Investigation of the corrosion behavior of carbon steel coated with fluoropolymer thin films

Hydrophobic thin fluoropolymer films were deposited on carbon steel specimens using inductively coupled radio frequency plasma. Octafluorocyclobutane (C4F8) was used as gas source. The anticorrosion resistance of the deposited films in 3% sodium chloride aqueous solution was estimated using X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), scanning electron microscopy (SEM) as well as by electrochemical techniques. Results have shown that a 90 nm fluoropolymer film shows the optimal film thickness in terms of adhesion stability and corrosive resistance. Upon aging in 3% sodium chloride aqueous solutions for a week a decrease of the fluorine concentration together with a layer-by-layer delamination of the polymer coating was observed together with some coating oxidation. A thin polymer film of about 9 nm remained on the steel interface which proved to stay unaltered over a period of a month. This makes the fluoropolymer film interesting as protective layer of metal and metal oxides.

Research Highlights
► Hydrophobic thin fluoropolymer coatings on carbon steel.
► Formation by inductively coupled RF plasma using octafluorocylcobutane.
► Investigation of the corrosion resistance in 3% sodium chloride aqueous solution.
► A 90 nm thick fluoropolymer film showed optimal mechanical and corrosive behavior.
► Layer-by-layer delamination together with coating oxidation and defluorination were observed with time.