Accelerated aging tests of chromium containing amorphous hydrogenated carbon coatings for solar collectors

Chromium containing amorphous hydrogenated carbon films (a-C:H/Cr) have been prepared by simultaneous rf plasma activated chemical vapour deposition of methane and magnetron sputtering of a chromium target. During deposition the substrates were heated (up to 300 degrees C) and DC biased (- 200 and - 600 V) in order to obtain films with high chemical stability. Constant temperature tests were performed at 250 degrees C in air with coatings deposited on silicon substrates. The degradation of the coatings was monitored by Raman spectroscopy and reflectance and transmission measurements. The main degradation mechanisms are discussed and the relevant parameters which improve the durability of the coatings are presented. Furthermore, the durability of solar selective, multilayered coatings which were deposited on copper sheets was investigated. Based on accelerated aging tests at different temperature loads in air (at 220 degrees C, 250 degrees C and 300 degrees C) and in a humid environment (80 degrees C sample temperature in humid air with 85 degrees C and 95% relative humidity) the service lifetime in a hat plate collector is predicted to amount to more than 25 years. (C) 1998 Elsevier Science B.V. All rights reserved.