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Polyaniline and polyaniline-clay nanocomposite were synthesized in supercritical carbon dioxide medium. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR) were used to determine the morphology and chemical structure of the synthesized samples, respectively. Synthesized polyaniline and polyaniline-clay nanocomposites were used as biocompatible corrosion inhibitor to reduce the corrosion rate of carbon steel in hydrochloric acid solution. For this purpose, polyaniline and polyaniline-clay nanocomposite was individually added to a 0.5 M hydrochloric acid solution and corrosion of carbon steel immersed in the solution, was evaluated using electrochemical impedance spectroscopy technique (EIS) and Tafel polarization. Tafel polarization results confirmed the corrosion rate reduction from 15 mm/ year to 6 mm/year in the presence of polyaniline-clay nanocomposite. Based on EIS Results the polarization resistance increased from 11 ohm.cm2 to 36 ohm.cm2 when polyaniline-clay nanocomposite was added to the acidic solution, and these results confirmed the reduction of corrosion rate at a rate higher than 60 percent.

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In this study, effect of Fumaria officinalis extract, as a natural inhibitor, on the corrosion of carbon steel in hydrochloric acid solution has been studied by using electrochemical polarization and electrochemical impedance spectroscopy methods. The results show that the Fumaria officinalis extract have 94.97% mean efficiency at 2.0 g/L concentrations which shows that this extract is a fairly good inhibitor. Polarization curves indicated that this inhibitor is a mixed (cathodic/ anodic) one. According to the obtained results, inhibition efficiency increases by increasing the inhibitor concentration. Investigation of the effect of temperature on the efficiency of the extract was done by electrochemical polarization method in the range of 35- 65°C which shows that efficiency of the extract decrease by increasing the temperature. Adsorption of inhibitor follows the Langmuir adsorption isotherm in this range of temperature. Thermodynamic adsorption parameters (Kads, ΔGads) of inhibitor were calculated by using the Langmuir adsorption isotherm. The values of ΔGads for all temperatures were close to -16 kJ mol-1, which indicates the electrostatic adsorption (physical adsorption) of the extracts molecules on the surface of the metal. Activation parameters of the corrosion process such as activation energies, Ea, activation enthalpies, ΔH* and activation entropies, ΔS*, were calculated by the obtained corrosion rates at different temperatures. The amount of activation energy of the acid solution with the extract is larger than it without the extract which confirm that the adsorption is physical.

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Polyaniline metal organic framework (PAni-MOF) nanocomposite was synthesized via facile batch process in atmospheric pressure. Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) were used to determine the morphology and chemical structure of the synthesized samples, respectively. Synthesized nanocomposite was added to a 0.5 M hydrochloric acid solution and corrosion of carbon steel immersed in the solution, was evaluated using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization corrosion testing. Results confirming the inhibition efficiency of PAni-MOF nanocomposite and its use reduce the rate of carbon steel corrosion in the environment of hydrochloric acid at a rate of 75 percent. Anodic protection mechanism of synthesize nanocomposite was confirmed via trend of open circuit potential changes and the analysis of electrochemical current noise data also showed a reduction in the probability of local corrosion in the presence of nanocomposite.

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In this study, the inhibition effect of a Schiff base with three C=N groups and three aromatic rings on corrosion of 1018 carbon steel in 0.1 M hydrochloric acid is investigated by two electrochemical methods, impedance spectroscopy and polarization, at 25 °C. The inhibition efficiency increases by increasing the concentration of Schiff base from 100 to 500 ppm and the highest inhibition efficiency was about 96% at 25 °C for the concentration of 500 ppm of Schiff base. The results of the polarization method showed that the Schiff base in acidic solution acts as a mixed inhibitor. The charge transfer resistance (Rct) for 1.0 M HCl solution increases from 39.5 Ω.cm2 to 949.7 Ω.cm2 by adding 500 ppm of Schiff base. The effect of temperature on the inhibitor performance is investigated by electrochemical polarization method in the range of 25-65 °C and it shows decreasing of inhibition efficiency with increasing temperature. The adsorption of Schiff base molecules on the surface of 1018 carbon steel at all temperatures follows the Langmuir adsorption isotherm. The values of ΔGads obtain -32.122 kJ and -35.124 kJ mol-1 at 25 °C and 65 °C, respectively, which shows increment in its absolute value. These results show that the adsorption of Schiff base molecules on the surface of 1018 carbon steel is a physico-chemical adsorption.