Corrosion inhibition of aluminium by rare earth chlorides

The corrosion inhibition of pure Al due to addition of different concentrations of LaCl3 and CeCl3 in 3.5% NaCl solution has been investigated. Polarization resistance studies revealed that LaCl3 additions provided enhanced increase in surface resistance compared to CeCl3 additions, with maximum increase noted for 1000 ppm addition for both additions. Electrochemical impedance spectroscopy also revealed the improved corrosion resistance with inhibitor addition. The formation of precipitates of oxides/hydroxides of lanthanum and cerium on cathodic intermetallic sites at low inhibitor concentration and the overall surface at high inhibitor concentration was confirmed by scanning electron microscopy. There was a difference in the morphologies of the rare earth oxides/hydroxides precipitated on the surface of pure Al, with CeCl3 addition resulting in faceted precipitates and LaCl3 addition in fine globular precipitates.