53.
A new metrological approach is proposed by the Laboratoire National de Metrologie et d’Essais to lower the uncertainty of measurements of enthalpy of fusion from 23 to 1000 °C. It consists, as in our previous works, in putting the studied sample inside a calibration crucible and in performing the heat calibration of the calorimeter by electrical substitution at two temperatures before and after the temperature of fusion of the sample during the same low-rate heating run. The novelty lies in the “electrical compensation” of the endothermic reaction of fusion. The quantification of the electrical energy needed to melt the sample, which can be measured with high accuracy, and the integrated remaining heat flow rate divided by the calibration factor (sensitivity) of the calorimeter at the temperature of fusion, leads to the determination of the enthalpy of fusion of the sample with low uncertainty. This methodology reduces the influence of the uncertainty component associated with the area of the peak of fusion by comparison with the former procedure when no electrical compensation was applied. The relative expanded uncertainty (k = 2) associated with the enthalpy of fusion measurements, performed using this facility and this new procedure, has been assessed to be < 0.2% for tin and indium and to be about 0.3% in the case of silver.
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