الفهرس 
chapter 1Only 14 pages are availabe for public view
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Abstract
The corrosion 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 Brass in 1M HNO3.
This work contains three basic chapters
Chapter one: “INTRODUCTION”
This chapter includes corrosion theory, the basics of metal corrosion, causes of corrosion, forms of corrosion, corrosion migration, types of inhibitors, methods of protection, Literature survey of Brass corrosion and aim of this study
Chapter two: ”EXPERIMENTAL SECTION”
It includes the chemical composition of the investigated material, preparation of the used nitric acid solution, preparation of the used polyethylene glycol and ethylene glycol with zinc sulphate, solutions and procedures used for the corrosion measurements such as a weight loss and electrochemical techniques. This chapter includes composition of α-Brass used the preparation of the test specimens for the different techniques of measurements and methods of preparation of materials of various solutions used. Also, the procedures followed for corrosion measurements, using weight loss, potentiodynamic, EIS and EFM techniques are included in this chapter.
Chapter three: ”RESULTS AND DISCUSSION”
Results and discussion chapter deals with the results obtained and their discussion and this chapter is divided into four sections:
Section (A):
The first one is the non-electrochemical method which make the evaluation of the inhibitor efficiency by weight loss method for inhibitors (polyethylene glycol and ethylene glycol with zinc sulphate) (50-300 ppm) in 1M HNO3 at 25°C revealed that the inhibitor efficiency increases with the increasing of the concentration.
Also, studying the effect of temperature on the corrosion rate of α-brass in 1M HNO3 over a temperature range from 25 to 45oC revealed that the inhibitor efficiency decrease with increase the temperature , indicating that the inhibition occurs through physical adsorption of the additives on α-brass surface, including the calculation and discussion of thermodynamic kinetic parameters (ΔH*, Ea*and ΔS*) of the investigated inhibitors on the α-brass surface by plotting various Transition state and Arrhenius curves .
Also the inhibitors under study obey Langmuir adsorption isotherm showing that the inhibition is by adsorption. The degree of surface coverage (θ) for the inhibitors on the metal surface increases with increasing the concentration in the corrosive medium. The action of the inhibitors in the aggressive acid was assumed to be due to their adsorption at the metal /solution interface. The results were treated to obtain the thermodynamic parameters for the adsorption of inhibitors from Langmuir isotherm model and kinetic-thermodynamic model of El-Awady ( ΔGoads ,ΔHoads,and ∆S◦ads )and the binding constant kads , indicating that the inhibition occurs through physical and chemial adsorption of the additives on α-brass surface. The negative values of ΔGoads indicate that the corrosion of α-Brass in 1M HNO3 is spontaneous process.
Section (B):
Potentiodynamic polarization measurements were carried out for α-Brass in 1M HNO3 in the absence and presence of different concentrations of polyethylene glycol and ethylene glycol with zinc sulphate. The polarization curves indicated that these inhibitors influence both cathodic and anodic processes Corrosion rate decreased with increasing of concentration of the compounds together with increase in both cathodic and anodic polarization, but the corrosion inhibition has a great effect on the cathodic polarization. Variation of inhibition efficiency with the structure of compounds was interpreted in terms of the number of adsorption sites in the molecule and their electron charge density, molecular size, mode of adsorption and the polar effect of the substitutent groups.
AC impedence spectroscopy measurements were carried out for brass in 1M HNO3 in the absence and presence of different concentrations of the inhibitors under study charge transfer control.
from the impedance data, we conclude that:
1-The value of charge transfer resistance in presence of inhibitor (Rct) increases with increase in the concentration of the inhibitors. This indicates an increase in the corrosion inhibition 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 brass surface, suggesting an increase of the surface coverage (Ɵ) of the inhibitor.
3- The inhibition efficiency % IE obtained from electrochemical impedance spectroscopy measurements (EIS) are close to those deduced from polarization.
The new technique is the electrochemical frequency modulation (EFM) was used as a rapid and non-destructive technique for corrosion rate measurements. It was carried out for Brass in 1M HNO3 in the absence and presence of different concentrations of the inhibitors under study. Corrosion current densities (icorr) obtained with this technique was in good agreement with those obtained from weight-loss, polarization and EIS methods. In addition of the causality factors were good internal check for verifying the validity of data obtained by this technique. The corrosion rate decrease with increasing the concentration of inhibitors and the inhibition efficiency (% IE) is found to increase with increasing the inhibitors concentrations.
Section (C):
SEM analysis showed that the inhibition of the polyethylene glycol and ethylene glycol with zinc sulphate was adsorbed on the metal surface forming a thin layer by which metal was protected from corrosion. Also, in order to see whether the polymer and its monomer molecules are adsorbed on the brass surface or not, both scanning electron microscopy (SEM) and atomic force micrographs (AFM) experiments were carried out.
Section (D):
Solvation of polyethylene glycol, ethylene glycol and ethylene glycol with zinc sulphate in methanol-water and ethanol-water mixed solvents with different alcohol mole fractions (x1 = 0 to 1.0) were studied in terms of density, refractive index and UV-Visible spectra.