الفهرس 
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Abstract
Studies of electrochemistry and corrosion behavior of Aluminum and its alloys are very important fields for scientific and industrial work. The present work includes detailed studies on the corrosion and corrosion inhibition of two aluminum alloys A5052 and A5754 in different aqueous solutions. (Acidic, neutral and alkaline solutions). In addition, the effect of plasma electrolytic oxidation (PEO) process on the corrosion resistance of pure aluminum was studied in HCl.
The following techniques were used in these studies:
i) Potentiodynamic polarization technique.
ii) Cyclic voltammetric technique.
iii) Electrochemical impedance technique
iv) Scanning electron microscopy (SEM) and EDX technique.
v) X-ray diffraction spectroscopy technique.
The present study consists of three chapters:-
1) Chapter I gives a general introduction on the corrosion and corrosion inhibition and give also a literatures survey on the electrochemistry and corrosion behavior of aluminum alloys in different aqueous solutions.
2) Chapter II includes the experimental part. This includes preparation of the various solutions, electrodes and methods for testing corrosion.
3) Chapter III includes the results and discussion of the corrosion and corrosion inhibition of aluminum alloys A5052 and A5754 in different aqueous solutions. Also, the effect of plasma electrolytic oxidation on the corrosion behavior of pure aluminum in HCl solution.
The present Chapter III was divided into five parts:-
Part (III.1): dealing with studying the quantum chemical studies of Tween 80 and Tween 20 surfactants. The quantum chemical study was carried out to determine the electron rich groups/atoms in Tween 80 and Tween 20 as well as calculation of the highest molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) will give further insights on the possibility [87].
Part (III.2): Dealing with studying the corrosion and corrosion inhibition of A5052 and A5754 aluminum alloys in sulfuric acid solutions. For comparison some experiment were carried using pure aluminum.
The following topics were investigated:
1) Study the corrosion behavior of A5052 and A5754 aluminum alloys in sulfuric acid solutions. The effect of sulfuric acid concentration, scan rate and temperatures was studied. It is found that the corrosion rate of pure aluminum, A5052 and A5754 alloys increased with an increase in acid concentration, scan rate and temperature. Their corrosion resistance increases in the order:
Al < A5754 < A5052
2) The corrosion inhibition of the two Al alloys in H2SO4 solution using Tween 80 and Tween 20 was investigated. The data clearly showed that the addition of the two surfactants inhibits the corrosion rate of two Al alloys in H2SO4 solution. The inhibition efficiency of the two surfactants increases with increasing their concentrations but decreases with increasing temperature of medium. The results of potentiodynamic polarization measurements demonstrate that the two inhibitors are considered mainly as anodic type inhibitors. The results reveal that inhibition is due to the adsorption of the surfactant molecules on the alloy surface and the adsorption of these inhibitors obey Langmuir adsorption isotherm. Tween 80 is more effective inhibitor then Tween 20.
3) The corrosion inhibition of the two Al alloys in H2SO4 solution using some inorganic anions (MoO42-and WO42-) was investigated. Inspection of the result reveals that the presence of either molybdate or tungstate oxy anions in the acid solution decreases the corrosion rate of the two Al alloys. The inhibition functions of these oxy anions enhance with increasing their concentrations. The inhibition efficiency of the inorganic inhibitor decreases with increasing temperature. The adsorption process on the alloys surface occurs spontaneously.
4) Pitting corrosion of the two aluminum alloys, A5052 and A5754 in H2SO4 solution by the addition of NaCl, NaBr or NaI as pitting corrosion agents was studied. It is worth observing that the presence of the aggressive halides anions increases suddenly and rapidly the anodic passive current density at a given critical pitting potential Epit without any sign for the oxygen evolution indicating initiation and growth of pitting corrosion. Cl- anions is the most effective as a pitting agent while I- ion is the lowest one. On the other hand, addition of MoO42- to the pitting corrosion solution shifts the pitting potential Epit to more positive potentials indicating the pitting corrosion resistance of the two alloys increases in the presence of this oxy anion.
Part (III.3): dealing with studying the corrosion and corrosion inhibition of A5052 and A5754 aluminum alloys in sodium hydroxide solutions. It is clear that the values of corrosion potential shift to more negative potentials and the values of corrosion rate enhance for the two alloys with increasing the NaOH concentration and with raising the solution temperature. Tween 80 and Tween 20 act as good inhibitors for the corrosion of A5052 and A5754 in 0.5 M NaOH solution. The inhibition efficiency increases with increasing Tween 80 or Tween 20 concentration but decreases with raising temperature to attain a maximum value at300 ppm at 298 K. Tween 80 and Tween 20 adsorbed on the metal surface according to Langmuir adsorption isotherm model with negative values of ΔGoads. The ΔGoads value suggests that the adsorption process may occur by both physical and chemical adsorption (mixed- type).
Part (III.4): dealing with studying electrochemical behavior of aluminum alloys A5052 and A5754 in sodium sulfate solutions. The data revealed that the rate of corrosion of the two aluminum alloys increases with sodium sulfate concentration and decreases with temperature. The presence of Cl- ions in sodium sulfate solution enhances the uniform corrosion of the aluminum alloys and tends to breakdown the passive film and promoting pitting corrosion.
The corrosion inhibition of the two Al alloys in sodium sulfate solutions using Tween 80 and Tween 20 was investigated in this part. Results reported that addition of these surfactants inhibits the corrosion of two Al alloys and the extent of inhibition depends upon the type and concentration of the surfactant. The inhibition efficiency for these surfactants increases with the increase of their concentration. Mixed - type of the two surfactants is responsible for their corrosion inhibition.
Part (III.5): dealing with studying the influence of plasma electrolytic oxidation (PEO) on the improvement of pure aluminum corrosion resistance in 0.5 M HCl solution.
Influence of many factors such as the composition of electrolytes, time and inorganic additive on the performance of PEO process have been investigated. The surface morphology of PEO films was inspected using SEM, EDX and XRD analysis. The electrochemical impedance spectroscopy (EIS) and polarization measurements were carried out to evaluate the corrosion resistance of aluminum. The hardness and reduced modulus of aluminum surface at different PEO process times were determined by nanoindenter measurements. The results showed that the PEO process is able to improve the corrosion of aluminum in HCl solution. The best conditions for formation high efficient oxide layer on the aluminum surface during PEO process were found in 0.001 M NaOH electrolyte for 5 min. The surface morphology analysis showed that PEO process produce a highly resistant protective oxide layer, mainly composed of orthorhombic crystalline phase of α-Al2O3. This oxide phase is characterized by its great hardness.