Crucibles, differential scanning calorimetry

DSC (differential scanning calorimetry) was performed using a Netzsch Phoenix El apparatus. Typically, samples of about 20 mg were applied in aluminium cold-sealed crucibles with heating/cooling rates of 5 °C/min. 

A more detailed investigation of the thermal behavior of the exploding [ ]rotanes by differential scanning calorimetry (DSC) measurements performed in aluminum crucibles with a perforated lid under an argon atmosphere revealed that slow decomposition of exp-[5]rotane 165 has already started at 90 °C and an explosive quantitative decomposition sets on at 150 °C with a release of energy to the extent of AH(jecomp = 208 kcal/mol. Exp-[6]rotane 166 decomposes from 100°C upwards with a maximum rate at 154°C and an energy release of AH(jg on,p=478 kcal/mol. The difference between the onset (115°C) and the maximum-rate decomposition temperature (125-136°C) in the case of exp-[8]rotane 168 is less pronounced, and AHjecomp 358 kcal/mol. The methy-... 

In differential scanning calorimetry, the selected chemical reaction is carried out in a cmcible and the temperature difference AT compared to that of an empty crucible is measured. The temperature is increased by heating and from the measured AT the heat production rate, q, can be calculated (Fig. 3.19). Integration of the value of q with respect to time yields measures of the total heats... 

FIGURE 15.10 A photograph of the interior of a small oven used for differential scanning calorimetry. The crucibles... 

Differential Scanning Calorimetry (DSC) was used for a long time in the field of process safety [21-23], This is essentially due to its versatility for screening purposes. The small amount of sample required (micro-calorimetric technique) and the fact that quantitative data are obtained, confer on this technique a number of advantages. The sample is contained in a crucible placed into a temperature controlled oven. Since it is a differential method, a second crucible is used as a reference. This may be empty or contain an inert substance. 

To get a more accurate picture of the behavior of SiO at elevated temperatures, we performed a differential scanning calorimetry (DSC) measurement up to 1100 °C. To this end, the SiO powder was heated in a Pt crucible at a rate of 20 K min under flowing Ar gas (75 ml min ) in a DSC Pegasus 404C from Netzsch. Figure 19.3 shows the heat flow rate plotted versus temperature in the range of 500... 

It is seen that the calibration constant disappears, which assumes that it is constant over the experimental conditions. The calculation is carried out using dedicated software. In some circumstances the crucible used for the sample may have to be different from that used for the calibrant. This means that a correction will be required to take into account the difference between the heat capacity of the two crucibles - readily calculated with sufficient accuracy. Measurements can be made at a series of temperatures but are meaningful only within the quasi-steady-state region of the experiment. The specific heat capacity of sapphire has been listed by ASTM in connection with the standard test method E 1269 (1999) for determining specific heat capacity by differential scanning calorimetry. 

The results of thermal analysis by differential scanning calorimetry (DSC) are influenced by various experimental parameters. Instruments designed and constructed by different manufacturers have distinct operating principles, but all instruments provide support for two crucibles of small volume in a single or a matched pair of furnaces that allow the temperature of the sample and a reference material to be subjected to a predefined temperature program. Various authors (Turi, 1981 Haines, 2002 Ehrenstein et al., 2004 Wunderlich, 2005 Brown and GaUacher, 2008 Menczel and Bruce Prime, 2009) have provided extensive descriptions of specific details of commercial instruments and therefore further aspects of equipment design will not be discussed in this chapter. 

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