Thermal conductivity of non-isotropic materials measured by various methods

zHigh-temperature thermal conductivity of insulating material is usually measured by application of the steady-state calorimeter method or the transient hot-wire method. However. when applied to non-isotropic materials, the methods yield results which show systematic differences depending on orientation of the material during the measurement. In this contribution results are presented for one and the same material measured between room temperature and 1300 °C in all three instruments (according to the steady-state plate, the steady-state cylinder, and the transient hot-wire methods). Additional experiments are carried out in these instruments with various fibre orientations. Differences between the measured conductivities are found to exceed 100% in the high-temperature range. The results are discussed and supplemented by raster electron microscope (REM) and differential thermal analysis (DTA) of the fibre material and numerical studies of the temperature fields inside the facilities.