Dispersion Analysis

Dispersion Analysis

 

in chemistry, the aggregate of methods for the determination of dispersity (the particle size characteristics in disperse systems). Dispersion analysis includes various methods of determining the sizes of free particles in liquid and gaseous mediums, the channel or pore sizes in finely porous bodies (in this case the concept of porosity is used instead of the concept of dispersity), and the specific surface. Some methods of dispersion analysis make possible the development of a complete particle (pore) distribution pattern according to the size (volume); others provide only the average characteristics of the dispersity (porosity).

The first group of methods includes, for example, those for determining the size of individual particles by direct measurements (sieve analysis; optical and electron microscopy) or by using indirect measurements, such as the sedimentation rates in viscous mediums (sedimentation analysis in a gravitational field and in centrifuges), or the magnitude of the electrical current pulses generated during the passage of particles through an opening in a nonconducting membrane (the conduction-measurement method).

The second group of methods combines an estimate of the mean diameters of free particles with the determination of the specific surface of powders and porous bodies. The mean diameter of particles is determined from the intensity of scattered light (nephelometry), by using an ultramicroscope, and by diffusion methods. The specific surface is determined by the adsorption of gases (vapors) or dissolved materials, from the gas permeability, or from the solution rates. The limits of applicability of the various methods of dispersion analysis are given in Table 1 (particle sizes in m).

Table 1. Limits of applicability of methods of dispersion analysis
Type of analysisParticle size (m)
Sieve ...............10−2-10−4
Sedimentation (in a gravitational field) ...............10−4-10−6
Conduction-measurement ...............10−4-10−6
Microscopy ...............10−4-10−7
Filtration method ...............10−5-10−7
Centrifuging ...............10−6-10−8
Ultracentrifuging ...............10−7-10−9
Ultramicroscopy ...............10−7-10−8
Nephelometry ...............10−7-10−8
Electron microscopy ...............10−7-10−8
Diffusion method ...............10−7-10−10

Dispersion analysis is being widely used in various areas of science and industry for estimating the dispersity of systems (suspensions, emulsions, sols, powders, adsorbents, and other materials) having particle sizes from several millimeters (10−3 m) to several nanometers (10−9 m).

REFERENCES

Figurovskii, N. A. Sedimentometricheskii analiz. Moscow-Leningrad, 1948.
Khodakov, G. S. Osnovye metody dispersionnogo analiza poroshkov. Moscow, 1968.
Kouzov, P. A. Osnovy analiza dispersnogo sostava pylei i izmel’chennykh materialov. Leningrad, 1971.
Rabinovich, F. M. Konduktometricheskii metod dispersionnogo analiza. Leningrad, 1970.
Irani, R. R., and C. F. Callis. Particle Size, Measurement, Interpretation, and Application. New York-London, 1963.
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