Thermal diffusivity and porosity of solid materials by the electromagnetic ultrasonic technique. Part 1. the principle of measurement

Carbon-carbon composites are important structural materials for high temperatures. However, their thermal properties and microscopic structures change with temperature and the time required for heat treatment. It is expected that the thermal diffusivity and the porosity have different values at every moment during heat treatment. The objective of this study is to evaluate the time dependencies of the thermal diffusivity and porosity simultaneously, using an electromagnetic ultrasonic technique. This paper describes the measurement principles and the experiments to confirm the principles separately at room temperature. The longitudinal ultrasonic velocities of aluminum and carbon brick in the evaluation of porosity are 6.35 km/s and 2.53 km/s with precision of [+-] 1.6 and [+-] 0.4 percent, respectively. It was confirmed that the aluminum and the carbon electrodes can be heated by an electromagnetic ultrasonic transducer. The thermal diffusivity of carbon brick measures 8--9 mm[sup 2]/s, but the accuracy of the measurement will have to be investigated using a standard material in the future.