Intercomparison of Thermal Conductivity Measurements on a Nanoporous Organic Aerogel

Due to their special combination of nanostructure and high porosity, aerogels are key materials for high performance thermal insulation. However, measuring reliable thermal conductivity values, which are essential for material’s optimization and as product parameter, is a challenging task in the case of aerogels. Experimentally derived thermal conductivity values for aerogels are so far more or less influenced by the experimental set-up and the experimental conditions and have to be carefully discussed. Here we present results of an intercomparison on thermal conductivity measurements performed for a polyurethane aerogel produced on a pilot scale as stiff panels by BASF. Prior to the intercomparison, the material was checked for reproducibility in production and homogeneity. The dependence of thermal conductivity on atmospheric pressure and temperature was also determined. We discuss the results submitted by 12 participants with respect to the different experimental techniques applied and identify experimental parameters with severe impact on the resulting thermal conductivities. The derived mean values for the thermal conductivity at 20 °C, 40 °C and 60 °C were related with relative uncertainties in the range from 0.6 % to 0.9 %. The dependence of the derived thermal conductivity values on the geographical location of the participating laboratory and the atmospheric weather conditions could be clearly observed and the precision of the results could be significantly improved by correcting for these effects. The values had to be partly corrected up to 2.5 %.