Abstract
The importance of the availability of Standard Reference Materials (SRM) to improve the accuracy of thermal diffusivity measurements is shown in the example of the modulated-light heating-beam technique. Systematic examinations of error sources led to the result that SRMs with conduction and radiation properties similar to the material to be investigated are useful for accurate measurements. Three types of SRM were investigated within the framework of the CODATA task group on thermophysical properties—graphite, refractory metal and stainless steel. Poco AXM-5Q1 graphite and austenitic Nb-stabilised steel 16Cr20Ni could be proved to be well suited relative to the reproducibility and stability of their thermal diffusivities. Measurement results of our own and of some other participants agreed with less than 2% deviation in the temperature range 1500 K to 2300 K for Poco graphite, and between 800 K and 1300 K for austenitic stainless steel. Such a good agreement could not be found with the third SRM, arc-cast tungsten; however, there are not enough data available within the CODATA programme for a final statement. Comparative measurements on Poco graphite have shown that, for the extrapolation of the results from one manufacturing lot to another, a deviation of the thermal diffusivity of at least 8% must be taken into consideration.
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