A fast measuring method for thermal expansion of metals using a feedback-controlled pulse heating technique


H. Watanabe1

1National Institute of Advanced Industrial Science and Technology (AIST), Japan

Keywords: pulse heating method, image processing, high temperature
property: thermal expansion, heat capacity, electrical resistivity, emissivity
material: metal, alloy

A Fast Measuring Method for Thermal Expansion of Metals Using a Feedback-Controlled Pulse Heating Technique Hiromichi WATANABE Thermophysical Properties Section, Material Properties and Metrological Statistics Division, NMIJ, National Institute of Advanced Industrial Science and Technology (AIST). Tsukuba Central 3, 1-1-1, Umezono, Tsukuba, Ibaraki 305-8563, JAPAN A fast measuring method of thermal expansion of electrically conductive materials at high temperatures has been developed. The feature of this method is the use of a feedback-controlled pulse heating technique[1], which can rapidly heat a thin plate sample up to a preset high temperature in less than 500 ms and then keep the sample at that temperature under steady-state conditions for a brief period (less than 1 s). The experimental system consists of the electrical pulse heating unit and an image processing unit for capturing the sample-edge images. The sample temperature was measured by the combination of an IR radiation thermometer and an R type thermocouple which was spot-welded at the side edges of the plate-like sample. The sample-edge images were captured using a CMOS camera with the backlighting system which consists of a green LED illuminator, a telecentric lens system, and a short-pass filter. The thermal linear expansion of the sample was determined from the measured changes of the sample width and temperature from those at the initial temperature (293 K), respectively. To avoid the oxidization of the sample surface, the sample was inserted into a vacuum chamber. The performance of the present method and system has been evaluated through the thermal expansion measurements of twelve kinds of metals (V, Nb, Ta, Zr, Hf, W, Ni, Pd, Pt, Co, Fe, and SUS316) in the temperature range from 600 to 1800 K. All the measured data of the metals are in reasonably good agreement with the corresponding recommended values.

References
  1. T. Matsumoto, A. Cezairliyan, Int. J. Thermophys. 18, 1539 (1997).

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