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Proceedings Paper

Low Emittance Coatings For High Temperature Solar Collectors
Author(s): D. R. McKenzie; N. Savvides; R. C. McPhedran; D. R. Mills
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Paper Abstract

We discuss the importance of low emittance and temperature stability for solar-selective high-temperature coatings. We show experimentally that high stagnation temperatures can be achieved by reducing the coating emissivity below previously-obtained values. We have investigated amorphous hydrogenated carbon (a-C:H) and silicon-carbon alloy (a-SixCi-x:H) films prepared by magnetically-enhanced glow discharge decomposition. In the latter case, we have prepared alloys from acetylene, ethylene and methane mixed with silane. We have shown by electron microprobe analysis that the atomic C/Si ratio in the film is the same as that in the gas. We show that both the emittance of a-C:H films and their high temperature stability can be enhanced by annealing in vacuum. The film properties change substantially in the first hour of heat treatment at 500°C, before stabilizing after about 24 hours. Thereafter, the properties do not change during a further 300 hours of heat treatment. The heat -stabilized films, when placed on copper substrates and used in non-concentrating systems, have been shown to yield stagnation temperatures up to 459°C in preliminary experiments. The a-SixC1-x :H films investigated have the potential to provide lower emittance coatings than the a-C:H alloys which are currently employed in composite metal-amorphous semiconductor films. The use of silicon/carbon alloys also provides greater flexibility in grading profiles for the composite films, permitting greater control in the trade-off between high solar absorptance and low emissivity.

Paper Details

Date Published: 1 December 1983
PDF: 9 pages
Proc. SPIE 0428, Optical Materials and Process Technology for Energy Efficiency and Solar Applications, (1 December 1983); doi: 10.1117/12.936316
Show Author Affiliations
D. R. McKenzie, The University of Sydney (Australia)
N. Savvides, The University of Sydney (Australia)
R. C. McPhedran, The University of Sydney (Australia)
D. R. Mills, The University of Sydney (Australia)

Published in SPIE Proceedings Vol. 0428:
Optical Materials and Process Technology for Energy Efficiency and Solar Applications
Carl M. Lampert, Editor(s)

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