Influence of Radiation Losses on Thermal Conductivity Determination at Low Temperatures

 

The thermal conductivity of electrolytic iron has been measured in the temperature range from 100 to 390 K. Electrolytic iron is a standard material for the measurement of thermal conductivity. The thermal conductivity was measured on a commercial device Thermal Transport Option (TTO) of a Physical Properties Measurement System (PPMS) produced by the Quantum Design company. The temperature gradient on the sample was determined using small highly accurate Cernox chip thermometers. The thermal conductivity of the standard material showed higher values than those cited by NIST for the temperature range from 100 to 390 K (NIST’s “Report of Investigation” for SRM 8420). The maximum deviation reached 30% at 390 K. Detailed analyses of the measured data and of the commercial software of the measuring device revealed that the large differences resulted from radiative losses of the interior parts of the device. The determination of the radiative losses takes into account the sample geometry, contacts, and cooling part of the device, and these differences in the thermal conductivity values were substantially reduced after accounting for these losses.