Preparation of high-temperature resistant selective paints for solar absorbers

Spectrally selective paint coatings were prepared from organically modified siloxane in combination with two types of different pigments (organic soot-FW2 or inorganic FeMnCuOx-P320). To optimize the low-emittance properties, various concentrations of pigments were used for the preparation of paints. From seven prepared paints, different thicknesses were applied on high-reflecting Al foil by draw bar coater. For all paints, optical and thermal properties were determined as well as their adhesion resistance. For higher concentration of used pigment better selectivities were obtained, but at the same time paints exhibited bad adhesion properties. The thickness of paints having different concentration of the added pigment was optimized in correlation with their spectrally selective properties and adhesion resistivities. The results of this study indicate that pigment to volume concentration ratio has to be about 20% for thicknesses of about 1.7 g/m2 - 2.0 g/m2. Solar absorbance for these samples were as equals 0.90 - 0.92 with thermal emittance of eT equals 0.20 - 0.25. Temperature stability of these samples was followed by FT-IR spectroscopy at 180 degree(s)C and 300 degree(s)C for three weeks and 68 hours, respectively. The obtained results indicate good temperature stability of prepared paints.