Precipitation kinetics

Steefel, C. I. and A.C. Lasaga, 1994, A coupled model for transport of multiple chemical species and kinetic precipitation/dissolution reactions with application to reactive flow in single phase hydrothermal systems. American Journal of Science 294, 529-592. 

In addition, it is found that the rate of reaction is directly proportional to the inoculating seed concentration, thus confirming that the growth of the crystals takes place without interference from secondary nucleation. To have obtained a kinetic precipitation stoichiometry to this precision by techniques previously used would have required concentration analysis to at least 4 0.03%. Although, as mentioned previously, it had been assiamed that the ratio, R, was close to that for TCP, thereby invoking TCP as the precursor, it is clear from the results in Table I that the ratio is significantly lower than the Ca P = 1.50 required for TCP. 

Chemical compaction is important both in carbonate sand and mud. The driving force here is also here the increased solubility due to stress at grain contacts or along stylolites and the dissolved ions must be transported by diffusion into the pore water and precipitated. Because of the high kinetic precipitation rate the dissolution of carbonate may be rate limiting and the chemical compaction will be a function of the effective stress. High fluid overpressures reducing the effectives stress thus will tend to reduce compaction. 

Figure 11.5 compares simulated and sampled Fe and Mn distributions when the model is only slightly extended from the state, presented by Holzbecher et al. (2001), i.e. in which Fe is included as additional redox process of minor priority. Both measured Fe and Mn concentrations are well reproduced by the model. Thus observed Fe and Mn concentrations in the Oderbruch can be simulated when the redox model is supplemented only by a kinetic precipitation/dissolution approach. 

In the metal industry studies have been made of the phase transitions of metal alloys, modelling capacitors,metal hydration kinetics, precipitation of solutionised aluminium,and mechanisms of solid state transitions. ... 

The physical chemist is very interested in kinetics—in the mechanisms of chemical reactions, the rates of adsorption, dissolution or evaporation, and generally, in time as a variable. As may be imagined, there is a wide spectrum of rate phenomena and in the sophistication achieved in dealing wifli them. In some cases changes in area or in amounts of phases are involved, as in rates of evaporation, condensation, dissolution, precipitation, flocculation, and adsorption and desorption. In other cases surface composition is changing as with reaction in monolayers. The field of catalysis is focused largely on the study of surface reaction mechanisms. Thus, throughout this book, the kinetic aspects of interfacial phenomena are discussed in concert with the associated thermodynamic properties. 

The presence of a time limitation suggests that there must be a kinetically controlled interference, possibly arising from a competing chemical reaction. In this case the interference is the possible precipitation of CaCOs. 

Both thermodynamic and kinetic aspects of mixed systems (e.g., the precipitation step in wet spinning) involve the properties of the other components (solvent and nonsolvent in wet spinning) as well as the polymer. 

Bulk Polymerization. The bulk polymerization of acrylonitrile is complex. Even after many investigations into the kinetics of the polymerization, it is stiU not completely understood. The complexity arises because the polymer precipitates from the reaction mixture barely swollen by its monomer. The heterogeneity has led to kinetics that deviate from the normal and which can be interpreted in several ways. 

Many factors affect the mechanisms and kinetics of sorption and transport processes. For instance, differences in the chemical stmcture and properties, ie, ionizahility, solubiUty in water, vapor pressure, and polarity, between pesticides affect their behavior in the environment through effects on sorption and transport processes. Differences in soil properties, ie, pH and percentage of organic carbon and clay contents, and soil conditions, ie, moisture content and landscape position climatic conditions, ie, temperature, precipitation, and radiation and cultural practices, ie, crop and tillage, can all modify the behavior of the pesticide in soils. Persistence of a pesticide in soil is a consequence of a complex interaction of processes. Because the persistence of a pesticide can govern its availabiUty and efficacy for pest control, as weU as its potential for adverse environmental impacts, knowledge of the basic processes is necessary if the benefits of the pesticide ate to be maximized. 

Polymerization Kinetics of Mass and Suspension PVC. The polymerization kinetics of mass and suspension PVC are considered together because a droplet of monomer in suspension polymerization can be considered to be a mass polymerization in a very tiny reactor. During polymerization, the polymer precipitates from the monomer when the chain size reaches 10—20 monomer units. The precipitated polymer remains swollen with monomer, but has a reduced radical termination rate. This leads to a higher concentration of radicals in the polymer gel and an increased polymerization rate at higher polymerization conversion. 

We will be looking at kinetics in Chapter 6. But before we can do this we need to know what we mean by driving forces and how we calculate them. In this chapter we show that driving forces can be expressed in terms of simple thermodynamic quantities, and we illustrate this by calculating driving forces for some typical processes like solidification, changes in crystal structure, and precipitate coarsening. 

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