Infrared optical properties of semitransparent pyrolytic boron nitride (pBN)

Because of the semitransparency of pBN in the infrared spectral region, the heat flux within this material does not only depend on its solid thermal conductivity, but also on its radiative properties. In order to characterise the heat transfer in pBN samples, the thermal and infrared optical properties were determined. From the measured spectral reflectance and transmittance of the samples, the radiative heat-transfer coefficient was derived. In addition, the thermal conductivity was determined via laser-flash and differential scanning calorimetry measurements. It was found that for temperatures above 600 K the radiative transport influenced the total heat-transfer coefficient significantly.