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Abstract
aim of the present work is to study the reactivity of some thiophene derivatives as corrosion inhibitors for AISI 304 stainless steel in HCl solution . The thesis comprises three main chapters.The first chapter : Deals with the Introduction, which includes corrosion theories, types of corrosion, corrosion protection, literature survey on corrosion behavior of AISI 304 stainless steel in aqueous environment and aim of the present work.The second chapter : Deals with the experimental techniques, which include the chemical composition of the investigated material and preparation of the used solutions.Also the experimental techniques contain the instruments and the procedures used for the corrosion measurements such as weight loss and galvanostatic polarization techniques.The third chapter : Deals with the results obtained and their discussion under four separated sections; (A), (B), (C) and (D).Section A : Contains the results of weight loss measurements for AISI 304 stainless steel in 3M HCl containing different concentrations of used thiophene derivatives.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 investigated thiophene derivatives. The order of decreasing inhibition efficiency of these compounds is follow: I > II > III > IV > VThe synergistic effect of potassium iodide, potassium thiocyanide and potassium bromide was examined by addition of 1x10-2M of KI, KSCN and KBr, individually with different concentrations of the selected thiophene derivatives to enhance the inhibitive effect of these compounds. The values of Synergism parameters, S, was also calculated and discussed.A number of mathematical relationships for the adsorption isotherms have been suggested to fit the experiment data of the present work.The simplest equations that fit our results are:• For the thiophene derivatives the equation that fits our results is that due to • Temkin and is given by the general equation : ln K C = a θThe results were treated to obtain the free energy of adsorption ΔGads and the binding constant, K, using the kinetic model and Temkin isotherm. Thermodynamic parameters for the adsorption of the compounds in 3M HCl on AISI 304 stainless steel surface were also calculated.The effect of temperature on the corrosion rate of AISI 304 stainless steel in 3M HCl over the temperature range (30-50oC) in absence and presence of different concentrations of the used thiophene derivatives has been studied.The % inhibition effeciency is found to decrease with increasing the temperature; this indicated that, these compounds are physically adsorbed on the AISI 304 stainless steel surface. Arrhenius plots of logarithm 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* / 2.303 RT )The values of the activation energy are calculated in absence and presence of different concentrations of the used thiophene derivatives and are found to decrease with increasing the concentration of these compounds.Plots of logarithm corrosion rate divided by absolute temperature (log k/T) against reciprocal of absolute temperature (1/T) were found to be linear and obeyed the following transition state equation : Rate = RT/ Nh exp (S*/ R) exp (-H*/ RT)Thermodynamic activation parameters (ΔH* and ΔS*) are also computed and discussed.The values of the activation energy, Ea*, and the activation enthalpy, ΔH*, are increased with increasing inhibitor concentration while the value of the activation entropy, ΔS*, is decreased at the same time.Section B : Contains the results of galvanostatic polarization measurements for AISI 304 stainless steel in 3M HCl in absence and presence of different concentrations of the used thiophene derivatives.The polarization curves indicated that these compounds influence both cathodic and anodic processes. The order of decreasing inhibition efficiency for the additives is : I > II > III > IV > V This is also in agreement with the observed order of corrosion inhibition determined by the weight loss technique.Mathematical relationships for the adsorption isotherms have been suggested to fit the experiment data of the present work.The simplest equations<that fit our results For the thiophene derivatives is Temkin.The results obtained from this technique give further support to that obtained from the previously mentioned weight loss measurements.Section C: Contains the results of potentiodynamic anodic polarization curves for AISI 304 stainless steel in 1M HCl in absence and presence of different concentrations of the used thiophene derivatives.The polarization curves indicated that these compounds influence both cathodic and anodic processes. The order of decreasing inhibition efficiency for the additives is I > II > III > IV > V Section D : The influence of the chemical structure of the used compounds on their % inhibition efficiencies was discussed. The order of these % inhibition efficiencies depends mainly upon the type and kind of the substetuent groups, skeletal representation of the molecules supported this examination.In conclusion the polarization and weight loss measurements support the assumption that corrosion inhibition primarily takes place through adsorption of the inhibitors on AISI 304 stainless steel surface.Agreement among these different independent techniques indicates the validity of the obtained results.This thesis contains also references, Arabic and English summaries.