# On the Use of Infrared Thermography for the Estimation of Melting Enthalpy
## 4 Discussion  
Significant improvements were obtained between the estimation made in Case 1 and Cases 2/3. It shows that the morphology of the sample and, therefore, the temperature gradient in the sample ensuing from it are important factors in obtaining accurate melting enthalpies with the IRT-based method.  
All infrared signals are characterized by a noise level more significant than what can be obtained with standard methods of temperature acquisition. This noise may induce errors during the calculation especially if the acquisition rate is set too low. Indeed, this noise is not an issue in the solid and liquid state, as the evolution of the signal is uniform and can clearly be identified. However, during phase change, abrupt variations may occur and the noise can in that case affect the average signal value. In fact, we see in Figure 2a that the noise band throughout phase change is not uniformly distributed and a narrower signal is obtained around 58 \({}^{\circ}\)C. Efforts may then be required to evaluate the influence of this noise and to eventually identify a suitable signal filtering technique to improve the quality of the results.  
In addition, it was previously mentioned that the accuracy of the method for the estimation of the melting enthalpy strongly relied on the accurate interpolation of the evolution of emissivity in the material between the solid and liquid state. We have seen from Figure 2a that there is a quasi-linearity in the signal between the two states, which may explain the relatively good agreement between DSC measurements and the IRT estimation. In order to show the essential nature of this aspect, the melting enthalpies of three fatty alcohols (1-Tetradecanol, 1-Hexadecanol and 1-Octadecanol) were estimated using the same calibration materials. Even using the same protocol than in Case 2 and 3, the measured relative deviations were never better than 50%. A study made in [22] highlighted this sensitivity of fatty alcohols and the large shift that may occur during phase change, as illustrated in Figure 3. It is important to mention that the same issue exists for the calculation of melting enthalpies with DTA [41]. It is, indeed, strongly recommended that calibration materials be close to studied samples in terms of overall thermal properties; otherwise, major errors may be encountered. This is a reason why DSC is usually favored for precise enthalpy measurements.  
Two options can be considered to be able to further improve the method and limit the influence of the emissivity on the accuracy of the estimation. Either an in-depth study of the evolution of the emissivity upon phase change is required, in order to obtain a consistent temperature interpolation during the process, or a solution must be found to obtain accurate temperature measurements independently of the emissivity. The first solution would require a time-consuming and extensive experimental study for each calibration material and for each sample studied, which is in contradiction with the purpose of the IRT method aiming at reducing the time spent on material screening. The second option appears more favorable and is in line with research efforts in quantitative infrared measurements [1,3,21]. In that frame, the use of polychromatic or multi-wavelength detectors may be required and is to be considered.