Particle size redistribution

The particle-size and size-distribution of solid materials produced in industrial processes are not usually those desired for subsequent use of these materials and, as a result comminution and recrystallization operations are carried out. Well known processes for particle size redistribution are crushing and grinding (which for some compounds are carried out at cryogenic temperatures), air micronization, sublimation, and recrystallization from solution. There are several practical problems associated with the above-mentioned processes. Some substances are unstable under conventional milling conditions, and in recrystallization processes the product is contaminated with solvent, and waste solvent streams are produced. Applying supercritical fluids may overcome the drawbacks of conventional processes. 

Through the choice of the appropriate combination of solvent and operating conditions for a particular compound, PGSS can eliminate some of the disadvantages of traditional methods of particle-size redistribution in material processing. Solids formation by PGSS therefore shows potential for the production of crystalline and amorphous powders with a narrow and controllable size-distribution, thin films, and mixtures of amorphous materials. 

The difference between sintered plate cells and pocket-type cells with regard to memory may be connected with the fact that pocket cadmium active material contains an addition of finely divided iron compounds. This addition is made to prolong life by preventing recrystallization and agglomeration of cadmium particles. It seems probable that the iron addition will not only prevent the normal tendency for crystal growth of the cadmium material, but will also eliminate the particle size redistribution that causes the memory effect. 

Where the waves and currents weaken, resuspended sediment settles back down to the seafloor. Given the small particle sizes of the suspended material (mostly 3 to 10 pm), redeposition can take many years. The resulting redistribution of sediments creates patches of clay, mud, and exposed rock on the continental margins. In other words, resuspension from waves and currents can cause some sediments to become reUct deposits. Hard bottoms can serve as good habitats for some members of the benthos as they promote the formation of coral reefs. For paleoceanographers, relict deposits are problematic because they represent gaps, or imconformities, in the sedimentary record. 

Reclamation of cured poly sulfide-perchlorate proplnts The waste cured proplnt is reduced to a small particle size by passing it thru a lab mill. It is then added to the extent of 20% of the total mixt to a normal mixt of proplnt. The waste proplnt re-liquefies to its precured state in the mixer by means of a molecular wt redistribution between the low raw liq polymer and the high mw solid polymer. The reaction is complete in about 10 mins 21... 

As the previous section showed, in a variety of examples severe enhancements of the ionic conductivity has been found and successfully attributed to space charge effects. Typical examples are silver halides or alkaline earth fluorides (see Section V.2.). How significantly these effects can be augmented by a particle size reduction, is demonstrated by the example of nano-crystalline CaF2.154 Epitaxial fluoride heterolayers prepared by molecular beam epitaxy not only show the thermodynamically demanded redistribution effect postulated above (see Section V.2.), they also highlight the mesoscopic situation in extremely thin films in which the electroneutral bulk has disappeared and an artificial ion conductor has been achieved (see Fig. 

While providing a simple method for analyzing the redistribution of energy in the combustion wave, the models discussed in the previous section do not account for the local structural features of the reaction medium. Microstructural models account for details such as reactant particle size and distribution, product layer thickness, etc., and correlate them with the characteristics of combustion (e.g., U,T,). 

This mechanism is similar to that of a deep-bed filtration process with some differences (12). In the filtration process the particle-size to pore-size ratio is small, and the particles are mostly captured on the media surface. Thus interceptive capture dominates, and this capture does not alter the flow distribution in the porous medium. Permeability reduction is not significant and is ignored. On the other hand, the emulsion droplet size is generally of the same order of the pore size, and the droplets are captured both by straining and interception. This capture blocks pores and results in flow redistribution and a reduced permeability. 

Alpha particles from plutonium cannot penetrate the epidermis, so toxicity is limited to conditions where the substance is present within the body. The primary routes of entry are inhalation, ingestion, or through wounds, cuts, or abrasions. The potential for adverse health effects caused by plutonium isotopes depends on the route of entry and subsequent deposition, redistribution, and retention, which in turn is highly influenced by the physical (e.g., particle size) and chemical forms of the isotope. 

Searcy and Benito [36] explain how, in crystalline solids, the minimization of particle free energy may be achieved through redistribution of vacancies. Because the vacancy concentration decreases as the particle size decreases, the vapour pressures of small crystals increase. 

In a photoinitiated system, in whTcF the reaction proceedes rapidly during exposure (resulting in relatively short gel times), it is thought that the epoxy matrix is set up during the initial irradiation thus influences the final morphology. The final particle size and distribution would then be dictated by the compatibility of the components in the uncured state since the rapid formation of the gel would be expected to preclude the redistribution of the phases. 

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