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Abstract
The aim of the present work is to study the corrosion behavior of γ-irradiated and non-irradiated carbon steel in 0.5 M HNO3 solution.
The thesis comprises three main chapters; the first one deals with the following fields of interest:
(1) Corrosion theory and corrosion protection.
(2) Literature survey of corrosion behavior of carbon steels.
(3) Aim of the present work.
Chapter two deals with the experimental part. It includes the chemical composition of the investigated material, the technique for irradiation of this material by gamma rays, preparation of the nitric acid solution, the used azole compounds solutions and the procedures used for the corrosion measurements such as weight loss and polarization techniques.
The results obtained and their interpretation are shown in chapter three under two separated sections; (A) and (B).
Section A: contains the results of weight loss measurements for non-irradiated carbon steel in 0.5M nitric acid solutions containing different concentrations of azole compounds. These results revealed that these compounds behave similarly and the weight loss is generally decreases with increasing the concentration of these compounds and also depends upon the nature and type of the azole compound used.
The inhibition efficiency of these compounds is in the following order:
1,2,3- benzotriazole< 2- methyl imidazole> imidazole.
The effect of temperature on the corrosion rate of non-irradiated carbon steel in 0.5M nitric acid solution in absence and presence of the selected azole compounds has been studied. Arrhenius plots of corrosion rate (log k) against reciprocal of absolute temperature (1/T) were found to be linear and obeyed the following equation:
log k = log A – Ea*/2.303RT
Thermodynamic parameters (ΔH* and ΔS*) are also computed and discussed.
The percentage inhibition is decreased with increasing temperature, this indicated that, these compounds are may be give physically adsorbed on non-irradiated carbon steel surface.
The results showed that the adsorption of these compounds obeyed Temkin adsorption isotherm.
The results were treated to obtain the free energy of adsorption ΔG*ads .and the binding constant K using the kinetic model and Temkin isotherms. The other thermodynamic parameters of adsorption process, entropy of adsorption ΔS*ads .and heat of adsorption ∆H* are also computed and discussed.
Section B: contains the results of potentiodynamic polarization measurements for both γ-irradiated and non-irradiated carbon steel in 0.5M HNO3 in absence and presence of different concentrations of azole compounds.
The polarization curves indicated that these compounds influence both cathodic and anodic processes, the order of increased inhibition efficiency for the additives is:
1,2,3- benzotriazole> 2- methyl imidazole> imidazole.
This is also in agreement with the observed order of corrosion inhibition by the weight-loss method and the γ-irradiation retard the corrosion rate of carbon steel, than the non-irradiated one.
The influence of the chemical structure of the used azole compounds on their inhibition efficiencies was discussed.
The γ-radiation retarding the corrosion rate of carbon steel in 0.5M nitric acid by improving the passive film and increasing its resistance to the nucleation of pits.
This thesis contains also references, English and Arabic summaries.