Spectroscopic characterization of Al2O3-Ni selective absorbers for solar collectors

Optical spectroscopy of electrochemically prepared Ni-pigmented aluminum oxide selective absorbers have been determined in the 200-20000 nm range. It was found that samples anodized under the same conditions and pigmented using nickel acetate resulted in better thermal emittance values when compared with nickel sulfate although both have comparable solar absorbance values. Electron spectroscopic investigation revealed that only a small fraction of Ni is present on the surface with an oxidation state of greater than or equal to + 2. The O/Al ratio determined by XPS is larger than 1.5. This information together with the measured Al2p Auger parameter indicated that the surfaces contain additional OH groups which was also confirmed by the presence of a broad hyrogen-bonded band in the region 3000-3400 cm(-1) observed in the reflection-absorption IR spectra of these samples. (C) 1998 Elsevier Science B.V. All rights reserved.