# Thermal Characterization of Phase Change Materials by Differential Scanning Calorimetry: A Review
## 4 PCM Properties Achieved by DSC
### Thermal Stability  
One of the important properties of PCMs is their thermal stability, which indicates how the enthalpy and the melting point of PCMs change undergoing multiple cycles of melting and solidification. Using a DSC machine, by customizing the test conditions (atmosphere of the test, open or sealed crucibles), the thermal cycling experiments from several to hundreds of cycles can be conducted [42; 69]. During thermal cycling experiments, the transition temperatures and enthalpies of subsequent cycles are compared with the first cycle. [PERSON] et al. [26] conducted a long-term thermal stability test (500 cycles) of MgCl\({}_{2}\cdot\)6H\({}_{2}\)O as a PCM using DSC thermal cycling experiments. The weight of the MgCl\({}_{2}\cdot\)6H\({}_{2}\)O sample was 10 mg under a heating rate of 10 \({}^{\circ}\)C/min. It was observed that  
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the melting temperature shifts to a higher temperature by 0.3 \({}^{\circ}\)C. The melting enthalpy experienced an increase in the first cycle and decreased afterward by about 99% of the starting value. [PERSON] et al. [42] investigated the thermal stability of two organic PCMs (adipic acid and PT151(r)) having a melting point of 150 \({}^{\circ}\)C. Good thermal stability for both PCMs was observed (less than 10% decrease in enthalpy after 50 cycles). Moreover, adipic acid exhibits a better performance compared to PT151(r), while it is available at a lower price. [PERSON] et al. [70] investigated the thermal stability of oxal acid dihydrate (OAD) and blends of OAD/polyethylene glycol (PEG) under 100 cycles of melting/solidification by DSC with different pan types. In a standard aluminum pan, OAD loses above 85% of its initial enthalpy due to the non-hermetically sealed crucibles, and the reaction of OAD with the aluminum pan leads to the corrosion of the crucible. The lower enthalpy loss (around 56%) was observed when they used a sealed, corrosion-resistant crucible (high-pressure gold-plated pan). [PERSON] et al. [70] also concluded that adding 2.5% of PEG 6000 can improve the thermal stability of OAD without considerable enthalpy reduction. Thermal stability of a PCM can be verified with an unconventional set-up or a conventional method like DSC. [PERSON] and [PERSON] [71] investigated the thermal performance of D-mannitol (DM) and DM with 0.1% and 0.5% weight percentage of Gallium (Ga) under 350 thermal cycles by a hot plate heater set-up (unconventional). The samples were taken after thermal cycling for further analysis, such as TGA (thermogravimetric analysis), DSC, and thermal conductivity, and were compared with the pure samples. They concluded that DM/Ga composite is stable in the temperature range between 50 \({}^{\circ}\)C and 150 \({}^{\circ}\)C and can be used as a TES material. However, they did not mention if the tested samples in TGA experiments were in closed or open crucibles. Conducting thermal stability experiments with a DSC machine is quite a bit faster than the other methods, such as T-history. However, DSC sample scale is limited to a few milligrams. [PERSON] et al. [69] carried out 50 cyclic DSC experiments on (\(E\))-3-phenylbut-2-enoic acid. According to their results, they concluded that single and similar endothermic/exothermic peaks mean that the PCM underwent a one-step melting and solidification during thermal cycles, which is a desired property for PCMs. The other method to carry out thermal stability experiments is to perform thermal analysis by the simultaneous DSC/TGA, which has a sensible balance to detect the mass loss during the measurements and allows one to conduct an experiment under the desired conditions (temperature range, heating rate and atmosphere) [48; 72]. [PERSON] et al. [72] conducted the thermal cycling test in an oven using around 150 g of PCM. After a certain number of cycles, a sample of 10 mg was tested in a DSC.