Passivation of iron in soil with cathodic protection

A study was made of cylindrical electrodes 20 mm in diameter made of Armco iron. The working surface was a polished and degreased end of a cylinder facing upwards, and the non-working surface was insulated. Electrodes were placed in the center of the bottom of a cell made of plexiglass 100 x 100 x 100 mm in size. The working media was carefully washed river sand with moisture content W = 10% (water unsaturated soil) or 20% (water-saturated soil), and also tap water used for wetting the soil. Anodic polarization curves were recorded with a delay of 15 min at each prescribed potential. Under certain cathodic polarization conditions for iron in water-saturated soil (with thorough gas channels) it was possible to provide metal passivation. The data obtained point in favor of assuming a correlation of this effect with the different thickness of the diffusion layer for O2 molecules and OH--ions.