Investigation of absorptance and emissivity of thermal control coatings on Mg-Li alloys and OES analysis during PEO process

Thermal control ceramic coatings on Mg-Li alloys have been successfully prepared in silicate electrolyte system by plasma electrolytic oxidation (PEO) method. The PEO coatings are mainly composed of crystallized Mg₂ SiO₄ and MgO, which have typical porous structure with some bulges on the surface; OES analysis shows that the plasma temperature, which is influenced by the technique parameters, determines the formation of the coatings with different crystalline phases and morphologies, combined with "quick cooling effect" by the electrolyte; and the electron concentration is constant, which is related to the electric spark breakdown, determined by the nature of the coating and the interface of coating/electrolyte. Technique parameters influence the coating thickness, roughness and surface morphology, but do not change the coating composition in the specific PEO regime, and therefore the absorptance (α S) and emissivity of the coatings can be adjusted by the technique parameters through changing thickness and roughness in a certain degree. The coating prepared at 10 A/dm², 50 Hz, 30 min and 14 g/L Na₂SiO₃ has the minimum value of α _S (0.35) and the maximum value of (0.82), with the balance temperature of 320 K.