Corrosion of pure aluminium in organic acid media in the presence and in the absence of chloride ions: Mass transport effects

The influence of mass transport on the corrosion behaviour of pure aluminium in 0.75% citric acid solution in the presence and in the absence of 104 ppm of chloride ions under anodic and cathodic polarisation was investigated with a rotating disk electrode and using electrochemical impedance spectroscopy. For anodically polarised electrodes, the impedance diagrams are composed of a high frequency (HF) capacitive loop followed by a low frequency (LF) inductive loop, whose shape and size are modified neither with immersion time nor with rotation speed. Addition of chloride ions causes a diminution of the diameter of the HF capacitive loop while the influence on the inductive loop cannot be clearly detected due to data scattering. Under conditions of cathodic polarisation, the diagrams present the shape described above, however, the diameter of both loops decreases with immersion time and electrode rotation speed.