Power compensation DSCs advantage

Irreversible transformations are those in which reactants do not reform from products upon cooling. Generally one of the reactants is in a metastable state, and only requires thermal agitation or the presence of a catalyst to initiate the transformation. Examples would be combustion of a fossil fuel or glass devitrification. Power-compensated DSC has a distinct advantage over heat-flux DSC in determining the kinetics of transformation from metastable phases. In these type of reactions,... 

DSC works on a similar principle but has several advantages over DTA, not least of which being the ability to easily measure the energy associated with the transition as well as the temperature at which it occurs. There are two main forms of DSC. power compensation and heat fiux. Power compensation DSC involves the use of two furnaces (rather than the one used for DTA), one placed under the. sample and the other under the reference (Fig. 1B). The system operates on the basis of keeping the sample and reference at the same temperature. This therefore means that energy must be supplied to the reference in order to make it follow the predetermined temperature programme and... 

An alternative method [2] of determining Mi uses the fact that in power compensation DSC the proportionality constant between the transition peak area and Mi is equivalent to the constant which relates the sample heat capacity and the sample baseline increment. By measuring the specific heat capacity of a standard sapphire sample, an empty sample vessel and the sample of interest, from the difference in the recorded DSC curves of the three experiments Mi for the sample transition can be calculated. The advantage of this method is that sapphire of high purity and stability, whose specific heat capacity is very accurately known, is readily available. Only one standard material (sapphire) is necessary irrespective of the sample transition temperature. The linear extrapolation of the sample baseline to determine Mi has no thermodynamic basis, whereas the method of extrapolation of the specific heat capacity in estimating Mi is thermodynamically reasonable. The major drawbacks of this method are that the instrument baseline must be very flat and the experimental conditions are more stringent than for the previous method. Also, additional computer software and hardware are required to perform the calculation. 

One of these techniques that brought into science the name DSC, called today power compensation DSC, was created by Gray and O Neil at the Perkin-Elmer Corporation in 1963. The other technique grew out of differential thermal analysis (DTA), and is called heat flux DSC. Differential thermal analysis itself originates from the works of Le Chatelier (1887), Roberts-Austen (1899), and Kurnakov (1904) (see Wunderlich, 1990). It needs to be emphasized that both of these techniques give similar results, but of course, they both have their advantages and disadvantages. 

Similar to the Mettler Toledo DSC, an advantage of the Perkin-Elmer power compensation DSC is the simplicity of its temperature calibration for any heating rate (Perkin-Elmer 1976). This was true for the sample holder of the Perkin-Ehner DSC-2, and it is true for the sample holder of the Diamond Pyris DSC, since the structure of the sample holder did not change. In general, the following equation describes the temperature calibration of a power compensation DSC on heating... 

Despite the theoretical advantages of the power compensated approach, the associated instrumentation is much more complex and, therefore, there are circumstances where the simpUcity of DTA has much to recommend it. DTA requires just two thermocouples and can, therefore, be used under demanding conditions. For example, high-pressure DTA experiments have been used extensively to generate phase diagrams of polyethylene and related low molar mass compounds— high-pressure DSC is rather more complex. 

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