A reflection electron diffraction study on some metal oxide solar collector coating: Part II

Abstract

Four prospective solar absorber coatings were observed during heat treatments using reflection electron diffraction, scanning electron microscopy and optical data to characterize the changes induced. The changes in the microstructures were related to the optical response of these coatings. Black zinc was found to degrade substantially only during heat treatments above 205°C, the degradation mechanism consisting of an increase in the surface roughening and thermal oxidation of the underlying zinc substrate. Copper oxide degraded substantially even at low temperatures (below 200°C), apparently forming a thicker and smooth copper oxide layer close to the substrate. Black chrome plated onto both copper and nickel was found to form polycrystalline chromium oxide at the surface during heat treatment, the average size of the crystallites increasing during heat treatment. In the case of black chrome plated on copper, oxidation of the copper substrate could also be observed. Black cobalt was found to be stable at high temperatures (up to 350°C), forming Co 3O 4 at the expense of the underlying cobalt layer.