The corrosion behavior of copper in deaerated and oxygenated 0.1 H2SO4 solutions has been investigated using the rotating cylinder electrode under turbulent flow conditions. Potentiostatic polarization measurements were carried out at different bulk temperatures of 283, 288, 293 and 298 K and various speeds of rotation viz 100, 200, 300 and 400 r.p.m. The anodic dissolution of copper and the hydrogen evolution reaction, in deaerated and oxygenated solutions, are activation controlled processes dependent on the temperature of the solution. The anodic dissolution of copper is not mass transfer controlled. The results are consistent with a mechanism which suggests that oxidation of copper takes place in two steps of one electron each. The second step, i.e., cuprous ion (Cu+) oxidation, is the rate controlling. Moreover, the mechanism of hydrogen evolution reaction is a proton discharge upon the metal surface. The charge transfer of the oxygen reduction reaction is a 2e process in the range of bulk temperatures employed, i.e., the oxygen reduction is controlled by 2e process. Furthermore, the limiting current density value of the oxygen reduction reaction increases as the velocity of the fluid increases. The results, at a constant bulk temperature are consistent with Eisenberg et al theory for mass transfer to a rotating cylinder electrode surface.
The corrosion behavior of carbon steel in circulating cooling water (C.T.) of Al Doura Refinery and performance of sodium nitrite (SN) and sodium hexametaphosphate (SHMP) inhibitor blend for inhibition of such corrosion process have been investigated at different temperatures, i.e., 303, 313, 323 K. Weight loss experiment, under isothermal conditions, together with polarization method were carried out at 303, 313, and 323K using C.T., and make up with SN:SHMP (500:100) solutions. The results proved that the inhibition efficiency of the corrosion inhibitor used in this work is better than that obtained by the corrosion inhibitor used in C.T. of Al Doura Refinery and less effected by the change in temperature.
The inhibition of the oxygen reduction reaction on a carbon steel rotating cylinder electrode in naturally aerated 600 ppm Cl-solution was studied using an optimum inhibitor blend, i.e., Sodium Nitrite (SN): Sodium Hexametaphosphate (SHMP) = 500:100 obtained via a weight loss technique. Potentiostatic technique, then, was applied at different bulk temperatures and various flow rates using un-inhibited and inhibited solutions under isothermal and controlled conditions of heat transfer. In an un-inhibited solution and under isothermal conditions, with limiting conditions of concentration polarization, the limiting current density of oxygen reduction reaction is flow and temperature dependent. The charge transfer of the oxygen reduction reaction is a 4 electron process in the range of bulk temperature employed from 303 to 323 K. Under heat transfer conditions, the charge transfer is still 4 electron process up to 336 K interfacial temperature, above which the contribution of the 2 electron process appeared. Moreover, the limiting current density values of the oxygen reduction reaction in inhibited solutions is much lower than those under identical conditions in un-inhibited solutions. This confirms the inhibition of the cathodic reaction, i.e., the oxygen reduction reaction under isothermal and heat transfer conditions, due to SHMP.
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