해수 중 CO2 기체의 유입에 의한 환경 친화적인 전착 코팅막의 형성과 그 내식특성

Abstract

The peculiar feature of cathodic protection in seawater has the capability to form mineral calcareous depositssuch as magnesium and calcium on metal surfaces. It is assumed that OH− ions are generated close to themetal surface as a result of cathodic protection and generated OH− ions increases the pH of the metal/seawaterinterface outlined as the following formulae. (1) O2+ 2H2O + 4e→4OH−, or (2) 2H2O + 2e→H2+ 2OH−. Andhigh pH causes precipitation of Mg(OH)2 and CaCO3 in accordance with the following formulae. (1)Mg2++ 2OH−→Mg(OH)2, (2) Ca2++ CO32−→CaCO3. The focus of this study was to increase the amount ofCO32− with the injection of CO2 gas to the solution for accelerating process of the following formulae. (1)H2O+CO2→H2CO3, (2) HCO3−→ H++ CO32−. Electrodeposit films were formed by an electro-depositiontechnique on steel substrates in solutions of both natural seawater and natural seawater dissolved CO2 gaswith different current densities, over different time periods. The contents of films were investigated by scanningelectron microscopy(SEM) and X-ray diffraction(XRD). The adhesion and corrosion resistance of the coatingfilms were evaluated by anodic polarization. From an experimental result, only CaCO3 were found in solutionwhere injected CO2 gas regardless of current density. In case of injecting the CO2 gas, weight gain of electrodepositsfilms hugely increased and it had appropriate physical properties.