10.07.2015   EUROSUN 2008

Optical properties of cerium oxide

The optical properties of the cerium oxide particles were calculated from the Mie-scattering theory [4]. From this theory the spectral absorption, scattering, and extinction cross-sections, as well as the scattering phase function can be calculated, with the complex refractive index of the particle material m, and particle radius rp as inputs. The complex refractive index of cerium oxide was

taken from different sources. From the papers by Ozer [5], and by Wiktorczyk and Oles [6], the optical properties for the visible and near IR were obtained. An expression for the IR properties CeO2 was taken from Santa et al. [7]. These latter authors fit the experimental reflectance values by using a quasi-harmonic damped multiple- oscillator model for the dielectric function.

We consider particles of 5 pm radius. The spectral volumetric extinction, absorption, and scattering coefficients (ay, Sv and B, v respectively), are shown in Fig.1. These coefficients are given by

av = Cext,, / V Sv = Cabs,, / V £, = Cscatt,, / V (3)

Where Cext, ,, Cabs, , and Cscatt, , are the spectral extinction, absorption and scattering cross-sections, respectively, and V is the particle volume.

Fig. 1. Spectral volumetric attenuation, absorption, and scattering coefficients for particle radius of 5 pm.

As seen on the graph, the extinction of radiation by these particles is mainly due to scattering; they are not very absorbing. Actually two main extinction peaks are visible, at 11 and 20 pm wavelengths. The first, one corresponds to resonance effects, while the second is due to absorption.

fvC

abs,,

V-1

Px

(4)

fvC

ext,,

V-1

fvC

scatt,,

V-1
Подпись: Px Подпись: (4)

The absorption (к), scattering (о) and extinction (ДО coefficients of the gas/particle fluidized medium are calculated from the spectral cross sections of the particles by

where fv is the particle volume fraction.

The phase function from Mie — scattering theory, as a function of the cosine of the scattering angle, is shown in Fig. 3. As seen from this graph, the particles scatter radiation mainly in the forward direction, for the UV, Vis, and near — IR, while for the far — IR they have an almost isotropic scattering (28.8 mp), with a slightly backward preference (38 mp).