film on the aluminum surface inhibits local metal corrosion, and a positively charged layer activates it in chloride containing media. The formation of the surface siloxane polymer by the modification of metals inhibits the metal dissolution under polymer coatings. It is caused by silane chemisorption and negative charging of the metal surface. The presence of negatively charged groups causes difficulties of an electrostatic character for the migration of aggressive ions to the metal surface. 9-14, 1994.

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