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 mu m. The enamel coating exhibited moderate spectral selectivity and excellent thermal stability at 600 degrees C. Solar absorbtance (alpha) ranged from 0.75 to 0.82 and calculated thermal emittance at 600 degrees C (epsilon) 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 alpha and epsilon (600 degrees C) of 0.81 and 0.35, respectively. (C) 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.