Solid-solution interactions

The behavior of carbonates will be used to illustrate heterogeneous processes, with emphasis upon the formation of inorganic surface coatings and solid solutions. This is a vital topic in the study of solid-solution interactions since it is coatings rather than bulk phases which are sensed by liquid solutions. Homogeneous reactions will be studied in terms of the competition of coulombic ion pairs with true complexes for anions. An extended form of the phase rule will be used. 

Redox processes are discussed in detail in Chapter 4. The rest of this chapter deals with solid-solution interactions, firstly for soils in general and then for submerged soils. Recent reviews of solid-solution interactions in soils include Sposito (1994), Sparks (2003) and the relevant chapters of Sumner (2000). 

Table 3.14 Rates of solid-solution interactions in soils...

LaFlamme BD, Murray JW. 1987. Solid/solution interaction The effect of carbonate alkalinity on adsorbed thorium. Geochim Cosmochim Acta 51 243-250. 

Solute adsorption is usually restricted to a mono molecular layer, since the solid-solute interactions, although strong enough to compete successfully with the solid-solvent interactions in the first adsorbed monolayer, do not do so in subsequent monolayers. Multilayer adsorption has, however, been observed in a number of cases, being evident from the shape of the adsorption isotherms and from the impossibly small areas per adsorbed molecule calculated on the basis of monomolecular adsorption. 

Tipping, E., and M. A. Hurley. 1988. A model of solid—solution interactions in acidic organic soils, based on the complexation properties of humic substances. Journal of Soil Science 39 505-519. 

When the solid inputs or the solid-solution interactions lead to weaker bonding of certain metal species, are the factors and processes of remobilisation as effective in contaminated as in natural systems ... 

Another type of solid/solution interaction is metathesis or ion exchange which actually alters the composition of the solid as well as that of the solution. Thus in the presence of bromide ions, AgCl will react to form the less soluble AgBr... 

Only some of the solid-solution interactions (A)-(E) can possibly take place in any given experimental situation. Any interactions not ruled out on thermodynamic grounds should then be tested for. A suitable choice of the following experiments is recommended for this purpose [115, 130]. 

The tests that can detect the various types of solid-solution interaction are shown by ticks in Table 1. The question marks indicate conditions where a positive response might be obtained, depending upon circumstances. The table can be used either to select suitable tests when a given type of interac-... 

Summary of the suitability of different tests for detecting the five main types of solid-solution interaction... 

In adsorption from solution, physisorption is far more common than chemisorption, although the latter is sometimes possible. Solute adsorption is usually restricted to a monomolecular layer, since the solid-solute interactions, although strong enough to compete successfully with solid-solvent interactions in the first adsorbed monolayer, do not do so in subsequent monolayers, because the interaction is screened by the solvent molecules. Thus, multilayer adsorption has only rarely been observed in a number of cases, and identified, when the number of adsorbate molecules exceeds the number of mono-layer molecules possible on the total adsorbent surface area. However, this analysis cannot be applied to polymer adsorption, because it is generally impossible to determine the surface area of a monomolecular layer of a polymer adsorbed flat on the solid surface. This is because the adsorbed polymer can only be anchored to the surface at a few points, with the remainder of the polymer in the form of loops and ends moving more or less freely in the liquid phase. 

J. W. Cooper, H. C. Ansel, and D. E. Cadwallader, Liquid and solid solution interactions of primary certified colorants with pharmaceutical gelatins,./. Pharm. Sci. 62, 1156-1164(1973). 

Next to the solid-solute interaction also the particle size is important for achieving a good distribution of the metal through the carbon particles. The smaller the particle the more homogeneous the metal division. The particle size is also important for the reaction rate during the application of the catalysts. Smaller particles give higher activity and as a rule less undesired side reactions. 

Figure 3 (a) Cold contact observation results (i) the cociystal grew from clavulanate crystal to amoxicillin solution in NaOH> (ii) amoxicillin melted at 194°C, clavulanate oxidized at 203°C> while the cocrystal oxidized least, (b) DSC data of amoxicillin trihydiate (top), potassium clavulanate (middle), and the physical mixture 1 1 (bottom). The exothermic peak of I 1 mixture shows that amoxicillin and clavulanate overlay and become 1 peak at 202°C which indicates a solid solution interaction. 

For ternary and stiU more complex systems, the general approaches are the same. But for these systems, not only must the relations for the liquid phase be modified, but also those for the solid phase. A comprehensive review on phase equilibria in ternary III-V systems has been written by Panish and Ilegems [21]. A useful semiempirical expression for the calculation of the solid-solution interaction parameter, based on the difference in the lattice constants of the binary constituent compounds, has been developed by Stringfellow [22]. 

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