الفهرس 
AIM OF THE WORKOnly 14 pages are availabe for public view
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Abstract
The present study includes the corrosion inhibition of iron in 1.0M of HCl solution by some new pyridine-pyrimidine heterocyclic derivatives using several techniques include potentiodynamic polarization method, electrochemical impedance spectroscopy ,EIS, and electrochemical frequency modulation, EFM.
The measurements were carried out on pure iron (99.999) in 1.0 M HCl in the absence and presence of various concentrations (10-3, 10-4, 10-5, 10-6and 10-7 M) of Pyr-1, Pyr-2, Pyr-3, Pyr-4, Pyr-5, Pyr-6, Pyr-7, Pyr-8, Pyr-9, and Pyr-10
All investigated pyridine-pyrimidine heterocyclic derivatives have shown inhibiting properties for iron corrosion in in 1.0 M HCl. The inhibiting efficiency of investigated inhibitors increases in the following order:
Pyr-1 Pyr-2 Pyr-3 Pyr-4 Pyr-5 Pyr-6 Pyr-7 Pyr-8
Pyr-9 Pyr-10.
Electrochemical frequency modulation EFM can be used as a rapid and non-destructive technique for corrosion rate measurements without prior knowledge of Tafel constants. Corrosion rates obtained with this technique were in good agreement with other traditional techniques as potentiodynamic polarization and EIS. Causality factors used by EFM are good internal check for verifying the validity of data obtained by this technique.
Polarization curves in 1.0 M HCl in absence and presence of pyridine-pyrimidine heterocyclic derivatives at 25oC±1 indicated that these compounds act as mixed type inhibitor with mainly anodic process,
they increase both the anodic and cathodic over potentials and shifts parallely the position of the Tafel lines to both directions. This means that these compounds have no effect on the corrosion mechanism and so the adsorbed molecules exert their action by simple blocking of the active sites on iron surface and hence act as blocking type inhibitors.
The results of EIS indicate that the values of charge transfer resistance and inhibition efficiency tend to increase by increasing the inhibitor concentration. This result can be attributed to increase of the thickness of the electrical double layer.
Equivalent circuit that described the studied system has two-time constants.
Inhibition occurs through adsorption of the inhibitor on the iron surface. The adsorption of studied inhibitors obeys Langmuir isotherm.
Standard Gibbs free energies of adsorption reveal that the inhibition of corrosion by pyridine-pyrimidine heterocyclic derivatives is due to chemical adsorption.
Quantum chemical parameters were computed using the DFT method. These are mainly the energies of the highest occupied (EHOMO) and lowest unoccupied (ELUMO) molecular orbitals and total energy (Etot). These quantum chemical parameters were obtained after geometric optimization with respect to all nuclear coordinates.
The three different electrochemical techniques showed similar behavior. As the inhibitor concentration increased the corrosion rate decreased and the inhibition efficiency increased.
Monte Carlo simulation technique incorporating molecular mechanics and molecular dynamics can be used to simulate the adsorption of Pyridine-pyrimidine derivatives on the Fe (111) surface in
1.0 M HCl.
There is relationship between the structural properties of the studied inhibitor molecules and their inhibition efficiency aiming to construct a model using QSAR paradigm, genetic function approximation (GFA) and neural network analysis (ANN) techniques.