Stability investigations of a chemically converted textured black copper selective surface

Abstract

We report here the optical and structural investigations conducted on a stable and degraded black copper selective surface prepared by the chemical conversion technique. This surface exhibits a high initial solar absorptance (α ≈0.97-0.98) and possess a relatively low emittance (ε₁₀₀≈0.2±0.02). The surface has been exposed to air and vacuum test conditions at elevated temperatures. The surface shows good and structural stability in both vacuum (10^-5 Torr) and under ambient conditions up to 250°C. In the case of a surface annealed in air between temperatures of 250 and 350°C the surface optically degrades with no structural changes. However, above 350°C drastic degradations in both optical and structural properties have been observed. These surfaces become rough along with a grain size enlargement. In contrast, upon vacuum annealing up to 370°C no significant change in the microstructure has been noticed. However, dramatic changes in the solar absorptance have been evident above 250°C. Further, these surfaces have been indicated good stability under UV radiation, external environment, humidity and steam exposure conditions. Chemical stability, such as corrosion resistance in 3% NaCl and 3% acetic acid spray have also indicated satisfactory results.