Thermal radiation dominates the heat transfer in coal gasification or combustion furnaces operated at high temperatures. This study is to evaluate the radiation properties of coal char or ash particles, which are necessary to predict the behavior of heat transfer of a multiphase flow in the furnace. The monochromatic extinction of the sample particles dispersed in liquid paraffin wax was measured by the FT-IR spectroscopic analysis at a room temperature. Carbon containing in char particles influences significantly extinction efficiency as a radiation property. The normalized extinction efficiency was correlated by an exponential function of carbon content if the sample was prepared appropriately although the spectra depended on the preparation method of the samples. (c) 2007 Elsevier Ltd. All rights reserved.