Particle size powder segregation

Another technique is to change the particle size distribution. There are, however, disadvantages. If segregation is occurring by the sifting mechanism, the particles must be almost identical in size before sifting is prevented. Alternatively, the mean particle size can be reduced below 100 p.m, but this size reduction (qv) increases the probabiUty of segregation by the too fine powder mechanisms. 

Segregation can take place whenever forces are applied to the powder, for example by way of gravity, vibration, or air flow. These forces act differently on particles with different physical characteristics, such as particle size, shape, and density. Most commonly, particles separate as a result of particle size differences. The result of segregation is that particles with different characteristics end up in different zones within the processing equipment (e.g., bin). 

Mixtures of powders of poly(vinyl chloride) (FVC) and various metals were compacted at a pressure of 10,000 psig at 120-130°C. The compacts appear to be strong, and density measurements show the porosity to be <1.5%, Electrical resistivity is reduced, from a value for unloaded FVC of about JO25 Clem, to < JO"1 Clem by a fractional volume loading of nickel or copper as low as 0.06. Microscopic examination of polished sections of the compacts show the metallic particles to be segregated around zones of unpenetrated polymer which correspond in size to the initial particles of FVC. The pattern of segregation favors the formation of continuous chains of metallic particles at unusually low volume loadings. 

Does extensive blending cause demixing and segregation of components This is important, especially if particle size/density of the powder/granula-tion vary widely. 

When manufacturing a tablet formulation by direct compression, the particle size and size distribution of excipients have a significant impact on blending homogeneity, powder segregation, and flowability. This can result in unacceptable content uniformity and high tablet weight variation. In such situations, control of excipients can be critical to product quality. 

Fluidization Segregation. In order for fluidization segregation to occur, particles in a blend must have different particle sizes and/or a broad particle size distribution as well as different particle densities. This type of segregation may occur when a bulk powder or blend is pneumatically conveyed, filled or discharged at high rates, or if... 

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