Scanning isoperibol

To better assess heat losses, twin calorimeters have been developed that permit measurement in a differential mode. A continuous, usually linear, temperature change of calorimeter or surroundings is used in the scanning mode. The calorimetry, described in Sect. 4.3 is scanning, isoperibol twin-calorimetry, usually less precisely called differential scanning calorimetry (DSC). 

The sample and reference thermometers and heaters are platinum resistance thermometers (see Sect. 4.1). Instead of relying on heat conduction from a single furnace, governed by temperature difference, reference and sample are heated separately as required by their temperature and the temperature difference between the two furnaces. The two calorimeters are each less than one centimeter in diameter and are mounted in a constant temperature block. This instrument is, thus, a scanning, isoperibol twin-calorimeter (see Sect. 4.2). 

Isoperibolic instruments have been developed to estimate enthalpies of reaction and to obtain kinetic data for decomposition by using an isothermal, scanning, or quasi-adiabatic mode with compensation for thermal inertia of the sample vessel. The principles of these measuring techniques are discussed in other sections. 

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. 

DSC differential scanning calorimetry Differential, ideal flux, or isoperibolic Screening, secondary reactions 1-50 mg -50 + 500 °C (2)b> 10... 

Low-temperature DTA and DSC needs special instrumentation [2]. In Fig. A. 10.1 a list of coolants is given which may be used to start a measurement at a low temperature. Fromabout 100 K, standard equipment can be used with liquidnitrogen as coolant. The next step down in temperature requires liquid helium as coolant. A differential, isoperibol, scanning calorimeter has been described for measurements on samples of 10 mg in the 3 to 300 K temperature range [3]. To reach even lower temperatures, especially below 1 K, one needs again another technique [4], but it is... 

Figure 5.4 Schematic design of a calorimeter with isoperibol scanning.

Scanning calorimeters, either adiabatic or isoperibol, single or twin design, allow the determination of the heat capacity of the sample as a function of temperature. Consequently, these instruments can be used to determine the temperature of a phase transition. The same holds for calorimeters, with which the temperature of the sample is not increased continuously but stepwise. 

The requirements with regard to a calorimeter can be derived on the basis of the above analysis of the measuring problem. The necessary operating conditions have to be defined first an isothermal, isoperibol, adiabatic, or a scanning calorimeter What temperature range What heating rate Any other boundary conditions a constant pressure, constant volume, gas flow rate, and so on ... 

Basically, the methods consist of a variety of calorimetric methods and a few non-calorimetric methods. In calorimetry the following methods are nsed adiabatic, isoperibol, isothermal, heat condnction, drop and differential scanning calorimeters, and differential thermal analysis. Cryoscopic, vapor pressure, and enthalpy of solution methods are considered to be non-calorimetric methods. 

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