Optical Properties of Pyromark 2500 Coatings of Variable Thicknesses on a Range of Materials for Concentrating Solar Thermal Applications

In this paper we present the results of solar absorptance measurements of four metallic substrate materials, either coated with Pyromark 2500 at various thicknesses, or uncoated and oxidised. Absorptance is measured prior to aging, and during and after aging at three elevated temperatures. In many cases, thin coatings perform as well, or better than thick coatings and do not appear to have a higher rate of failure. However, a thicker coating did show an advantage after aging at the highest temperature tested (850 degrees C), and it is expected that with longer exposure, similar trends may emerge for the 600 degrees C and 750 degrees C aging cases. Another finding is that the two nickel-based alloys tested, Haynes 230 and Inconel 625, both formed an oxide with very good absorptance, although durability requires further testing.