Stability and characterisation of Pyromark 2500 cured at different temperatures

Pyromark 2500 is a silicone-based high-temperature solar absorber coating commonly used for concentrating solar power receivers. It has good optical efficiency in its pristine condition but is prone to optical and/or mechanical degradation and failure after years of operation. This work studies the effect of curing temperature on the long-term stability of Pyromark. Pyromark painted on Inconel 625 was cured at 750℃, 850℃, and 950℃, and then isothermally aged at 900℃ for 3000 h. Pristine Pyromark cured at higher temperatures was shown to have a lower solar absorptance, but better optical and mechanical stability over the testing period. For example, the solar absorptance of pristine Pyromark cured at 950℃ was 1.2 % and 1.0 % lower than when cured at 750℃ and 850℃, respectively, but due to better optical stability during aging, had the highest solar absorption of all cases after completion of the 3000 h of testing. In terms of physical failure, spallation occurred for Pyromark cured at 750℃ and significant detachment between layers occurred for Pyromark cured at 850℃, whereas there was no sign of these failure modes for samples cured at 950℃. Therefore, despite the disadvantage of lower initial optical efficiency, curing Pyromark at a higher temperature appears to bring advantages in terms of long-term mechanical stability and a reduced optical degradation rate.