Differential scanning calorimeters heat capacity calibration

The heat flux and energy calibrations are usually performed using electrically generated heat or reference substances with well-established heat capacities (in the case of k ) or enthalpies of phase transition (in the case of kg). Because kd, and kg are complex and generally unknown functions of various parameters, such as the heating rate, the calibration experiment should be as similar as possible to the main experiment. Very detailed recommendations for a correct calibration of differential scanning calorimeters in terms of heat flow and energy have been published in the literature [254,258-260,269]. 

Heat capacities were determined by using a differential scanning calorimeter (DSC). A sapphire standard was used for DSC cell calibration. Samples were cut directly from the samples used in the thermal diffusivity measurements. Heat capacity was determined, as usual, from the heat requirement of the sample in response to a particular change in temperature. Multiple scans were performed to verify that sample degradation did not influence the results. Char samples could be heated up to 850 K in these experiments. The DSC cell was continuously purged with nitrogen, in order to avoid oxidation of the samples. 

The heat capacities were measured with a computer controlled Perkin-Elmer Differential Scanning Calorimeter DSC-II [17]. Data were taken in 0.2K increments at 20K/minute, corrected for instrumental variations and temperature lag and calibrated point by point with the heat capacity of sapphire. Polymers investigated were Conoco 5425 (ijgp = 0.42) poly vinyl chloride anionic... 

Differential Scanning Calorimetry. Differential scanning calorimetry is in some respects a modification of differential thermal analysis, and the schematic diagram of a differential scanning calorimeter (dsc) is similar to that of the dta device shown in Figure 12. The essential difference, however, is that the measured quantity here is the differential power supplied to the two wells, rather than the temperature difference. In other words, the dsc device maintains the same programmed temperature in each well and records the power required to achieve this. If a transition takes place in the sample, a characteristic excursion in the measured differential power is observed. The nature of these excursions can be related to the transitional properties of the sample. Furthermore, by proper calibration with a reference material of known thermal properties, the specific heat capacity of the sample may be obtained. 

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