The thermal diffusivity/conductivity of FeO scales produced on iron substrates by thermal oxidation have been determined as functions of temperature. Iron plates (99.99%) were oxidised at 973 K in air to obtain oxide scales of FeO, Fe 3 O 4 , and Fe 2 O 3 , and then were reduced at 1 273 K in nitrogen to obtain FeO-only. The densities of these scales were 5.85-6.05 g cm − 3 . The laser flash method was used to measure the apparent thermal diffusivity of the whole sample from room temperature to 1 164 K during the heating/ cooling cycles. This was converted to the thermal diffusivity of the scale only, which in turn was converted to the thermal conductivity. However, these values depended on the scale thickness, which suggests an interfacial heat resistance occurs between the scale layer and iron substrate. In addition, scanning electron microscopy (SEM) observations revealed that the scales contained Fe and Fe 3 O 4 phases after heating. The scale thermal diffusivity/conductivity were corrected considering the interfacial heat resistance and dispersed phases to derive the corresponding values for FeO only. The interfacial heat resistance derived from the thickness dependence of the scale thermal conductivity was 8.3 × 10 − 6 m 2 K W − 1 . Using this value, the thermal diffusivity of FeO was derived as 3.7 × 10 − 7 -5.8 × 10 − 7 m 2 s − 1 and the thermal conductivity as 1.8-2.5 W m − 1 K − 1 between room temperature and 1 164 K. The temperature coefficients of the thermal conductivity were mostly negative, which would be dominated by the phonon mean free path.

Thermal conductivities of iron oxide scales have been determined in a temperature range of room temperature to 1 176 K by the laser flash method, where the interfacial thermal resistance between FeO and iron has been corrected for each temperature. Two series of samples were prepared from iron plates with 99.99% purity. One was samples with FeO scale only and the other was samples with multi-layered scale of Fe 2 O 3 /Fe 3 O 4 /FeO. The laser flash method was applied to measure apparent thermal diffusivities, which were converted to apparent thermal conductivities. Apparent thermal conductivities obtained are contaminated by the interfacial thermal resistance between scale and iron, and are in linear proportion to scale thickness. Using apparent thermal conductivities at room temperature, thermal conductivities of scale have been derived from the slope of the linearity as 2.4 Wm − 1 K − 1 for FeO scale and 1.8 Wm − 1 K − 1 for multilayered scale, and interfacial thermal resistances have been derived from the intercept as 7.3 × 10 − 6 m 2 KW − 1 for the interface at FeO/iron and 6.4 × 10 − 6 m 2 KW − 1 for the interface at multi-layered scale/iron. The interfacial thermal resistance between FeO and iron decreases with increasing temperature. Considering these temperature-dependent interfacial thermal resistances, thermal conductivity values of FeO scale have been determined as a function of temperature. The values are roughly 2.2 Wm − 1 K − 1 up to 1 176 K except 6.9 Wm − 1 K − 1 at 674 K where the decomposition of FeO tends to take place.

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