OBTAINING ALUMINA COATINGS ON STEEL SUBSTRATES BY ELECTRODEPOSITION AND SOL-GEL METHODS

The main subjects of this presentation are layers made of alumina obtained from organic and aqueous sols deposited on the steel substrates by the sol-gel and electrophoretic deposition (EPD) methods. Aluminum oxide has a very large specific surface area. As a result of the calcination process, in the burned aluminum layer acid-base active centers are created. It determines the use of aluminum oxide as a catalytic material. Due to its properties it is prospective as a carrier of catalysts. In the case of the sol-gel method, the sol was obtained by hydrolysis of the butoxy derivative of aluminum. Obtained sol was applied to the steel substrate by a dip-coating technique. Using the dip-coating technique, due to the ability to easily regulate the speed of immersion and ascent of the substrate from the sol, allows relatively easy control of the thickness of the obtained layers. In the case of EPD method, stable aqueous colloidal suspension of alumina was used. The main advantage of the EPD method is the ability to easily and quickly obtain homogeneous layers on conductive substrates (also on the profiled surfaces). The thickness of the layers can be easily controlled by changing the process conditions. Fresh layers obtained by both methods were heated for densification and better adhesion to the substrate. The structure (MIR) and microstructure (SEM with EDS) tests carried out showed that in both cases there were obtained tight layers of aluminum oxide on steel substrates. In order to determine the nature of the surface, the contact angle and surface free energy tests were also performed. The conducted research allowed to state that the coatings obtained by electrodeposition are characterized by better homogeneity and adhesion to the substrate. They also present a higher thickness than the sol-gel coatings. The contact angle tests show that both coatings are hydrophilic. The obtained layers are extremely promising materials due to their physicochemical and surface properties.