Determination of high-temperature radiative properties of porous silica by combined image analysis, infrared spectroscopy and numerical simulation

The influence of the texture of fused silica glasses − containing unconnected spherical bubbles − on their thermal radiative properties was investigated by combining experimental measurements and numerical simulations. Exact numerical replicas of the porous samples were obtained from X-ray microtomography and image analysis showed that their bubble populations include two lognormal distributions of radii. The complex refractive index of the silica matrix was extracted from emittance measurements acquired at 1200 K on two reference silica samples. The comparison between direct measurements of the normal spectral emittance of the porous samples and those generated by applying Monte-Carlo ray tracing, performed on the numerical replicas, validated the use of geometric optics. The OH content of the porous samples was evaluated to be around 210 ppm. Ray tracing simulations carried out on a set of virtual samples having a similar texture proved to be a flexible means to address experimental limits when characterizing semi-transparent materials. The simulations also provided a natural framework to test the ability of the modified two-flux approximation model to predict the thermal radiative response of the porous silica investigated.