Study of influence of micro-arc oxidation process duration on the characteristics of thermal control coatings for space applications

Thermal control coatings were obtained on the AMg6 aluminum alloy with the aid of micro-arc oxidation (MAO) process. The dependences of the thickness, roughness, porosity and thermal control properties of the coating on MAO process duration were studied. The thermal control properties (solar absorbance αs and emissivity ε) were investigated by ultraviolet–visible-near infrared spectrophotometer instrument and solar absorption reflectometer. The analysis of thickness, roughness and MAO process duration influence on the thermal control properties of the coating was carried out.

Synthesis of nano-porous ZNO as pigment for white silicone thermal control coating and investigation of structure, optical and thermal properties

Purpose The harsh environment of space, especially radiation of direct solar rays, can potentially raise the temperature of the spacecraft to harmful levels. Thermal control coatings (TCCs) fix the thermal condition of the spacecraft acceptable for its components. This is possible by diffusely reflecting all effective ultraviolet (UV), visible (VIS) and near infrared (IR) (NIR) wavelengths of solar radiation and emmition of IR energy. The most commonly used TCCs have used ZnO as a pigment, but absorption of the UV light by ZnO pigment can change the ideal condition of these TCCs. The aim of his study is the using the porous ZnO particles as pigment to prevent the UV absorption. Design/methodology/approach To enhance the efficiency of these coatings, in the present study, nano-porous zinc oxide particles were synthesized and used as pigments for white TCCs. Findings The results revealed that the proposed TCC (TPZ), Thermal control coating with porous ZnO had better reflection (scattering) and emittance properties in comparison with the coating using ZnO as a pigment (TZ coating); so this coating had a solar absorptance value equal to 0.141, whereas this value for TZ was 0.150. Furthermore, TPZ showed higher thermal emittance (0.937) in comparison with TZ (0.9). These changes were because of the improvement in the refractive index, shape and surface area of the pigments. The general trend of the scattering coefficients for the prepared coating, as calculated from the Kubelka–Munk equation, showed that scattering was more efficient in the UV region, as compared with the TCC containing ZnO pigments. Originality/value This type of pigment for the first time is evaluated in TCCs.