Optimization design of CuCrxMn2−xO4-based paint coatings used for solar selective applications

CuCrxMn2−xO4 (x=0.5, 1) spinels, novel pigments for spectrally selective paints, have been prepared through a sol–gel combustion synthesis process. Thickness Sensitive Spectrally Selective (TSSS) paint coatings, using CuCrxMn2−xO4 (x=0.5, 1) obtained at varied calcined temperatures (500∼1100 °C) as pigment, were deposited on top of aluminum substrates by an cost-effective spray coating method and characterized by reflectance measurements over the spectral range of 0.3–20 μm. Influence of pigment species and coating thickness on optical properties of paint coatings was investigated. Results suggest that CuCr0.5Mn1.5O4-based coatings are more favorable than CuCrMnO4-based ones and coatings using 700 °C calcined CuCr0.5Mn1.5O4 as pigment exhibit the optimum spectral selectivity (αs=0.92∼0.93, εT=0.22∼0.31). Difference in powder thermal emittances reveals that suitable pigments can be pre-chosen before fabricating paint coatings to obtain optimum spectral selectivity. Long-term stability tests of the TSSS paint coatings were performed according to the methodology worked out within IEA-SHC Task X and the results confirmed that coatings in this study could be safely used during collectorʹs lifetime without degradation in performance.