Corrosion behaviors of polysiloxane-ferroferric oxide coating coated on carbon steel in NaCl solution and geothermal water

Corrosion from plants and pipelines made of carbon steel is a severe problem for the utilization of geothermal energy. In order to control corrosion, various polysiloxane-ferroferric oxide composite coatings were successfully fabricated on carbon steel substrates. The morphologies and chemical compositions of these composite coatings were characterized. The thermal stability was tested by thermal gravity analysis (TGA). Wettability was investigated by contact angle measurement. Equivalent thickness was measured by weight method. The corrosion behaviors of composite coatings were tested by potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) in 3.5 wt.% NaCl solution and simulated geothermal water of Huabei oilfield. According to potentiodynamic polarization curve and EIS, the inhibition of corrosion for each carbon steel coated with composite coating is improved, because the corrosion current density decreases by one or two orders of magnitude. Corrosion mechanism for carbon steel coated with composite coating was analyzed with EIS measurement and equivalent circuit simulation. TGA of various polysiloxane coatings shows less than 8% weight losses for all polysiloxane coatings tested at 300 degrees C. The composite polysiloxane coatings show good corrosion resistance and thermal stability.