Effect of Fe ³⁺ ions on the thermal and optical properties of the ceramic coating grown in-situ on AZ31 Mg Alloy

This research investigates the effect of Fe ₂(SO ₄) ₃ on the thermal and optical properties of the ceramic coatings formed on AZ31 Mg alloy. The different ceramic coatings were obtained by plasma electrolytic oxidation (PEO) in electrolytes that contain varied concentrations of Fe ₂(SO ₄) ₃. The microstructure, element distribution, composition as well as the thermal and optical properties of the coatings were studied with scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray Diffraction (XRD), UV-VIS-NIR spectrophotometer and infrared reflectometer. The results show that all of the coatings prepared were mainly composed with MgO, with trace-amount of Fe ₃O ₄ presents and Fe seems entered into the MgO crystal structure. With the increasing of the concentration of Fe ₂(SO ₄) ₃, the solar absorptance and infrared emittance increased initially but then remain stable. We found that at the concentrations 8 g L ^-1, the coating has the highest solar absorptance (0.94) and infrared emittance (0.83). Our results show that coatings formed with this method could be useful as a thermal control coating in a variety of applications, such as in the spacecraft.