الفهرس 
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Abstract
This work contains three chapters:-
Chapter 1:’’Introduction’’
An introduction about the importance of corrosion study, corrosion types, corrosion control, Inhibitors, Adsorption isotherms, surfactants, and Literature survey on corrosion inhibition of carbon steel in aqueous solution.
Chapter 2: ’’Materials and experimental techniques’’
The experimental part included complete description of synthesis of inhibitors as the following:
1-Synthesis of inhibitors
a- Synthesis of novel Schiff bases
b- Synthesis of cationic surfactants
2- Evaluation of the prepared Inhibitors as corrosion inhibitors for carbon steel.
Determination of corrosion parameters, inhibition efficiency and surface coverage by gravimetric measurements, potentiodynamic polarization measurements and electrochemical impedance spectroscopy (EIS).
Determination of quantum parameters such as Energy of the highest occupied molecular orbital (EHOMO), Energy of the lowest unoccupied molecular orbital (ELUMO), Difference between highest occupied molecular orbital and lowest unoccupied molecular orbital (ΔE), Ionization potential (I), Electron affinity (A), Global hardness (γ), the fraction of electrons transferred (ΔN) and The Softness(δ). High value of EHOMO probably indicates a tendency of the molecule to donate electrons, energy of the lowest unoccupied molecular orbital (ELUMO) indicates the ability of the molecule to accept electrons. The lower value of ELUMO, the more probable is that the molecule would accept electrons ΔE is the more probable to donate and accept electrons. The values of ΔE suggesting the strongest ability of the synthesized inhibitors to form coordinate bonds with d-orbitals of metal through donating and accepting electrons, for the dipole moment (μ), higher value of μ will favor the enhancement of corrosion inhibition, value of number of electron transrered (ΔN) shows inhibition efficiency resulting from electron donation, and the inhibition efficiency increases with the increase in electron-donating ability to the metal surface.All of this parameters are in good agreement with the experimental results and show that Schiff bases are in order C < A < B in inhibition efficiency.
Determination of surface tension (γ), critical micelle concentration (CMC), effectiveness (πCMC), surface excess (Γmax), minimum surface area (Amin), and standard free energy (ΔGmic).These data show that the prepared cationic surfactants are surface active materials where the greater lowering in surface tension for a critical micelle concentration (CMC) is the most effective surfactant. According to the results the prepared cationic surfactants act as effective inhibitors for carbon steel.Chapter 3: “Results and discussion”
This chapter included the following parts:-
1- characterization of the synthesized inhibitors
The chemical structure of the prepared compounds was confirmed by spectroscopy analysis include 1HNMR and Mass Spectra.
2-The prepared compounds were investigated as corrosion inhibitors using three techniques:-
a) Weight loss measurements
The data revealed that:-
1- The inhibition efficiency of six compounds increased with increasing the concentration and increased by increasing the temperature rang (20-65 ºC).
2- The inhibition efficiency of the cationic surfactants increased with increasing the time in the range (1-28 day) at 20 ºC.
c) Potentiodynamic polarization measurements
The data indicated that:-
1- All prepared Inhibitors does not remarkably shift the corrosion potential (Ecorr), also the values of Icorr decreased including not changed significantly in both anodic and cathodic Tafel slopes βa, βc in the presence of the prepared Inhibitorss. This behaviour confirmed that the prepared compounds acted as mixed type inhibitor.The inhibition efficiency of all prepared compounds increased with inhibitor concentration increment. This fact suggested that the inhibitor molecules may be adsorbed on the steel surface and cover some sites of the electrode surface.
d) Electrochemical impedance spectroscopy (EIS)
The data showed that the increase of charge transfer resistance and decreased of the pseudo capacity with increasing inhibitor concentration indicated that these compounds have the ability to inhibit the corrosion rate of carbon steel according to adsorption mechanism (formation of a surface film).
The results obtained from the weight loss measurements were in good agreement with those obtained from potentiodynamic polarization method and electrochemical impedance spectroscopy (EIS).
e- Thermodynamic parameters
1- Activation thermodynamic parameters
The values of activation energy (Ea) were calculated from Arrhenius equation. The data indicated that, the activation energy decreased in the presence of the prepared Inhibitors which indicated that chemisorption (sharing or transferring of electrons from inhibitor molecules to the metal surface to form a co-ordinate type of bond. The change in enthalpy and entropy of activation values (ΔH*, ΔS*) were calculated from the transition state theory.
2) Adsorption thermodynamic parametersThe adsorption of the prepared compounds on the carbon steel surface obeyed the Langmuir adsorption isotherm. Thermodynamic parameters for adsorption process such as free energy (ΔGoads), enthalpy (ΔHoads) and entropy (ΔSoads) for the prepared compounds were determined. The negative values of ΔGoads indicated that the adsorption of inhibitors on the metal surface is spontaneous process. The positive sign of ΔHoads indicated that the adsorption of prepared Inhibitors on the carbon steel surface in 1 M HCl solution is endothermic process. The positive sign of ΔSoads attributed to the increase of disorder due to the adsorption of only one inhibitor molecule by desorption of more water molecules.
f) Quantum parameters
The smaller gap between EHOMO and ELUMO favors the adsorption of the synthesized Schiff bases on iron surface and enhancement of corrosion inhibition, also Ionization potential (I), Electron affinity (A), Global hardness (γ), the fraction of electrons transferred (ΔN) and The Softness (δ) have been calculated.
g) Surface parameters
The surface active properties of the prepared surfactants:-
The data showed that the values of surface tension (γ) decreases as the concentration of inhibitors increased. The values of effectiveness (πcmc), Maximum surface excess(Γmax) and the minimum surface area (Amin) were calculated. The data showed that the most effective surfactant is one that gives the greater lowering in surface tension,
Specific conductivity measurements of cationic surfactants were performed in order to evaluate the CMC and the degree of counter ion dissociation, β. The data indicated that degree of dissociation was in the following order:
Cationic surfactant B > Cationic surfactant A > Cationic surfactant C
This order due to cation bulkiness increased.
The values of standard free energy (ΔGomic) were calculated. The data showed that the standard free energies of micellization for the synthesized surfactants are always negative, indicating that the micellization is a spontaneous process.