الفهرس 
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Abstract
Studies of electrochemistry of metals and alloys are very important fields of scientific and industrial work. The present work includes detailed electrochemical studies on the corrosion of carbon steel in hydrochloric acid solution with and without some plant extract as eco-friendly corrosion inhibitors.
This work contains three basic chapters
Chapter one: “INTRODUCTION“
This chapter discusses corrosion theory, the basics of metal corrosion, causes of corrosion, forms of corrosion, corrosion migration, types of inhibitors, methods of protection, Literature survey of carbon steel corrosion and aim of this study
Chapter two: ”EXPERIMENTAL AND TECHNIQUES”
It includes the chemical composition of the investigated material, preparation of the used hydrochloric acid solution, the used Delonix regia flower extract, Delonix regia Leaves extract, Tilia Leaves extract solutions and procedures used for the corrosion measurements such as a weight loss method and electrochemical techniques.
Chapter three: ”RESULTS AND DISCUSSION”
It deals with the results obtained and their discussion. This chapter is divided to five sections (A-E):
Section (A):
Evaluation of the inhibitor efficiency by weight loss method in the presence and absence of three compounds in 1M HCl at 25oC. This revealed that the inhibitor efficiency increases with increasing the concentration.
These inhibitors obey Temkin adsorption isotherm showing that the inhibition is by adsorption. The degree of surface coverage (θ) for the inhibitors on the metal surface increases with increasing the concentration in the corrosive medium. The action of the inhibitors in the aggressive acid was assumed to be due to their adsorption at the metal /solution interface. The effect of temperature on the corrosion inhibition of carbon -steel in 1M HCl was determined in temperature range from 25 to 450 C using weight loss measurements. The rate of corrosion increases with increasing the temperature together with an increase in inhibition efficiency, indicating that the inhibition occurs through chemical adsorption of the additives on the carbon steel surface. Thermodynamic functions of activation were calculated of extracts.
Section (B):
Potentiodynamic polarization measurements were carried out for carbon steel in 1 M HCl in the absence and presence of different concentrations of Delonix regia flower extracts, Delonix regia leaves extracts and Tilia leaves extract. The polarization curves indicated that these inhibitors influence both cathodic and anodic processes. Corrosion rate decreased with increasing of concentration of the extracts together with increases in both cathodic and anodic polarization, but the corrosion inhibition has a great effect on the cathodic polarization. Variation of inhibition efficiency with the structure of compounds was interpreted in terms of the number of adsorption sites in the molecule and their electron charge density, molecular size, mode of adsorption and the polar effect of the substituent groups. The inhibition efficiency for carbon steel corrosion in 1M HCl at all concentrations in the range 50 – 300 ppm is increased by polarization technique
Section (C):
AC impedance spectroscopy measurements were carried out for carbon steel in 1 M HCl in the absence and presence of different concentrations of the extracts under charge transfer control.
from the impedance data, we conclude that:
1- The value of Rct increases with an increase in the concentration of the inhibitors and this indicates an increase in the corrosion inhibition in acidic solution.
2- The value of double layer capacitance Cdl decreases with increasing the inhibitor concentration. This is due to the adsorption of these compounds on the electrode surface leading to a film formation on carbon steel surface, suggesting an increase of the surface coverage (θ) of the inhibitor.
3- The % IE obtained from EIS measurements is close to those deduced from polarization.
Section (D):
The electrochemical frequency modulation (EFM) was used as a rapid and non-destructive technique for corrosion rate measurements. It was carried out for carbon steel in
1 M HCl in the absence and presence of different concentrations of the investigated three plant extracts.
Corrosion current densities (icorr) obtained with this technique were in good agreement with those obtained from weight-loss, polarization and EIS methods.
In addition to the causality factors were good internal check for verifying the validity of data obtained by this technique.
The corrosion rate decrease with increasing the concentration of inhibitors and the inhibition efficiency (% IE) is found to increase with increasing the inhibitor concentrations.
Section (E):
SEM analysis showed that the inhibition of the plant extracts was adsorbed on the metal surface forming a thin layer by which metal was protected from corrosion.
Conclusion:
The weight loss, polarization, electrochemical impedance spectroscopy (EIS) and EFM measurements support the assumption that corrosion inhibition primarily takes place through adsorption of the inhibitors on the carbon steel surface. Agreement among these different independent techniques indicates the validity of the obtained results.