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Optical constant database - Level: measurement/paper

Begemann et al. (1997) paper's page


Source:
Begemann B., Dorschner J., Henning Th., and Mutschke H. (1997)
Aluminum oxide and the opacity of oxygen-rich circumstellar dust in the 12-17 micron range.
Astrophys. J., v. 476, pp. 199 - 208.

Optical constants: Some details:
The sol-gel technique was applied to prepare amorphous alumina. This technique is totally different from the condesation process of Al2O3 in astrophysical environments but is commonly used in material sciences. The samples were annealed in an oxygen stream at different temperatures (383 < T < 1773K). The amorphous state of a selected sample (T=873K) was confirmed in several ways. Sedimentation in acetone was used to separate grain size fractions: smaller than 2 micron (coarse fraction) and smaller than 2 micron (fine fraction).
  Transmission spectroscopy was applied to the fine fraction embeded in KBr (wavenumber range 400-5000 cm-1) and the coarse fraction embeded in PE (wavenumber range 20-650 cm-1). The optical constants directly obtained from the data by Lorentz oscilator fitting for the range 20-1300 cm-1 correspond to porous alumina. Assiming that the pores are filled with liquid water the optical constants for "compact" alumina were derived using the Bruggeman rule of effective medium theory.

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Last modified: 11/10/98, V.I.