Solar optical properties and scattering of monolithic aerogel materials

摘要

Optical properties of some aerogel samples were investigated. The samples were provided by Japan, Norway and Sweden as part of a collaborative program of research on behalf of the International Energy Agency. For each sample the total near-normal hemispherical spectral transmittance and reflectance as well as the diffuse near-normal hemispherical spectral transmittance and reflectance were measured for the solar spectral range using a Beckman integrating sphere. The ratio of diffuse to total transmittance was calculated at each wavelength. Solar optical parameters as well as chromaticity coordinates were determined for both the total and the diffuse components. The influence of bulk and surface scattering is discussed and the effect of sample thickness and incident beam size in relation to sample area in respect of measured optical properties was also investigated and significant differences were observed which are relevant for good practice aspects of the measurement technique. No significant specular reflectance component was detected for any sample. The investigated samples vary considerably in density, but it was found that the visible scattering was nearly the same for all samples. Much stronger absorption is evident in the near infrared spectral range for the Norwegian sample and this is attributed to enhanced water content and higher density.