Uncertainty assessment of enthalpy of fusion measurements performed by using an improved Calvet calorimeter

Abstract

The French National Metrology Institute LNE-LCM has developed a new in situ electrical calibration system which is integrated into a heat flux Calvet calorimeter in order to perform accurate and reliable measurements of enthalpy of fusion from 23 °C to 1000 °C. The measurement procedure consists in putting a sample inside the calibration system and in performing the heat calibration of the calorimeter by electrical substitution (Joule effect) before and after the enthalpy of fusion measurement during the same heating run. This procedure directly takes into account the temperature dependence of the calibration factor (sensitivity) and keeps the calibration and measurement experimental conditions strictly the same. Uncertainties of the enthalpy of fusion measurements, performed by using this facility and procedure, have been assessed according to the ‘guide to the expression of uncertainty in measurement’. The detailed uncertainty budgets are presented here in the case of three pure metallic materials (indium, tin and silver). The relative expanded uncertainty (k = 2) of the enthalpy of fusion measurement is estimated to be less than 0.4% for the high purity indium and tin, and less than 1% in the case of silver.