Thermal effusivity of iron oxide scale formed on iron sheet measured by pulsed light heating thermoreflectance technique

The pulsed light heating thermoreflectance technique has been applied to measure thermal effusivities of thermally grown FeO and Fe3O4 scales. Samples were iron sheets with single phase FeO or Fe3O4 scale on the surfaces. The surfaces of FeO and Fe3O4 were well polished. After polishing, the thicknesses of FeO and Fe3O4 were over 73 m and 27 m, respectively. One surface of the sample was coated with Mo film. In the experiment, periodical laser pulse train with a pulse width of 0.5 ps and a frequency of 20 MHz was irradiated onto the Mo film of a sample to cause a periodical change in temperature at the Mo surface. The temperature change was detected by a probe laser with a pulse width of 0.5 ps and a frequency of 20 MHz, and the thermoreflectance phase signal was outputted via a lock-in amplifier. This phase signal reflects the thermal effusivity of the material measured. Numerical simulation was made so as to reproduce the phase signal by inputting thermophysical property values of Mo and the oxide scales. Thermal effusivities of FeO and Fe3O4 obtained for room temperature are 2.40 × 10³ and 3.60 × 10³ Jm^-2s^-0.5K^-1, respectively. The value of FeO is close to a reported value measured by the hot strip method; for Fe3O4, however, more inspections are required to confirm the reproducibility of the result.