Cationic displacement

Added salts accelerate the (micelle-inhibited) reaction of CN with a triphenylmethyl dye cation. The salt order is Cs+ > K+ > Na+ > Li+ and here too the cation displaces hydronium ion from the anionic micelle and so increases the concentration of bound CN- (Srivastava and Katiyar 1980). 

Fig. 4.7 A schematic representation of a cationic displacement along a polymeric chain above its Tg. (a) An initial activated step (ft) allows the formation of an interstitial pair, the migration of which (c) and (d) is assisted by local free volume redistribution.

The equilibrium speciation of a metal ion influenced by cation exchange is dependent on the relative concentrations of the cations competing for the negatively charged sites on the particle s surface and their relative affinities for adsorption. Since one cation displaces another from the negatively charged sites, this process is termed cation exchange. 

Post, J. E., Von Dreele, R. B. Buseck, P. R. 1982. Symmetry and cation displacements in hollandites structure refinements of hollandite, cryptomelane and priderite. Acta Crystallogra-phica, B38, 1056-1065. 

Fig. 7.14 A Frenkel defect, a cation displaced from its normal sue.

When the cation displaced from the extractant is a hydrogen ion, as in reaction (10), the extract-ability of the metal shows a distinct dependence on the pH value of the aqueous phase. Such systems are conveniently characterized by the pH value at which the concentrations of metal in the organic and aqueous phases are equal at a stated concentration of extractant, this being denoted the pH0.s value for the given metal. 

Other consideration for selective separation are related to the basic principles of ion exchange. For example, cation displacement should proceed until the column is loaded to capacity with plutonium and americium. If this procedure is not employed, the excess resin simply sorbs the displaced cations (e.g., Mg, Na, K, Ca, etc.) and they are rejoined with the actinides during the elution cycle. 

Ordering of orthophosphate anions results in ferroelectricity in K2Bi30(P04)2 whereas in AM2(P04)3 types (A = Li-Cs, Ag, Cn M = Ce, Th, U) it results from the alignment of A cation displacements from the center of AOg polyhedra. A m P04 materials (e.g. A = Rb, Cs M = Mg, Co, Zn) containing tetrahedral MPO4 frameworks can undergo ferroelectric transitions due to the coupled rotations of the tetrahedra. 

CS planes across which the MoOe octahedra share edges rather than comers. These extended defects exist even at modest temperature due to the large mobility of oxygen vacancies, Further, the defects are stabilized by relaxation as a result of Mo cation displacement from their centers of symmetry to interstices. Homologous series of molybdenum oxides [1, 3, 12, 34, 154, 158, 160, 163, 164], which are based on CS plane formation starting from a ReOs-type structure, include MOn03n-i and Mon03 .2 systems. 

D Souza SE, Haas TA, Piotrowicz TS, et al. Ligand and cation binding are dual functions of a discrete s ment of the integrin beta3 subunit cation displacement is involved in ligand binding. Cell 1994 79 659-667. 

Loading Sodium form column operation at a linear velocity of 5-80 m m h , whereby hardness cations displace sodium according to the ion exchange reaction ... 

The Donnan equilibrium theory implies that dilution of a clay/water system containing monovalent and divalent cations displaces the equilibrium in such a manner that the absorption of divalent ions increases, whereas the absorption of monovalent ions decreases. The ionic charge is not the only determining factor in the absorption effect. Factors such as temperature, pH, and specific ions also play important roles. Hydration energy, which appears to be one of the most important factors for the absorption and fixation of cations, displaces the ionic equilibria in a manner opposing the Donnan equilibrium theory. According to Sawhney (1972), "cations with low hydration energy such as Ca, Mg and Sr, produce expanded interlayers and are not fixed". 

In the course of attempts to determine adsorption isotherms of anionic surfactants on selected clays two other phenomena requiring separate investigation were noted, namely, salting-out of surfactants by NaCl, and surfactant precipitation as calcium or magnesium salts by multivalent cations displaced from clays. 

This section shows the derivation of some formulae reported in the text. Derivation of tetrahedral cation displacement , Tdisp. 

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