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RESEARCH PAPERS

Development of Sputter-Deposited Pt/Al2O3 Selective Absorber Coatings

[+] Author and Article Information
J. A. Thornton

Department of Materials Science and Coordinated Science Laboratory, University of Illinois, Urbana, IL 61801

J. L. Lamb

Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109

J. Sol. Energy Eng 109(4), 241-252 (Nov 01, 1987) (12 pages) doi:10.1115/1.3268214 History: Received March 01, 1987; Online November 11, 2009

Abstract

The Pt/Al2 O3 cermet system is extremely stable against oxidation. Therefore, effective high temperature selective absorber coatings can be formed by depositing Pt/Al2 O3 cermets onto Pt low emittance base layers. Three Pt/Al2 O3 cermet configurations have been investigated for photothermal receiver applications: (1) cermets with graded Pt composition and Al2 O3 antireflection layers; (2) cermets with uniform Pt compositions and Al2 O3 antireflection layers; and (3) Al2 O3 -M-Al2 O3 multilayer coatings where the M-layer is a Pt/Al2 O3 mixture containing about 20 volume percent Al2 O3 . The coatings were deposited by cosputtering from Pt and Al2 O3 sources. Both direct rf sputtering from an alumina target and Ar-O2 dc reactive sputtering from an aluminum target were investigated as methods for depositing the Al2 O3 components of the cermet and the antireflection layers. Cr, Mo, Ta, W, and ZrB2 were investigated as alternative low emittance base layer materials. Most of the coatings were deposited onto flat plates of glass, although type 316 stainless steel, type 1020 low carbon steel, and Incoloy 800 substrates were also examined. Hemispherical absorptances as high as 0.97, with room temperature emittances in the 0.06 to 0.08 range, were achieved. The optical properties of the coatings with rf-sputtered Al2 O3 , and Pt low emittance base layers were stable at 600° C in air for as long as 2000 hr, consistent with data for evaporated Pt/Al2 O3 coatings reported by Cornell University. The coatings with reactive sputtered aluminum oxide, or alternative base layers such as Mo, exhibited somewhat reduced thermal stability but should be adequate for intermediate temperature applications (up to 400° C in air).

Copyright © 1987 by ASME
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