The influence of carbon dioxide on the aqueous corrosion of steel

The corrosion behaviour of mild steel, platinum, nickel, copper and lead in 4% NaCl deaerated acidified solution was studied.  Another investigation on these metals was made in solution saturated with CO 2 to see the effects of CO 2 partial pressure and temperature on the cathodic  hydrogen  evolution reaction. Polarization curves in different conditions were determined and different values of limiting and exchange  current  densities were measured. It was found that the limiting current density I L increases by the introduction of CO 2 to each one of the metals investigated. The increase is either due to a pH or a temperature effect, assuming no effect of gas bubbling.  It was confirmed that the limiting current does not depend on the nature of the material used as a working electrode. The exchange current density of the cathodic hydrogen reaction was found to be metal electrode and solution pH dependent. The analysis of the activation energy shows that the increase in exchange current could be due to a pH or a temperature effect,  depending on the nature of the material studied. There was an increase in the exchange current density I 0 by the introduction of CO 2 to the systems investigated. The corrosion rates on steel, nickel, copper and lead were calculated in the presence and absence of CO 2 and found to increase in the presence of CO 2 .  However, platinum does not corrode but the limiting current density of the hydrogen reaction increased by the introduction of CO 2 .