Particle Size and Particle size distribution, short tutorial.

Particle size is a geometric characteristic that is usually assigned to material objects with sizes on scale from nano-meters to millimeters. There are multiple definitions of the particle size depending on the method of its measurement. For instance, sedimentation yields equivalent hydrodynamic particle size. Microscopy provides information on the area projection particle size. In order to reflect innate basis for a particular particle size measurement three different basses are used: numerical, area and weight.

Particle size analyzers could be roughly organized in three groups: 1) counters; 2) fractionation methods; 3)macroscopic fitting methods. Below we present links to several International Standards that provide description some of this methods.

Our Acoustic spectroscopy belongs to the group of macroscopic fitting methods. This group includes also light scattering, x-rays scattering, neutron scattering. All these particle size measurement methods display particle size on the weight basis. However, this basis is innate only for Acoustic spectroscopy. Attenuation of ultrasound caused by a single particle is proportional to the weight or volume of the particle. In contrary, for instance, light scattering depends on the 6th power of the particle size. This would require special recalculation down to the weight basis. Consequently, light scattering tends to overestimate contribution of large particles.

Particle size measurement is extremely important method for research and development and for quality control in many industries. This includes pharmaceuticals, cement (see Newsletter #20), ceramics (see Newsletter #3), paints, emulsions (see Newsletters #4,10,17), etc.

Acoustic spectroscopy makes possible particle size measurement in concentrated dispersions and emulsions with no dilution and no sample preparation. This is critical in many cases when dilution affects particle size distribution. Also, this method can be applied for structured dispersions. Structure contributes to ultrasound attenuation by itself, but this contribution can be subtracted using appropriate existing theory (see Newsletter #8). In addition, acoustic spectroscopy could resolve particle size distributions of different species of particles in mixed dispersions, assuming that they have different densities (see Newsletter #6).

This method can be used for continuous monitoring of particle size during milling (see Newsletter #18), crystallization, and other industrial processes. One of the most important applications is particle sizing of nano-dispersions and other nano-particulates. Acoustics can monitor presence of nano-particles with precision of 1%, see Newsletter #21. Nano-particles can be masked by larger particles if other methods are involved.

International Standards for particle sizing:

ISO 9276-1:1998 Representation of results of particle size analysis -- Part 1: Graphical representation: http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=25860

ISO 9276-5:2005: Representation of results of particle size analysis -- Part 5: Methods of calculation relating to particle size analyses using logarithmic normal probability distribution: http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=39388

ISO 22412:2008 Particle size analysis -- Dynamic light scattering (DLS)http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=40942

ISO 13320:2009 Particle size analysis -- Laser diffraction methods http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=44929

ISO 13317-1:2001 Determination of particle size distribution by gravitational liquid sedimentation methods -- Part 1: General principles and guidelines: http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=21703

ISO 20998-1:2006 Measurement and characterization of particles by acoustic methods -- Part 1: Concepts and procedures in ultrasonic attenuation spectroscopy: http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=39869

ISO 13322-1:2004 Particle size analysis -- Image analysis methods -- Part 1: Static image analysis methods: http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=38664