الفهرس 
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Abstract
The present study deals with preparation and evaluation of novel cationic surfactants as corrosion inhibitors for carbon steel in 1.0 M HCl. In addition improving the protection efficiency of paint for carbon steel by surfactants assembling on nanoparticles.
1. Synthesis of the cationic surfactant.
A. Synthesis of the cationic thiol surfactants
The cationic thiols, namely (octyl, decyl, and dodecyl-4-mercapto pyridine-1-ium bromide), I, II and III respectively, were synthesized from reaction 4-mercaptopyridine with alkyl halides with different alkyl chain lengths (octyl, decyl and dodecylbromide) in ethanol at 70oC for 50h.
B. Synthesis of amphoteric and di-cationic surfactants. These compounds, namely (4-((((1-dodecylpyridin-1-ium bromide)-4-yl)methylene)amino)benzoate sodium (IV) and 1-dodecyl-4-(((1-dodecylpyridin-1-ium-4-yl)imino)methyl)pyridin-1-ium bromide (V)) have been successfully synthesized in two steps: In the first step, a mixture of equimolar 4-nicotine aldehyde and sodium 4-aminobenzoate and 4-aminopyridine in acetone was refluxed for 4 h at 70 oC. In the second step, the amphoteric and di-cationic surfactants products from first step were refluxed with 1-bromododecane, respectively, in ethanol for 12 h.
2. Chemical structures of the prepared surfactants were confirmed by 1H NMR, FTIR and Mass spectra.
3. Preparation of silver nanoparticles solution (AgNPs).
Silver nanoparticles solution was prepared by chemical reduction method. AgNO3 solution was heated with trisodium citrate this process the solution was mixed vigorously and heated until color’s change is evident (pale yellow).
4. Preparation of the cationic surfactants-coated silver nanoparticles: 20 ml of citrate-capped silver nanoparticles solution was mixed with 5 mL saturated surfactant solution in deionized water and stirred effectively. Stirring was continued for 24 h until the yellow colour vanished.
5. Preparation of gold nanoparticles solution
Gold nanoparticles solution was prepared by the reduction of chloroauric acid (HAuCl4) with tri sodium citrate then the resulting mixture was stirred for 1 h and then cooled. To formed mixture tri sodium citrate was added slowly and stirred until the color turned orange.
6. Preparation of the cationic surfactants-coated gold nanoparticles: 20 ml of the gold nanoparticles solution was mixed with 5 ml of cationic surfactants solution in distilled water. The mixture was stirred for 24 h until the orange color faded
7. The Surface active properties of the prepared surfactants were evaluated. The data for thiol surfactants show that the results: the increase in hydrophobic chain length (III > II > I) makes the surfactant molecule more active at air / water interface. Also the Amin values were decreased, though the Γmax values were increased with increasing both the carbon chain length and corrosion inhibition efficiency of cationic surfactants. In case of series two surface tension of di-cationic (V) less than amphoteric (IV).
8. The adsorption of surfactant on carbon steel obeyed the Langmuir adsorption isotherm. Thermodynamic parameters for adsorption process such as free standard energy (ΔGοads), enthalpy (ΔHoads) and entropy (ΔSoads) of the surfactants were calculated. The negative values of (ΔGοads) indicate that the adsorption on the metal surface is a spontaneous process. The negative value of (ΔHoads) indicates that the adsorption is exothermic process. The positive sign of (ΔSoads) is attributed to an increase of disorder due to the adsorption of only one surfactant molecule by desorption of more water molecules.
9. The prepared cationic surfactants were evaluated as corrosion inhibitor using different techniques:
i. Weight loss measurements
The data revered that, the inhibition efficiency of synthesized cationic surfactants (I, II, III, IV and V) increased with increasing its concentration and decreased with increased temperature.
The maximum corrosion inhibition efficiency for all compounds was obtained at 1x10-2 M. The corrosion inhibition efficiency of the investigated cationic surfactants decreased in the following order:
III > II > I (in series 1)
The corrosion inhibition efficiency of the di-cationic surfactant is greater than amphoteric surfactant. This related to the presence of two pyridine ring in di-cationic molecule, two double bond and N=C group more effective in addition of two fatty length chain while amphoteric surfactant have one pyridine ring, benzene ring, two oxygen atoms and only one fatty length chain V > IV (in series 2).
ii. Potentiodynamic polarization measurements
The data indicated that by increasing the inhibitor concentration the inhibition efficiency increased. The results showed that inhibitor species may be adsorbed on the steel surface and cover some active sites of the electrode surface.
iii. Electrochemical impedance spectroscopy (ElS)
In the Nyquist plots, the data showed that an increase of charge transfer resistance and a decrease of double layer capacitance with increasing the inhibitor concentration related to formation of a barrier surface film.
10. characterization of (AgNPs) and (AuNPs) capped by synthesized cationic surfactants (I, II, III, IV, V) were examined by FTIR, UV and TEM. The results confirmed that the synthesized surfactants form nanoshells arround the prepared (AgNPs) and (AuNPs).
11. The performance of epoxy paint of carbon steel in 3.5% NaCl solution after addition of capped (AgNPs) and (AuNPs) by surfactants in paint by different techniques:
i. Potentiodynamic polarization measurements.
we find that increasing of the amount of nanoparticles exhibit much better barrier until reached to (1 wt %) agglomerations observed between the nanoparticles and therefore the modified coatings which can easily agglomerate and are converted to micron size as a result of a large specific surface area of agglomerate nanoparticles and high surface and decreased the inhibition efficiency.
The data showed that, icorr decreases by increases the amount of nanoparticles thereby causing inhibition of corrosion.
It noted that icorr values for AgNPs are higher than icorr values for AuNPs as inferred from icorr values.
ii. Electrochemical impedance spectroscopy (ElS). The obtained data showed that, with increasing the amount of capped (AgNPs) and (AuNPs) by surfactants in the epoxy paint to a certain extent. The paint became more protective toward corrosion of carbon steel electrode in 3.5% NaCl solution. This is due to decrease of porosity and increased tourtousity to corrosive species to diffusion through the coating film.
iii. Salt spray test showed that, the spreading of corrosion underneath the modified epoxy paint decreased by increasing the amount of (AgNPs) and (AuNPs) capped by surfactants. This behavior further supported the results obtained from the electrochemical measurements.