Determination of thermal diffusivity and its temperature dependence of Fe_1-xO scale at high temperature by electrical- optical hybrid pulse-heating method

Thermal diffusivity of Fe_1-xO scale formed on iron sheets have been measured using an electricaloptical hybrid pulse-heating method, which can avoid decomposition of Fe_1-xO scale even at elevated temperatures by executing the experiment rapidly. The samples were 50 μm-thick Fe_1-xO scale, which had been obtained by oxidation of a 0.5 mm-thick iron coupon at 1 123 K in the air followed by sandblasting to remove the outer oxide layers of Fe3O4 and Fe₂O₃. In the experiment, the sample was heated by a large current pulse supplied to the iron layer of the coupon, and the Fe_1-xO scale was indirectly heated up to experimental temperature from room temperature within 0.2 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. The laser irradiation position was adjusted by two ceramics blocks to make the temperature profile better. The effective thermal diffusivity produced the value for Fe_1-xO scale based on a three-layered analysis for the Fe1 - x O/iron/Fe_1-xO structure. Thermal diffusivities of Fe_1-xO scale were around 4.8 × 10^-7m²s^-1, and there can be seen no obvious temperature dependence from 600 K to 900 K. X-ray diffraction analysis confirmed that phase transformation did not occur in the Fe_1-xO scales during the experiment and x value was calculalted to be 0.09. Non-stoichiometry is supposed to have a significant effect on thermal diffusivity of Fe_1-xO scale and its temperature dependence in this research.