الفهرس 
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Abstract
The corrosion problem is a great importance, which faced the world from the last years until now, we can’t hide this problem from our live but we can reduce it in the metals by several methods as the environment need.
This work discusses the corrosion of C-steel in 1M HCl.
This work consists of three basic chapters
Chapter one: ”INTRODUCTION”
This chapter discusses: corrosion theory, causes of corrosion, forms of corrosion, corrosion migration, types of inhibitors, Literature survey of corrosion of C-steel and aim of this study.
Chapter two: ”EXPERIMENTAL AND TECHNIQUES”
It includes the chemical composition of the investigated material, preparation of the used HCl solution, the used pharmaceutical compounds, solutions and procedures used for the corrosion measurements such as a weight loss and electrochemical techniques.
Chapter three: ”RESULTS AND DISCUSSION”
It deals with the results obtained and their discussion and this chapter is divided into four sections:
Section (A):
Evaluation of the inhibitor efficiency by weight loss method in the presence and absence of the three used pharmaceutical compounds in 1M HCl at 25 ± 10C. This reveled that the inhibitor efficiency increases with the concentration.
These pharmaceutical additives obey Temkin’s adsorption isotherm showing that the inhibition is by adsorption. The degree of surface coverage (θ) of the inhibitors on the metal surface was found to increase with increasing the concentration of the additives in the corrosive medium.
The effect of temperature on the corrosion inhibition of C-steel in 1M HCl was determined over the temperature range 25-55oC using weight loss measurements. The rate of corrosion increases with increasing the temperature indicating that the inhibition occurs through physical adsorption of the additives on C-steel surface. Thermodynamic functions of activation were calculated in the presence of different concentrations of inhibitors.
Section (B):
I- Contains the results of potentiodynamic polarization. The results obtained are presented in many Tables and Figures; also the effect of inhibitors on the cathodic and anodic polarization of C-steel in 1M HCl solution was investigated. Corrosion rate was found to decrease with increase in the concentration of the pharmaceutical compounds.
The polarization curves indicated that these compounds influence both cathodic and anodic reactions.
II- The results obtained from (EIS) show that the corrosion reactions in the absence and presence of pharmaceutical compounds precede under charge transfer control. The increase in concentration of the inhibitors leads to an increase in the value of the charge transfer resistance (Rct) i.e. a decrease of the corrosion rate of C-steel. The double layer capacitance (Cdl) of the corroding C-steel interface decreases with increase in the inhibitor concentration, suggesting an increase of the surface coverage of the inhibitor due to the adsorption of the inhibitor species at the C-steel surface.
III- The results obtained from electrochemical frequency modulation (EFM) measurements. Inter modulation Spectrum for C-steel in 1 M HCl solution in the absence and presence of different concentrations of pharmaceutical compounds is studied. The harmonic and inter modulation peaks are clearly visible and are much larger than background noise. The corrosion parameters such as inhibition efficiency (% IE), corrosion current density (icorr.),
Tafel constants (βa and βc) and causality factors; CF-2, CF-3, at different concentrations of pharmaceutical compounds in 1 M HCl solution 25ºC are calculated.
Section (C):
Some quantum-chemical quantities were calculated which is a theoretical analogue to ionization potential that illustrates the electron affinity of the molecule affect the inhibition efficiency of these pharmaceutical compounds. The inhibition efficiency was found to increase with increasing the energy of (HOMO).
Section (D):
(SEM) analysis showed that the inhibitions of the investigated pharmaceutical compounds were adsorbed on the metal surface forming a thin layer by which metal was protected from corrosion.
The influence of the chemical structure of the investigated pharmaceutical compounds on their inhibition efficiencies was discussed: the order of these inhibition efficiencies depends mainly upon the number of adsorption active centers and molecular weight.
Conclusion:
The weight loss, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) measurements, electrochemical frequency (EFM), quantum calculations and (SEM) analysis supports the assumption that corrosion inhibition primarily takes place through adsorption of the inhibitors on C-steel surface.
Agreement among these different independent techniques indicates the validity of the obtained results.