الفهرس 
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Abstract
Carbon steel is a very important alloy used in industry so I tried to decrease its corrosion rate in 0.5 M HCl using some additives namely; two prepared polymeric surfactants, nicotinic acid , nicotinamide and three amino acids (cysteine, serine and α- amino butyric acid). Synergistic effect by Zn+2 and sodium dodecyl sulphate is applied to some of the used additives.
The thesis contains three main chapters:
• Chapter (I)
This chapter deals with an introduction about carbon steel, its occurrence, its electrochemical reactions in aqueous solutions, theories of corrosion and types of corrosion inhibitors. Moreover, the chapter contains a literature survey of the previous works introduced on carbon steel corrosion.
• Chapter (II)
This chapter deals with experimental part, which includes a description of the used additives. Experimental techniques, including the full description of the used instruments and detailed procedures used for determination of the corrosion rate and inhibition efficiencies of the used additives.
• Chapter (III)
This chapter contains the results obtained from the used techniques as well as the interpretation of these results in view of the theories of corrosion thermodynamics and kinetics. Moreover, a proposed mechanism was given at the end of the chapter based on the obtained results.
This chapter divided into three parts:
Section I: Polymeric surfactants
This section is divided into part I and part II
Part I: Weight loss measurements were carried out for carbon steel in 0.5 M HCl in the absence and presence of different concentrations of the two used polymeric surfactants at 298 K. The obtained results show that, corrosion rate of carbon steel decreased with increasing the concentration of investigated inhibitors. The order of decreasing inhibition efficiency for the used additives is:
Polymeric surfactant II > Polymeric surfactant I
Part II: Potentiodynamic polarization measurements were carried out for carbon steel in 0.5 M HCl in the absence and presence of different concentrations of the two used polymeric surfactants at 298 K. The polarization curves indicated that these compounds influence both anodic and cathodic processes without change in the corrosion potential. This means that these compounds act as mixed type inhibitors. The order of decreasing inhibition efficiency for the used additives is:
Polymeric surfactant II > Polymeric surfactant I
The obtained results show that the adsorption of polymeric surfactants on the carbon steel surface follows Langmuir adsorption isotherm and there adsorption is physiochemical in nature.
The effect of temperature on the corrosion rate of carbon steel in 0.5 M HCl over the temperature range (313 – 343K) in the absence and presence of the most effective concentrations of the used polymeric surfactants. It’s found that inhibition efficiencies decrease with increasing temperature. This also indicates that inhibitors are physically adsorbed on the carbon steel surface. Activation energies Ea٭ were calculated and it was found that its values for inhibited systems are higher than those for uninhibited systems.
The activation enthalpy and activation entropy values were calculated. The positive valued of activation enthalpy indicate endothermic nature of the reaction.
The negative values of activation entropy can be attributed to the adsorption process which is accompanied by an increase in the order of the system resulting from the associated complex of inhibitor and carbon steel.
Section II: Nicotinic acid and Nicotinamide
This section is divided into part I and part II
Part I: Weight loss measurements were carried out for carbon steel in 0.5 M HCl in the absence and presence of different concentrations of nicotinic acid and nicotinamide, respectively, at 298 K. The obtained results show that, corrosion rate of carbon steel decreased with increasing the concentration of investigated inhibitors. The order of decreasing inhibition efficiency for the used additives is:
Nicotinic acid < Nicotinamide
Studying synergistic effect of Zn+2 on corrosion of carbon steel in 0.5 M HCl in absence and presence of nicotinic acid and nicotinamide using weight loss technique. The obtained results show that as concentration of Zn+2 increase corrosion rates decrease and inhibition efficiencies increase. Synergism parameter (S1) values were found to be more than 1. This indicates that the addition of Zn+2 to nicotinic acid and nicotinamide, respectively, is synergistic in nature.
Part II: Potentiodynamic polarization measurements were carried out for carbon steel in 0.5 M HCl in the absence and presence of different concentrations of nicotinic acid, nicotinamide, respectively, and synergistic effect of Zn+2 on the most effective concentrations of nicotinic acid, nicotinamide, respectively, at 298 K. The polarization curves indicated that these compounds influence both anodic and cathodic processes without change in the corrosion potential. This means that these compounds act as mixed type inhibitors. The order of decreasing inhibition efficiency for the used additives is:
Nicotinamide + Zn+2 > Nicotinic acid + Zn+2 > Nicotinamide > Nicotinic acid
The obtained results show that the adsorption of nicotinic acid, nicotinamide, mixture of nicotinic acid with Zn+2 and nicotinamide with Zn+2, respectively, on the carbon steel surface follows Langmuir adsorption isotherm and there adsorption is physiochemical in nature.
The effect of temperature on the corrosion rate of carbon steel in 0.5 M HCl over the temperature range (313 – 343K) in the absence and presence of the most effective concentrations of the nicotinic acid, nicotinamide, mixture of nicotinic acid with Zn+2 and nicotinamide with Zn+2, respectively. It’s found that inhibition efficiencies decrease with increasing temperature. This also indicates that inhibitors are physically adsorbed on the carbon steel surface. Activation energies Ea٭ were calculated and its values for inhibited systems are higher than those for the uninhibited systems.
The activation enthalpy and activation entropy values were calculated. The positive valued of activation enthalpy indicate endothermic nature of the reaction.
The negative values of activation entropy can be attributed to the adsorption process which is accompanied by an increase in the order of the system resulting from the associated complex of inhibitor and carbon steel.
Section III: Amino acids (Cysteine, Serine and α- amino butyric acid)
This section is divided into part I and part II
Part I: Weight loss measurements were carried out for carbon steel in 0.5 M HCl in the absence and presence of different concentrations of the three used amino acids at 298 K. The obtained results show that, corrosion rate of carbon steel decreased with increasing the concentration of investigated inhibitors. The order of decreasing inhibition efficiency for the used additives is:
Cysteine > Serine > α- amino butyric acid
Studying synergistic effect of different concentrations of Zn+2 and SDS, respectively, on corrosion of carbon steel in 0.5 M HCl in absence and presence of the most effective concentrations of the three tested amino acids and synergistic effect of the most effective concentration of Zn+2 and SDS, respectively, corrosion of carbon steel in 0.5M HCl in absence and presence of different concentrations of the three tested amino acids using weight loss technique. The obtained results show that as concentration of Zn+2, SDS increase corrosion rates decrease and inhibition efficiencies increase. Synergism parameter (S1) values were found to be more than 1. This indicates that the addition of Zn+2 and SDS to the three tested amino acids is synergistic in nature.
Part II: Potentiodynamic polarization measurements were carried out for carbon steel in 0.5 M HCl in the absence and presence of different concentrations of the three tested amino acids, mixture of different concentrations of Zn+2 and SDS with the most effective concentrations of the three tested amino acids, respectively, and mixture of the most effective concentration of Zn+2 and SDS with different concentrations of the three tested amino acids, respectively, at 298 K. The polarization curves indicated that these compounds influence both anodic and cathodic processes without change in the corrosion potential. This means that these compounds act as mixed type inhibitors. The order of decreasing inhibition efficiency for the used additives is:
Cysteine + Zn+2 > Serine + Zn+2 > α- amino butyric acid+ Zn+2 > Cysteine > Serine > α- amino butyric acid
Cysteine + SDS > Serine + SDS > α- amino butyric acid + SDS > Cysteine > Serine > α- amino butyric acid
The obtained results show that the adsorption of the three tested amino acids, mixture of different concentrations of Zn+2 and SDS with the most effective concentrations of the three tested amino acids, respectively, and mixture of the most effective concentration of Zn+2 and SDS with different concentrations of the three tested amino acids, respectively, on the carbon steel surface follows Langmuir adsorption isotherm and there adsorption is physical in nature.
The effect of temperature on the corrosion rate of carbon steel in 0.5 M HCl over the temperature range (313 – 343K) in the absence and presence of the most effective concentrations of the three tested amino acids, mixture of the most effective concentrations of Zn+2 and SDS with the most effective concentrations of the three tested amino acids, respectively. It’s found that inhibition efficiencies decrease with increasing temperature. This also indicates that inhibitors are physically adsorbed on the carbon steel surface. Activation energies were calculated and it was found that Ea٭ values for inhibited systems are higher than those for the uninhibited systems.
The activation enthalpy and activation entropy values were calculated. The positive valued of activation enthalpy indicate endothermic nature of the reaction. The negative values of activation entropy can be attributed to the adsorption process which is accompanied by an increase in the order of the system resulting from the associated complex