C. I. Elsner

Evaluation of steel/primer based on chestnut tannin/paint film systems by EIS

The influence of a tannin pretreatment applied to slightly rusted steel panels on the anticorrosive performance of alkyd paint systems has been investigated using electrochemical impedance spectroscopy (EIS) and open circuit potential measurements. From EIS and corrosion potential data analysis it was found that (1) there is not a significant influence of the tannin pretreatment on the anticorrosive protection level, which depends particularly on the barrier effect afforded by the applied paint system (however, as the corrosion process starts, tannins may cause the repassivation of steel); (2) the enhancement of the protection level afforded by the tannin primer was restricted to short immersion periods and corrosive media that were not very aggressive; and (3) water uptake was not significantly affected by the presence of the tannin primer.

Atmospheric corrosion of painted galvanized and 55 % Al-Zn steel sheets: results of 12 years of exposure

Zinc or 55%Al-Zn alloy-coated steel sheets, either bare or covered by different painting systems, have been exposed for 12 years to the action of the urban atmosphere at the CIDEPINT station located in La Plata (34° 50′ South, 57° 53′, West), province of Buenos Aires, Argentina. The samples exposed surface was evaluated through periodical visual inspections, standardized adhesion tests, and electrochemical impedance measurements. The ambient variables monitored were average annual rains and temperatures, time of wetness, sulphur and chloride concentration, relative humidity, and speed and direction of the winds. It was found that in this atmosphere, the corrosion resistance of the bare 55% Al-Zn/steel sheets was higher than of the galvanized steel, and the polyurethane painting system was more protective than the alkyd and epoxy ones, which degraded after 6-7 years of exposure.

Correlation between accelerated tests and outdoor exposure of coil coated chromate and chromate free systems

Abstract Despite the good corrosion resistance of chromate coatings, there is a general agreement in eliminating the Cr(VI) compounds for corrosion protection owing to their health hazards. Coil coaters are looking for maintained or improved anticorrosion properties. Therefore, coil coated materials painted with conventional polyester topcoat and with either standard strontium chromate or water based epoxy Cr(III) primer were evaluated through a battery of accelerated and outdoor exposure tests. Physicochemical properties, corrosion potential and electrochemical impedance were measured before and after exposure of coated panels in salt spray, humidity or weathering chambers. Experimental results showed that the conventional chromatised polyester primer/polyester topcoat system provides better protective properties than the water base epoxy primer with Cr(III)/polyester system. This was also observed in replicated panels exposed outdoor but just after two years. The protection mechanism was analysed on the basis of the experimental results and the applied formulation type.

Study of Commercially Available Epoxy Protective Coatings by Using Non-Destructive Electrochemical Techniques

SAE 1020 steel panels coated with different thicknesses of either epoxybituminous or epoxy enamel films of commercial quality in a naturally aerated 3% NaCl solution were investigated. The progression of corrosion as a function of exposure time was studied with electrochemical impedance spectroscopy and corrosion potential measurements. Simultaneously, böth the salt spray cabinet test (ASTM Standard D 117/79) and the monitoring of the rusting grade (ASTM Standard D 610/85) were also performed. Based on the overall experimental results, the coatings have been ranked in terms of the effectiveness of their anticorrosive properties in a chloride containing electrolyte. Furthermore, a comparison of the visual assessment, water permeability, impedance and corrosion potential data indicates that the nondestructive and fairly straightforward electrochemical techniques are a very powerful tool for studying the highly complex metal/organic coating/aqueous electrolyte interface.

Effect of the Cathodic Protection on Coated Steel/ Artificial Sea Water Systems

In normal corrosion, the current required for the complementary cathodic reaction is supplied by electrons coming from the dissolution of the anodic metallic surfaces; however, such electrons can also be obtained by an external source (impressed current system). In the latter case, for protecting buried or submerged metallic structures against corrosion, the necessary current is transported from the anode (either active or inert) to the mentioned structure in such a way as to turn it totally cathodic. Taking these concepts into account, the influence of the cathodic protection on the physicochemical behaviour of some carbon steel/organic coating/artificial sea water systems, for different type and thicknesses of epoxydic coatings as well as cathodic potential values was investigated. In order to accelerate the tests, several coated samples were scratched in different places. It was concluded that data obtained from both the accelerated electrochemical laboratory tests and the normalized procedures afford a fairly reasonable performance prediction about the painting scheme-cathodic protection compatibility under specific operation conditions.