Solubility of fine particles

The change in the free energy AG involved in subdividing a coarse solid suspended in aqueous solution into a finely divided one of molar surface S is given by 

1) can be derived (Schindler, 1967) from the thermodynamic statement that at constant temperature and pressure and assuming only one mean type of surface 

Because the surface and the volume of a single particle of given shape are s = kd2 and v = Id3, 

The specific surface effect can also be expressed by substituting S = Ma/pd where a is a geometric factor which depends on the shape of the crystals (a = k/l) (compare Fig. 6.5). 

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Solubility of Fine Particles 413 7.8 SOLUBILITY OF FINE PARTICLES... 

Eniistiin BW, Turkevitch J (1960) Solubility of fine particles of strontium sulfate. J Phys Chem 82 4503-4509... 

If a particle is small enough, the surface energy produces measurable effects on the observable properties of a substance. Two examples are the enhanced vapor pressure of small droplets and the increased solubility of fine particles. 

Eniistiin, B.V. and Turkevich, J. (1960) The solubility of fine particles of strontium sulphate. Journal of the American Chemical Society, 82, 4502-4509. 

Early efforts to produce synthetic mbber coupled bulk polymerization with subsequent emulsification (9). Problems controlling the heat generated during bulk polymerization led to the first attempts at emulsion polymerization. In emulsion polymerization hydrophobic monomers are added to water, emulsified by a surfactant into small particles, and polymerized using a water-soluble initiator. The result is a coUoidal suspension of fine particles,... 

The secondary source of fine particles in the atmosphere is gas-to-particle conversion processes, considered to be the more important source of particles contributing to atmospheric haze. In gas-to-particle conversion, gaseous molecules become transformed to liquid or solid particles. This phase transformation can occur by three processes absortion, nucleation, and condensation. Absorption is the process by which a gas goes into solution in a liquid phase. Absorption of a specific gas is dependent on the solubility of the gas in a particular liquid, e.g., SO2 in liquid H2O droplets. Nucleation and condensation are terms associated with aerosol dynamics. 

Soluble polymers are widely used to control the state of dispersion of fine-particle suspensions. Depending on the polymer, and how it is applied, they can serve to enhance stability (dispersants) or to promote aggregation of the particles (flocculants). The topics covered in this chapter are intended as an overview of the use of polymers for stability control in mineral-particle suspensions with particular emphasis on flocculation processes. A brief discussion of stabilisation by polymers is included for completeness. 

Controlled release. For practical use the active ingredient must be released. A drug must be delivered with well defined kinetics. Sometimes it is not the encapsulated ingredient that is released but a by-product. This is the case when the encapsulated product is an enzyme or a catalyst. Encapsulation may have the objective to limit release, but in some cases to make it more rapidly available. A typical example is an instant powder consisting of aggregates made of fine particles that are insoluble, in a very soluble matrix. 

You already know that soluble materials completely dissolve in a solvent to form a clear true solution , and the particles of the solute do not separate out from the solution. Also there are, in some situations, materials that form a suspension of fine particles of a solid in a liquid. These are not true solutions and given time the particles slowly separate out, for example, when earth is stirred with water the fine... 

Addition of a low viscosity hydrocarbon solvent often extracts the oil from the water the extract layer of solvent and solute separates from the water. The large amount of solvent needed to separate emulsions of water in a viscous heavy oil is uneconomic because of the dilute solution needed to obtain a continuous water phase. Addition of solvent, possibly up to an equal amount, is reasonable and is desirable to reduce the viscosity sufficiently to pump and transport the heavy oil. A cheap aliphatic solvent— e.g.9 kerosene—is preferable, but bituminous oil fractions are much more soluble in aromatic solvents, particularly at temperatures near the ambient. However, the water and solid particles are not at acceptable limits even after much dilution, especially in the presence of fine particles as in some crudes from California and Venezuela and particularly from tar sands as those in Athabasca (Alberta, Canada). 

Recent research on more coercive media with a low noise ratio involved addition of Zn to the Co alloy system [76-79]. Addition of Zn to the cobalt alloy very effectively produces a film with a fine particle structure, which results from codeposition of elements which are hardly soluble in the matrix. Such codeposition causes segregation and hence produces a film microstructure consisting of fine particles. The fine particulate structure lowers the noise ratio and increases the coercivity of the medium. 

This new product was called Skin Exposure Reduction Paste Against Chemical Warfare Agents (SERPACWA), SERPACWA consisted of fine particles of polytetrafluoroethylene (PTFE) solid dispersed in a fluorinated polyether. The excellent barrier properties of this polymer blend were related to the low solubility of most materials in it. SERPACWA is now a standard issue item to U.S. forces when there is a threat of CWA use. 

This expression is the familiar solubility product. This equilibrium constant does not contain a term for CaCOa (calcite). To the extent that the calcite is pure (does not contain dissolved impurities) and consists of particles large enough that surface effects are unimportant, this equilibrium does not depend on the "concentration" of calcite or particle size. Exceptions to this case are important in the formation of cloud droplets (where the particle size dependence is known as the Kelvin Effect) and in the solubility of finely divided solids. 

Modeling of the Slurry Oxidation. In 1969 Ramachandran and Sharma(18) first proposed a film model for gas absorption accompanied by a fast chemical reaction in a slurry containing sparingly soluble, fine particles. A first case assumed that the solid dissolution in the liquid film next to the gas-liquid interface was unimportant. The second case assumed that it was important. Numerical solutions were given for the second case which indicated hat the specific rate of absorption of gas in the presence of fine particles could be considerably higher than in the absence of solids. 

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