ELECTROCHEMICAL BEHAVIOR OF ALUMINUM ANODE IN A CHLORIDE-CONTAINING ELECTROLYTE AND ITS QUANTITATIVE CHARACTERISTICS

The electrochemical behavior of aluminum in a chloride-containing medium was studied. An aluminum electrode was polarized using a potentiostat-galvanostat in the galvanostatic mode at a current density of 0 to 400 μA/cm2. To assess the electrochemical behavior of the aluminum anode, chronopotentiograms obtained during anodic polarization and in its absence were analyzed. The minimum and maximum values of the potential, its average value, averaged amplitude and frequency of oscillations during a given period of polarization time were determined. In the chronopotentiograms in the absence of polarization (j = 0), oscillations of the electrode potential with a frequency of 0.18 Hz are observed. At low current densities (1-5 μA/cm2), the frequency of potential oscillations lies in the range of 0.18 - 0.25 Hz, which may indirectly indicate a certain number of metal surface areas on which periodic activation-passivation processes occur, accompanied by the formation of individual corrosion foci. With further increase of current density (7 - 50 μA/cm2) fluctuations of potential of practically the same frequency range are recorded: 0.18-0.28 Hz, with drift of average potential value towards more positive values. At the same time, occurrence of some number of stably functioning local corrosion centers on the surface of the studied samples is noted. The amplitude of oscillations is within 10±4 mV and decreases only with increase of current density to 400 μA/cm2. Analysis of the obtained results allows to draw a conclusion about average value of frequency of potential oscillations of about 0.2 Hz with preservation of amplitude and shift of average potential values towards more positive values with increase of current density. The latter can be connected with periodic violation of continuity of passive layer, accompanied in case of relatively high densities of anodic current (˃10 μA/cm2) by stable development of corrosion centers, confirmed by microimages of metal surface.