Chapter 6 - Simultaneous DSC Techniques

Abstract

Depending on the enthalpy change and the sensitivity of the device, in principle, all physical and chemical changes could be detected by differential scanning calorimetry (DSC). However, the enthalpy change does not specify the nature of the corresponding process. To understand the thermochemical reactions, other information is required in addition to the DSC data. To provide a straightforward relationship between the enthalpy of a reaction and the corresponding structural rearrangements or composition change, the measurements should be conducted under very similar conditions. This could be achieved easily with instruments that record the structural/composition data simultaneously with the DSC data, on the same sample. The thermal reactions usually involve the decomposition of the sample, accompanied by the evolution of gaseous products. To determine the mechanism of the decomposition, the detection of the gases is carried out by instruments attached to the purge gas outlet of the DSC device. The most frequently used simultaneous DSC technique is simultaneous differential scanning calorimetry - thermogravimetry (DSC-TGA). The instruments of DSC-TGA are abbreviated as STA (Simultaneous thermal analyzer) or SDT (simultaneous differential thermal analyzer). This setup allows the distinction between the decomposition and structural rearrangement of the sample. SDA/SDT instruments are often connected to instruments to carry out evolved gas analysis (EGA). Instruments for simultaneous DSC-spectroscopic and other electromagnetic radiation measurements are also commercially available. Other simultaneous techniques used for the characterization of the sample are DSC-dielectric analysis (DEA), DSC-thermomechanical analysis (TMA), and DSC-rheology (Rheo-DSC). Some of the simultaneous techniques are not utilized any more. However, they had an important role in the development of up-to-date instruments. In this chapter, the principles of operations of various simultaneous techniques and detectors are briefly discussed. The aim is to help the reader in the selection of the most suitable system for their research purpose. Since DSC-TGA is the most commonly used simultaneous technique, in this chapter, the utilization of simultaneous DSC-TGA measurements combined with EGA techniques is described in detail. The examples are selected to encompass diverse research fields. The development of DSC instruments with simultaneous optical devices is described. To follow the structural transformations during the thermal treatment of the sample, the application of simultaneous DSC-spectroscopic and DSC-X-ray (XRD) measurements is discussed. Examples are selected to demonstrate the significance of simultaneous DSC-DEA, DSC-TMA, and Rheo-DSC measurements. The experimental conditions are also discussed to emphasize their impact on the measured data.