| Metal corrosion and protection is a permanent challenge for us, so it has been the focus research to design and synthesis new anti-corrosion material in this field. Now, the inhibitor which is heat-resistant, acid-resistant and long time-resistent is urgent needed. The inorganic corrosion inhibitors do not meet the sustainable development strategy due to they are poisonous; the metal are not protected well by small organic molecule inhibitors at high temperature and strong acid environment; the bad inhibitive effect of general polymer is related to their poor solubility and low diffusion rate in aqueous solution due to their large molecular weight. Therefore, in this paper, the feature of the aniline being able to polymerize in acid solution and of the surfactant being self-assembly at interface was took advantage by us. Four new alkyl anilines has been designed and synthesized, and the anticorrosion properties of the poly alkylphenyl amine in solution and of the in situ polymerized film of alkylphenyl amine on X70 steel surface were investigated. The main contents of this paper are as follows:1) In this paper, a series of alkyl amines with different length of alkyl chain which were marked as Am-n(Am-6, Am-8, Am-10, Am-12) had been synthesized. Alkyl amines were polymerized by the way of solution polymerization and in situ polymerization(K2S2O8 as the initiator), and the polymers were marked as PAm-n(PAm-6, PAm-8, PAm-10, PAm-12). The synthesized alkyl aniline and polymers were qualitatively characterized by NMR, FT-IR, GPC, XRD and UV-vis. The results of TGA indicated that the polymer were stabler than monomer. AFM images of P-n showed that the range of diameter about the PAm-10 were 300-500 nm. Polymerization Kinetics were studied by ECL, the order of free radical polymerization reaction were 1 for the concentration of monomer and 1 for the concentration of KPS. The Kinetic equation was as follow:2) The inhibition efficiency of PAm-n in 5 M HCl solution for X70 steel were studied by weight loss experiment and electrochemical experiments. The results indicated that the inhibition efficiency of PAm-n in 5 M HCl solution for X70 steel were increased by the increasing concentration of PAm-n and the rising temperature. However, the length of alkyl chain had a little effect on the inhibition efficiency of PAm-n for X70 steel. Inhibition efficiency of PAm-6 were 97% when concentration were 70 ppm in 5 M HCl solution at 90℃, and it were 96.05% for PAm-12 on the same conditions. Thermodynamics and kinetics of the adsorption of inhibitor molecules elaborated that the adsorption of PAm-n molecules on surface of X70 steel followed Langmuir isotherm which belonged to the monolayer adsorption model. Moreover,-40 k J/mol < 0ads(35)G <-20 k J/mol, indicated that the adsorption of PAm-n involved both physisorption and chemisorption; 0ads(35)(39) > 0,0ads(35)S > 0, suggested the adsorption process were spontaneous and endothermic with the increasing entropy. For inhibitors of PAm-n, the value of Ea(inhibited solution) were less than Ea(uninhibited solution), which further confirmed the adsorption mechanism of PAm-n were the typical of chemisorption. The results of EIS measurements showed that the charge transfer resistances ctR were increased with the increasing concentration of PAm-n, which indicated that the molecules of PAm-n were adsorbed on the surface of X70 steel and formed a compact film. The results of Tafel polarization indicated that corrosion current densities of X70 steel in HCl solution decreased with the increasing concentration of the PAm-n. In addition, the corrosion potential slightly shifted towards negative or positive direction which demonstrated PAm-n acted as a mixed-type inhibitor and could inhibit both anode and cathode reaction. The results of EIS measurement, Tafel polarization and Weight loss experiments were consistent with each other.3) The situ polymerization process of Am-n and the inhibition of the X70 steel corrosion may occur at the same time which could reduce the time for experiments. Experimental results showed that the inhibition efficiency of situ polymerization of Am-n on the surface of X70 steel were increased with the increasing concentration of monomer and HCl solution, elevated temperature and prolonged immersion time. Inhibition efficiency of Am-10 in situ polymerization on the surface of X70 steel were 96% when the concentration were 60 ppm in 5 M HCl solution at 90 ℃. At the same time, the inhibition efficiency of the Am-10 were only 78%.4)Surface topography of X70 steel before and after corrosion in HCl solution were inspected by SEM, AFM, XPS and UV-vis.The results of SEM proved that PAm-10 molecules were adsorbed on the surface of X70 steel and formed a protective film. The polymers were self-assembed into small particles on the surface of X70 steel and their diameter were 300-500 nm. The topography of Am-n in situ polymerization on the surface of X70 steel could be affected by the order of adding HCl and initiator in situ polymerization corrosion test. When the acid were added firstly, the morphology of the samples were, and their diameter were 200-400 nm; however, when the initiator were added firstly, the morphology were solid spheres and the diameter was 150-300 nm. The film of both hollow spheres and solid spheres could provide good protection for X70 steel. The particles of Am-10 in situ polymerization on the surface of X70 steel were smaller than that PAm-10 self-assembed. Moreover, the film of Am-10 in situ polymerization on the surface of X70 steel were more closely aligned, and exhibited better inhibition efficiency.The results of AFM were consistent with the morphology analysis about SEM. In addation, the results of AFM interpreted the roughness, height difference and volt potential difference of X70 steel surface before and after the corrosion. Specifically, the X70 steel were badly corroded in the absence of inhibitor, their surface roughness, hight difference and volt potential difference were 200 nm, 430 nm and 1464.72 m V, respectively. However, the surface roughness, hight difference and volt potential difference were 145.06 nm, 200 nm and 288.88 m V, when PAm-10 were self-assembed on the surface of X70 steel, respectively. when Am-10 in situ polymerization on the surface of X70 steel, their surface roughness, hight difference and volt potential difference were 84.96 nm, 150 nm and 85 m V at the same condition, respectively. Compared with the above data, it could be clerely showed that the values of the surface roughness, hight difference and volt potential difference of X70 steel were smallest when Am-10 in situ polymerization on the surface of X70 steel which indicated that situ polymerization corrosion had more advantages. To our knowledge, the volt potential difference was a index of homogeneity of the surface. The smaller value of volt potential difference showed the more uniform surface material, which further indicated the monomers in situ polymerization on the surface of X70 steel could provide better protection for X70 steel.The results of XPS showed that, compared with the blank corrosion X70 steel, the relative content of Fe decreased, and the relative content of N increased when adding PAm-10 in HCl solution and Am-10 in situ polymerization on the surface of X70 steel. The values of the relative content of Fe and N in HCl solution in the prescence of PAm-n on X70 steel surface were 5.05% and 7.2%, respectively. The relative content of Fe and N of X70 steel surface were 5.85% and 6.8% when Am-10 in situ polymerization on the surface of X70 steel, respectively. These facts further demonstrated that the way of monomer in situ polymerization on the surface of X70 steel could provide better protection.The strength of the UV diffuse reflectance peak increased, the max absorbance wavelength shifted to the longer wavelength with the increasing concentration of PAm-n, elevated temperature and extending immersion time which indicated that the conjugated structure prolonged with the molecules of PAm-n absorbed on the surface of X70 steel. The similar results were acquired when Am-10 in situ polymerization on the surface of X70 steel. However, compared with the self-assembled, the strength of the peak were higther due to more polymers on the surface of X70 steel.The results of experiments proved that the way of the PAm-n solution and Am-10 situ polymerization could protect X70 steel from corrosion in HCl solution. However, compared with the self-assembled, the way of stiu polymerization had better inhibiton efficiency. |
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