Dissolution, heat

Atoms of interstitial Impurity Metal A (or B) Dissolution heat of impurity, J mol-1... 

In the case of the FeNi3-H alloy at temperature T 500°C the atomic order-disorder phase transition takes place. In this alloy in accordance with Eq. (25) for f0 with the value of dissolution heat (see Table 2), the atomic order must increase the hydrogen solubility. This theoretical conclusion is also in accordance with the experimental data. 

Special devices for classification of crystals may be used in some applications. Figure 14 shows a draft-tube-baffle (DTB) crystallizer that is designed to provide preferential removal of both fines and classified product. As shown, feed is introduced to the fines circulation line so that any nuclei formed upon introduction of the feed can be dissolved as the stream flows through the fines-dissolution heat exchanger. The contents of the crystallizer are mixed by the impeller, which forces the slurry to flow in the indicated direction. A quiescent zone is formed between the... 

Since the diffusion coefficient can be measured, the prediction of transport-controlled dissolution rates depends on a calculation of 6, which is itself a function of D, as well as of stirring rate and viscosity. A complete solution of this problem has been obtained in only one case by Levich (7 that of an ideal rotating disk under non-turbulent conditions. The derivation was made for electrode processes, but is equally applicable to dissolution, heat transfer and other heterogeneous processes. 

In order to evaluate the dissolution heat, it is necessary to compare the crystalline lattice energy with hydration energy (Figure 2.25) ... 

The balance of these two energies at dissolution may be either positive (exothermal) or negative (endothermal). The very amount of heat released or absorbed at dissolution of 1 mole of salt AH, is called solution heat. Its value is equal to the difference between the crystalline lattice energy and sum hydration energies of dissociated ions. For halite NaCl the solution heat is 783 - (415 + 365) = +3 kJ-mole" for sylvin KCl - 709 - (324 + 354) = +31 kJ-mole" and for MgCl - 2,326 - 2,631= -305 kj-mole". NaCl and KCl dissolution under standard conditions is accompanied by heat release and MgCl dissolution, by heat absorption. Values of dissolution heat for the least stable salts are listed in Table 2.17. 

The method of differential calorimetry is one of the best method of cement heat of hydration measurements especially at early period [39]. In Ihe world standards the method of the dissolution heat is also very popular [40]. This method is particularly suitable for long period of hydration, even for one year [41-43]. It caimot be used in the case of cements with the addition of slag or fly ash, which are not totally dissolved in the acids mixture. 

Most techniques for polymer composition measurement require long sampling intervals, i.e. either the analysis requires a long dissolution, heating, or reaction time, or manpower or equipment limitations preclude more frequent analysis. 

Heat of dissolution (heating/cooling jackets may be required). 

For all isothermal measurements the heats to be determined, such as heats of crystallization, heats of dissolution, heats of combustion, and other chemical reactions, are obtained in a rather straightforward matmer at the temperature of measurement. Outside of the instrument corrections, no further data treatment is necessary. The thermochemical data handling was illustrated in Fig. 2.14, using the examples of heats of combustion and enthalpies of formation. An entry into the extensive literature on heats of chemical reactions can be found by studying the references 6 and 52 at the end of the chapter. 

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