Precipitation growth kinetics

Nielsen, A. E. 1964. Diffusion controlled growth. Kinetics of Precipitation. Pergamon Press, Oxford, UK. p. 34. 

In summary, the nucleation rate R (t) is difficult to assess and kinetic theories for transforming systems often assume (ad hoc) R (t) dependencies. In contrast, the growth kinetics of an individual particle of p precipitate in the supersaturated matrix (a) is a transport problem with well defined boundary conditions, as long as... 

Mucci A. (1986) Growth kinetics and composition of magnesian calcite overgrowths precipitated from seawater Quantitative influence of orthophosphate ions. Geochim. Cosmochim. Acta 50, 2255-2265. 

Mucci A., Canuel R. and Zhong S. (1989) The solubility of calcite and aragonite in sulfate-free seawater and the seeded growth kinetics and composition of precipitates at 25°C. Chem. Geol. 74, 309-329. 

Precipitation — The formation of a solid in a solution during a chemical reaction or from a solution that has been oversaturated by a compound [i]. See also -> oversaturation, - nucleation, - nucleation and growth kinetics. 

The particle size distribution produced during precipitation is a result of the relative rates of reaction, nudeation, growth, and agglomeration, as well as the degree of backmixing in the precipitator. The kinetics of each of these steps will be discussed next. 

Van Cappellen and Berner (1991) smdied the growth kinetics of FAP in seeded precipitation experiments using carbonate-free solutions. The growth of FAP was inhibited by Mg " " at concentrations typical of marine pore waters and enhanced by H" " ions in the pH range of 7-8.5. At moderate degrees of supersaturation, a precursor phase similar in composition to octacalcium phosphate formed on the FAP... 

Barium sulfate precipitation has been reported to be controlled initially by nucleation reaction and, finally, by growth reaction. The growth kinetics was represented by the equation ... 

Stone and Tilley have shown that the spectral changes which occur on spinel formation can be related to the extent of reaction of the component oxides, although the kinetics were also followed by chemical analysis. Keyser et have studied the reaction of zirconium silicate with calcium oxide by a radio tracer method. Wagenblast and Damask have used internal friction measurements to study the rate of precipitation of carbon in iron. The rate of decrease of the Snoek peak can be related to the growth kinetics of the iron carbon precipi-... 

Where might this be important As discussed above, biological activity can result in the simultaneous precipitation of mixtures of nanoscale sulfide minerals under certain conditions. Each mineral will exhibit a particular particle size distribution, dependent on the solution composition, bacterial activity, rate of crystal growth, and the nature of electrochemical interactions between the particles. These electrochemical reactions could lead to oxidation of one type of nanophase sulfide mineral of a certain size, and reduction of another type of nanophase sulfide particle or other species in the solution. In this way, a tremendous number of mineral-solution-mineral galvanic cells could develop, with potentially significant impact on dissolution kinetics, growth kinetics, and the mixture of phases observed. In addition to environmental relevance, these processes may shape the mineralogy of low-temperature ore deposits. 

In a typical CC growth kinetics experiment, carefully prepared and well-characterized seed crystals are introduced to a thermo-stated crystallization cell containing solution at a preset supersaturation. The reactant solutions are prepared with appropriate stoichiometry matching that of the precipitating phase. To maintain the composition of the supersaturated solution at a constant value, both reactants (titrant solutions) are added at the rate sufficient to replace reactant ions that precipitated, and to bring the supersaturation of the resultant total volume to the value of the initial supersaturated solution. 

As stated above, control of the crystallization or precipitation process is essential to obtain crystals of biochemical compounds having appropriate properties. The phenomena, techniques, and analysis discussed in many of the previous chapters solubility and supersaturation, nucleation and growth kinetics, population balance methods, batch and continuous crystallizers, and factors governing crystal purity, habit and morphology are all relevant to the discussion of the crystallization of pharmaceuticals. We shall analyze the crystallization/precipitation of biomolecules in terms of these concepts. 

Solvent Effects. Changes of solvent, as in the use of alcohols as anti-solvents for precipitation from aqueous solution, may also influence particle shape through altering growth kinetics on... 

If mass transport is possible between the particles in a polydisperse precipitate, the large will grow at the expense of the small. If the growth kinetics are first-order, diffusion-controlled, then for a change in particle radius with time (see equation 6.37)... 

The growth kinetics of this process are reported to be second order and surface reaction controlled. The precipitation of silver iodide in ethanol by the reaction... 

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