Precipitation in-situ

The in situ precipitation route towards obtaining composites of polymer and calcium phosphate is similar to the strategy employed in naturally occurring biocomposites and well may prove a viable method for the synthesis of bone substitutes. 

In situ precipitation of gold nanoparticles onto glass for potential architectural applications. Chemistry of Materials, 16, 2259-2266. 

In situ precipitation technique Reduces the concentration of the scale-forming ingredients [858,859]... 

M. J. Hrachovy. Hydraulic fracturing technique employing in situ precipitation. Patent WO 9406998, 1994. 

In part II of the present report the nature and molecular characteristics of asphaltene and wax deposits from petroleum crudes are discussed. The field experiences with asphaltene and wax deposition and their related problems are discussed in part III. In order to predict the phenomena of asphaltene deposition one has to consider the use of the molecular thermodynamics of fluid phase equilibria and the theory of colloidal suspensions. In part IV of this report predictive approaches of the behavior of reservoir fluids and asphaltene depositions are reviewed from a fundamental point of view. This includes correlation and prediction of the effects of temperature, pressure, composition and flow characteristics of the miscible gas and crude on (i) Onset of asphaltene deposition (ii) Mechanism of asphaltene flocculation. The in situ precipitation and flocculation of asphaltene is expected to be quite different from the controlled laboratory experiments. This is primarily due to the multiphase flow through the reservoir porous media, streaming potential effects in pipes and conduits, and the interactions of the precipitates and the other in situ material presnet. In part V of the present report the conclusions are stated and the requirements for the development of successful predictive models for the asphaltene deposition and flocculation are discussed. 

The tendency of gold(III) chlorocomplexes to adsorb on iron (hydrous) oxides that tend to form via in situ precipitation in acidic pressure leaching operations needs to be controlled to avoid undesirable metal losses. 

PDMS nanocomposites with layered mica-type silicates were also reported.374 A two-step sol-gel process of the in situ precipitation of silica led to the development of siloxane-based nanocomposites with particularly high transparencies.3 5 Some unusual nanocomposites prepared by threading polymer chains through zeolites, mesoporous silica, or silica nanotubes were reviewed.3 6 Poly(4-vinylpyridine) nanocross-linked by octa(propylglycidyl ether) polyhedral oligomeric silsesquioxane was reported.377... 

Some basinal evaporites appear to have been deposited by turbidity currents as shown in Figure 17.10c. In this mode of formation, salts originally deposited in shallow waters are transported into the basin by turbidity currents. These salts fill in the basin. The decline in water depth then promotes in situ precipitation of evaporites. Subsidence would have kept the basin floor below the sill. 

A. In-situ precipitation of Py catalyst into Nafion membrane... 

Figure 5 In situ precipitation. (Courtesy of Eastman Kodak Co., NY.)...

In situ precipitation Chemical immobilization Use of wastewater precipitation techniques applied directly to the soil in place... 

In situ precipitation by vapor phase application Chemical immobilization ... 

A number of experiments are possible which will add final clarification to questions concerning the details of the mechanism. Modem column chromatographic methods can be used to evaluate the role of the adsorbent. In a column, no solvent concentration profile exists, and there are at least two papers which indicate adsorption separations can be successful (22, 23). More extensive work is necessary to characterize the solvent concentration profile to improve the quantitative agreement between bulk precipitation concentrations and in situ precipitations in TLC. 

Iron and manganese oxides are characterized by high specific surface areas and high affinity of their surface hydroxyl groups for adsorption of a variety of trace elements. In addition to adsorption processes, oxidation reactions are catalyzed by these surfaces (18-20). The in situ precipitation and dissolution of these oxides are thus significant for the fate of various trace... 

Figure 8.1 Transmission electron micrograph of a PDMS network containing 34.4 wt % in situ precipitated silica particles.25 The average particle diameter is 150 A. Reproduced by permission of John Wiley and Sons.

Figure 8.6 Effect of cyclic stress on unfilled PDMS and PDMS elastomers filled with in situ precipitated silica (A) unfilled, ( ) 12.0 or 19.4 wt % silica.43...

Figure 8.7 Comparison of thermogravometric plots for PDMS networks that were unfilled (U), or contained either in situ precipitated silica (A) or commercial fume silica (COMM-MO and COMM-AE).44 The heating of the samples was carried out under nitrogen.

Whang, J. M., Adu-Wusu, K., Frampton, W, H., Staib, J. G. (1997). In situ precipitation and sorption of arsenic from groundwater laboratory and ex situ field tests, Proceedings of the 1997 International Containment Technology Conference and Exhibition, St. Petersburg, FL, Feb. 9-12, 1997, 737-743. 

Recently it was demonstrated that the rate of oxidation can be increased by the introduction of surface under basic conditions [111]. This work has introduced a new catalyst concept that meets the above criteria for use under moderate SCWO conditions in a continuous tubular flow reactor. The concept involves -in situ precipitation of the catalyst (e.g., sodium carbonate) under SCWO conditions, but the catalyst is otherwise soluble under ambient conditions. -In situ precipitation is a unique way to generate a high-surface-area catalyst in the reaction zone, thereby ensuring maximum surface contact with the medium while minimizing catalyst poisoning. 

In situ precipitation also provides a method for preparing surfaces with uniform stoichiometry and purity, a small range of grain and particle diameters, and minimum excess surface energy. These properties should maximize catalyzed rates and minimize differences between experiments caused by nonuniformity of mixing and contact between solution and surface [112]. 

Figure 16.23. Proton image of the polymer in a crosslinked silicone polymeric block that contains in situ precipitated silica filler.

Fine structure is significantly changed under mechanical activation. Fig. 6.41 shows that steady densification took place on the sample of in situ precipitation during grinding... 

Thus, densification of ITO ceramics starting from the in situ precipitation of the stannic components during grinding in an aqueons milieu is based on the formation of co-precipitated complex hydrogels around the surface of the particles due to dissolution-reprecipitation. This results in the decrease in the width of the channel for SnO effusion, and hence, the vaporization of Sn02 in the form of SnO (g). 

Studies using TEM and in situ precipitation to follow the pathway of topically applied compounds have focused on distinguishing between the intracellular and intercellular routes of transport of substances across the SC. In 1968, Silberberg [24] first used this technique to provide evidence that mercury, after topical application of 0.1% aqueous mercuric chloride, traverses across the SC in vitro via the intercellular spaces. But difficulties with fixation and processing prevented demonstration that the mercury aggregates were also present in the SC cells. Thus, the possibility that mercury may also have taken a transcellular route through the SC could not be excluded. 

Figure 2 Electron micrograph of human stratum comeum after in situ precipitation of butanol (for 2 hr) following osmium vapor treatment. The authors found an irregular pattern of deposits throughout the intercellular spaces of the stratum comeum. The magnification is 45,600x. (Reproduced with permission from Ref. 26.)...

The in situ precipitation technique and transmission electron microscopy have been used to investigate the effect of DMSO on percutaneous absorption in the mouse barrier [27] and human SC [46]. Sharata and Burnette examined ultrastructural changes in mouse stratum comeum by determining the distribution of sulfide precipitates of topically applied, water-soluble tracers (Hg and Ni ) after application of enhancer [27]. For skin pretreated with DMSO, mercury and nickel precipitates were found within swollen basal stratum comeum cells as well as intercellularly and associated with the cell envelopes, but not below the stratum comeum-stratum granulosum interface. It was concluded that treatment with DMSO, as well as with other dipolar aprotic solvents such as DMF and DMA, alters the passive intercellular diffusion pathway by expanding the size of the basal stratum comeum cells, resulting in an increased free volume for tracer diffusion. 

---