Carbon steel has wide applications in industry (especially in petroleum industry, e.g. pipelines out from the top of distillation towers (over head pipes), pressure vessels, nozzles etc.) and domestic life. Study the phenomenon of electropolishing which is important as metallic finishing process which takes place before electroplating of metal. This work is devoted to study the electropolishing of carbon steel in phosphoric acid in presence of polymers molecules (Starch, Gelatin, Agar, Chitosan, Arabic gum, Cellulose acetate, Cellulose and Carboxymethyl cellulose sodium salt). The rate of electropolishing of carbon steel in phosphoric acid solution in case of applied various affecting factors was investigated by estimated polarization curves from values of current and voltage that were obtained from the electrochemical cell. Morphology of the specimens after the experiment is monitored using scanning electron microscope (SEM). The (SEM) micrographs support the experimental measurements and give more light on carbon steel surface. Finally, samples of industrial waste water are collected from a drain of vacuum distillation tower over head pipes in Alexandria petroleum company and ferrous ions Fe +2 concentrations are determined in case of presence and absence of polymers molecules in order to judge the role of these polymers as a corrosion inhibitors on the ability to control the corrosion on carbon steel over head pipes.
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Many corrosion inhibitors can be used to eliminate the undesirable destructive effect and prevent carbon steel dissolution. Polymers were found to inhibit the process of anodic dissolution. It is found that the limiting current of anodic dissolution decreases with increasing concentration of the natural polymers (viz., starch, chitosan, cellulose acetate and carboxymethyl cellulose sodium salt) which indicated the increase in inhibition efficiency and the stabilization of passive layer of polymers molecules as protective film on carbon steel surface. The effect of viscosity of the solution at different concentrations and temperatures were studied. Dissolution rate and percentage inhibition was determined by weight loss method. Values of activation energy indicate that the rate controlled step is the diffusion of aqueous species in the boundary layer and the isokinetic temperatures were estimated. Those polymers verify Flory-Huggins isotherm. Negative values of free energy of adsorption revealing to the spontaneous adsorption of polymers molecules on carbon steel surface. The adsorption of these polymers molecules on the anode surface was confirmed by scanning electron microscopy. Forced convection mechanism were applied and we obtained that the flow in system were turbulent flow.
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