In recent years, composite materials containing hollow glass or ceramic microspheres have attracted considerable attention. These materials have very good heat-insulation characteristics, which are largely defined by special features of absorption and scattering of thermal radiation by thin-walled hollow particles (German and Grinchuk, 2002; Dombrovsky, 2005). The paint coatings containing hollow glass microspheres have already found applications for reducing heat loss from the walls of buildings owing to a decrease in thermal radiation at night.
Infrared radiative properties of a polymer containing hollow glass microspheres are studied by means of the measurements of direc- tional-hemispherical reflectance and transmittance in the wavelength range from 2.6 to 18 lm. The measurements are performed for sev- eral samples containing different series of microspheres of volume fraction from about 6% to 66%.
Relatively strong peak of reflectance at the wavelength 4.5 lm was observed. This peak is explained in terms of theoretical model based on Mie theory calculations for single microspheres and modified two-flux approximation proposed recently by the authors. The reflectance of the composite material in the important range from 8.5 to 13.5 lm is determined mainly by rough surface layer of microspheres and it does not described by the model for semi-transparent media. The conditions of a considerable decrease in radiative heat losses from the buildings due to paint coatings containing hollow glass microspheres are discussed.
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