الفهرس 
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Abstract
The aim of the present work is to study the reactivity of four plant extracts as a
corrosion inhibitors for C-steel in 1 M HCl solution.
The thesis started with Introduction, which includes corrosion theories, types of
corrosion, corrosion protection, literature survey on corrosion behavior of C-steel in 1
M HCl solution.
Evaluation of the extracts efficiencies by weight loss method in the presence and
absence of four plant extracts in 1 M HCl at 25º C, revealed that the extracts
efficiencies increase with the concentration. from these studies the order of inhibition
efficiency of investigated extracts in 1 M HCl is found to be:
Peganum Harmala > Melissa Officinalis > Tribulus Terrestris > Alpinia Galanga
These extracts obey Langmuir adsorption isotherm. These extracts showing
that the inhibition is by adsorption.the action of the extracts in 1 M HCl was assumed
to be due to their adsorption at the metal /solution interface.
The Potentiodynamic polarization curves indicated that these extracts influence both
cathodic and anodic processes, although mainly the cathodic one.
Impedance spectroscopy measurements were carried out for steel in 1 M HCl in the
absence and presence of different concentrations of the investigated plant extracts,
from the impedance data, we conclude that the value of Rct increases with increase in
the concentration of the extracts and this indicates an increase in the corrosion
inhibition efficiency in 1 M HCl solution.
The obtained results from Electrochemical frequency modulation measurements
(EFM) showed good agreement of corrosion kinetic parameters obtained with the
EFM, weight loss, Tafel extrapolation and EIS methods
SEM and FT-IR showed that the plant extracts were adsorbed on the metal
surface forming a thin layer that protects metal from corrosion.
Weight loss, potentiodynamic polarization, electrochemical impedance spectroscopy
(EIS), electrochemical frequency modulation (EFM) measurements, FTIR and SEM
support the assumption that corrosion inhibition takes place through adsorption of the
extracts on the C-steel surface. Agreement among these different independent
techniques indicates the validity of the obtained results.