Passivation of low-carbon steel with sodium dodecylphosphonate for protection against atmospheric corrosion

The efficiency of passivation of St3 low-carbon steel in an aqueous solution of sodium dodecylphosphonate (C12PNa) for protection against atmospheric corrosion was studied. In particular, the effect of passivation conditions (inhibitor concentration in the passivating solution, temperature of the passivating solution and subsequent drying, and duration of treatment) on the protective properties of films formed in the presence of alkylphosphonate was studied. The paper presents the results of accelerated corrosion tests under neutral salt spray atmosphere and atmosphere of 100% humidity with daily condensation of moisture on the samples, measurements of the water contact angle (Phi(c)). It was found that in an aqueous solution of C12PNa an thin hydrophobic layer with Phi(c)=97 degrees is formed on the surface of mild steel, which significantly increases its corrosion resistance in atmospheres of different corrosivity. The protective properties of the alkylphosphonate film are enhanced by increasing the temperature of a solution of C12PNa, the duration of treatment and the drying temperature. The use of the layer-by-layer method of producing thin films allows one to increase the efficiency of passivation of St3 steel with C12PNa without increasing its duration. The protective film obtained on the steel surface in a 2.5 mM solution of C12PNa for 120 minutes at a solution temperature and at temperature of subsequent drying equal to 80 degrees C using the layer-by-layer method has the highest anti-corrosion efficiency under atmospheric conditions.