해수 중 CO2기체의 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 deposits such as magnesium and calcium on metal surfaces. It is assumed that <TEX>$OH^-$</TEX> ions are generated close to the metal surface as a result of cathodic protection and generated <TEX>$OH^-$</TEX> ions increases the pH of the metal/seawater interface outlined as the following formulae. (1) <TEX>$O_2+2H_2O+4e{\rightarrow}4OH^-$</TEX>, or (2) <TEX>$2H_2O+2e{\rightarrow}H_2+2OH^-$</TEX>. And high pH causes precipitation of <TEX>$Mg(OH)_2$</TEX> and <TEX>$CaCO_3$</TEX> in accordance with the following formulae. (1) <TEX>$Mg^{2+}+2OH^-{\rightarrow}Mg(OH)_2$</TEX>, (2) <TEX>$Ca^{2+}+CO{_3}^{2-}{\rightarrow}CaCO_3$</TEX>. The focus of this study was to increase the amount of <TEX>$CO{_3}^{2-}$</TEX> with the injection of <TEX>$CO_2$</TEX> gas to the solution for accelerating process of the following formulae. (1) <TEX>$H_2O+CO_2{\rightarrow}H_2CO_3$</TEX>, (2) <TEX>$HCO^{3-}{\rightarrow}{H^+}+CO{_3}^{2-}$</TEX>. Electrodeposit films were formed by an electro-deposition technique on steel substrates in solutions of both natural seawater and natural seawater dissolved <TEX>$CO_2$</TEX> gas with different current densities, over different time periods. The contents of films were investigated by scanning electron microscopy(SEM) and X-ray diffraction(XRD). The adhesion and corrosion resistance of the coating films were evaluated by anodic polarization. From an experimental result, only <TEX>$CaCO_3$</TEX> were found in solution where injected <TEX>$CO_2$</TEX> gas regardless of current density. In case of injecting the <TEX>$CO_2$</TEX> gas, weight gain of electrodeposits films hugely increased and it had appropriate physical properties.