In situ high-temperature emissivity measurements of heat-treated, silicon coated stainless steel for solar thermal applications

Understanding thermal emissivity at high temperatures is crucial for developing efficient materials for solar thermal applications. We present a new approach for creating an efficient material for solar absorber by developing a nano structured surface on stainless steel substrate through Si deposition and annealing. We prepare five samples by annealing them at five temperatures between 700 °C and 1100 °C. Afterwards, we perform a systematic study of the spectral emissivity at elevated temperatures, focusing on different parameters: angle dependence, wavelength dependence, and temperature dependence. The spectral directional emissivity experiments performed in the mid-infrared range reveal a dielectric behavior of the samples in the short wavelength region (λ < 6 μm) and metallic behavior in the long wavelength region (λ > 12 μm). The results indicate an increase in hemispherical and total normal emissivity with measurement temperature (from 200 °C to 700 °C), influenced by oxide/silicide formation due to interdiffusion, and by surface roughness. Notably, samples annealed at 900 °C and 1000 °C demonstrate enhanced thermal stability at 700 °C, showcasing promising characteristics for high-temperature applications. Consequently, this study presents a viable method for developing cost-effective silicon-based solar absorber coatings on stainless steel with tailored properties for solar thermal applications along with its real time high temperature emissivity details.