High Temperature Thermal Diffusivity Measurement for FeO Scale by Electrical-Optical Hybrid Pulse-Heating Method

Abstract

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-H 2-H 2 O 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 m 2 s − 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.

Determination of Thermal Diffusivity and Its Temperature Dependence of Fe_1−<i>x</i>O Scale at High Temperature by Electrical-Optical Hybrid Pulse-Heating Method

“…An R-type thermocouple was welded at the center of a 40 × 4 mm 2 face of the coupon to measure the temperature. 8) Nine pieces of coupons were prepared by the method introduced above.…”

“…Figure 1 shows the schematic diagram of the electricaloptical hybrid pulse-heating method used in this work, which was almost same as that Yang et al 8) used. The apparatus consisted of an Nd: glass laser generator, a pyrometer, data acquisition, and heating control system and the circuits for heating the sample.…”

“…There have been several reports available for thermal diffusivity of iron oxides; [2][3][4][5][6][7][8] however, a large discrepancy exists among the reported values. The discrepancies would be due to the difference in microstructures of samples originating from sample preparation methods, i.e., sintering of iron oxide powders 2,3) or thermal oxidation of iron sheets.…”

“…[4][5][6][7] The iron oxide samples prepared by the thermal oxidation of iron would have a closer microstructure of oxide scale formed on the steel plate in the actual steelmaking process and more suitable for measurements of thermophysical properties of oxide scale. There are four reports available on the thermal diffusivity for Fe 1 − x O scales formed on iron sheets; [5][6][7][8] reported by Taylor et al, 5) Li et al 6,7) and Yang et al, 8) where all reports applied the laser flash method. However, discrepancies still exist between reported values for Fe 1 − x O scales because of the decomposition of Fe 1 − x O into Fe 3 O 4 and Fe during the experiment.…”

“…After the correction, the values became much smaller. Yang et al 8) applied another heating technique, i.e., the electrical-optical hybrid pulse-heating method because it is difficult to measure the thermal diffusivity of Fe 1 − x O under normal heating rate. The pulse-heating method can heat the sample rapidly and minimize the duration of high-temperature exposure of the Fe 1 − x O scale in the thermal diffusivity measurement.…”