Measurement of Thermal Diffusivity Distribution for Murray and Murchison Meteorites Using Lock-in Thermography

It is important to know the thermophysical properties (thermal diffusivity, specific heat, etc.) for meteorites and small samples from asteroids to understand the thermal history of the solar system origin. However, there is no research on thermophysical properties measurement with a non-destructive and non-contact method for small and/or irregularly shaped samples such as meteorites or asteroid particles. In this study, a new method to measure in-plane and out-of-plane thermal diffusivities of flat-plate shape and granular shape samples by using lock-in thermography is developed. This method enables the ability to measure the thermal diffusivity of both flat-plate and granular shape samples by selecting the suitable detecting direction of the temperature response. In this paper, the thermal diffusivity of five kinds of meteorites samples made of two types of CM2 chondrites (Murray and Murchison) were evaluated. As a result, the detailed angular distribution of the in-plane thermal diffusivity and the out-of-plane thermal diffusivity was revealed. The measurement results showed that there is local thermal anisotropy caused by the heterogeneity in the composition of the chondrules and matrix. The results also showed that the high compositional content ratio of chondrules leads to a high average value of thermal diffusivity. The range of the obtained thermal diffusivity was 0.24–0.78 mm²·s⁻¹, and this result showed good agreement with the reported value by the conventional method consisted of pulsed heating method with sample destruction and processing.