On the thermal characterization of solids by photoacoustic calorimetry: thermal diffusivity and linear thermal expansion coefficient

• A methodology for photoacoustic calorimetry is proposed.
• Thermal diffusivity and linear thermal expansion coefficient measurement are possible
• For linear thermal expansion coefficient measurement sample must be ideally thermally thick.

In this paper, we resume a straightforwardly methodology that can be employed for accurate thermal diffusivity measurement by photoacoustics. The proposed methodology involves measurements in the thermally thick sample regime with normalization using a thermally thin reference sample, as well as consideration of the sample’s thermoelastic bending in both the thermally thin and thick regime. The usefulness of the method has been demonstrated with measurements in test samples of different materials. The possibilities of the method to account for linear thermal expansion coefficient have been discussed too. It has been demonstrated that for the determination of this parameter the sample must be in the ideal thermally thick regime, i.e. the range of modulation frequencies used must lie well above the cut-off frequency between the thermally thin and thick regimes. In other words, this cut-off frequency must be very small. Although this condition is very difficult to be achieved in praxis, in order to account for it, a method is proposed here that involves measurements in samples with different thicknesses and uses an extrapolation procedure.