The cathodic corrosion of aluminium during the electrodeposition of paint: Electrochemical measurements

The cathodic electrodeposition of paint on metals proceeds under the influence of an alkalization of the diffusion layer, which is caused by the cathodic reduction of water to yield hydrogen. Three independent electrochemical methods, namely the rotating cone electrode at constant current density, chronopotentiometry and cyclic voltammetry, both at stationary electrodes in stagnant electrolytes, were employed to study the influence of cathodic corrosion of aluminium. It generates initially aluminate as a corrosion product. It was found that the tendency for electrocoagulation is strongly enhanced at AI surfaces in comparison to steel. This is attributed to a higher efficiency due to the in situ formation of intensively dispersed aluminium-oxidhydrate through hydrolysis of the aluminate anions. Thus, the electrocoagulation process is not only an acid/base-reaction with the macro-ions: p-NR(2)H(+) + AlO2- --> p-NR(2) down arrow +AlOOH down arrow, but the presence of AlOOH nuclei improves the formation of a new polymer phase.