STUDY OF THE SPECTRAL PROPERTIES OF INHOMOGENEOUS GRANULAR-MATERIALS

The variation of the spectral properties of semi-transparent (polystyr ene: PS), transparent (potassium bromide: KBr) and opacified particles (sliver coated silica spheres: Ag-SiO2) is presented from 0.25 to 20 pm. The spectral properties of binary mixtures PS/KBr and PSIAg-SiO2 a re also studied. The sensitivity of the spectral properties to the par ticle diameters causes the near-normal hemispherical spectral reflecta nce R to decrease when the particle size increases from 10 to 1800 mu m. The addition of KBr transparent particles to PS powders results in an increase in the reflectance values of the mixtures in the near and mid-infrared wavelength range. Furthermore, the effect of the addition of opacified reflecting particles depends on the wavelength region an d on the PS content ([PS]). For lambda < 1.64 mu m, R decreases when [ PS] decreases from 1 to 0.56 and then R increases for [PS] values decr easing from 0.56 to 0. For lambda > 1.64 mu m, R decreases when PS con tent increases from 0 to 1.