Calorimeter temperature program

A batch reaction can also be analysed in a reaction calorimeter, the temperature program being the same as for the industrial process. Figure 6.16 shows the substitution example reaction starting from 30 °C and being heated to 100 °C at lOXlT1. 

The DSC curve for reference standard chlorpro-thixene was obtained using a Perkin Elmer DSC - IB Calorimeter. With a temperature program of lO C/min., a melting endotherm was observed starting at 92.8°C (shown in Figure b] and another endotherm starting at 246°C which corresponds to the decomposition of the chlorprothixene. 

The DSC scan for triclobisonium chloride, shown in Figure 4, was obtained using a Perkin-Elmer DSC-IB Calorimeter. The sample pan contained a small hole in the top to allow the decomposition products formed to escape. With a temperature program of 10°C/min., an endotherm was observed starting at 253,4°C which is due to the melt and/ or decomposition of the molecule (6). Due to the nature of this peak no AHf was calculated. 

After insertion of one emulsion-filled cell into the calorimeter, and thermal equilibrium has been reached, the calorimeter is programmed to be cooled down and heated between two limits of temperature. As the test is especially suitable for W/0 emulsions, focus is placed on the freezing of water and the melting of ice. Therefore, the scanning is performed from +20°C down to -80°C at least, as late solidification, due to undercooling and dissolved solute in water, may occur. The other cells left at room temperature are studied in the same way. 

Historically, DSC is a development of differential thermal analysis (DTA) and both techniques have a common origin in the measurement of temperature. The fundamental concept of both techniques is sim-ple-to measure thermal changes in a sample relative to a thermally inert reference as both are subjected to a controlled temperature program. In classical DTA, the temperature difference between sample and reference is measured as a function of temperature in classical DSC, the energy difference between sample and reference is measured as a function of temperature. Hence, DSC is simply quantitative DTA , or more precisely, DSC is a combination of DTA and adiabatic calorimetry. DSC is the more recent technique and was developed for quantitative calorimetric measurements over a wide temperature range from subambient to 1500 C. DTA is not appropriate for such precision measurements and has been progressively replaced by DSC, even for high-temperature measurements, as the major thermal anal-ysis/calorimetric technique. DSC is a differential calorimeter that achieves a continuous power compensation between sample and reference. 

The underlying temperature of the experiment, typically linear with time or constant, is applied by temperature control of the surrounding furnace to which the calorimeter chip is connected. The heater, which is part of the chip, is used for further temperature programs such as continuous (scanning) or periodical or pulse-like heating. 

The sample is stabilized at a temperature Tj in a low-inertia thermal fluxmeter (differential scanning calorimeter). Linear programming of the temperature with the constant slope dT dt = is then imposed in die kiln of the instrument, up to the temperature of T2. The thermal flux signal is then recorded between times t and t2 (Figure 4.4), which are sufficiendy far apart for the flux signal to be stable. The experimental temperature T is taken as the mean of the two temperatures T and T2. 

As previously mentioned in 2.1, ASTM standard E473 defines differential scanning calorimetry (DSC) as a technique in which the heat flow rate difference into a substance and a reference is measured as a function of temperature while the substance and reference are subjected to a controlled temperature program. It should be noted that the same abbreviation, DSC, is used to denote the technique (differential scanning calorimetry) and the instrument performing the measurements (differential scanning calorimeter). 

Using the model of Fig. 15.8, we have simulated an event leading to an energy adsorption AE. To evaluate the corresponding temperature increase AT, at different heat sink operating temperatures, a T3 dependence of the absorber heat capacity was supposed. To obtain the calorimeter response (temperature change on the 7) thermal node) for a simulated event, a SPICE program was used. 

The calorimetry lexicon also includes other frequently used designations of calorimeters. When the calorimeter proper contains a stirred liquid, the calorimeter is called stirred-liquid. When the calorimeter proper is a solid block (usually made of metal, such as copper), the calorimeter is said to be aneroid. For example, both instruments represented in figure 6.1 are stirred-liquid isoperibol calorimeters. The term scanning calorimeter is used to designate an instrument where the temperatures of the calorimeter proper and/or the jacket vary at a programmed rate. 

While the dilatometer method is the preferred method of determining the glass transition temperature, it is a rather tedious experimental procedure and measurements of Tg are often made in a differential scanning calorimeter (DSC). In this instrument (18), the heat flow into or out of a small (10-20 mg) sample is measured as the sample is subjected to a programmed linear temperature increase (typically 10 C/min). The heat flow is proportional to the specific heat of the sample. At the glass transition, there is an increase in the heat flow into the sample due to the increase in specific heat at this point. Values obtained in this manner are only a few degrees higher than the dilatometer values. 

OIT is a relative measure of a material s resistance to oxidative decomposition. It is determined by the thermoanalytical measurement of the time interval of exothermic oxidation of a material at a specified temperature (typically between 140 and 210°C) in an oxygen atmosphere. The procedure employs a differential scanning calorimeter (DSC). It is very practical to use an automatic sample, that is a carousel, which typically holds 50 specimens, and descriptions for 65 specimens can be programmed into the instrument before the runs. For low OIT numbers (less than... 

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