Black enamel for concentrated solar-power receivers

High SiO₂ content frit modified with commercial black spinel-type pigment K 6038 of chromium and iron oxide mixed with 40-100 wt% per 100 wt% by weight of frit were deposited on stainless steel alloys by the slip-casting technique and their optical properties were characterised by total reflectance of 300 nm to 20 μm. The enamel coating exhibited moderate spectral selectivity and excellent thermal stability at 600 °C. Solar absorbtance (α) ranged from 0.75 to 0.82 and calculated thermal emittance at 600 °C (ε) ranged from 0.35 to 0.45. Both depended on coating surface and pigment volume in the frit. The highest solar selectivity was measured in enamel with 50% pigment with α and ε (600 °C) of 0.81 and 0.35, respectively.