Long-term thermal stability testing of the CoteRill®750 solar absorber coating

The long-term thermal stability of the silicon-based coating CoteRill®750 was examined via isothermal and thermal cycling aging tests. The coating was aged isothermally at three different temperatures of 800, 850, and 900℃, for 2000 or 3000 hours, and its optical durability compared with Pyromark 2500. CoteRill®750 has a higher absorptance and better optical and mechanical durability during the aging compared to Pyromark, e.g. no signs of failure were observed for CoteRill®750 after aging, while Pyromark 2500 mechanically failed at 900℃. Based on a figure of merit that accounts for both sunlight absorption and thermal emission at a representative temperature, the results show 1% better performance for CoteRill®750 than Pyromark 2500 (after aging at 800℃ for 2000 hours). Two different thermal cycling tests were carried out – a cycle and hold, and a rapid cycling test – and both indicated better solar-weighted absorptance for CoteRill®750 than Pyromark 2500. The coating can be applied at a large scale using the same spraying method as for Pyromark 2500. Therefore, with superior optical performance and a simple application method, CoteRill®750 is positioned to compete with Pyromark 2500 as the reference absorber coating for high-temperature CSP receivers.