الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 254 |  |  |
| | | from | 254 | | |
Abstract
The work discusses the corrosion inhibition of carbon steel and copper-zinc alloy in 1M HCl solution by four synthesized inhibitors A1, A2, S1 and S2. In this work, the inhibition effects of those compounds have been studied by several experimental methods.
This work contains three chapters:-
Chapter 1:’’Introduction’’
This chapter includes a general introduction about corrosion (definition, economic cost, forms, factors, prevention and types of inhibitors), heat exchanger (definition, classification) and surfactants (definition, classification and applications).
Chapter 2: ’’Materials and experimental techniques’’
The experimental part included complete description of synthesis of inhibitors and all details of measurements as the following:
1- Synthesis of inhibitors
* Synthesis of novel amides
* Synthesis of cationic surfactants
2- Confirmation the chemical structure of the prepared amides and cationic surfactants using 1HNMR and Mass spectroscopy.
3- Evaluation the inhibition efficiency for the synthesized inhibitors as corrosion inhibitors for carbon steel and copper-zinc alloy in 1M HCl solution by weight loss, potentiodynamic polarization and electrochemical impedancespectroscopy (EIS) techniques.
4- Determination of activation and adsorption thermodynamic parameters of the synthesized inhibitors on the carbon steel and copper- zinc alloy surfaces in 1M HCl solution.
5-Determination of surface tension (γ), critical micelle concentration (CMC), effectiveness (πCMC), surface excess (Γmax), minimum surface area (Amin), and standard free energy (ΔG ͦ mic).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 synthesized cationic surfactants act as effective inhibitors for carbon steel and copper alloy.
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 the synthesized compounds for the carbon steel and copper alloy in 1 M HCl increased with increasing the concentration and slightly increased by increasing the temperature rang (20-65 ºC). The inhibition efficiency increases in the order A1< A2< S2< S1. The corrosion inhibition is due to adsorption of these compounds and formation of barrier film on the surface of the carbon steel and copper-zinc alloy.
c) Potentiodynamic polarization measurements
The data indicated that:-
The presence of the synthesized inhibitors in 1M HCl solution for the carbon steel and copper-zinc alloy slightly increases the cathodic and anodic polarization. This indicates that the synthesized inhibitors acted as a mixed type inhibitor. For all synthesized inhibitors, the corrosion current (icorr) decreased whereas inhibition efficiency (ηp) increased with increasing the inhibitor concentration. This could be related to the adsorption of the inhibitors over the cathodic and anodic active sites of the corroded surface. The increase in corrosion inhibition efficiency of the studied inhibitors indicated that the synthesized inhibitors had efficient inhibitive properties for the metal 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 and copper alloy according to adsorption mechanism (formation of a barrier 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 equation.
2) Adsorption thermodynamic parameters
The adsorption of the prepared compounds on the carbon steel and copper alloy surfaces 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 and copper alloy surfaces 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.
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: S1 > S2
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.
f) Scanning Electron Microscope (SEM) study
The surface morphology of the carbon steel and copper-zinc alloy samples in 1 M HCl solution in the absence and presence of optimum concentration of the synthesized inhibitors was characterized. The uninhibited solutions cause the highest damage to the metals surface. However, in the presence of inhibitors, the surface morphology of the carbon steel and copper-zinc alloy improved markedly in terms of smoothness, indicating a considerable reduction of corrosion attack.