Measurement of thermal diffusivity with a guarded-hot-plate device using a dynamic method

An evacuable, guarded-hot-plate device, typically used for steady-state measurements of thermal conductivity, has been extended to allow dynamic measurements of thermal diffusivity. This apparatus is now applicable to both steady-state and dynamic measurements, which can be carried out in succession without time-consuming modifications of the sample or the apparatus. The diffusivity is determined from the dynamic measurement alone. Knowledge of the heat capacity allows us to derive the conductivity. If both the steady-state and the dynamic measurements are performed, the thermal conductivity, the diffusivity and the heat capacity of insulating specimens can be determined. The dynamic technique makes use of the correlation between a controlled uniform heating rate on the sample surface and the resulting temperature response at the sample centre. This dynamic technique allows us to scan a temperature range from 20 to 650 degrees C within some hours and to determine the thermal diffusivity as a function of temperature. The range of thermal diffusivities of insulating materials that can be examined with this guarded-hot-plate device is between 10 -9 and 10 -7 m 2 s -1 . The uncertainty of this technique is about 10%.