Thermal Diffusivity and Porosity of Solid Materials by the Electromagnetic Ultrasonic Technique. 1st Report, The Principle of Measurement.

Abstract

Carbon-cabon composites are important structural materials at high temperature. Their thermal properties and microscopic structures change with the temperature and the time required for heat treatment. It is expected that the thermal diffusivity and porosity show different values at every moment during heat treatment. The objective of this study is to evaluate the time dependence of the thermal diffusivity and porosity simultaneously using the electromagnetic ultrasonic technique. This report describes the principles of measurement of the properties and the experiment to confirm the principles separately at room temperature. The longitudinal ultrasonic velocities of aluminum and carbon brick in the evaluation of porosity are 6350 m/s and 2530 m/s with precision of ±1.6% and ±0.4%, respectively. Is was confirmed that the aluminum and the carbon electrodes were able to be heated by the electromagnetic ultrasonic transducer. The thermal diffusivity of carbon brick measures 8-9 mm2/s but the accuracy of measurement will have to be investigated using the standard material in the future.