Comparison of different forms of black cobalt selective solar absorber surfaces

Abstract

Five different forms of spectrally selective black cobalt solar absorber surfaces have been prepared using techniques of electrodeposition, chemical conversion and thermal oxidation in air respectively. The dependence of surface optical properties on deposition process parameters has been investigated. Composition and microstructure have been examined using a range of surface analytical techniques. Surfaces have been exposed to elevated temperatures in air and optical properties have subsequently been remeasured. Two forms of black cobalt, a cobalt oxide hydroxide coating formed by chemical conversion and a cobalt oxide coating formed by thermal oxidation in air, are shown to exhibit favourable optical properties for long term use as selective solar absorbers.