Influence of purge gas and spacers on uncertainty of high-temperature heat flux DSC measurements

Inert purge gases are commonly used in high-temperature differential scanning calorimetry (DSC) to prevent sample oxidation. However, little research has been published regarding their influence on DSC measurements and the corresponding uncertainties. By comparing helium, nitrogen, and argon—three common purge gases with significantly different physical properties—the effects on temperature and heat calibration are determined and quantified for a heat flux DSC at temperatures from 100 to 1,500 °C. Diffusion bonding between the probe holder and the crucibles is another problem often encountered in high-temperature DSC, which can result in device damage if the crucibles are forcefully removed. To prevent bonding, thin spacer discs of different thicknesses made of synthetic sapphire are placed underneath the crucibles during the DSC run. Their influence on various measurements is analysed and results are shown for the entire temperature range. As an accurate determination of uncertainty is essential for precision measurements, the measurement repeatability—which is the major contribution to overall uncertainty of heat capacity evaluation—is characterized for various purge gas/sapphire spacer combinations.