الفهرس 
acknowledgmentOnly 14 pages are availabe for public view
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Abstract
The thesis consists of three chapters. Chapter I is the introduction, Chapter II
represents the experimental techniques, and Chapter III contains the results and their discussion Chapter I: In this chapter, an introduction was given which deals with the following fields of interest Electrochemical nature of corrosion Corrosion resistance of metals Thermodynamics of corrosion reactions Potential-pH equilibrium diagrams (Pourbaix diagrams Potential of zero charge Electrochemical techniques for measuring corrosion rates including DC techniques; Tafel extrapolation method (TE), linear polarization method (LP) and also AC techniques; electrochemical impedance spectroscopy (EIS Structure and properties of the electrical double layer (EDL Inhibitors and their types: inorganic inhibitors; passivators, non-passivators precipitation inhibitors), hydrogen evolution poisons, oxygen scavengers, and also organic inhibitors; adsorption type inhibitors, vapour-phase or volatile corrosion inhibitors (VCI Effect of temperature on the inhibitors action Adsorption, factors affecting the adsorption process and adsorption isotherms Literature survey on the inhibition of the corrosion of steel in acidic medium Literature survey on the inhibition of the corrosion of copper in acidic medium Literature survey on the inhibition of the corrosion of zinc in acidic medium Chapter II: The main contents of this chapter were the experimental techniques used in the present investigation: Electrochemical impedance spectroscopy (EIS) and
potentiodynamic polarization technique. The detailed description of electrodes, solutions cells, and experimental procedure were included Chapter III: In this chapter, the experimental results were discussed in three partsPart I represents the inhibition characteristics of pantoprazole sodium (PAN) for the
corrosion of mild steel in acidic medium. The polarization curves of steel in aqueous solution of 0.5 M H2SO4, 1M HCl and 1M HClO4 in the absence and presence of different concentrations of pantoprazole sodium (PAN) at 30°C showed that PAN behaves as mixed type inhibitor and that its addition caused a decrease in the corrosion current density, icorr
with slight change in the corrosion potential, Ecorr, indicating that it could be used as pickle
inhibitor while the anodic and cathodic acid corrosion Tafel slopes (βa , βc) were approximately constant suggesting that the inhibiting action occurred by simple blocking
of the available cathodic and anodic sites on the metal surface. The Nyquist plots consisted
of depressed semicircles indicating that the dissolution mechanism of steel is being xi controlled by the rate of the charge transfer process across the phase boundary in the
uninhibited and inhibited acid solutions, therefore the addition of this compound to the acid
solution does not alter the mechanism of steel dissolution. The size of semicircles increased with increasing the concentration of PAN. The impedance spectra of different
Nyquist plots were explained by fitting the experimental data to a simple Randles
equivalent circuit model, this circuit included Cdl, capacitance of double layer and Rct,
charge transfer resistance, which is a measure of electron transfer across the surface.
Increasing the concentration of PAN has led to an increase in the Rct value accompanied by
a decrease in the double layer capacitance, Cdl. The inhibition efficiency was calculated
from polarization technique using the equation:
% inh = [( io – i ) / io ] x 100
where io and i are the corrosion current density, in the absence and presence of PAN
respectively, while the inhibition efficiency obtained from EIS technique was calculated by
applying the equation:
% inh = [(Rct - Rcto ) / Rct] x 100
where Rcto and Rct are the charge transfer resistances, in the absence and presence of PAN
respectively.
The degree of surface coverage (θ) of the metal surface by an adsorbed PAN
molecule was calculated using the equation:
θ = (Rct- Rcto)/Rct
Application of Langmuir adsorption isotherm to the data of PAN indicated that
Langmuir isotherm is not applicable to fit the data of PAN in 0.5 M H2SO4 indicating that
there might be non-ideal behavior in the adsorption process of the compound on the steel
surface in sulphuric acid solution but ideal behavior is observed in the adsorption of PAN
in hydrochloric and perchloric acid solutions.
The values of binding constants calculated for PAN in different acid solutions from
the application of different models were found to be in the order Perchloric acid > Hydrochloric acid > Sulphuric acid This trend is in a good agreement with the % inhibition values obtained from polarization and impedance measurements.Part II represents the inhibition characteristics of pantoprazole sodium (PAN) for the corrosion of copper in acidic medium. The polarization curves of copper showed that PAN behaves as mixed type inhibitor in 0.5M H2SO4, 1M HCl and 1M HClO4 and that its addition caused a decrease in the corrosion current density, icorr with slight change in the corrosion potential, Ecorr, indicating that it could be used as pickling inhibitor while the anodic and cathodic Tafel slopes (βa , βc) were approximately constant suggesting that the inhibiting action occurred by simple blocking of the available cathodic and anodic sites on the metal surface. The Nyquist plots for copper in the presence of 0.5M H2SO4 consisted of depressed semicircles indicating that the dissolution mechanism of copper is being
controlled by the rate of the charge transfer process across the phase boundary in the xiiuninhibited and inhibited acid solutions, therefore, the addition of this compound to the acid solution does not alter the mechanism of copper dissolution in sulphuric acid solution The impedance spectra of different Nyquist plots for copper in 0.5M H2SO4 were explained by fitting the experimental data to the same simple Randles equivalent circuit model used for steel. Increasing the concentration of PAN has led to an increase.