Differential thermal analysis melting temperature determination using

Differential scanning calorimetry (DSC), X-ray diffraction (XRD), and infrared spectroscopy are the common techniques used in the characterization of the structure of the congealed solid. Thermal analytic methods, such as DSC and differential microcalorimetric analysis (DMA), are routinely used to determine the effect of solutes, solvents, and other additives on the thermomechanical properties of polymers such as glass transition temperature (Tg) and melting point. The X-ray diffraction method is used to detect the crystalline structure of solids. The infrared technique is powerful in detecting interactions, such as complexation, reaction, and hydrogen bonding, in both the solid and solution states. 

Differential thermal analysis was the first major improvement developed over simple melting point analysis, and in countless studies was used to determine the characteristic temperature ranges associated with a variety of thermally induced reactions. Differential scanning calorimetry subsequently effectively replaces the DTA method, primarily because of its ability to yield quantitative information regarding the magnitude of the heat associated with the thermal reaction. For this reason, DSC has become accepted as the most widely used method of thermal analysis for the pharmaceutical industry. 

The use of the differential thermal analysis in the phase diagram determination is illustrated in Figure 3.52. A hypothetical binary eutectic system A-B with the formation of the incongmently melting compound A4B was chosen. There are three thermograms (a) to (c) shown as examples. In thermogram (a), the first heat effect at temperature ai... 

The phase diagram in the CaO-Ca(OH)2 system was determined by thermodynamic calculations from equilibria determined in Reactions 13 and 14. The phase diagram for the Ca(0H)2-CaC03 system was determined by differential thermal analysis using the equipment shown in Figure 4. Two thermocouples were used, one in the melt and one positioned at the wall of the inner vessel. A temperature differential corresponding to the appearance of the first solid phase developed on... 

Differential thermal analysis is widely used for determining exotherm and endotherm of reactive substances. It can also be used for determining transition temperatures, such as the glass transition temperature and the melt temperature of polymers (ASTM D3418). ASTM D472 provides directions for reporting thermoanalytical data. 

Differential thermal analysis permits more detailed analysis of thermal events and can be used to determine equilibrium freezing temperature, phase changes, and onset temperature for ice melting. An advantage is that analysis can be performed in the same containers in which lyophilization will occur. 

In DSC the measured energy differential corresponds to the heat content (enthalpy) or the specific heat of the sample. DSC is often used in conjunction with TA to determine if a reaction is endothermic, such as melting, vaporization and sublimation, or exothermic, such as oxidative degradation. It is also used to determine the glass transition temperature of polymers. Liquids and solids can be analyzed by both methods of thermal analysis. The sample size is usually limited to 10-20 mg. 

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