Fractionation of precipitation

In a first series of experiments, we have studied the phase separation of a same composition (Ca and c constant), for varying pH. The fraction of precipitated polymer was determined by... 

Figure 11.27. Calculated mole fraction of precipitated carbides vs penetration depth for a Ni-30Cr (wt%) alloy after carbonization at 850°C for 1000 h (Engstrom et al. (1994).

Table I. Antioxidative effect and amount of material in each fraction after fractionation of precipitate by paper electrophoresis.

Here, da/di)sy and (da/dt)py are the rates of crack growth associated with the secondary and primary precipitates, and the areal fraction of precipitates is assumed to be equal to the volume fraction, and is the volume fraction of y at the onset of coarsening (or the transformation from secondary to primary precipitates). Alternatively, the area fraction may be taken to be equal to the 2/3-power of the volume fraction. The possible dependence of sustained-load crack growth rates on y volume fraction, in oxygen at = 50 MPa-m, is shown in Fig. 8.34 [37, 38]. The volume fraction of y precipitates in Waspaloy and the associated trend hne for crack growth rates are estimates, whereas those at the higher volume fractions are supported by data [37,38],... 

Equilibrium isotopic-fractionation factors for O and D during evaporation and condensation are temperature-dependent, but the main control on degree of fractionation of precipitation 0 and D from the source composition is the fraction of water extracted from an air mass before condensation of the precipitation of interest (e.g. Dansgaard 1964). This in turn is controlled primarily by the difference between the temperature at which condensation first begins for an air mass, and the temperature at which the precipitation of interest condenses. The first-condensation temperature in turn is tied closely to the ocean surface temperature by the high and more-or-less constant relative humidities over most ocean surfaces (Vimeux et al. 2001). Hence, and 5D of precipitation depend in part on the temperatures at all contributing moisture sources, and not just on the temperature at the site. 

Table 9. Influence of pH on Surface Activity G and the Fraction of Precipitated Polyam-...

Figure 10 Fraction of precipitated B6 asphaltenes as a function of toluene content (v/v) in heptane. Experiments were performed gravimetrically by weighing the % of precipitated asphaltenes which were retained by a 1.6- xm filter.

Davies CKL, Nash P, Stevens RN (1980) Effect of volume fraction of precipitate on Ostwald ripening. Acta Metall 28 179-189... 

There are two main candidate models which describe the effect of the solute clusters on hardness. The modulus hardening model by Russell and Brown" has been successfully employed for many years to link microstructural and mechanical properties. It predicts very little effect of particle size on hardening at a given volume fraction of precipitates, when particle diameters are in the range 2-4 nm. A more modern model based... 

The precipitate hardening efficiency iOyp/fp) vs fp for solute cluster hardening within the IVAR database, compared with trends derived from the Russell-Brown (RB) and Bacon and Osetsky (B-O) models. o ,p, irradiation-induced yield stress increment associated with precipitation fp, volume fraction of precipitates fp, average precipitate radius derived from SANS measurements. 

Application of TT to evaluate. MWD means to correctly solve two reverse problems. The first, optical problem consists in calculating a precipitation curve x - x( j) from the meausiired properties of scattered light the second, thermodynamic problem must provide a means of converting this curve x - 2(7) into the corresponding. VfWD function (7 is the volume fraction of precipitant in the system). 

Under compression, the collapsc-swclling transition occurs at a lower precipitant content (dioxane and methanol), but these data can hardly be compared with Figure 3.56, as the transition from the volume fraction of precipitant to x, n to be diflicult... 

Despite the idealized and restrictive set of assumptions, the LSW theory provides a remarkably successful description of many coarsening observations. However, for diffusion-controlled coarsening, it is often found that real systems exhibit a broader and more symmetric steady-state distribution. Furthermore, while the average precipitate size is usually observed to increase qualitatively with the predicted dependence, the rate constant is generally found to be different from that predicted by the LSW theory. For purely reaction-controlled coarsening where the mechanism is strictly a surface phenomenon, the process should be independent of the volume fraction of precipitates as long as the precipitates do not touch. On the other hand, for diffusion control, the interaction of the diffusion fields of the precipitates must be taken into account, and there have been several attempts to incorporate volume fraction effects into the LSW theory (7). 

Differential Scanning Calorimetry (DSC) has become a convenient and widely used tool for studying the kinetics of phase transformations. The volume fraction (x) of the sample transformed in crystalline phase during the crystallization event has been obtained from the DSC curve as a function of temperature (T). The volume fraction of precipitated crystal can be obtained from the DSC curve by using... 

There, the volume fraction of precipitates /v is used, which is equivalent to the concentration c of the solid solution. 

At the beginning of the addition of silver nitrate, a colloidal precipitate of halide chloride forms. This first fraction of precipitate tends to preferentially adsorb bromide ions (for example) and not the anionic anions A of the indicator. This phenomenon occurs until the silver ions are completely exhausted. 

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