PANI/CeO2 nanokompozit kaplamalar ile karbon çelik ve alüminyum metallerinin korozyonunun önlenmesi

Carbon steel and aluminium are the most common metals for industrial applications. Corrosion is one of the biggest drawbacks of using these metals in equipments. Corrosion may be defined as a destructive phenomenon, chemical or electrochemical, which affects the appearance of an object, and in extreme cases may cause structural failure. Economic losses resulting from metallic corrosion costs billions of dollars per year worldwide. In addition to the economic costs, there are times when corrosion is responsible for the even greater costs of human life and safety. Polymers have already replaced most of the materials we use in our daily life. Innovations on polymeric materials allow them to be used in corrosion inhibition. The use of organic coatings is one of the most common method for minimizing corrosion losses. Conducting polymers have been increasingly investigated for their use in organic coatings. Many studies showed that conducting polymers improve the corrosion inhibition properties of coatings. Polyaniline (PANI) is one of the most widely used conducting polymer because of its superior properties. Inorganic nanoparticles are a class of new materials having wide variety of applications in many fields. To obtain the materials with synergetic or complementary behavior between polymer and inorganic nanoparticles, various composites of polymer with inorganic nanoparticles have been synthesized in recent years. Among those inorganic nanoparticles, cerium oxide (CeO2) nanoparticles have been intensively studied due to their unique catalytic, electrical, and optic properties, as well as their extensive applications in diverse areas. The main objective of this study is to investigate the corrosion behaviour of PANI/CeO2 nanocomposite and pure PANI coatings on carbon steel and aluminium metals in corrosive environments such as 0.1 M H2SO4 and 3.5 % sea water. In the first part of the study, synthesis of PANI and PANI/CeO2 nanocomposite were carried out and they were characterised by Fourier Transform Infrared Spectroscopy, UV-Visible Spectroscopy, conductivity measurements and SEM analysis. It is confirmed by the analysis results that the polymer and nanocomposite were sucsessfully synhesized. Coatings including pure PANI and PANI/CeO2 nanocomposite were prepared at different concentrations and coated on carbon steel and aluminium electrodes and they were investigated for their corrosion protection properties. In addition to emeraldine salt forms of the polymers, emeraldine base forms of both species were used in order to have more concentrated polymer solutions due to better solubility which increased PANI content of coatings. It is evident from the SEM images of the coatings that PANI/CeO2 nanocomposite formed a more uniform coating which can lead to a better corrosion protection efficiency; whereas pure PANI polymer formed a rough and curved coating. Since corrosion occurs via electrochemical reactions, electrochemical techniques are ideal for the study of the corrosion processes. The electrochemical impedance spectroscopy (EIS) is one of the most effective and reliable method to extract information about electrochemical characteristics of the electrochemical system. Electrochemical measurements, including potentiodynamic polarization curves and EIS were performed in a three-electrode cell. EIS data is also analyzed by fitting it to an equivalent electrical circuit model and experimental results were confirmed. Steady-state current-voltage curves and electrochemical impedance spectroscopy measurements of the coatings in 0.1 M H2SO4 for carbon steel and aluminium and in 3.5 % seawater for carbon steel were conducted. The initial measurements were conducted in 0.1 M H2SO4 both for carbon steel and aluminium electrodes after 1 hour immersion to corrosive media. It is evident that both coatings inhibit corrosion of bare electrodes. The increase in polymer concentration effects the corrosion protection efficiency of the coating positively. PANI/CeO2 polymer coatings showed slightly better corrosion protection efficiency over pure PANI coatings both for carbon steel and aluminium electrodes, which shows the advantage of CeO2 nanoparticle contrubition in the coating. It is evident from the polarization curves that the coatings retard both anodic and cathodic reactions. In other words, they reduce the anodic dissolution and also retard the hydrogen evolution reaction. PANI/CeO2 nanocomposite coating with 1,62 % showed the best corrosion protection performance on carbon steel and aluminium electrodes in 0.1 M H2SO4. The corrosion protection efficiencies of the coatings including emeraldine base form of polymers were also measured with increasing exposure time. It was observed that the coating degradetion increased and consequently corrosion currents and corrosion rates increased as the exposure time to corrosive media increased. The differnace in corrosion protection property of the coatings became close to each other by increasing exposure time, which may be due to the effect of corrosion product formation on the electrode surface. EIS measurements were also supported by equivalent circuit models and it is observed that a reasonable accuracy of the fitting was obtained. Chi-square is in the order of 10-3 and 10-4 for all the experimental data. Rp values obtained by equivalent circuits and experiments are in agreement with each other. In order to see the protection performance of coatings in different corrosion media, measurements in 3.5 % seawater for carbon steel electrodes were also carried out. Results suggest that the same concentration of PANI/CeO2 nanocomposites have better corrosion protection efficiency compared to pure PANI coatings even in emeraldine salt form which has lower concentration owing to the contrubition of CeO2 nanoparticles in the coating.