Preparation and Deposition of Particles on Surface

Many different methods are used on a broad scale to obtain spherical particles with sizes of 0.2-100 /urn from steel, polystyrene, vulcanized and unvulcanized rubber, plastics, mercury, animal and vegetable waxes, paraffin wax, and other materials. 

A monodisperse fraction of fused particles may be segregated by simple screening or by separation processes in water or air. Fractionation of a powder by means of adhesion can hardly be regarded as applicable, because of the indeterminacy of the adhesive forces, even for monodisperse particles under indentical conditions [103]. 

A vibratory separation method has been used to obtain monodisperse powder fractions [104]. This technique is based on the principle of particle separation into fractions under the influence of vibration of the working surface, which is inclined at a certain angle. As a result of vibrations of the inclined surface, the fine particles shift toward the upper part of the surface, and the coarse particles to the lower part, thus achieving separation of the particles into fractions. 

Polydisperse powders can be separated into fractions in this vibroseparator, for example into fractions 5, 5-10,10-20, and 20-30 jum. The productive capacity this apparatus depends on the particle size distribution of the powder being separated. In separating 1 kg of powder consisting of particles with diam- 

The vibroseparation principle can be used to separate particles of different shapes [105]. Irregularly shaped particles adhere to the vibrating surface, whereas spherical particles, at certain frequencies and with certain angles of surface inclination, will move upward, overcoming the force of gravity. Various materials have been used as surfaces to which irregularly shaped particles will adhere here we may mention cellulose acetate, epoxy and phenolic resins, polyvinyl fluoride, and polystyrene. 

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