Melts calorimetric solvents

Possible determinations from DSC or DTA measurements include (1) heat of transition, (2) heat of reaction, (3) sample purity, (4) phase diagram, (5) specific heat, (6) sample identification, (7) percentage incorporation of a substance, (8) reaction rate, (9) rate of crystallization or melting, (10) solvent retention, and (11) activation energy. Thus, thermo-calorimetric analysis can be a useful tool in describing the chemical and physical relationship of a polymer with respect to temperature. 

The calorimeter will perform with high precision to about 900 C. It is possible to measure heat effects as small as calorie in magnitude with a precision of 2 to 5. Heat effects of 5 200 calories can be obtained to within a standard deviation of 1%. This gives the necessary precision and sensitivity for solution calorimetry in oxide melts, where heats of solution of 0-30 kcal/mole are measured on samples of 50-100 m.y. (O.1-1.0 mmoles). Calorimetric solvents used, molten oxide mixtures suitable for dissolving solid silicate samples, will be described below. 

Low melting metals (Sn and also Bi, In, Pb, and Cd) are extensively used as solvents in calorimetric studies of metallic phases [35]. Transition metals do not, however, dissolve readily in tin [43] and other solvents such as Cu and A1 have been used. An experimental probe for high-temperature solution calorimetry is shown in Figure 10.8. 

In the calorimetric approach, it is necessary to know the heat of fusion of the totally crystalline polymer. This can be obtained from melting-point depression measurements, as described in the following section. The basic idea depends on the fact that the melting temperature is independent of the size of the system, since it is an intensive property. The extent to which it is depressed by the presence of solvent can be used to calculate a heat of fusion characteristic of the crystallites, irrespective of how many are present. This is therefore the heat of fusion of the 100% crystalline polymer. The fractional crystallinity in an actual sample is then the ratio of its calorimetrically measured heat of fusion per gram to that of the 100% crystalline polymer. For example, if the actual polymer has a heat of fusion of 7 cal per gram, and the 100% crystalline polymer a heat of fusion of 10 cal per gram, then the fractional crystallinity is 0.7, and the percentage crystallinity is 70%. 

The enthalpy of melting can be readily determined by non-calorimetric methods. One method involves the determination of the cryoscopic constant of the solvent from the temperature depression observed by the addition of a non-associating solute. The second method, using the Clapeyron equation, involves measuring the volume change on melting for the solvent and the pressure dependence of the melting temperature of the solvent. ... 

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