الفهرس 
INTODUCTIONOnly 14 pages are availabe for public view
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Abstract
Corrosion is a very common phenomenon that has wide-ranging effects in industrial, municipal and private settings. The method for corrosion protection of metals based on the use of corrosion inhibitors, i.e., chemical compounds or their compositions which when present in a corrosive system at a sufficient concentrations, decrease the corrosion rate of metals without changing significantly the concentration of any of the corrosive reagents, has been known for a long time. The inhibition efficiency depends on many factors such as the chemical structure of the inhibitors and the nature of the surface of metal.
The aim of present study is protect mild steel from corrosion in 0.5 M H2SO4 by using inhibitors and plasma technique. It divides to five chapters. The First one covers the basic concepts of corrosion and its cost. In addition includes organic inhibitors that use to prevent corrosion especially Schiff bases compounds. Moreover, it contains a short note about electrolytic plasma processing (EPP) that used to modify the surface several metals.
The second chapter contains literature reviews of synthesis of N-aminophthalimide, Schiff bases as corrosion inhibitors and EPP. The methods that used to get high yield of Schiff bases are mentioned in this chapter. The role of nitrogen, sulfur and oxygen atoms beside Schiff bases shows in this part. Using EPP technique to treat the surface of metals in different solutions was summarized in this chapter.
The third and fourth chapters shows the results and discussion. The third chapter deals in details with Schiff bases preparation and their characteristics by FTIR, mass spectra and 1HNMR spectra. In addition, some reactions of newly reported Schiff bases with Carbon Nucleophiles. Then it shows the inhibiting efficiency by potentiodynamic polarization measurements and EIS. The effect of iodide ions were studied in this part. The effect of temperature on inhibiting efficiency and the adsorption isotherm were also studied in this chapter. The fifth chapter shows the results of EPP and the analysis of coating layer by different techniques. The coating layer were examined by electrochemicals measurements and hardness. At the end the best inhibitor and the best sample treated by EPP are combined together to get the best condition to protect the mild steel from corrosion.
The fourth chapter covers the chemicals, test specimens and experimental plan. It describe the method that used to prepare Schiff bases, mild steel analysis and specimen preparation for EPP. The laws of electrochemical measurements such as Tafel, EIS and CV are mentioned in this chapter. It also contains the instruments that used in this study such as FTIR, XRD, SEM and EDX. In addition, it contains the baths that used for electrochemical measurements and EPP.
In the present study, Schiff base compounds were prepared and studied as corrosion inhibitors and their structures were confirmed by identify of melting point and spectral data. The presence of imino group, −CH= N −, of Schiff bases were confirmed by FTIR spectroscopy studies. The newly reported Schiff bases reacted with Carbon and Nitrogen Nucleophiles. They underwent reactions with Aromatic Hydrocarbons under Friedel-Crafts conditions and with Primary Amines. The structure of products were confirmed by melting point and mixed melting point, and infrared spectrum.
The inhibition efficiency of these inhibitors obtained from the polarization method was found to be increased with respect to the concentration of inhibitor. The synergistic effect of these inhibitors by iodide ions on the inhibition of corrosion of mild steel has been evaluated. Polarization study shows that inhibitor - iodide ions function as anodic inhibitors in controlling the anodic reaction predominantly and to some extent controls the cathodic reactions. The maximum inhibition efficiency obtained from the polarization method was 92.7% in presence of iodide ions. The inhibiting influence of the Schiff bases are related to their chemical structure. The parallel Tafel slopes reveal that the inhibitors control both anodic and cathodic reactions by blocking the active sites of mild steel surface and thus the Schiff base inhibitors are of mixed type.
AC impedance spectra confirms the formation of protective film on the metal surface. The values of charge transfer resistance obtained were increased with increase in concentration of inhibitors whereas double layer capacitances were decreased implying that the inhibitor performance is due to the adsorption of inhibitor molecules on the metal surface. Inhibition process was controlled by the charge transfer process. The inhibition efficiency obtained by the polarization method was in good agreement with and impedance methods.
The negative value of ∆Gads implies that these inhibitors are spontaneously adsorbed on the mild steel surface. However, the inhibition efficiency decreases as temperature increases. The Ea values reveal that the adsorption occurs through the mechanism of physical adsorption. In addition, adsorption of them follows Langmuir adsorption isotherms.
In this study, EPP was used to change the surface of mild steel to enhance corrosion protection. The spark and discharge phenomena has amazed people from the beginning of our history and scientists have been studying these phenomena for decades. The major study and application of plasma and discharge are commonly confined in a low-pressure environment. This electrolytic plasma is one of the few plasma related techniques, operating in atmospheric pressure and it attracts industrial attention recently. It is desirable to explore the basic aspects and the feasibility of utilizing this phenomenon in different applications.
Carbonitriding, carburizing and oxidation processes were carried out in alkaline solution in presence of urea for mild steel by (EPP).
The surfaces modified by EPP was characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and energy dispersive X-ray spectrometer (EDS). Both XRD data and EDS analysis shows that EPP carbonitriding and carburizing produces occurs at potential less than 220 V and it produces oxide layers at higher potentials.
Cyclic voltammogram (CV) showed that the coating layers have a good resistance corrosion behavior. Electrochemical Impedance Spectroscopy (EIS) used to check the strength of passive layers compared to base metal. Electrochemical behaviour of the coating layers enhances after EPP. from EIS results, the impedance Z values increased with potential and urea concentrations and decreased with treatment time. Tafel plots were used to evaluate the corrosion behaviour of coatings and it was seen that the treated sample show better corrosion behaviour. Corrosion studies show that the process has the ability to move corrosion potential to the noble direction and at the same time, the corrosion current density will decrease significantly. The coating layers produced by EPP did not break after attacking by chloride ions. The microhardness of coating layers are greater than base metal.
Finally, Tafel plots show that using of the best Schiff base inhibitor and the best plasma sample together increases the corrosion protection of steel mild.