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Elzone Particle Size Analyzer Technique Overview

Effective Method for Sizing/Counting Organic and Inorganic Materials

Electrical Sensing Zone Method

The Elzone uses the electrical sensing zone method (Coulter principle) of particle measurement. One advantageous characteristic of this measurement technique that differentiates it from the laser light scattering method is that Elzone data are unaffected by samples that have mixed optical properties, colors, and shapes. Furthermore, samples composed of materials having different densities also can be measured accurately. Particle size determination is dependent only on the volume of electrolyte displaced by a particle as it flows through the sensing zone.

Another advantage of this technique is that the size distribution is determined by analyzing, one at a time, each particle from a representative subset of the introduced sample quantity. This particle-by-particle analysis technique provides accurate particle count data and, when combined with Micromeritics’ precision volume metering option, provides accurate number concentration data.

Sensitivity as it relates to particle size analysis is the ability to detect small changes in the amount of material at a given size.This ability is very important to processes where a few particles either larger than or smaller than the bulk of the 

population is critical. As examples, a few large abrasive particles can leave deep gouges in a finished surface and a few small particles of chromatography packing materials can increase back pressure. The Elzone is sensitive to small quantities of over-sized and undersized particles in a given sample.

The sample (a dry powder, paste, or emulsion) is dispersed at low concentration in an electrolyte solution. This dispersion is placed in a sample cup that also contains an electrode. A closed end glass tube is immersed in the dispersion. In the side of this tube and below the liquid surface is a precision hole (orifice) and within the glass tube is a second electrode. Applying a partial vacuum to the tube

interior causes the dispersion to be drawn through the orifice forming a conductive path between the electrodes.

The small diameter of the orifice, its short path length, and the dilute dispersion assures that for the great majority of the time particles pass through the orifice one at a time. Each particle while in the orifice displaces a volume of electrolyte equal to its own volume. Displacement of the electrolyte impedes the current flow between the electrodes and produces an electrical pulse, the amplitude of which is proportional to the particle volume. The Elzone counts the pulses and sorts them by amplitude and pulse width. This provides the data from which is calculated the particle population.