STUDY OF THEMAL DIFFUSIVITY AND POROSITY OF COMPOSITE MATERIALS BY THE ELECTROMAGNETIC ULTRASONIC TECHNIQUE

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1. Development of the electromagnetic ultrasonic technique : The electromagnetic ultrasonic wave was successfully generated and detected in the sample, and the method to measure the velocity of sound by monitoring the phase difference between these waves was studied. The ultrasonic velocities in aluminum, stainless steel and carbon brick were measured successfully by the through-transmission method. But in this measurement, the temperature rise due to the induction heating by one pulse current was not large enough to apply a electromagnetic ultrasonic transducer to the surface heating in the measurement of thermal diffusivity. Therefore the pulse current of a few amperes and of 1 kHz as the peak value in repetition frequency was supplied into the transducer. The temperature profile was observed at the sample surface, and the thermal diffusivities of stainless steel and carbon brick were measured by the stepwise heating method. The influence of the distribution of internal heat production on the thermal diffusivity was also investigated and further, the conditions to measure the thermal diffusivity and the ultrasonic velocity simultaneously at high temperature was discussed.2. Development of the method and measurement at high temperature : The system to detect the electromagnetic ultrasonic wave had to be sealed against the unnecessary electromagnetic wave. It was confirmed that the temperature of the carbon-carbon (C/C) composite rose by the induction heating at the temperature of up to 1200ﾟC. The temperature profile of C/C composite with Fourier's number of less than 1 was observed and the thermal diffusivity was measured successfully in the temperature range up to 700ﾟC. The thermal diffusivity of these samples showed negative temperature dependence.