Particle size of precipitates

The particle size of precipitated potassium heptafluorotantalate is one of the more important parameters. In order to achieve a certain particle size, potassium salts are added to the hot tantalum strip solution as a hot solution. The mixture is cooled down at a specific rate in order to enable the precipitation and ciystallization of K-salt in the form of small, individual crystals. 

Therefore, the scope of this chapter is to describe the results obtained using SAS with particular emphasis on the production of particles with controlled PS and PSD in the micrometric as well as in the nanometric range. We will try to understand the role of high pressure vapor-liquid equilibria (VLEs) in determining the morphology and particle size of precipitates. 

Factors That Determine the Particle Size of Precipitates The particle size of solids formed by precipitation varies enormously. At one extreme are colloidal suspensions, whose tiny particles are invisible to the naked eye (10 to 10 cm in diameter). Colloidal particles show no tendency to settle from solution and are not easily filtered. At the other extreme are particles with dimensions on the order of tenths of a millimeter or greater. The temporary dispersion of such particles in the liquid phase is called a crystalline suspension. The particles of a crystalline suspension tend to settle spontaneously and are easily filtered. 

Von Weimam discovered that the particle size of precipitates is inversely proportional to the relative supersaturation of the solution during the precipitation process ... 

DS Halverson. Precipitation from supercritical fluids effects of process conditions on the morphology and particle size of precipitation products. MS thesis, Princeton University, Princeton, NJ, 1989. 

Thus, at a concentration of 0.95 g Na2S /100 g solution, the solubihty of mercuric sulfide has increased to 2100 ppm. It is customary to use no greater than a 20% excess of the alkah sulfide. Because the particle size of the precipitated mercuric sulfide is so small, it is helpful to add a ferric compound such as ferric chloride or ferric sulfate to effect flocculation. Sometimes other flocculating agents (qv) may also be added, eg, starch or gum arabic. 

Polymer Solvent. Sulfolane is a solvent for a variety of polymers, including polyacrylonitrile (PAN), poly(vinyhdene cyanide), poly(vinyl chloride) (PVC), poly(vinyl fluoride), and polysulfones (124—129). Sulfolane solutions of PAN, poly(vinyhdene cyanide), and PVC have been patented for fiber-spinning processes, in which the relatively low solution viscosity, good thermal stabiUty, and comparatively low solvent toxicity of sulfolane are advantageous. Powdered perfluorocarbon copolymers bearing sulfo or carboxy groups have been prepared by precipitation from sulfolane solution with toluene at temperatures below 300°C. Particle sizes of 0.5—100 p.m result. 

The color obtained is a function of both the composition and the particle size of the precipitated crystals. A redder color results from both increased selenium to sulfur ratio and from larger crystals, caused by a more severe heat treatment. Hence, it is possible to make, from the same glass, a series of color filter types, by controlled reheating. 

Settling and rainout are important mechanisms of contaminant transfer from the atmospheric media to both surface soils and surface waters. Rates of contaminant transfer caused by these mechanisms are difficult to assess qualitatively however, they increase with increasing soil adsorption coefficients, solubility (for particulate contaminants or those adsorbed to particles), particle size, and precipitation frequency. 

In addition to the possibility of controlling the particle size of the hydroxides, application of ammonium carbonate affords several other advantages compared to traditional precipitation of hydroxides using ammonia solution. First, ammonium carbonate does not increase the total volume of the solution as much as does the addition of ammonia. Second, the method enables to perform the interaction so as to precipitate stoichiometric mixtures, which... 

These results indicated that the particle size of a precipitate decreases with increasing concentration of the reactants. For the production of a crystalline... 

In addition it should be added that microdisperse forms of CP can precipitate proteins from solutions. Figs. 21-23 show that CP microdispersions with particle size of 1-2 pm precipitate serum albumin from solutions [81] in complete agreement with general flocculation laws for polyelectrolytes. The figs, show an extreme... 

Methods of dust removal depend mainly on the particle size of the dust and the temperature and moisture content of the gas. The methods used are broadly divided into dry methods and wet methods. The dry methods involve the use of gravity and baffle chambers, cyclones, filters, and electrostatic precipitators, while the wet methods involve the use of spray towers and venturi scrubbers. In principle, wet cleaning is preferred to dry cleaning because of the excessive wear associated with and the difficulty in handling the fine dusty material removed in the dry methods. The wet methods, however, must be followed by such operations as filtration, drying of filter cakes, and recycling of water. 

The release rate and therefore the duration of action of injectable insulin, in the form of insulin zinc, is controlled by its crystallinity coupled with its particle size. The crystallinity and particle size of insulin zinc, which is precipitated as an insoluble complex when insulin is reacted with zinc chloride, is controlled by the pH. The amorphous complex of small particle size, Prompt Insulin Zinc Suspension USP, is rapidly absorbed and has a relatively short duration of action. In contrast, the crystalline complex of large particle size, Extended Insulin Zinc Suspension USP, is slowly absorbed and has a relatively long duration of action. The intermediate form, Insulin Zinc Suspension USP, consists of seven parts of the crystalline form to three parts of the amorphous form and has an intermediate rate of absorption and duration of action. 

Microstructures of CLs vary depending on applicable solvenf, particle sizes of primary carbon powders, ionomer cluster size, temperafure, wetting properties of carbon materials, and composition of the CL ink. These factors determine the complex interactions between Pt/carbon particles, ionomer molecules, and solvent molecules, which control the catalyst layer formation process. The choice of a dispersion medium determines whefher fhe ionomer is to be found in solubilized, colloidal, or precipitated forms. This influences fhe microsfrucfure and fhe pore size disfribution of the CL. i It is vital to understand the conditions under which the ionomer is able to penetrate into primary pores inside agglomerates. Another challenge is to characterize the structure of the ionomer phase in the secondary void spaces between agglomerates and obtain the effective proton conductivity of the layer. 

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