High temperature thermal diffusivity measurement for FeO scale by electrical-optical hybrid pulse-heating method

Thermal diffusivity of FeO scale formed on iron has been determined at high temperature using an electrical-optical hybrid pulse-heating method, which can avoid the compositional change of the sample even at elevated temperatures by executing the experiment rapidly. The sample was a 90 μm-thick FeO scale layer, which had been thermally grown on a 0.5 mm-thick iron coupon at 1 123 K in an Ar–H₂–H₂O gas mixture. In the experiment, a large current pulse was supplied to the iron coupon, and the FeO scale was indirectly heated up to about 932 K from room temperature within 0.5 s. The temperature was maintained at the experimental temperature and the laser flash method was conducted to measure the effective thermal diffusivity of the coupon. Thermal diffusivity of FeO scale at 932 K was calculated to be 5.27 × 10⁻⁷ m²s⁻¹ based on a multi-layered analysis for the effective thermal diffusivity on the three-layered structure (FeO/Fe/FeO). X-ray diffraction analysis for the post-experiment coupon confirmed that no compositional change had occurred during the experiment. The uncertainty of the measured value was discussed. The effect of boundary resistance on the measured value was also estimated in this study.