# Thermal Characterization of Phase Change Materials by Differential Scanning Calorimetry: A Review
## 4 PCM Properties Achieved by DSC
### Specific Heat Capacity  
Measuring accurately the heat capacity of PCMs is of prime importance for (i) understanding the sensible contribution of a PCM to its thermal energy storage capability; (ii) having accurate data for modelling purposes and (iii) indirectly calculating the thermal conductivity [54]. Adiabatic calorimetry is the most reliable method to measure heat capacity [6]. However, these instruments are not regularly used for PCMs, because they are not commercialized like the regular DSCs and it remains an expensive method. The usual method to measure heat capacity is the one established by the American Society for Testing and Materials (ASTM), which includes three steps despite the DSC machine. First, the heat flow signal to the empty pan is measured. Then, the heat flow to a reference material, which is a high purity synthetic sapphire, is measured. Finally, an actual material is measured. All these three steps should be done under the same conditions, such as same pan/lid, heating rate and atmosphere conditions. The three-step method is represented schematically on Figure 15. Using the same pan reduces the uncertainty caused by the difference in the pan mass. However, the mass of the pan does not vary significantly and their specific heat capacity remains quite similar. Each heating program for heat capacity measurements consists of three segments: two isothermal steps at the starting temperature and at the end (for example, 5 min) and heating segments with a specific heating rate. The ASTM standard recommends a fast heating rate of 20 \({}^{\circ}\)C/min but researchers found that the 10 \({}^{\circ}\)C/min rate is suitable to determine the heat capacity. Another way to find the suitable heating rate and mass for heat capacity measurement is considering that the maximum deflection needed for sapphire is about 5 mW. Thus, one can adjust the mass and heating rate in order to achieve the signal close to 5 mW. Consequently, the test condition  
\begin{table}
\begin{tabular}{p{12.3 pt} p{128.0 pt} p{128.0 pt} p{128.0 pt}} \hline \hline
**Ref. ** & **PCM** & **Objective** & **Recommendations to Determine Transition Temperatures** \\ \hline \multirow{4}{*}{[57]} & n-octadecane 15 \({}^{\circ}\)C & Determining suitable heating rate and sample & In case of hydrated salts, high heating rates hide more information about the kinetics. \\  & calcium chloride & & \\ hexahydrate 25 \({}^{\circ}\)C & & & \\  & & & \\  & & & \\  & & & \\ \hline \multirow{4}{*}{[59]} & Octadecane (98.11\%), & Study dynamic and step method and test their accuracy on the h(T) relationship & Run a baseline test Use low heat rate & \\  & & & \\ \hline \multirow{4}{*}{[45]} & \multirow{4}{*}{Commercial RT27} & Influence of two different modes of heating (dynamic and step modes) on the accuracy of enthalpy–temperature relationship. & The step method is less sensitive to the measurement parameters. In dynamic mode, by decreasing heating rate the uncertainty is decreased, but at the cost of increasing uncertainty. (sample mass and heating rate) for the sample should be the same as that of sapphire [43]. It is recommended, before each heat capacity measurement, to perform an indium test to check if the cell constant of the DSC is close to one. If the cell constant is not close to one, one needs to check the DSC cell for any contaminations. In order to analyze the data, one should subtract the empty crucible signal from the reference and sample. According to ASTM E1269-11 [44] and the work conducted by [PERSON] et al. [54], the sample heat capacity \(C_{p(s)}\) can be calculated through Equation (17), where \(C_{pst}\) is the heat capacity of sapphire, \(C_{pnm}\) is the heat capacity of empty Al crucible, \(D_{s}\) is the vertical distance between empty crucible and sample signal, \(D_{st}\) is the vertical distance between empty crucible and sapphire signal, \(W_{st}\) is the mass of sapphire, \(W_{pnm}\) is the mass of crucible and \(W_{s}\) is the mass of sample. [PERSON] et al.