Über den Mechanismus der Lochfraßkorrosion bei Aluminium

On the mechanism of pitting corrosion of aluminum In an extensive study the dependencies of the pit growth of aluminum on time, potential and electrolyte conductivity have been quantitatively analysed. From this analysis it could be concluded that the pit growth kinetics is governed by the ohmic potential drop inside the pit. This explains the square-root time law experimentally found for the pit growth and the low activation energy of 3.14 kcal/mole. Moreover this analysis led to the conclusion that pitting is caused by a primary change of the properties of the pit surface due to the adsorption of chloride ions, since high local composition changes are prevented by the gas bubbles generated in the pits increasing the mass transport enormously, and since the total ohmic potential drop inside and outside the pits can not be larger than the difference between the actual potential and the pit growth limiting potential. Additional statements refer to the reaction order of the chloride ions, to the minimum chloride concentration for pitting and to the influence of pH and motion of the electrolyte.