A new laser flash apparatus for thermal diffusivity and specific heat capacity measurements down to 30 K


A. Göbel1, F. Hemberger1, H. Ebert1, M. Jansen2 and J. Wilfert2

1Bavarian Center for Applied Energy Research (ZAE Bayern), Germany
2Max Planck Institute for Solid State Research, Germany

Keywords: laser flash; low temperatures
property: thermal diffusivity; specific heat capacity
material: BK7

The laser flash method is a standard method for thermal diffusivity measurements of solids [1]. One side of a disk-shaped specimen is heated by a short laser pulse and the thermal diffusivity can be calculated from the time-dependent temperature rise at the other side of the specimen. Knowing the absolute temperature rise and the amount of energy absorbed by the specimen, the specific heat capacity can also be calculated.

The adaption of the laser flash technique to temperatures far below ambient temperature is restricted due to the limited spectral responsivity of the commonly used mercury cadmium telluride infrared-detectors which are used for measurement of the time-dependent temperature change. Therefore, an alternative detection method is applied which makes use of the temperature-dependent change of the resistance of a thin gold strip which is sputtered onto the rear side of the specimen [2]. Advantages of this method are its applicability at cryogenic temperatures and a higher signal to noise ratio compared to the commonly used IR-detectors [3].

A laser flash setup operating in the temperature range between 30 and 300 K that utilizes this temperature detection system is described. To achieve these low temperatures, the sample is placed in a helium cold head.

By calibrating the gold strip, the absolute temperature rise at the rear side of the specimen can be determined. Thus, with using a reference material to determine the heat quantity absorbed by the specimen, the specific heat capacity can be obtained.

Finally, the thermal conductivity is calculated by multiplying the thermal diffusivity, specific heat capacity and the density of the specimen. The results of these first measurements with the new experimental setup on standard materials like BK7 glass as well as on a newly developed amorphous Si/B/N/C ceramic will be presented.

References
  1. W. J. Parker et al., J. Appl. Phys. 32, 1679 (1961)

  2. Y. Kogure et al., J. Phys. Soc. Jap. 55, 3469 (1986)

  3. F. Hemberger et al., Int. J. Thermophysics 31, 2187 (2010)

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