ISSN:
1432-0630
Schlagwort(e):
68.20
;
78
;
86.30
Quelle:
Springer Online Journal Archives 1860-2000
Thema:
Maschinenbau
,
Physik
Notizen:
Abstract A new optical model is presented for solar-selective black chrome. Surface texture is shown to be the primary factor which gives thin films of black chrome a uniformly high absorptance in the visible and near-infrared regions. Internal composition of the films is a secondary influence on their optical properties. We present results consistent with experimental data obtained from films having widely varying structures and compositions, both before and after heat treatment. Our optical model does not rely on the quasistatic approximation, hitherto universally employed in theoretical studies of solar-selective black chrome. Instead, we use a rigorous diffraction formulation for doubly-periodic surfaces (bigratings). The key parameters of the surface morphology are determined from stereo-pair electronmicrographs, and are used in the bigrating model. We present the predicted variation of spectral absorptance with wavelength, as well as integrated absorptance and thermal emittance, for roughened chromium. We give results both for bare metal, and for the metal conformally overcoated either with a thin layer of Cr2O3 or with a Cr/Cr2O3 cermet. Various shapes of surface features are examined, and surface profile is shown not to be crucial in determining optical properties.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1007/BF00616552
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