The sol-gel process is a way of preparing materials from a solution. The materials produced by sol-gel route can be in the form of powders, fibers or thin films. The advantages of the process are simple manufacturing, low synthesis temperature, low cost production and easier control of chemical composition.
As a part of master's thesis, Al2O3 and SiO2 coatings were prepared using plain carbon C45 steel according to the sol-gel production route. Thin films of sóls for the desired coatings were applied to the steel by dip-coating method. This was followed by drying the coatings at different temperatures. Single-layer coatings of Al2O3 and SiO2, as well as multi-layered composite coatings with different combinations of both sóls were manufactured. The coatings were analyzed by scanning electron microscope (SEM) with attached EDXS detector.
Corrosion tests were carried out to examine the effect of the sol-gel coatings on the corrosion protection of C45 steel in details. Corrosion potential measurements, linear polarization, potentiodynamic measurements and electrochemical impedance spectroscopy were performed. After the corrosion tests were completed, macroscopic imaging of the corroded surfaces of the samples was carried out.
SiO2 coatings and composite coatings were homogeneous and free of cracks, while Al2O3 coatings were homogeneous but mostly cracked. Based on the results, all coatings were found to improve the corrosion resistance of C45 steel. Coating of steel surface increases the corrosion potential and lowers the corrosion current density and reduces the extent of corrosion damage. The best properties are achieved by applying a SiO2 sol-gel coating. For composite multilayered coatings, better properties are achieved by coating with the first layer of SiO2.
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