Experimental Research on the Determination of Experimental Parameters for Measuring Thermal Diffusivity with a Wide Temperature Range Based on Laser Flash Method

Thermal diffusivity is an essential thermophysical factor for designing thermal protection materials. At present, the laser flash method is widely employed for measuring thermal diffusivity, and reasonable determination of experimental parameters is a prerequisite for accurate measurement. In this paper, high-purity graphite is used as the reference specimen, and measurement temperature ranges from 25 °C to 1500 °C. Besides, experimental investigations on the influence of the laser flash method such as specimen thickness, laser pulse energy, and temperature increase rate on the measurement of thermal diffusivity for high-purity graphite are carried out. The results indicate that for high-purity graphite samples, a sample thickness of 3 mm is more appropriate. Additionally, the setting of laser pulse voltage and width is related to the measurement temperature, and the measurement results are more easily affected by the laser pulse width. When measuring temperatures below 600 °C, it is necessary to set both the laser pulse width and voltage to the smallest possible values, provided that a stable signal can be collected. When the temperature is above 600 °C, the laser pulse voltage does not affect the measurement results, but the influence of laser pulse width still needs to be considered to a certain extent. It is only when the measured temperature exceeds 900 °C that neither the laser pulse voltage nor the laser pulse width influences the measurement results. Furthermore, the temperature increase rate has a relatively small impact on the measurement results and can be adjusted according to the measured temperature. The research results can provide a basis for the calibration of experimental parameters in the high-temperature flash method measuring instrument.