الفهرس 
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Abstract
Al-Si alloy is consider as one of the most popular alloys which occupy a vital position in our daily life owing to its wide application in automotive industry due to their strength to weight ratio which increase performance and fuel economy. The aim of the present work is to study the corrosion behavior of Al-Si alloy in 1 M HCl solution. The thesis contains three chapters; Chapter one: ””INTRODUCTION”” It deals with the following fields of interest: Corrosion definition, causes and forms of corrosion, corrosion mechanism and types of inhibitors. Literature survey of the corrosion behavior of Al-Si alloy. Aim of the present work. Chapter two: ’’ EXPERIMENTAL AND TECHNIQUES’’ It includes the chemical composition of the investigated Al-Si alloy, preparation of Hydrochloric acid solution, preparation of carbamidic thioanhydride derivatives and the procedures used for the corrosion measurement such as the potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), electrochemical frequency modulation (EFM) and hydrogen evolution techniques. Chapter three: ’’RESULTS AND DISCUSSION’’ The results obtained and their interpretations are shown into this chapter under five separated parts. Part (1): Includes the results of potentiodynamic polarization measurements for Al-Si alloy in 1 M HCl solution in the absence and presence of different concentrations of carbamidic thioanhydride derivatives. The polarization curves indicated that the investigated compounds influence both cathodic and anodic processes, the order of decreased inhibition efficiency of the additives is as follows: (1) > (2) > (3) > (4) > (5). Part (2): Includes ac impedance spectroscopy measurements for Al-Si alloy in 1M HCl in the absence and presence of different concentrations of the investigated carbamidic thioanhydride derivatives. from the impedance data, we conclude that: i-The value of Rct increases with increase in the concentration of the inhibitors and this indicates an increase in the corrosion inhibition efficiency in acidic solution. ii-The value of double layer capacitance Cdl decreases by increasing the inhibitor concentration. This is due to the adsorption of these compounds on the electrode surface leading to a film formation on the Al-Si surface. iii -The %η obtained from EIS measurements are close to those deduced from polarization. The order of decreasing inhibition efficiency of the additives is as follows: (1) > (2) > (3) > (4) > (5). Part (3): Includes the results of electrochemical frequency modulation measurements for Al-Si alloy in 1M HCl solution in the absence and presence of different concentrations of carbamidic thioanhydride derivatives. The results indicated that the values of corrosion rate decrease with increasing the inhibitors concentration. The order of decreased inhibition efficiency %η of the additives is as follows: (1) > (2) > (3) > (4) > (5). The effect of temperature on the corrosion rate of Al-Si alloy in 1 M HCl solution has been also studied over the temperature range 25-55o C in the absence and presence of the investigated carbamidic thioanhydride derivatives using electrochemical frequency modulation measurements. Arrhenius plots of the corrosion current density (log kcorr) against reciprocal of absolute temperature (1/T) were found to be linear and obeyed the following equation: log kcorr = log A- Ea*/ 2.302RT from calculated parameters we found that; the rate of corrosion increases with increasing the temperature together with decrease in inhibition efficiency, indicating that the inhibition occurs through physical adsorption of the additives on alloy surface. Thermodynamic functions of activation (ΔH* and ΔS*) were also calculated and discussed. The results showed that the adsorption of these compounds obeyed Langmuir adsorption isotherm. The results were treated to obtain the free energy of adsorption ΔG°ads and the binding constant Kads using the kinetic model and Langmuir isotherm. Part (4): Includes evaluation of the inhibitors efficiency by gasometric measurements by hydrogen evolution technique for Al-Si alloy in 1M HCl solution in the absence and presence of different concentrations of carbamidic thioanhydride derivatives. Addition of the inhibitors to the acid solution led to a strong reduction in the corrosion rate of alloy and was found to decrease as the inhibitor concentration increases and so the volume of hydrogen evolved was reduced on introduction of the inhibitors onto the blank corrodent compared to the free acid and further decreases as the concentration of the inhibitor increases. Inhibition efficiency and surface coverage increases with increase in the inhibitor concentration. The %η obtained from hydrogen evolution measurements are close to those deduced from electrochemical measurements. The order of decreasing inhibition efficiency of the additives is as follows: (1) > (2) > (3) > (4) > (5). Part (5): Include the calculation of some quantum chemical parameters for the investigated Carbamidic thioanhydride derivatives, such as highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy values, frontier orbital energy gap (∆E), dipole moment (µ), chemical potential (Pi) and absolute hardness (ƞ) and softness (σ) of the molecules using semi-empirical PM3 method. The theoretical results obtained have been compared with the experimental data and the relations between the inhibition efficiency and quantum parameters have been discussed. It is clear that the inhibition efficiency increases with decreasing the energy gap (ΔE) and with increasing EHOMO. So, the order of decreasing inhibition efficiency is as follows: (1) > (2) > (3) > (4) > (5). In conclusion: The potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), electrochemical frequency modulation and gasometric measurements support the assumption that corrosion inhibition primarily takes place through adsorption of the inhibitors on the Al-Si alloy surface. Agreement among these different independent techniques indicates the validity of the obtained results.This thesis contains also references, Arabic and English summaries.