Phase dissolution

Notice that the asterisk designation is not required when the third phase is air, or the vapor of one or more of the components already present in the system, since interfacial interactions are not significantly affected by phase dissolution and adsorption of air or a common vapor. Hence the asterisk designation was not required in Girifalco and Good s original work (17-18). In a similar fashion, the asterisk is not used with Ysw since the solid is assumed insoluble in both the soil and bath. 

Yan, J. Neretnieks, I. 1995. Is the glass phase dissolution rate always a limiting factor in the leaching processes of combustion residues The Science of the Total Environment, 172, 95-118. 

Both field and laboratory observations are consistent with the idea that dissolution can proceed faster than precipitation in carbonate sediments (also see Pytkowicz, 1971 Berner et al., 1978 Moulin et al 1985 Burton and Walter, 1987), and that the pore waters reach steady-state ion activity products close to those of the most unstable phase (dissolution processes will be discussed later in this chapter). Carbonate ion may be "pumped" down to values at saturation with less soluble phases, as dissolution of the more soluble material eventually causes its removal. However, the persistence of high magnesian calcites in sediments for long periods of time indicates that this process does not involve a large amount of mass transfer under normal marine conditions. 

Vapor phase dissolution (VPD) is commonly used for surface and contamination analysis of semiconductor wafers [374-379]. HF vapor is used to remove a silicon oxide or native silicon layer. A drop of hydrofluoric acid or deionized water (with a volume of 50 to 200 jxL) is placed on the surface and rolled around the surface to dissolve the metals. The small drop is then analyzed by ICP-MS by using either a direct injection nebulizer, a micronebulizer, or ETV. The ability of ICP-MS to measure several elements rapidly in a small volume of solution is essential. 

Besides fluid mechanics, thermal processes also include mass transfer processes (e.g. absorption or desorption of a gas in a liquid, extraction between two liquid phases, dissolution of solids in liquids) and/or heat transfer processes (energy uptake, cooling, heating, drying). In the case of thermal separation processes, such as distillation, rectification, extraction, and so on, mass transfer between the respective phases is subject to thermodynamic laws (phase equilibria) which are obviously not scale dependent. Therefore, one should not be surprised if there are no scale-up rules for the pure rectification process, unless the hydrodynamics of the mass transfer in plate and packed columns are under consideration. If a separation operation (e.g. drying of hygroscopic materials, electrophoresis, etc.) involves simultaneous mass and heat transfer, both of which are scale-dependent, the scale-up is particularly difficult because these two processes obey different laws. 

This article reviews the phase behavior of polymer blends with special emphasis on blends of random copolymers. Thermodynamic issues are considered and then experimental results on miscibility and phase separation are summarized. Section 3 deals with characteristic features of both the liquid-liquid phase separation process and the reverse phenomenon of phase dissolution in blends. This also involves morphology control by definite phase decomposition. In Sect. 4 attention will be focused on flow-induced phase changes in polymer blends. Experimental results and theoretical approaches are outlined. 

Kinetics of Phase Separation and Phase Dissolution in Polymer Mixtures. 54... 

The second is to examine the dynamics of phase separation and phase dissolution which can be pursued by scattering techniques. This topic involves the fundamental problem of self-organization in polymer systems under non-equilibrium conditions. 

In this section we would like to deal with the kinetics of the liquid-liquid phase separation in polymer mixtures and the reverse phenomenon, the isothermal phase dissolution. Let us consider a blend which exhibits LCST behavior and which is initially in the one-phase region. If the temperature is raised setting the initially homogeneous system into the two-phase region then concentration fluctuations become unstable and phase separation starts. The driving force for this process is provided by the gradient of the chemical potential. The kinetics of phase dissolution, on the other hand, can be studied when phase-separated structures are transferred into the one-phase region below the LCST. 

Phase dissolution in polymer blends. The reverse process of phase separation is phase dissolution. Without loss of general validity, one may assume again that blends display LCST behavior. The primary objective is to study the kinetics of isothermal phase dissolution of phase-separated structures after a rapid temperature-jump from the two-phase region into the one-phase region below the lower critical solution temperature. Hence, phase-separated structures are dissolved by a continuous descent of the thermodynamic driving force responsible for the phase separation. The theory of phase separation may also be used to discuss the dynamics of phase dissolution. However, unlike the case of phase separation, the linearized theory now describes the late stage of phase dissolution where concentration gradients are sufficiently small. In the context of the Cahn theory, it follows for the decay rate R(q) of Eq. (29) [74]... 

In the case of phase-separation dynamics, the non-linear terms become increasingly important in the course of time. In contrast, for phase-dissolution kinetics, the non-linear terms are most important in the beginning and their importance declines with progressing dissolution. 

Results are shown in Figs. 12 and 13. All blend specimens were set iso-thermally above LCST and kept there for a maximum of 5 min. As will be seen, this corresponds only in some cases to an early stage of spinodal decomposition depending on temperature. The diffusion coefficients governing the dynamics of phase dissolution below LCST are in the order of 10"14 cm2 s"1. Figure 12 reflects the influence of the mobility coefficient on the phase dissolution. As can be seen, the apparent diffusion coefficient increases with increasing temperature of phase dissolution which expresses primarily the temperature dependence of the mobility coefficient. Furthermore, it becomes evident that the mobility obeys an Arrhenius-type equation. Similar results have been reported for phase dis-... 

The basic idea is to reconstruct geochemical evolution of the groundwater from its chemical composition. For example, knowing the chemical composition of a well on the one hand and an analysis of the rainwater on the other, it will be possible to reconstruct which geological formation the rainwater must have passed after its infiltration to change its chemical composition as the result of reactions with mineral and gas phases (dissolution, precipitation, degassing) in a way that accounts for the composition of the water from the well. 

J. T. H. Roos, A Simple Vapour-Phase Dissolution Technique for Biological Materials, a paper presented at the Symposium on the Analysis of Biological Material, Spectroscopy Society of South Africa, October 1977, Pretoria, South Africa. 

Chemical weathering of minerals results not only in the introduction of solutes to the aqueous phase but often in the formation of new solid phases. Dissolution is described as congruent, where aqueous phase solutes are the only products, or incongruent, where new solid phase(s) in addition to aqueous phase solutes are the products. These reactions... 

Dissolved Aqueous Phases Dissolution Reaction and Ionic Concentration Equation No. pH Range... 

Figures 10a and b show the plots of logarithmic intensity (after Cook s correction) versus elapsed time for the phase separation and phase dissolution, respectively. The plots in the former are hardly linear, and deviations are severe, particularly at late stages of phase separation. This observation is not surprising in view of the fact that the peak invariance is only seen at a very short interval of 80 to 94 s in Figure 8a. Thus, the R(q) can not be determined with good accuracy as it is affected by the non-linear contribution. The data points in the phase dissolution show linear relationships as predicted by the linearized theory. However, it is important to test the linearized theory quantitatively in terms of Equation 4.

Figure 9. Time-evolution of scattering curves during phase dissolution of the 107. HPC-L solution following a T-quench from 45 to 43 C.

Figure 10. Log I versus t for the 107. aqueous HPC-L solution during (al phase separation following a T-jump from 23 to 44°C and (b) phase dissolution following a T-quench from 45 to 43°C.

The absolute values of Da for the phase separation and phase dissolution are plotted against e in log-log scale together in Figure 13. In the present case, the value of v turns out to be unity for the phase separation as well as for the phase dissolution, thereby confirming the prediction of linearized theory. A similar observation was also made by Snyder and coworkers (2Q) for the polystyrene (PS) polyvinyl methyl ether (PVME) blends. It is concluded that the diffusion rate is the same for the 60,000 and 100,000 molecular weight HPC specimens, if the diffusivities are referenced to the spinodal temperature. 

Figure 3 Acid leaches of ground granitoid samples from the Sierra Nevada, Cahfomia, show three stages of accessory phase dissolution. The initial leach (Ci, Di) is a mixture of major and accessory phases. The successive leaches show first an increasing influence of monazite and/or allanite dissolution (C1-C4, D1-D3), followed by an increase in the importance of sphene and apatite (C4-C6, D3-D4), and finally the depletion of accessory phases and the evolution of the leach composition to a value closer to that of plagioclase (Ce-Cn, D4-D9). Also plotted are the average and ° Ph/ ° Pb values of whole rock (WR) and mineral separates from the literature (TD = total...

Field and laboratory observations are consistent with the idea that dissolution in carbonate sediments can proceed faster than precipitation, and that the pore waters reach steady-state lAPs close to those of the most unstable phase (dissolution processes will be discussed later in... 

Air Atmosphere, unsaturated zone gas Water Solid phases Dissolution Sorption... 

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