Synthesis of a CoO-ZnO nanocomposite and its study as a corrosion protection coating for stainless steel in saline solution

A novel CoO-ZnO nanocomposite was synthesized by the photo irradiation method using a solution of cobalt and zinc complexes and used as a coating applied by electrophoretic deposition (EPD) for corrosion protection of stainless steel (SS) in saline solution. The samples were characterized using powder XRD, scanning electron microscopy (SEM) and electrochemical polarization. It was also found that the coating was still stable after conducting the corrosion test: it contained no cracks and CoO-ZnO nanocomposites clearly appeared on the surface. SEM showed that the significant surface cracking disappeared. XRD confirmed that CoO-ZnO nanocomposites comprised CoO and ZnO phases without any impurity. The SEM images of CoO-ZnO nanocomposites revealed the average particle size (23.66 nm). The corrosion behavior of the stainless steel in saline environment in the temperature range of 298- 328 K was assessed by means of electrochemical techniques such as potentiodynamic polarization curves. The corrosion protection of the alloy increased with an increase in temperature from 99.97 to 99.99%, which indicates that the nanocomposite CoO-ZnO coating on the stainless steel surface is slightly affected by temperature. The results showed that CoO- ZnO nanocomposite provided powerful corrosion protection in saline solutions. The maximum protection efficiency was 99.99% in saline solutions at 328 K. The apparent activation energy (E-a) and pre-exponential factor (kinetic parameters) are calculated and discussed. Also, thermodynamic values such as the activation entropy (Delta S*) and activation enthalpy (Delta H*) were calculated.