Improved mechanical and anticorrosion properties of metal oxide-loaded hybrid sol–gel coatings for mild steel in a saline medium

A hybrid organic–inorganic sol–gel coating was successfully prepared and subsequently functionalized individually with five different metal oxide additives. The effect of the incorporated oxides on the corrosion protection performance and scratch-resistance properties of the hybrid base coating on mild steel substrates was investigated using electrochemical techniques, namely electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) as well as mechanical testing. The steel-coated specimens were immersed in 3.5 wt.% NaCl corrosive medium for two weeks and the results reveal an excellent corrosion protection performance by all coating formulations with a significant high corrosion-resistance property for the sample loaded with molybdenum oxide. Scanning electron microscopy (SEM) images proved the absence of corrosion signs, defects, micro cracks, or delamination on the surface of the coated samples. Compared with the pure hybrid coating, all the metal oxide-embedded coatings (except for the sample loaded with yttrium(III) oxide) show comparable aqueous contact angle values as well as enhanced hardness and adherence properties. No noticeable dependence was observed for the surface roughness parameters as a function of the type of incorporated metal oxide within the sol–gel matrix. Overall, the results of this study demonstrate that metal oxides can be advantageous to the desired properties of hybrid sol–gel coatings applied to steel surfaces.