Temperature and enthalpy of fusion calibration of Calvet calorimeter from -150°C to 156°C

To calibrate a commercial Calvet calorimeter and promote accurate measurement for an unknown sample, a calibration method using reference materials was studied within a wide temperature range of -150 ~ 156°C. We present the results of two experiments that we conducted to calibrate the calorimeter for temperature and enthalpy of fusion measurements. The calibration materials included cyclopentane and n-heptane in the low-temperature region, in addition to water, gallium, and indium, which are fixed-point realisation materials specified in ITS-90 at temperatures above 0°C. We determined the onset temperature and enthalpy of fusion at a heating rate of 0.1-0.4 K/min by analysing the heat flow signal and calculating the area under the corresponding curve. For each material, we obtained calibrated temperatures that showed a valid range with a maximum deviation of 0.17°C from the fitted line. We successfully calibrated enthalpies of fusion with relative uncertainties ranging from 0.38% for water to 3.56% for gallium. We found that the overall uncertainty of the Calvet calorimeter was within 5.3%. Future research efforts will aim to further reduce the uncertainty by using a heating cell with Joule heating to enable continuous data collection over the entire temperature range.