Effect of High-Temperature Thermal Shock on Solar Absorption Rate of Alumina Coating

Abstract

With the development of the aerospace industry, the close exploration of the Sun has become a human demand. However, close-range exploration means that the detection satellite needs to accept the test of high temperatures above 1400 °C, so a thermal protective coating is a necessary part of the detection satellite to isolate heat and reflected light. Al2O3 coating has the characteristics of high emissivity and low absorptivity, and it is the best choice for thermal protection coating. However, the coating is subjected to thermal cycles, including heating and cooling, as the satellite rotates around the Sun, which could result in a change in the structure and properties of the coating. Therefore, thermal shock experiments were carried out, and the influence of microstructure on the absorption rate of the Al2O3 coating was investigated. In this study, an Al2O3 coating was prepared by atmospheric plasma spraying (APS). The coating was subjected to a thermal shock (TS) test at 1400 °C using a self-made flame shock device, and coating samples under different thermal shock degrees were obtained. A scanning electron microscope (SEM) was used to characterize the coating pores, and the effects of the coating pore size, aspect ratio (A/R) and cracks in the coating on the optical properties of the coating under different thermal shock degrees were analyzed. In order to clarify the influence of coating microstructure changes on the optical properties of the coating under different thermal shock degrees, not only relevant experiments were carried out, but also the solar reflectivity of Al2O3 coatings with different pore structures was analyzed by the finite element method using finite-difference time-domain (FDTD). The results show that increasing the porosity and aspect ratio of the pores can improve the partial solar absorption of the coating. It was also found that the transverse crack propagation improves the solar reflectance of the coating.