The procedure for measuring the thermal conductivity, , is difficult and time consuming. The typical experiment places a temperature gradient across the sample and insulates its sides. Once the sample reaches steady state, a Differential Scanning Calorimeter (DSC) is used to measure heat flux. However, because relatively large samples are used in this test (about 12 mm diameter and 25 mm thick), considerable time is required for the specimen to reach steady state. Fortunately, an alternative method, The Flash Method, can be employed to measure the thermal diffusivity, , of a material.

The test is performed by placing the sample in a fixture located between a flash lamp and an infrared pyrometer. The flash lamp is pulsed for about one millisecond, and the temperature of the back face is determined with the pyrometer and recorded with a computer. The data then are plotted in dimensionless form. From this data the thermal diffusivity can be calculated.. Once the thermal diffusivity, , the density, , and the specific heat, C_p, of the material are known, then the thermal conductivity is calculated as follows.

_{= ·· Cp}

The specific heats of most graphites are relatively similar and can be estimated fairly accurately at 0.684 J/g·°C. The diffusivity test fixture requires cylindrical pellets (12 mm diameter by 25 mm thick) in order to minimize edge effects.

URL: http://www.ms.ornl.gov/cimtech/cfcms/2001.html--Last updated 4/14/97