OPACIFIED SILICA AEROGEL POWDER INSULATION

We have investigated the thermal conductivity of powder and granular SiO2-aerogels with a density in the 80 to 150 kg/m3 range; the specimens were opacified with carbon soot. The caloric measurements were performed as a function of temperature, gas pressure and mechanical load. The smallest total conductivities for non-evacuated specimens are around 0.017 W/(m.K) at 300 K. The extracted solid conductivities are in the range 0.002 to 0.004 W/(m.K), depending on density, mechanical load and grain size; the radiative conductivity at 300 K is about 0.001 W/(m.K) for a fine powder; this corresponds to an extinction E almost-equal-to 6000 m-1 or a specific extinction e = 60 m2/kg. For a coarse granular fill a considerably smaller specific extinction of e almost-equal-to 20 m2/kg is found. The gaseous conductivity is about 0.013 to 0.017 W/(m.K), depending on the inter-grain pore space fraction. The investigated aerogel powders can be easily filled into hollow spacings and used as an effective non-evacuated insulation or, if evacuated, as a thermal superinsulation.