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Abstract This work contains three chapters:-Chapter 1: IntroductionAn introduction about surfactants (definition, classification and applications), an introduction about corrosion (definition, forms,corrosion control and coating), and an introduction about nanotechnology and nanoparticles.Chapter 2: Materials and experimental techniquesThe experimental part included complete description of synthesis of inhibitors as the following: 1- Synthesis of novel cationic surfactants a- Synthesis of novel N- (3-morpholinopropyl)dodecan- 1-aminium bromide (I) by alkylation reaction of one mole 3-morpholinopropane- 1-amine and one mole of 1-bromododecane. b- Synthesis of novel N- (2-(2-mercaptoacetoxy)ethyl)-N,Ndimethyldodecan- 1-aminium bromide (II) was carried out in two steps as follows: (i) Synthesis of N- (2-hydroxyehtyl)-N,N-dimethyldodecane- 1-aminium bromide by quaternization reaction of one mole of 2-(dimethylamino)ethanol and one mole of 1-bromododecane. Summary and Conclusions (ii) The product from the previous step was esterified with 2-mercaptoacetic acid to produce N- 2-mercaptoacetoxy)- ethyl)-N,N-dimethyldodecan- 1-aminium bromide (II). c- Preparation of copper nanoparticles (CuNPs). CuNPs were prepared by chemical reduction of CuCl 2 solution in the presence of synthesized cationic surfactants (I or II). 2- The chemical structure of the prepared compounds was confirmed using FTIR, 1HNMR and Mass spectroscopes. 3- Description of corrosion tests which used to evaluate the inhibition efficiency of the used inhibitors for carbon steel pipelines corrosion in 1.0 M HCl. 4- Applications of the unmodified and modified paints and performance of these paints as anti corrosion coats for carbon steel in 3.5 wt% NaCl solution by different techniques. Chapter 3: Results and discussion This chapter included the following parts:- 1- Characterization of the synthesized surfactants by FTIR, 1HNMR and Mass spectroscopy. 2- The surface active properties of the prepared surfactants:- The data showed that linear decrease in surface tension was observed with an increase in the surfactants concentrations up to the Ccmc, beyond which no considerable change was noticed. The values of effectiveness (πcmc), maximum surface excess (Γmax) and the minimum surface area (Amin) were calculated. Summary and Conclusions iii Specific conductivity (K) measurements of cationic surfactants were performed in order to evaluate the Ccmc and the degree of counter ion dissociation, β. The values of standard free energy for micellization (ΔGo m) were calculated. The data showed that the standard free energies of micellization for the synthesized surfactants are always negative, indicating that the micellization is a spontaneous process. 3-The prepared compounds were investigated as corrosion inhibitors using three techniques:- a) Weight loss measurements The data revealed that, the inhibition efficiency of the synthesized cationic surfactants (I and II) increased with increasing their concentrations and temperature. b) Potentiodynamic polarization measurements The data indicated that all prepared cationic surfactants (I and II) shifted slightly the polarization curves toward both cathodic and anodic directions and did not show any definite trend in 1.0 M HCl and also the values of icorr decreased with increase of inhibitors concentration. This behavior confirmed that the synthesized cationic surfactants acted as mixed type inhibitors. Moreover, βc values increased with increase of inhibitors concentration. The inhibition efficiency of all prepared surfactants increased with inhibitors concentration increment. This fact suggested that Summary and Conclusions iv the inhibitors species may be adsorbed on the steel surface and cover some active sites of the electrode surface. c- Electrochemical impedance spectroscopy (EIS) a- Nyquist plots For the two prepared surfactants, the data showed that an increase of charge transfer resistance and decrease of the pseudo capacity of the double layer with increasing any inhibitor concentrations indicated that these inhibitors have the ability to inhibit the corrosion rate of carbon steel by adsorption mechanism (formation of a barrier surface film which separates the steel surface from the corrosive medium). The results obtained from the weight loss measurements were in good agreements with those obtained from potentiodynamic polarization method and electrochemical impedance spectroscopy (EIS) method. b- Bode plots The increase of absolute impedance at low frequencies in Bode plots confirmed the higher protection with increasing the concentration of the prepared inhibitors (I and II), which is related to adsorption of the inhibitors on the carbon steel surface. The depression of phase angle at relaxation frequency occurs with decreasing of any inhibitor concentrations which indicated the decrease of capacitive response with the decrease of inhibitor Summary and Conclusions v concentrations. Such a phenomenon could be attributed to higher corrosion activity at low concentrations of inhibitors. 4- Thermodynamic parameters:- a- Activation thermodynamic parameters. The values of activation energy (Ea) for corrosion process were calculated from Arrhenius equation in the absence and presence of the prepared surfactants (I and II). The data indicated that, the activation energy decreased in the presence of the two cationic surfactants which indicated the occurrence of chemisorption (sharing or transferring of electrons from inhibitor molecules to the metal surface to form a coordinate type of bond). The change in enthalpy and entropy of activation values (ΔH*, ΔS*) were calculated from the transition state equation. b- Adsorption thermodynamic parameters The adsorption of these cationic surfactants on the carbon steel surface obeyed the Langmuir adsorption isotherm. Thermodynamic parameters for adsorption process such as free standard energy (ΔGo ads), enthalpy (ΔHo ads) and entropy (ΔSo ads) of the prepared surfactants were determined. The negative values of (ΔGo ads) indicated that the adsorption of inhibitors on the metal surface is spontaneous process. The positive value of ΔHo ads indicated that the adsorption of investigated inhibitors (I and II) on the carbon steel surface is endothermic. The positive sign of (ΔSo ads) attributed to the increase of disorder due to the adsorption Summary and Conclusions vi of only one surfactant molecule by desorption of more water molecules. 5- Quantum chemistry calculations For all prepared inhibitors, ΔN shows inhibition efficiency resulted from electron donation, and the inhibition efficiency increases with the increase in electron-donating ability to the metal surface. The synthesized inhibitors (I and II) were donors of electrons, and the steel surface was the acceptor, and this favors chemical adsorption of the inhibitors on the electrode surface. 6- Scanning electron microscopy (SEM) investigation revealed that, the surface was strongly damaged in absence of corrosion inhibitors, where the surface in the presence of corrosion inhibitors was free from pits and smooths indicating the presence of a good protective film on the steel surface of the metal and also confirms the high inhibition efficiency of the prepared surfactants. 7- Characterization of the CuNPs capped by synthesized cationic surfactants (I and II) was confirmed by FTIR spectroscopy and TEM. Results confirmed that the synthesized cationic surfactant form nanoshells on the prepared CuNPs. 8- Performance of paint by using three techniques:-. a- Potentiodynamic polarization measurements Addition of capped CuNPs in the paint inhibited the corro sion of carbon steel in 3.5 % NaCl solution. The inhibition efficiency Summary and Conclusions vii decreased with increasing the amount of capped CuNPs in the paint. Ecorr for all prepared surfactants slightly shifted towards the cathodic side. The value of icorr for electrode painted with blank (unmodified) paint is usually larger than those obtained using modified paints containing different amounts of capped CuNPs (0.5, 1, 2, 4 wt%) and increased with increase of the capped CuNPs concentration in paint. b- Electrochemical impedance spectroscopy (EIS) The data showed that, a decrease of charge transfer resistance and an increase of the capacity of the double layer by increasing of concentration of capped CuNPs in the paint. c- Salt spray test The salt spray tests of the carbon steel coated by unmodified and modified paint carried out for 500h at 35 oC showed that, the spreading of corrosion underneath the modified coating film decreased by decreasing of the capped CuNPs concentration. This behavior further supported the results obtained from the electrochemical measurements. |