Complex precipitation sequences

Chapter 10 provides an exhaustive description of how these techniques can be applied to a large number of industrial alloys and other materials. This includes a discussion of solution and substance databases and step-by-step examples of multi-component calculations. Validation of calculated equilibria in multi-component alloys is given by a detailed comparison with experimental results for a variety of steels, titanium- and nickel-base alloys. Further selected examples include the formation of deleterious phases, complex precipitation sequences, sensitivity factor analysis, intermetallic alloys, alloy design, slag, slag-metal and other complex chemical equilibria and nuclear applications. 

Curtis, C.D. Coleman, M.L. (1986) Controls on the precipitation of early diagenetic calcite, dolomite and siderite concretions in complex depositional sequences. In Roles of Organic Matter in Sediment Diagenesis (Ed. Gautier, D.L.), Spec. Publ. Soc. Econ. Paleont. Miner., Tulsa, 38, 23-33. 

A common method for producing a precipitate is to mix two reactant solutions together as quickly as possible, but the analysis of this apparently simple operation can be exceedingly complex. Precipitation processes, almost by definition, involve the creation of highly supersaturated systems and the main practical difficulty is to maintain reasonably uniform conditions throughout the reaction vessel. The choice of the method of mixing the reactants is therefore very important and the aim should be to avoid any accidental development of zones of excessive supersaturation. The sequence of reactant mixing can... 

In this reaction sequence, equation 47, the formation of the complex ion, Zn(OH)3, is the rate determining step. Once the solubiUty of 2incate, Zn(OH), is exceeded, 2inc hydroxide [20427-58-17, Zn(OH)2, precipitates. The crystal form that falls out of solution depends on the concentration of the alkah. 

Greater adsorption of trace metals is found at higher pH and C02(g) concentrations. Sites available for Zn2+ sorption are less than 10% of the Ca2+ sites on the calcite surface, and Zn adsorption is independent of surface charge. This indicates a surface complex with a covalent character (Zachara et al., 1991). Furthermore, the surface complex remains hydrated and labile because Zn2+ is rapidly exchangeable with Ca2+, Zn2+ and ZnOH. At the dolomite-solution interface, the carbonate(C03)-metal (Ca/Mg) complex dominates surface speciation at pH > 8, but at pH 4-8, hydroxide (OH) -metal (Ca/Mg) dominates surface speciation (Pokrovsky et al., 1999). Calcite has an observed selectivity sequence Cd > Zn > Mn > Co > Ni > Ba = Sr, but their sorption reversibility is correlated with the hydration energies of the metal sorbates. Cadmium and Mn dehydrate soon after adsorption to calcite and form a precipitate, while Zn, Co and Ni form surface complexes, remaining hydrated until the ions are incorporated into the structure by recystallization (Zachara et al., 1991). 

For the synthesis of carbohydrate-substituted block copolymers, it might be expected that the addition of acid to the polymerization reactions would result in a rate increase. Indeed, the ROMP of saccharide-modified monomers, when conducted in the presence of para-toluene sulfonic acid under emulsion conditions, successfully yielded block copolymers [52]. A key to the success of these reactions was the isolation of the initiated species, which resulted in its separation from the dissociated phosphine. The initiated ruthenium complex was isolated by starting the polymerization in acidic organic solution, from which the reactive species precipitated. The solvent was removed, and the reactive species was washed with additional degassed solvent. The polymerization was completed under emulsion conditions (in water and DTAB), and additional blocks were generated by the sequential addition of the different monomers. This method of polymerization was successful for both the mannose/galactose polymer and for the mannose polymer with the intervening diol sequence (Fig. 16A,B). 

The relative importance of the EDL for reactions other than adsorption is not well understood. Surface complexation models have recently been applied to processes in which adsorption represents the first step in a sequence of reactions. For example, Stumm et al. (22) have applied a model with an EDL component in their studies of the role of adsorption in dissolution and precipitation reactions. The effect of surface charge and potential on precipitation and the... 

The structure of the (l- 2)-a-D-mannopyranan has been confirmed by methylation analysis, and its interaction with concanavalin A has been tested. Concanavalin A forms a weak complex with this oligosaccharide, and this is precipitated. Two molecules of concanavalin A must, therefore, be able to link to a sequence of two, or three, (1— 2)-a-D-mannopyranosyl residues. The polymer thus gives some insight into the steric requirements, and the size of the active site, of this lectin.120... 

This was originally defined as the order of effectiveness in precipitating colloids or protein molecules. The ions to the left are less hydrated than those to the right. A similar series can be defined for anions. The following, a well-known sequence of the stabilities of complexes of metals of the first transition series, applies to many different types of complexes including those of the a-amino acids, as is shown in Fig. 6-11. 

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