Recent developments and applications of the hot disk thermal constants analyser for measuring thermal transport properties of solids

When thermal conductivity and diffusivity are measured with the hot disk thermal constants analyser, hot disk sensors or G-probes of different designs are used. The design of these sensors can be described as a double spiral etched out of a 10 μm thick metal foil sandwiched between two thin insulating sheets of an electrically insulating material. So far mostly nickel and in a few instances platinum foil have been used as the sensing' material, For experiments from 30 K up to about 450 K the polyimide Kapton with a thickness of 25 μm has been used as insulating material while for temperatures beyond 450 K and up to about 1200 K a 100 μm thick mica material is used. Attempts are presently being made also to use other insulating materials, which might further increase the temperature range of the sensors. Beside work on the further development of the sensors, work is going on to extend the application of this experimental technique to cover new experimental situations, Presently, some options in addition to the standard system can be utilised. These options include possibilities to measure the thermal transport properties of anisotropic bulk materials, thin insulting sheets of low conducting materials, and slabs of material with medium to high thermal conductivity. in addition there is a facility to measure the specific heat capacity of different materials directly. When the standard experimental technique is applied, the usual experimental arrangement is to place one piece of the sample material on either side of the sensor. However, attempts have recently been made to cover one side of the sensor with a material with known thermal properties and then place the material with unknown properties in contact with the other side of the probe.