Fouling and Corrosion Properties of SiO2 Coatings on Copper in Geothermal Water

Two critical problems in geothermal utilization are corrosion and fouling on the surfaces of plants and fittings, and use of surface coatings is a good method to overcome such difficulties. Silica coatings with film thickness of several hundred nanometers on copper substrates were prepared by the liquid-phase deposition technique and characterized with respect to surface morphology, composition, surface free energy, roughness, and film thickness. Examinations of both fouling in calcium carbonate solution and corrosion in corrosive geothermal water on the surfaces of SiO2-coated samples were performed. The results showed that the fouling rate on the SiO2-coated surface was obviously reduced compared with that on the polished surface. Moreover, the inhibition of corrosion on the modified surface was found even though, after a long immersion time, the corrosion resistance action decreased because of the surface peeling of SiO2-coated samples. The corrosion behavior of the SiO2 coating was further studied with electrochemical measurements by electrochemical impedance spectroscopy. This work suggests a new possibility for solving the fouling and corrosion issues encountered in the use of geothermal water.