Power compensation DSCs scanning calorimeters

In a power compensation differential scanning calorimeter (DSC), the base of the sample holder unit is in direct contact with a reservoir of coolant (Figure 2.12). The sample and reference holders are indiv idually equipped with a resistance sensor, which measures the temperature of the base of the holder, and a resistance heater. Upon detection of a temperature difference between the sample and reference, due to a phase change in the sample, electrical power is supplied so that the temperature difference falls below a threshold value, typically <0.01 K. 

Another type of DSC, the power-compensated differential scanning calorimeters (see Section 7.9.4.2), follows in principle the model shown in Figure 6.15, but instead of one, there are two furnaces for the sample and the reference system, respectively. The current in the heaters (furnaces) (T) is so controlled that the average temperature of the two systems always matches the preset temperature. 

The term differential scanning calorimetry has become a source of confusion in thermal analysis. This confusion is understandable because at the present time there are several entirely different types of instruments that use the same name. These instruments are based on different designs, which are illustrated schematically in Figure 5.36 (157). In DTA. the temperature difference between the sample and reference materials is detected, Ts — Tx [a, 6, and c). In power-compensated DSC (/), the sample and reference materials are maintained isothermally by use of individual heaters. The parameter recorded is the difference in power inputs to the heaters, d /SQ /dt or dH/dt. If the sample is surrounded by a thermopile such as in the Tian-Calvet calorimeter, heat flux can be measured directly (e). The thermopiles surrounding the sample and reference material are connected in opposition (Calvet calorimeter). A simpler system, also the heat-flux type, is to measure the heat flux between the sample and reference materials (d). Hence, dqjdi is measured by having all the hot junctions in contact with the sample and all the cold junctions in contact with the reference material. Thus, there are at least three possible DSC systems, (d), (c), and (/), and three derived from DTA (a), [b), and (c), the last one also being found in DSC. Mackenzie (157) has stated that the Boersma system of DTA (c) should perhaps also be called a DSC system. 

DTA as well as power compensation DSC instruments, and is called temperature modulated DSC, or TMDSC. The following trade marks are used by different TA instrument manufacturers for their temperature modulated differential scanning calorimeters Modulated DSC (MDSC ) of TA Instruments Inc., Oscillating DSC (ODSC ) of Seiko Instruments Inc., Alternating DSC (ADSC ) of Mettler-Toledo Inc. and Dynamic DSC (DDSC ) of Perkin-Elmer Corp. 

Adiabatic calorimeters are complex home-made instruments, and the measurements are time-consuming. Less accurate but easy to use commercial differential scanning calorimeters (DSCs) [18, 19] are a frequently used alternative. The method involves measurement of the temperature of both a sample and a reference sample and the differential emphasizes the difference between the sample and the reference. The two main types of DSC are heat flux and power-compensated instruments. In a heat flux DSC, as in the older differential thermal analyzers (DTA), the... 

Figure 4. The present evolution of Standard DSC towards a range of low- to high-speed calorimeters [32]. Commercial instruments like heat-flux and power-compensation Standard DSCs work typically at scan rates of 0.1 to 60 C/min High Performance DSC (HPer DSC), using a modified PerkinElmer power-compensation Pyris 1 or Diamond DSC, covers the range 0.1 to 500 C/min thin-film (chip) calorimeters have scan rates from 1000 to 1.2-10 C/min and rates as high as 6-10 C/min are attainable using the high-speed pulse-calorimeter (all numbers are approximate indications).

Mathot, V, Pyda, M., Pijpers, T., Vanden Poel, G., van de Kerkhof, E., van Herwaarden, S., van Herwaarden, F., and Leenaers, A. (2011) The Flash DSC 1, a power compensation twin-type, chip-based fast scanning calorimeter (FSC) first findings on polymers. Thermochim. Acta, 522, 36-45. 

Figure 1 Different types of differential scanning calorimeters, (a) Three-dimensional cylindrical calorimeter (Tian-Calvet). (b) Three-dimensional calorimeter with power compensation, (c) Two-dimensional plate-like calorimeter, (d) Scheme of a twin-chip sensor (Mettler Toledo Flash 1 DSC ) for fast scanning calorimetry.

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