الفهرس 
GENERAL ASPECTS OF CORROSIONOnly 14 pages are availabe for public view
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Abstract
Studies of electrochemical and corrosion behavior of metal are very important fields for
scientific and industrial work. The present work includes detailed studies on the influence of
organic surfactants on the corrosion behavior of carbon steel in different acidic aqueous
solutions under different conditions.
The following techniques were used in these studies:
i) Weight loss method
ii) Potentiodynamic polarization technique.
iii) Cyclic voltammetric technique.
iv) Electrochemical impedance technique.
v) Scanning electron microscopy (SEM) technique.
The present study consists of numerous chapters:-
1) Chapter I gives a general introduction on the corrosion theory and gives also a
literatures survey on the corrosion and corrosion inhibition behavior of steel in different
aqueous solutions.
2) Chapter II includes the experimental part. This includes preparation of the various
solutions, electrodes and methods for testing corrosion.
3) Chapter III includes the results and discussion of the obtained data. The data are
presented in the form of Figures, Tables and SEM pictures.
The present studies are divided into four main parts:-
Part (1): dealing with studying the quantum chemical studies of nonionic surfactant nonoxinol-9
(N9) and cetrimonium bromide cationic surfactant (CB). The quantum chemical study was
carried out to determine the electron rich groups/atoms in N9 and CB as well as a calculation of
the highest molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) will
give further insights on inhibition efficiency.
Part (2): dealing with the studying the corrosion inhibition of carbon steel in 1 M hydrochloric
acid solution by using nonoxynol-9 (N9) as a nonionic surfactant and cetrimonium bromide (CB)
as a cationic surfactant.
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The following conclusions may be drawn from the study:
1. The investigated surfactants (N9and CB) inhibit the corrosion of carbon steel in 1 M HCl.
2. The effects of inhibitor concentration and temperature on the performance and extent
of adsorption of surfactants are studied.
3. Results reported in this study show that the additions of these surfactants inhibit the
uniform corrosion of carbon steel and the extent of inhibition depends upon the type
and concentration of the surfactant.
4. The inhibition efficiencies of these surfactants increase with increasing their
concentrations while decrease with increasing temperature.
5. The inhibition is due to adsorption of the inhibitor species on the carbon steel surface
and blocking its active sites without altering the mechanism of corrosion process.
6. The data reveal that the inhibition efficiency decreases with an increase in temperature.
This can be due to the decrease in the strength of adsorption process at higher
temperatures, suggesting that physical adsorption may be the type of adsorption of the
surfactant on the carbon steel surfaces.
7. The addition of N9 and CB to blank acid solution enhances the apparent activation
energy.
8. The positive values of ΔHa both in absence and presence of N9 and CB reflect the
endothermic nature of the carbon steel dissolution process.
9. Polarization data shows that the investigated inhibitors act as mixed-type inhibitors in 1
M HCl solution.
10. Results obtained from weight loss, DC polarization, AC impedance techniques are in
good agreement.
11. Double layer capacitances decrease with respect to blank solution when the
investigated inhibitors are added. This fact confirms the adsorption of investigated
inhibitor molecules on the carbon steel surface.
12. Adsorption of the inhibitors fit Langmuir and Frumkin isotherm models.
13. In all cases the negative values of ΔG◦
adsshow the spontaneity of the adsorption process,
and the adsorption process is a physical adsorption process.14. The percentage of corrosion inhibition of these surfactants decreases in the order: N9<
CB.
Part (3): dealing with studying the corrosion inhibition of carbon steel in 1 M H2SO4 solution in
the absence and presence of nonoxynol-9 (N9) as a nonionic surfactant and cetrimonium
bromide (CB) as a cationic surfactant.
The following conclusions may be drawn from the study:
1. The data reveal that the presence of either N9 or CB in the blank 1 M H2SO4 solution
inhibits the uniform corrosion of the carbon steel in 1 M H2SO4 solution.
2. Potentiodynamic polarization measurements, weight loss measurements and EIS
measurements showed that the inhibition efficiencies of the two inhibitors increase with
increasing their concentrations.
3. The inhibition efficiency depends on the type of inhibitor. N9 is more effective as inhibitor
than CB.
4. The inhibition efficiency of each surfactant is due to its adsorption and formation of
protective film on the electrode surface.
5. The two inhibitors act mainly as mixed type inhibitors.
6. The inhibition efficiency in all cases decreases with increasing the temperature as a result
of shifting the adsorption-desorption equilibrium towards desorption.
7. Adsorption of each inhibitor obeys Lungmuir and Framkin isotherms.
8. The activation thermodynamic parameters, Ea, ΔH and ΔS for the dissolution (corrosion)
of carbon steel in 1M H2SO4 solution devoid of and containing N9 or CB were determined.
The data reveal that the value of Ea for inhibited solution is higher than that for
uninhibited solution indicating the formation of barrier film of the inhibitors on the
electrode surface.
9. The values of ΔH are positive indicating that in all cases the corrosion process is
endothermic.
10. The thermodynamic parameters for adsorption process were calculated and the results
indicate that adsorption process in all cases is spontaneous and exothermic.11. EIS measurements confirm the assumption that the inhibitor function of N9 and CB is due
to their adsorption and formation of barrier film on the electrode surface and the
corrosion process is under charge-transfer control.
12. Addition of small amount of NaCl to H2SO4 solution enhances the inhibition efficiency of
CB and Cl- ion (cooperative synergism).
13. The anodic polarization curves of carbon steel in 1M H2SO4 solution without and with
different concentrations of N9 and CB were recorded.
14. The data reveal that the anodic polarization curves in all cases exhibit active/ passive
transition.
15. The presence of the inhibitors decreases the active anodic dissolution and increases the
passive regions of carbon steel electrode.
Part (4): dealing with studying the corrosion and corrosion inhibition of carbon steel electrode
in 1M CH3COOH and in mixtures of CH3COOH + CH3COONa by polarization and EIS
measurements at 298K.
The following conclusions may be drawn from study.
1- The rate of corrosion of carbon steel in 1M CH3COOH is very small as compared with its
corrosion rate in 1M HCl and 1M H2SO4. This because CH3COOH is very week electrolyte.
2- The addition of either N9 or CB inhibits the uniform corrosion of the electrode in pure
acetic acid and in the mixture of acetic acid + sodium acetate solution.
3- The inhibition efficiencies depend on the type and concentration of the inhibitors.
4- The inhibition is due to the adsorption of the inhibitor species on the electrode surface.
5- The inhibition efficiency of each inhibitor increases with its concentrations
6- Addition of sodium acetate to the acetic acid enhances the rate of the uniform corrosion
of carbon steel.
7- The anodic polarization curves for carbon steel electrode in pure acetic acid solution and
in mixture of acetic acid and sodium acetate were recorded. In pure acetic acid the
anodic polarization involves active dissolution while in the mixture the anodic
polarization curves exhibit active / passive transition.8- The active dissolution enhances with increasing the scan rate.
9- Cyclic voltammetric measurements reveal that reversed anodic scan retraces its self-up
to a certain reactivation potential at which the passive current density increases and
forming a reactive anodic peak AII within the forward active anodic peak AI.
10- Repeated cycling enhances both the anodic active and anodic reactive dissolution of
carbon steel.
11- Addition of either N9 or CB inhibits the active dissolution of the electrode and the
extent of inhibition depends on the type and concentration of the inhibitor added.
12- The influence of adding NaCl to the mixture (blank) depends on its concentration. Very
small amount of NaCl (0.005M) has no significant effect on the passivity of the
electrode. Addition of higher concentrations of NaCl (0.007-0.05M) breaks down the
passive layer and causes pitting corrosion. Further increase in Cl- concentration (0.1M)
prevents the passivation.
13- Addition of N9 or CB in solution containing 0.5M acetic acid + 0.5M sodium acetate +
0.007M NaCl increases the pitting corrosion resistance.
14- The occurrence of pitting corrosion was confirmed by SEM.