Effect of graphite coating on measurement of thermal diffusivity of high-thermal-conductivity silicon nitride thin substrates by flash method

The influence of graphite coating on the measurement of thermal diffusivity by the flash method was systematically investigated using thin, high-thermal-conductivity silicon nitride (Si 3 N 4 ) substrates (≈90 W/(m·K) and 120 W/(m·K)) with thicknesses of 2.0 mm, 0.32 mm, and 0.25 mm. While coating had negligible influence for 2.0 mm samples, the measured diffusivity decreased with increasing coating weight for 0.32 mm and 0.25 mm samples, with stronger effects for thinner and more thermally conductive substrates. The results highlight the need to strictly control graphite-coating amount for thin, high-conductivity materials, and the observed trend was quantitatively explained using a laminated structure model accounting for through-thickness heat transfer.