Sol–gel derived solar selective coatings on SS 321 substrates for solar thermal applications

• Sol–gel derived multilayered solar selective coatings developed on SS321
• Solar absorptance and thermal emittance at par with toxic chrome coating
• Thermal stability and corrosion resistance of coatings studied
• Coating performance found to be promising for large scale applications
• Scale-up amenability investigated by coating generation on 1 m tubes

Sol–gel derived multilayered solar selective coatings were generated on AISI SS 321 substrates using Ag-TiO2 as the cermet layer, titania and silica as the dielectric layers with high and low refractive indices respectively. The phase compositions of the individual layers were independently confirmed using grazing angle incidence X-ray diffraction, which was corroborated by X-ray photoelectron spectroscopic analysis. Thickness of the layers was measured using variable angle spectroscopic ellipsometry. The solar absorbance was measured over the UV–Vis-NIR wavelength range. Thermal emissivity was determined using FTIR spectroscopic analysis. The durability of the coatings was ascertained using accelerated corrosion testing methods as well as by measuring the optical properties after thermal cycling experiments. The promising nature of hexavalent chrome-free, environmental friendly, multilayered solar selective coating was ascertained with respect to amenability to scale-up.