Particle segregation

In particle segregation, particulate solids and also quasi solids, such as foams tend to segregate by virtue of differences in the size, and also physical properties such as volume, density, shape and other properties of particles of which they are composed.[1] The process of segregation occurs during as well as during subsequent handling of completed mix and it is pronounced with free-flowing powders. Powders that are not free flowing or that exhibit high forces of cohesion or adhesion between particles of similar or dissimilar composition are often difficult to mix owing to agglomeration. The clumps of particles can be broken down in such cases by the use of mixtures that generate high shear forces or that subject the powder to impact. When these powders have been mixed, however, they are less susceptible to segregation because of the relatively high interparticulates forces that resist interparticulate motion, leading to unmixing.

Particles segregation is commonly called "demixing" in industrial environment.

Segregation mechanisms

The five major segregation mechanisms [2] are

  • Percolation segregation
  • Flotation segregation
  • Elutriation
  • Transport segregation
  • Agglomeration segregation

Percolation

Sifting occurs when there is a significant variation of particle diameter in a mix. Interparticle motion causes the finer particles to sift through the coarser ones.

Flotation

Vibration of the mixture is bringing the small particles below the coarse one, which has as an effect to have coarse particles closer to the surface of the mixture.

Elutriation

In this mechanism, the lighter or fluffier particles form a 'fluidized' layer. Only coarser particles can penetrate the fluidized fines and the finer particles remain in the top layer.

Transport

The finer particles in a mix are susceptible to be airborne in the presence of airflow. They move away from the deposition point whereas the coarser particles tend to remain close to the deposition point.

Agglomeration

It can happen that some components form lumps. Those lumps will create non homogeneity in the mix since locally they will concentrate a lot of material of one case.

References

  1. ↑ Khan Ahmad;Smalley,I.J. 1973. Observation of particle segregation in vibrated granular systems. Powder Technology 8, 69-74
  2. ↑ https://www.powderprocess.net/Segregation_demixing.html
This article is issued from Wikipedia. The text is licensed under Creative Commons - Attribution - Sharealike. Additional terms may apply for the media files.