Microstructure and optical properties of black chrome before and after exposure to high temperatures

Conference · Mon Jan 01 04:00:00 EST 1979

OSTI ID:6078007

Lampert, C M; Washburn, J

The chemical and microstructural stability of the CHROM-ONYX type of black chrome solar coating was investigated at different temperatures and atmospheres. This was done to give a better understanding of the mechanism of solar energy selectivity and its variability when subjected to short term heat treatments. The as-plated structure was found to consist of a suspension of metallic chromium particles within the size range of 100A in an amorphous oxide matrix. This assembly was in turn formed into larger particles within the size range of 0.05-0.30 microns. Short term high temperature heat treatments were used to simulate stagnation conditions. Samples were annealed in both air and vacuum, which resulted in similar characteristics. Annealing in air appeared to mildly accelerate optical degradation at high temperatures. For short term heat treatments below 300/sup 0/C the reflective and microstructural properties appeared to be unchanged. By in situ vacuum annealing of the coating above 400/sup 0/C microcrystalline Cr/sub 2/O/sub 3/ was identified. By observation of diffraction patterns it was concluded that a-Cr/sub 2/O/sub 3/ was transformed into crystalline Cr/sub 2/O/sub 3/. The Cr/sub 2/O/sub 3/ phase continued to grow at higher temperatures at the expense of chromium content. At temperatures above 500/sup 0/C in vacuum, a new phase identified as NiCr/sub 2/O/sub 4/ formed. It was found that black chrome failed optically between 500-600/sup 0/C for 1 hour heat treatments in both air and vacuum; also the coating heated in air failed mechanically by peeling at 600/sup 0/C.

• Research Organization: California Univ., Berkeley (USA). Lawrence Berkeley Lab.
• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 6078007
• Report Number(s): LBL-8632(Rev.); CONF-790120-2(Rev.)
• Country of Publication: United States
• Language: English

Related Subjects

14 SOLAR ENERGY
141000* -- Solar Collectors & Concentrators
ANNEALING
BLACK CHROME
BLACK COATINGS
CHALCOGENIDES
CHROMIUM COMPOUNDS
CHROMIUM OXIDES
COATINGS
COHERENT SCATTERING
CRYSTAL STRUCTURE
DIFFRACTION
HEAT TREATMENTS
HUMIDITY
MICROSTRUCTURE
OPTICAL PROPERTIES
OXIDES
OXYGEN COMPOUNDS
PARTICLES
PHYSICAL PROPERTIES
SCATTERING
SIMULATION
SIZE
SOLAR ABSORBERS
SPECTRALLY SELECTIVE SURFACES
STABILITY
STAGNATION
SURFACES
THERMAL DEGRADATION
TRANSITION ELEMENT COMPOUNDS