# Thermal Characterization of Phase Change Materials by Differential Scanning Calorimetry: A Review
## 3 Calorimetric Characterization
### Calibration Step and Measurement Accuracy
They concluded that multipoint calibration with three reference materials is much better than a two or single point calibration, because it could minimize the temperature inaccuracy over a wide temperature range. In the case of a single point calibration, a good accuracy can still be achieved if the reference is selected according to the target temperature [39]. Moreover, even in multipoint calibration, selecting the reference materials while considering the temperature range of interest leads to more accurate results. Furthermore, different heating rates (1, 2, 5 and 10 \({}^{\circ}\)C/min) were considered in measurements of reference materials, and it was observed that the temperature range becomes broader by increasing the heating rate. Overall, low heating rates lead to more uniform results in terms of melting temperature. Regarding DSC's temperature calibration, it is recommended to perform it with at least three reference materials in the temperature range of interest (one at lower temperature, one close to the PCM transition range and one at upper temperature range). However, [PERSON] et al. [6] concluded that the number of existing reference materials is insufficient to cover the expanding temperature range of PCMs (\(-\)40 to 400 \({}^{\circ}\)C). Furthermore, the existing metallic calibrants are too expensive for large-scale calibration in methods such as T-history. Therefore, they conducted a study to introduce and recommend new reference materials [6]. In the range from \(-\)10 to 30 \({}^{\circ}\)C, water at 0 \({}^{\circ}\)C and n-alkanes including C12 at \(-\)10 \({}^{\circ}\)C, C14 at 6 \({}^{\circ}\)C, C16 at 18 \({}^{\circ}\)C and C18 at 28 \({}^{\circ}\)C could be used for temperature and enthalpy calibration. Biphenyl might be used in the range lower than indium temperature at 68.9 \({}^{\circ}\)C. For C\({}_{\text{P}}\) calibration, mixtures of water-salt, water-alcohol and n-alkanes in liquid state might be used. However, one has to consider that these materials are not certified references, but detailed and accurate information on them could be found. Several DSC calibrants at different temperatures can be seen in Table 4. [PERSON] [38] studied the crystal-crystal transition point of ammonium salts to calibrate DSC temperature. It was concluded that ammonium dihydrogen phosphate (\(-\)121.4 \({}^{\circ}\)C) and ammonium sulphate (\(-\)48.8 \({}^{\circ}\)C) can be considered for subambient temperature calibration. [PERSON] and [PERSON] [40] investigated the influence of crucible position on the value of enthalpy with two different measurement procedures: procedure A, without replacing the crucible sample inside the DSC, and procedure B with replacing the crucible at each measurement. The standard deviations for enthalpy obtained for procedures A and B are 0.04 and 0.5 %, respectively. [PERSON] et al. [19] also recommended ensuring the best symmetry possible between sample and reference crucibles. A summary of the related studies on DSC calibration can be observed in Table 3.