Growth and Dissolution

The stability, growth, and transport of voids during composite processing is reviewed. As a framework for this model, the autoclave process was selected, but the concepts and equations may be applied equally effectively in a variety of processes, including resin transfer molding, compression molding, and filament winding. In addition, the problem of resin transport and its intimate connection with void suppression are analyzed. 

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Garside, J. and Jancic, S.J., 1976. Growth and dissolution of potash alum crystals in the sub-sieve size range. American Institution of Chemical Engineers Journal, 22, 887. 

Ristic, R.L and Sherwood, J.N., 2001. The influence of mechanical stress on the growth and dissolution of crystals. Chemical Engineering Science, 56, 2267-2280. 

The electrochemical behavior of single-crystal (100) lead telluride, PbTe, has been studied in acetate buffer pH 4.9 or HCIO4 (pH 1.1) and KOH (pH 12.9) solutions by potentiodynamic techniques with an RRDE setup and compared to the properties of pure Pb and Te [203]. Preferential oxidation, reduction, growth, and dissolution processes were investigated. The composition of surface products was examined by XPS analysis. It was concluded that the use of electrochemical processes on PbTe for forming well-passivating or insulating surface layers is rather limited. 

As Fig. 6.13 illustrates growth and dissolution are not symmetric with respect to the saturation state. At very high undersaturation, the rate of dissolution becomes independent of S and converges to the value of the apparent rate constant. This is why studies of dissolution far from equilibrium allow to study the influence of inhibition/ catalysis on the apparent rate constant, independently from the effect of S. The same is not true for crystal growth. 

In carbonate diagenesis V we deal usually with a combination of low supersaturation and absence of mechanical agitation. Homogeneous nucleation will certainly not occur. The important factors to be investigated are heterogeneous nucleation and rates of growth and dissolution of crystals. 

The geochemical fate of most reactive substances (trace metals, pollutants) is controlled by the reaction of solutes with solid surfaces. Simple chemical models for the residence time of reactive elements in oceans, lakes, sediment, and soil systems are based on the partitioning of chemical species between the aqueous solution and the particle surface. The rates of processes involved in precipitation (heterogeneous nucleation, crystal growth) and dissolution of mineral phases, of importance in the weathering of rocks, in the formation of soils, and sediment diagenesis, are critically dependent on surface species and their structural identity. 

Precise ion probe measurements on the micrometer scale allow the detection of the growth and dissolution history of minerals. 

A computer model has been generated which predicts the behaviour of a continuous well mixed gypsum crystallizer fed with a slurry of hemihydrate crystals. In the crystallizer, the hemihydrate dissolves as the gypsum grows. The solution operating calcium concentration must lie in the solubility gap. Growth and dissolution rates are therefore limited. 

The growth and dissolution rates depend on the driving forces within the solubility gap and are Interrelated by the material balance of relation 1 (In suitable form). 

The operating calcium concentration for a gypsum crystallizer fed with hemlhydrate crystals must lie In the solubility gap between the solubilities of the two species. This places severe limits on the range of growth and dissolution rates possible. 

A computer model has been produced that Incorporates the solubility, growth and dissolution mechanisms. It predicts the behaviour of a single crystallizer or a crystallization section, given Input conditions. 

Geochemical kinetics is stiU in its infancy, and much research is necessary. One task is the accumulation of kinetic data, such as experimental determination of reaction rate laws and rate coefficients for homogeneous reactions, diffusion coefficients of various components in various phases under various conditions (temperature, pressure, fluid compositions, and phase compositions), interface reaction rates as a function of supersaturation, crystal growth and dissolution rates, and bubble growth and dissolution rates. These data are critical to geological applications of kinetics. Data collection requires increasingly more sophisticated experimental apparatus and analytical instruments, and often new progresses arise from new instrumentation or methods. 

Interface reaction is another necessary step for crystal growth and dissolution. After formation of crystal embryos, their growth requires attachment of molecules to the interface. The attachment and detachment of molecules and ions to and from the interface are referred to as interface reaction. (During nucleation, the attachment and detachment of molecules to and from clusters are similar to interface reaction.) For an existing crystal to dissolve in an existing melt. 

Figure 4-6 Interface reaction rate as a function of temperature, pressure, and composition. The vertical dashed line indicates the equilibrium condition (growth rate is zero), (a) Diopside growth and melting in its own melt as a function of temperature with the following parameters Te= 1664K at 0.1 MPa, A5m-c = 82.76J mol K , E/R —30000 K, 4 = 12.8 ms K, and AV c l. l x 10 m /mol. The dots are experimental data on diopside melting (Kuo and Kirkpatrick, 1985). (b) Diopside growth and melting in its own melt as a function of pressure at 1810 K (Tg = 1810 K at 1 GPa from the equilibrium temperature at 0.1 MPa and the Clapeyron slope for diopside). (c) Calcite growth and dissolution rate in water at 25 °C as a function of Ca " and CO concentrations.

More examples and mathematical details of crystal growth and dissolution under various conditions can be found in Section 4.2. Furthermore, Lasaga... 

If mass transfer in the melt controls olivine growth and dissolution rate, explain why there may be dendritic growth but no dendritic dissolution. 

With regard to the attachment and detachment energies, the corners of a crystal or a rough interface that is constructed by kinks alone are sites where the process proceeds most quickly, whereas the low-index crystal faces, corresponding to smooth interfaces, represent the direction with the minimum rate of normal growth and dissolution. As a result, if a single crystalline sphere is dissolved in an isotropic environmental phase, a dissolution form bounded by both flat and curved crystal faces appears. This is called the dissolution form, which is not the same as the growth form. 

I. Sunagawa and P. Bennema, Observations of the influence of stress fields on the shape of growth and dissolution spirals,/. Grystal Growth, 53,1981,490-504... 

F. C. Frank, On the kinetic theory of crystal growth and dissolution process, in Growth and Perfection ofGrystals, eds. R. H. Doremus, B. W. Roberts, and V. Turnbull, New York, John Wiley Sons, 1958... 

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