Impurity effectiveness factor, role

The impurity effectiveness factor, a, plays an important role in the assessment of impurity action. Its physical meaning is discussed here briefly. 

The main objectives of this chapter are to clarify the roles of the hydrophobic emulsifier additives added in the oil phase of O/W emulsions how they modify fat crystallization and where they interact within the emulsion droplets. One may ask why the hydrophobic emulsifiers accelerate the nucleation process. The answer may not be straightforward, because their influences on fat crystallization are controlled by their physical and chemical properties and the nature of the interactions with the fat molecules occurring in the oil phase and at the oil/water interfaces. However, the results we have obtained so far indicate that the addition of hydrophobic emulsifiers in the oil phase has remarkable effects on crystallization. Fat crystals typically form a number of polymorphs, whose crystallization properties are influenced by many factors, such as temperature, rate of crystallization, time evolution for transformation, and impurity effects, as is commonly revealed in various examples [27,28], It is reasonable to expect that these polymorphic properties of fats may interfere with the clarification of the essential properties of the interface heterogeneous nucleation that occurs in O/W emulsions. 

Before expanding on the role of impurities in defining polymerization rates and yields, it must be acknowledged that there is a dose-rate effect which may be a contributing factor to the discrepancies mentioned. Reports of such an effect have been made, but they are at variance as to the nature of the change in kinetics associated with changes in dose rates (1, 6, 15). In the current work the dose rates have been kept constant. 

The uptake(pH) curves for the systems metal cation—activated carbon reported in the literature are very divergent, and they indicate significant role of the oxidation of the surface on the one hand and of the impurities on the other. These factors were often not controlled, thus it is difficult to quantify their effect on the adsorption. 

For as long as studies are carried out in which no more than the correspondence between the general level of reactivity and the total dislocation content is examined, little real advance will be accomplished in our understanding of the role of defects in chemical reactivity. An effort has to be made to characterize more fully the nature of the dislocations, and to exclude wherever possible effects which may arise from extraneous factors such as the presence of impurities. Quite clearly, model systems need to be investigated using techniques which readily reveal the presence and influence of the dislocations. In this subsection we shall concentrate, in detail, on three major model systems the oxidation of graphite, the thermal decomposition of calcium carbonate, and the solid-state dimerization of anthracene. Related systems will also be discussed where appropriate. 

The effectiveness of the relaxation processes with thermal excitations of electronic states of the matrix ions diminishes as 6xp(-A/A b7 ) with the decrease of temperature. At fairly low temperatures the mechanism of nuclear relaxation via impurity paramagnetic centers, common for dielectrics, comes into effect (Abragam 1961, Khutsishvili 1968, Atsarkin 1980). This is well illustrated in fig. 20 the temperature motion of the nuclear relaxation rate is sharply slowed down for F at T < 5 K and fbr Tm at T < 3 K, and at the lowest temperatures the thulium nuclear moments relax only ten times faster than those of fluorine. This fact clearly shows that the relaxation of different nuclei proceeds by a single channel. The observed factor-of-ten difference is easily obtained, if one multiplies the concentration ratio nxm/nF = 4 by the ratio of the squares of their magnetic moments Thus, the role of 4f electrons is reduced here to the enhancement of dipole-dipole interactions of nuclei of the VV ions with impurity paramagnetic centers. 

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