Impact of corrosion on microstructure and mechanical properties of ZrOx/ZrC-ZrN/Zr absorber-reflector tandem solar selective structures

We investigated the impact of corrosion on pristine and thermally treated ZrOx/ZrC-ZrN/Zr absorber-reflector tandem solar selective coatings (ARTSSCs) on stainless steel (SS) and copper (Cu) substrates using microstructure, electrochemical and nanoindentation measurements. Electrochemical measurements are carried out in 3.5 wt% NaCl solution, emulating the corrosion environments, under potentiodynamic polarization states. The corrosion treated samples exhibit strong correlations among microstructural, mechanical properties and their solar thermal responses. The thermally treated ZrOx/ZrC-ZrN/Zr structures on SS substrates show degraded corrosion resistance from 1379 KΩ to 104 KΩ for vacuum and 435 KΩ for air thermal conditions. The measured mechanical properties, such as Young's modulus and hardness, substantiate the observed corrosion mediated degradation of thermally treated structures under both vacuum and air environmental conditions. The solar thermal performance shows degradation for both pristine and thermally treated sample after corrosion and room temperature after corrosion emissivity 'ε27 °C' values are ~0.28, 0.35, 0.42 for pristine and thermally treated ZrOx/ZrC-ZrN/Zr structures respectively.