الفهرس 
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Abstract
The corrosion problem is a great problem, which faced the world from the last years until now, we can’t hide this problem from our live but we can reduce “inhibit” it in the metals by several methods as the environment need. This work discusses the corrosion of zinc in 1 M HCl in the absence and presence of three different plant extracts. This chapter one deals with Forms of corrosion, causes of corrosion, corrosion inhibition, types of inhibitors and Literature survey of zinc corrosion and aim of this study. Chapter two includes the chemical composition of the investigated material, preparation of the used hydrochloride acid solution, the used extract compounds, solutions and procedures used for the corrosion measurements such as chemical and electrochemical techniques, as well as, surface investigation. It deals with the results obtained and their discussion and this chapter is divided into four sections: Evaluation of the inhibitor efficiency by chemical methods (weight loss) in the presence and absence of different concentrations from the three plant extract compounds in 1 M H Cl at 25 o C. Data reveled that the inhibitor efficiency increases with the concentration. These extract compounds adsorbed on zinc surface according to Langmuir adsorption isotherm, showing that the inhibition is controlled by adsorption process. The degree of surface coverage (θ) for the inhibitors on the metal surface increases with increasing the concentration in the corrosive medium. The effect of temperature on the corrosion inhibition of zinc in 1 M H Cl was determined, from the thermodynamic parameter indicating that the inhibition occurs through physical adsorption of the additives on zinc surface. Also, some Thermodynamic functions of activation were calculated and discussed. The results obtained from (EIS) show that the corrosion reactions in the absence and presence of extract compounds occurred under charge transfer control. The increase in concentration of the inhibitors leads to an increase in the value of the charge transfer resistance (Rct) and decrease in the double layer capacitance (Cdl) of the corroding zinc interface with increasing in the inhibitor concentration. This behavior suggests an increase of the surface coverage of the inhibitor due to the adsorption process at the zinc surface. The new technique electrochemical frequency modulation (EFM) was used as a rapid and non-destructive technique for corrosion rate measurements. Corrosion current densities (icorr) obtained with this technique was in good agreement with those obtained from Tafel extrapolation technique. In addition of the causality factors were good internal check for verifying the validity of data obtained by this technique. The results were summarized as follows: SEM, EDX, FT – IR and AFM experiments were carried out in order to verify if the investigation of extract compounds is in fact adsorbed in the zinc surface. SEM and AFM Shows that zinc topography of the surface suffers from severe corrosion attack in the blank corroded sample. In contrast, in presence of the extract compounds the metallic surface seems to be less affected by corrosion where the specimen surfaces were less damaged. FT-IR spectra are shown addition (curve), demonstrating the existence function group like (hydroxyl, carbonyl, and amine) adsorbed on the surface of zinc. Also, shows that function group covered the specimen surface. UV absorption spectroscopy can-characterize those types of compounds which absorbs UV radiation thus used in qualitative determination of compounds. The UV spectra was carried out using UV spectrometer T80+ (UV TIS model, UK), for solutions of 1 M HCl and 300 ppm of the three plants extracts before and after Zn immersion for 24 hours. Biological effect of the plants extracts on Escherichia coli after the bacterial agriculture was examined using Doc-it colony counter instrument.