Differential thermal analysis sample holders

In many of the methods of quantitative differential thermal analysis, the calibration coefficient can be mathematically deiermined and no experimental procedures are necessary. For example, Kronig and Snoodjik ((04) calculated K for a cylindrical sample holder as... 

Another technique related to DSC is DTA, differential thermal analysis. In this method sample and reference are heated by a single source and temperatures are measured by thermocouples embedded in the sample and reference or attached to their pans. Because heat is now supplied to the two holders at the same rate, a difference in temperature between the sample and the reference develops, which is recorded by the instrument. The difference in temperature depends, among other things, on the value of K, which needs to be low to obtain large enough differences in temperature to measure accurately. The area under a transition peak now depends on k and it is difficult to determine this accurately or to maintain it at a constant... 

The first term in Eq. (14) is only the approximate heat capacity in a differential thermal analysis experiment. It is derived already in part in Fig. 4.16 as the steady-state difference between block and sample temperatures. The second term is made up of two factors. The factor in the first set of parentheses represents (close to) the overall sample and sample holder heat capacity. The factor in the second set of parentheses contains a correction factor accounting for the different heating rates of reference and sample. For steady-state a horizontal base line is expected, or dAT/dTj. = 0 the heat capacity of the sample is simply represented by the first term, as suggested in Fig. 4.16. When, however, AT is not constant, the first term must be corrected by the second. 

Figure 10.4 Differential scanning calorimetry (DSC) instrumentation design (a) heat flux DSC and (b) power compensation DSC. A, furnace B, separate heaters and C, sample and reference holders. (Reproduced with permission from E.L. Charsley and S.B. Warrington, Thermal Analysis Techniques and Applications, Royal Society of Chemistry, Cambridge, UK. 1992 Royal Society of Chemistry.)...

In previous chapters, the principles and applications of differential scanning calorimetry (DSC) have been outlined, and it should be clear that the technique is both versatile and extremely sensitive. Using DSC, it is possible to analyze a wide range of systems quickly and cheaply so that thermodynamic parameters may be obtained. These qualities have led to the widespread use of DSC for not only pure research but also for routine thermal analysis. DSC does, however, have some drawbacks. To achieve good thermal contact with a sample, most DSC instruments are equipped with a pair of sample holders into which prepared sample and reference materials are placed. These materials are usually encapsulated in crimped aluminum ampoules, a typical sample mass being 5 to 10 mg. Such a small mass of sample contributes... 

Figure 17.69 depicts the schematic representation of the three principal thermal analysis systems—the classical DTA system with a single heat source and temperature sensors within the sample and the reference the Boersma DTA with a single heat source having the temperature sensors on the outside of the sample and reference and the DSC, where the power to individual heaters located in the sample and reference holders is varied continuously in response to sample thermal effects to prevent the development of a differential temperature between the sample and reference channels [142]. 

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