الفهرس 
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Abstract
That the problem of corrosion of the problems facing the world a long time ago, and even now, where he cannot permanently prevent corrosion, but can reduce the risk of metals and alloys, this letter discusses aluminum alloy corrosion in an acid environment and how to protect it. The thesis comprises three main chapters. The first chapter Deals with introduction, which included the basics of metal corrosion, corrosion forms and methods of protection .Were also reviewed published research on aluminum alloy corrosion in acidic solutions and the ability of plant extracts on the corrosion resistance, also included on the target of the thesis. The second chapter Includes the chemical composition of alloy aluminum used in the study , also ways to prepare solutions of acid (HCl) , disincentives used , description of measurement methods Electrochemical that was used to measure the rate of corrosion, the preparation and Chemical structure of compounds from used extracts, the preparation of the electrodes , the cell electrophysiological and explain the methods testing process and methods of calculations. The third chapter Deals with the results obtained and their discussion and is divided into five sections: Section A: Contains the practical results of the method of weight loss and discussed have been reviewing the results in tables and curves where the study revealed alloy aluminum in a solution of 1M of HCl in the presence of these plant extracts that all vehicles used in the study reduce corrosion alloy aluminum regardless matter where a replacement, and has found that the order of inhibition efficiency of the solution depends on groups associated by boat and how they affect it. And have used this method to find out the effect of temperature on the inhibition of corrosion alloy aluminum in a solution of HCl at four different grades in the range 25 - 45° C, and found that the corrosion rate increases with temperature with the lack of efficiency of inhibition which shows that inhibition occurs for through physical adsorption inhibitors and follow isotherm langmuir and after drawing a relationship between θ/1-θ vs C in case of Xanthium spinosum and Withania somnifera inhibitors,but inhibition occurs for through chemical adsorption inhibitors and follow isotherm Temkin and after drawing a relationship between θ vs log C in case of Cynara scolymus and Primula inhibitors. The Langmuir isotherm is given as: The Temkin isotherm is given as: θ = 2.303/a log K + 2.303/a log C where C is the inhibitor concentration and Ka is the equilibrium constant of adsorption process and is related to the standard free energy of adsorption ΔG˚ads by the equation: Ka= 1/55.5 exp (-ΔG°ads/RT) The negative values of ΔG˚ads ensure the spontaneity of the adsorption process and the stability of the adsorbed layer on the aluminum surface. And has been the study of transactions activation of vehicles: that draw a relationship between the log corrosion rate and (1000 / T) of a mile lines might find the energies activation was also the expense of some thermodynamic functions for the process of activation with a discussion of semantics values and so draw the relationship between Log (corrosion rate / T) vs. 1000 / T. The influence of temperature on the corrosion rate of aluminum alloy in 1 M HCl the electrochemical frequency modulation technique in temperature range 25 – 45˚C. The % inhibition efficiency is found to decrease (Xanthium spinosum and Withania somnifera) and increase (Cynara scolymus and Primula) with increasing the temperature; this indicated that, these inhibitors are physically and chemically Respectively adsorbed on the aluminum alloy 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 calculated values of the activation energy in the absence and presence of the inhibitors were found to increase with increasing the temperature. 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. The results obtained from thermodynamic parameters give further support to that obtained before. A number of mathematical relationships for the adsorption isotherms have been suggested to fit the experiment data of the present work. The Langmuir (Xanthium spinosum and Withania somnifera) and Temkin (Cynara scolymus and Primula) mode is the best for plant extracts Respectively. Section B: Potentiodynamic polarization measurements were carried out for aluminum alloy in 1 M HCl in the absence and presence of different concentrations of the plant extracts such as (Xanthium spinosum, Withania somnifera,Cynara scolymus and Primula) . The polarization curves indicated that these inhibitors influence both cathodic and anodic processes. Section C: AC impedance spectroscopy measurements were carried out for aluminum alloy in 1 M HCl in the absence and presence of different concentrations of plant extracts. from the impedance data, we conclude that: 1. 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. 2. 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 aluminum alloy surface. 3. The % IE obtained from EIS measurements are close to those deduced from polarization. 4. Section D: Electrochemical frequency modulation measurements (EFM) were carried out for aluminum alloy in 1 M HCl in the absence and presence of different concentrations of plant extracts.The obtained results showed good agreement of corrosion kinetic parameters obtained with the EFM, Tafel extrapolation and EIS methods. Section E: Surface morphology of polished aluminum samples prior to and following immersion in 1 M HCl. in the lack and existence of plant extracts for 24 hrs. were executed utilizing Nano Surf Easy scan 2 Flex AFM instruments where AFM analysis showed the surface of the metal before immersion in HCl acid is smoothened after immersion 1 M HCl the surface is destroyed and the roughness increases while the Al sample treated with 300 ppm of plant extracts the surface become smoother and the roughness decreased in comparison with blank sample as a consequence of the adsorption of extracts on the surface of Al metal forming protective film. In addition, X-ray photoelectron spectroscopy (XPS) measurements were performed using ESCALAB 250Xi, Thermo Scientific, USA. XPS analysis gets profound knowledge approximately the chemical nature of the interface between plant extracts and the surface of Al.