Petri Konttinen

Microstructural analysis of selective C/Al2O3/Al solar absorber surfaces

Abstract The elemental composition and geometrical structure of mechanically manufactured spectrally selective C/Al 2 O 3 /Al solar absorber surfaces were characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy, energy dispersive X-ray spectroscopy and optical microscopy. The XPS analysis revealed that the surface contains Al 2 O 3 and C in graphite form. Optical microscopy confirmed that graphite forms inhomogeneous agglomerated clusters on the surface. The thickness of the clusters varies, the maximum measured thickness being in the range of 300 nm. A solar absorptance of 0.90 and a thermal emittance of 0.22 have been achieved so far. Increasing the graphite coverage and decreasing the graphite cluster thickness could increase the absorptance to ⩾0.94 and lower the emittance. This could be achieved by altering the composition and the structure of the grinding pad used and by finding the suitable manufacturing parameters for the advanced pad.