Effect of thermal post-treatment on the corrosion resistance of octadecylphosphonic acid thin films on galvanized steel surface

This study investigated the effect of post-treatment temperature (from 60 to 2001) on the composition, structure, protective and hydrophobic properties of thin films formed in an ethanol solution of octadecylphosphonic acid (C18P) on the galvanized steel surface, using a combination of techniques (corrosion tests, potentiodynamic voltammetry, contact angle measurement, X-ray photoelectron spectroscopy).It was established that the dependence of hydrophobic and protective properties of the alkylphosphonate film on post-treatment temperature exhibits an extreme character with a maximum at 100.The film prepared in 2.5 mM ethanolic C18P solution for 2 hours at 40 with subsequent post-treatment (drying) at 100 demonstrated maximum protective efficiency.Treatment of galvanized steel in this method superhydrophobizes its surface even without any special preliminary texturing.The thin alkylphosphonate film increases the corrosion resistance of galvanized steel by 26.8 times in 100% humidity atmosphere with moisture condensation on the metal surface, and by 49.3 times in salt spray atmosphere.The study confirmed chemisorption of C18P on the zinc coating with formation of an ultrathin (<10 nm) protective film consisting of ZnO, Zn(OH)2, zinc octadecylphosphonate, and physically adsorbed C18P molecules.