Influence of opacifiers on thermal insulation properties of composite aerogels

Aerogels are almost transparent to the near-infrared wavelengths, and therefore the opacifiers are widely doped to enhance aerogels insulation performances. Mie scattering theory was employed to calculate the mean extinction coefficient of composite aerogels doped with different kinds of opacifiers with different diameters and their shading effects were compared. A Hot Disk TPS2500S thermal analyzer based on the transient plane source method was used to measure the thermal conductivity of composite aerogels at different temperature and comparison with the theoretical analysis was conducted. The predicted thermal conductivities by theoretical model are in good agreement with the experimental data obtained by the Hot Disk thermal analyzer at different temperature. The results show that the optimal diameter of doped opacifiers is approximately at 3.5 μm, the shading effect of SiC opacifier is better than that of TiO₂ and ZrO₂, and there exists an optimal volume content of opacifiers (~3.75%) making the overall thermal insulation performance best. The developed theoretical model can be adopted to predict the influence of doped opacifiers on the effective thermal conductivity of composite aerogels.