Formation of ultrathin protective coatings on low-carbon steel from borate buffer-dodecylphosphonic acid solution

In the presence of dodecylphosphonic (DDP) acid emulsion in a borate buffer electrolyte (pH 7.3), the critical passivation current on the electrodes made of a low-carbon steel (St3) is found to decrease. The minimal critical passivation current values are reached when the DDP acid emulsion is present in the electrolyte already at the stage of cathodic polarization, which precedes the electrochemical measurements. It is found that the decrease in the critical passivation current to the values, which cannot be experimentally determined in the presence of DDP acid, is not accompanied by the formation of surface oxides. Therefore, the phenomenon can be considered as nonoxide passivation.