Dissolution/re-precipitation

Catalyst evolution. As stated above, the reaction is accompanied by a Pd dissolution/re-precipitation process (16.) This catalyst evolution is also reflected by Transmission Electron Microscopy (TEM) investigations of catalyst 3W before and after die reaction (Figure 3.)... 

Ostwald ripening Ageing evolution of particles in a liquid by dissolution re-precipitation,... 

Crystalline CPs have long degradation time in vivo, typically on the order of months or even years [13]. The degradation follows a dissolution-re-precipitation mechanism... 

The radiochemical assays were done as follows At the end of a polymerisation experiment, when the conductivity had become constant, a ten-fold excess of tritiated water was added from a burette (see Figure 1), the cell was warmed rapidly to room temperature, and any polymer which had been precipitated during the polymerisation was allowed to re-dissolve. It was always noted that no hydrolysis occurred until the solutions reached 0 °C. This could be seen from a rapid drop of conductivity to a very low value. The solvent and most of the tritiated water were then distilled out, within about 15 minutes. The polymer was then dissolved in toluene, also run from a burette into the reaction vessel, which was then cut from the vacuum line. The polymer was precipitated in methanol and prepared for the determinations of radioactivity and DP. For the radiochemical assay the polymers were dissolved in toluene, re-precipitated in methanol, dried, weighed, re-dissolved in toluene, and the activity determined. The processes of precipitation and dissolution were repeated until the activity of the polymer became constant, (up to 7 repetitions). It was assumed that when the activity had become constant, all the excess of tritium had been removed. 

Figure 12. Extent of dissolution and re-precipitation between aqueous Fe(III) and hematite at 98°C calculated using Fe-enriched tracers. A. Percent Fe exchanged (F values) as calculated for the two enriched- Fe tracer experiments in parts B and C. Large diamonds reflect F values calculated from isotopic compositions of the solution. Small circles reflect F values calculated from isotopic compositions of hematite, which have larger errors due to the relatively small shifts in isotopic composition of the solid (see parts B and C). Curves show third-order rate laws that are fit to the data from the solutions. B. Tracer experiment using Fe-enriched hematite, and isotopically normal Fe(lll). C. Identical experiment as in part B, except that solution Fe(lll) is enriched in Te, and initial hematite had normal isotope compositions. Data from Skulan et al. (2002).

Figure 7. Measured and corrected A Fe Fe(ni)-Hem.tite values ( and O, respectively) relative to average hematite precipitation rate for Experiments 5, 7, and 8 of Skulan et al. (2002). The A Fe jj(ni).Hem.tite values are defined as those measured at the termination of the experiments the corrected A Fe i,e(ni).Hem.tite values reflect the estimated correction required to remove any residual kinetic isotope fractionation that was produced early in experiments that was not completely removed hy dissolution and re-precipitation over the long term. Extrapolation of the corrected A Fe jj(ni).Hem.tite values to zero precipitation rates yields an estimate for the equilihrium Fe(III),q-hematite fractionation, A Fci,e(in).hem.tite,...

Bolton EW, Lasaga AC, Rye DM (1996) A model for the kinetic control of quartz dissolution and precipitation in porous media flow with spatially variable permeability Eormulation and examples of thermal convection. J Geophys Res 101 22,157-22,187 Bolton EW, Lasaga AC, Rye DM (1997) Dissolution and precipitation via forced-flux injection in the porous medium with spatially variable permeability Kinetic control in two dimensions. J Geophys Res 102 12,159-12,172... 

In the wetted condition, hydrothermal transformations of the waste form may occur at the temperature of service. Changes may occur either by dissolution and re-precipitation or by assimilation of water into the internal structures of the oxide matrices. The thermochemical essentials for hydrothermal recrystallisation have already been referred to previously in this paper. We also need to develop an adequate knowledge of the water-catalysed structural transformations. 

Subdivision (dispersion) is also common in geologic systems. In this case dispersion involves weathering of parent rock (physical disintegration and/or chemical dissolution with re-precipitation) followed by suspension of the particles in liquid. The physical disintegration can be caused by a range of events [49] ... 

E) Dissolution (physical or chemical) of the solid and its re-precipitation. All these situations have been encountered in the literature and several... 

Figure 2 presents some SEM pictures taken directly from suspensions of the fluffy precipitate of [Pt(NH3)4](HC03)2 in ethanol before addition of TEOS and representing the formation process of the templating Pt-salt nanofibers. Figure 2a shows the salt as it was received from the supplier. The micrograph 2b was taken after dissolution of the salt in water and re-precipitation with ethanol and, finally, micrograph 2c after the addition of TEOS and calcination. 

Apatites must undergo a solid-state transition to amorphous calcium phosphate before they can dissolve and the spontaneous replacement of hydroxide with fluoride ions slows the rate at which this transition occurs (Fig. 16.6b). Conversely, as an acid environment becomes more alkaline, fluoride ions promote the precipitation and crystallization of amorphous calcium monohydrogen phosphate/calcium fluoride into fluoro- and difluoro-apatites faster than amorphous calcium phosphate would crystallize into hydroxyapatite. Thus, fluoride ions have two effects on enamel that protect from caries they slow enamel dissolution in lactic acid and promote its re-precipitation and crystallization when the lactic acid is neutralized. 

The polystyrene is isolated by removing the solvent on the rotary evaporator, dissolving the polymer in the minimum volume of dichloromethane, and then pouring this solution into a beaker containing aqueous methanol (1 4, ca. 10 X volume). Further purification is achieved by repeated dissolution in dichloromethane, followed by re-precipitation into methanol finally, the white solid is dried in a vacuum oven at 60°C. 

When carbonate cements are subjected to physicochemical conditions that vary considerably from those under which they formed, they may dissolve and re-precipitate at various scales. Carbonate dissolution and the creation of secondary porosity may occur during eodiagenesis or telodiagenesis or in response to progressive burial. Eogenetic secondary pores may survive subsequent burial and compaction in sandstones that have been subjected to early overpressuring or hydrocarbon emplacement, or if dissolution is incomplete, and leave evenly distributed remnants of carbonate cement. 

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