Abstract
In this paper the first results of a project concerned with the development of low cost transition metal nitride selective absorbers with a high solar absorptance and a low thermal emittance are presented. These absorbers are intended for application at operating temperatures up to 200 °C in high performance solar collectors. We found that reactively d.c.-sputtered chromium nitride films on a copper substrate exhibit a low emittance (about 0.04) and a moderate solar absorptance (about 0.80). The relatively high production cost and capital investment associated with sputtering can be avoided by producing such films by (electro)chemical deposition. Encouraging results have been obtained with the nitridation of electrodeposited chromium films. The drawback of the moderate solar absorptance can be overcome by depositing the nitride films onto electrodeposited rough copper base layers. We found that the addition of small carbon particles (india ink pigment) to the copper deposition bath gives rise to layers with a suitable surface roughness. This surface roughness causes the solar absorptance to increase to 0.90. However, because of the small characteristic dimensions (about 0.5–2 μm) of the roughness, the low thermal emittance is hardly affected.
Published Version
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