Solution precipitation technique

Figure 1. Scanning electron photograph of urea -formaldehyde re sin. This specimen was prepared by the dilute solution precipitate technique (7).

Effort in this unit operation includes comminution of powder blends and addition of yttria (4w%) in aqueous suspensions using a solution precipitation technique. The procedure for aqueous milling is being developed in a vibratory mill. After solution precipitation of yttria, the slurry is rinsed and concentrated to be used for colloidal consolidation or dried to powder for test tiles and injection molding. The powder is CIP ed into rectangular tiles and subsequently HIP ed to achieve near theoretical density. MOR bars, 3mm x 4mm x 50rnm,... 

For example, Li et al. [153] used a simple solution-precipitation technique to improve the dispersion of CNTs in a polycarbonate solution by sonication at a frequency of 20 kHz for 10 min. They showed that the CNTs were uniformly dispersed in polycarbonate matrix on its consolidation. Safadi et al. [154] dispersed MWNTs in PS using ultrasonication and dismembrator at 300 W for 30 min. Uniform dispersions of CNTs in PS were achieved by using sonication. Recently, Cho and coworkers successfully prepared polyurethane (PU)/MWNT composites with better dispersion of CNTs up to 20 wt% in PU [155]. 

The co-precipitation technique starts with an aqueous solution of nitrates, carbonates, chlorides, oxychlorides, etc., which is added to a pH-controlled solution of NH4OH, allowing the hydroxides to precipitate immediately. This method requires water-soluble precursors and insoluble hydroxides as a final product. The hydroxides are filtered and rinsed with water when chlorides are employed as starting materials and chlorine is not desired in the final product. After drying the filtrate, it is calcined and sintered. This method is being applied very successfully for oxygen-ion conducting zirconia ceramics [30],... 

Jha and Bhowmick [51] have reported the development and properties of thermoplastic elastomeric blends from poly(ethylene terephthalate) and ACM by solution-blending technique. For the preparation of the blend the two components, i.e., poly(ethylene terephthalate) and ACM, were dried first in vacuum oven. The ACM was dissolved in nitrobenzene solvent at room temperature with occasional stirring for about three days to obtain homogeneous solution. PET was dissolved in nitrobenzene at 160°C for 30 min and the rubber solution was then added to it with constant stirring. The mixture was stirred continuously at 160°C for about 30 min. The blend was then drip precipitated from cold petroleum ether with stirring. The ratio of the petroleum ether/nitrobenzene was kept at 7 1. The precipitated polymer was then filtered, washed with petroleum ether to remove nitrobenzene, and then dried at 100°C in vacuum. 

The solubility product (. sp) describes the equilibrium of a salt dissolving in water. In the laboratory and in industry, solubility equilibria are often exploited in the opposite direction. Two solutions are mixed to form a new solution in which the solubility product of one substance is exceeded. This salt precipitates and can be collected by filtration. Example illustrates how precipitation techniques can be used to remove toxic heavy metals from aqueous solutions. 

Four types of techniques for separating the bound fraction P Q from the reagent mixture are in common usage, loosely termed double antibody, solid phase, charcoal adsorption and solution precipitation. The first type is used with radioimmunoassay methods specifically, while the other three types can be used with both radioassay and radioimmunoassay methods. 

As presented by this paper, our aim was to describe some preliminary results demonstrating that amorphous manganese-oxide-based materials synthesised by means of precipitation technique from aqueous solutions could serve as effective cathodes in lithium batteries. 

In the RESS method, the solute of interest is solubilized in a supercritical fluid, which is then rapidly expanded through a nozzle. As the fluid expands, it loses its solvent capabilities and the solute precipitates out. While this technique has the advantage of not using any organic solvent, it is restricted by the generally poor solubility of most polymers in supercritical fluids. Indeed, polymers generally have to be below 10,000 MW in order to be eligible for this method of particle production [126]. 

Modifications of surface layers due to lattice substitution or adsorption of other ions present in solution may change the course of the reactions taking place at the solid/liquid interface even though the uptake may be undetectable by normal solution analytical techniques. Thus it has been shown by electrophoretic mobility measurements, (f>,7) that suspension of synthetic HAP in a solution saturated with respect to calcite displaces the isoelectric point almost 3 pH units to the value (pH = 10) found for calcite crystallites. In practice, therefore, the presence of "inert" ions may markedly influence the behavior of precipitated minerals with respect to their rates of crystallization, adsorption of foreign ions, and electrokinetic properties. 

The practical use of the desorption reaction requires a catalyst for the improvement of the kinetics. The first work on catalyzed alanates at MPI - Miilheim was derived from studies that used transition-metal catalysts for the preparation of MgH2- The NaAlH4 was doped with Ti by solution chemistry techniques whereby nonaqueous liquid solutions or suspensions of NaAlH4 and either TiCl3 or the alkoxide Ti(OBu )4 [titanium(IV) w-butoxide] catalyst precursors were decomposed to precipitate solid Ti-doped NaAlH4 [57, 58]. 

For mixed metal oxides obtained from their hydroxide or carbonate precursors after calcination, it is generally difficult to determine whether the as-prepared precursor is a single-phase or multiphase solid solution [35]. Non-aqueous solvents appear superior for achieving two dissimilar metal oxides such as MM Oz or MM 04 precipitates such reactions cannot be carried out simultaneously in aqueous solution due to the large variations in pH necessary to induce precipitations [41,42]. Table 6.1 summarizes some of the nanoparticulate semiconducting metal oxides and mixed metal oxides prepared via co-precipitation techniques. The general procedure of achieving metal loaded nanoparticles on an oxide support is shown in Fig.6.5. 

Alkali metal doping of Cjq is also possible by solution-phase techniques [1,118-121]. K CgQ and Rb CgQ containing small fractions of the superconducting M3C50 phases were prepared by allowing toluene solutions of Cjq to react with the alkali metal [118, 119]. During the reaction, the alkali metal fullerides form a black precipitate. In another example, sonication of a solution of Cjq and excess potassium in TMEDA yields K3C5q(THF)j4 with a defined stoichiometry [104],... 

For practical (real) catalyst systems, precipitation, ion exchange, impregnation and sol-gel processing procedures are used. In precipitation methods, a hydroxide or a carbonate of a metal may be precipitated from a solution of a metal salt onto the support material held in the solution. Thus, a copper-silica catalyst may be prepared using a Cu-nitrate solution in which silica is suspended. Additives of any alkali cause the precipitation of copper hydroxide onto the silica support. This is then dried and normally reduced in hydrogen at moderate temperatures ( 400-500 °C) to form the catalyst. In co-precipitation techniques , the support is precipitated simultaneously with the active catalyst. In the ion-exchange method, for example, highly dispersed Pt on... 

Free radical polymerization processes [41] are carried out in bulk, solution, suspension, emulsion, or by precipitation techniques. In all cases the monomer used should be free of solvent and inhibitor or else a long induction period will result. In some cases this may be overcome by adding excess initiator. 

Series B 11 g monomer / 3 g polymer / 0.25 millimole initiator 390min at 95° C. Selective precipitation technique from acetone solution by adding methanol (twice at y — 0.7). 

The most common protein precipitation technique involves the use of ammonium sulphate, which has been the subject of a recent review (3). The widespread use of ammonium sulfate can be ascribed to the fact that it is very soluble (saturated solutions have a concentration in the region of AM), the density of solutions do not compromise collection of precipitates by centrifugation and its use does not promote denaturation of proteins. The addition of ammonium sulfate will cause a neutralization of the surface charge of the protein and a decrease in the effective concentration of water leading to a decrease in protein solvent interactions. 

The theory behind such techniques is complex and not clearly understood, but the techniques themselves are straightforward. To say that an increase in protein-protein interactions leads to precipitation whereas protein-solvent interaction favors solubility is a simplistic but nonetheless useful paradigm. Precipitation techniques do not, by themselves, achieve a great increase in the purity of a protein solution, but generally they result in an increase in concentration and have a role to play in many protein purification protocols. 

Subject areas for the Series include solutions of electrolytes, liquid mixtures, chemical equilibria in solution, acid-base equilibria, vapour-liquid equilibria, liquid-liquid equilibria, solid-liquid equilibria, equilibria in analytical chemistry, dissolution of gases in liquids, dissolution and precipitation, solubility in cryogenic solvents, molten salt systems, solubility measurement techniques, solid solutions, reactions within the solid phase, ion transport reactions away from the interface (i.e. in homogeneous, bulk systems), liquid crystalline systems, solutions of macrocyclic compounds (including macrocyclic electrolytes), polymer systems, molecular dynamic simulations, structural chemistry of liquids and solutions, predictive techniques for properties of solutions, complex and multi-component solutions applications, of solution chemistry to materials and metallurgy (oxide solutions, alloys, mattes etc.), medical aspects of solubility, and environmental issues involving solution phenomena and homogeneous component phenomena. 

Perhaps the simplest solution-precipitation membrane preparation technique is thermal gelation, in which a film is cast from a hot, one-phase polymer/solvent solution. As the cast him cools, the polymer precipitates, and the solution separates into a polymer matrix phase containing dispersed pores filled with solvent. Because cooling is usually uniform throughout the cast film, the resulting membranes are relatively isotropic microporous structures with pores that can be controlled within 0.1-10 i m. 

Most anisotropic membranes are produced by solution precipitation, interfacial polymerization or solution coating. A number of other techniques developed in the laboratory are reviewed briefly below none are used on a large scale. 

From the above results it may be concluded that separation by the precipitation technique is effective if it is carried out in such manner so that poly-A and poly-A-B graft copolymers are coprecipitated and only poly-B is left in solution. If a -solvent which has widely different -temperatures is available for the two homopolymers, the modified precipitation technique is very advantageous because solution and precipitation of polymers can be done merely by raising and lowering the solution temperature. 

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