Particle characterization in general comprises analysis of the porous properties
as well as particle size of powders and solids. Various techniques can be applied to cover a
wide range of pore sizes from lower nm range to several hundreds of micrometers, whereas in
case of particle size analysis the particle size range even extends into the mm range.
Porosity of powders and porous solids can be measured by different techniques based on
adsorption of inert gases. Physical gas adsorption or physisorption is important in the
determination of porosity in general and more specific the specific surface area (BET surface
area, according to the Brunauer, Emmet and Teller theory), pore volume and pore size
distribution of porous materials and non-porous materials. Screening of the porous
properties of a catalyst or other porous material can be achieved by dynamic adsorption where
very rapidly information is obtained on the BET surface area and total pore volume.
Analysis of CO2 adsorption is performed at 273 K on microporous carbons or activated
carbons or charcoals for determination of the micropore size and micropore surface area and
microporosity.
Using these methods, the pore size distribution can be assessed in the range from micropores to
macropores according to IUPAC classification, resulting in pores from ca. 0.5 nm up to ca.
100 nm. The pore size analysis range can be extended by using mercury intrusion
porosimetry.
Mercury porosimetry or mercury intrusion is measured for characterization of
mesoporous and macroporous solids. The non-wetting behaviour of mercury enables the
determination of pores in a wide pore size range and provides information on total porosity,
pore size distribution, pore surface area, pore volume and apparent density and bulk density.
Helium pycnometry gives information on the skeletal density of solid materials and combined
with the apparent density derived form mercury porosimetry can give information on the overall
porosity. Helium does not adsorb at ambient conditions and can therefore be used as a
density analysis of solid samples. The analysis is performed on the Quantrachrome
penta pycnometer.
Chemisorption or chemical gas adsorption is used to analyze mostly catalysts for
determination of the active metal surface area and metal dispersion and
metal crystallite size by chemical adsorption of reactive gases as hydrogen (H2) and
carbonmonoxide (CO) on metals as platinum (Pt), palladium (Pd), nickel (Ni), ruthenium (Ru)
and rhodium (Rh). The chemical adsorption isotherm is measured after in-situ reduction and
evacuation of the catalyst. This technique does not provide information on the porous
characteristics. Other techniques in catalyst characterization are desorption of
ammonia to analyze acidity and physical gas adsorption to analyze the porous properties.
In laser diffraction (static light scattering) the scattering pattern, obtained from
illumination of dispersed particles with a laser beam, contains information about particle size.
The interaction between particles and light is mainly dependent on particle size, shape, surface
roughness and refractive indices of material and dispersing medium.
For a specific material, the scattering pattern of a particle is unique for its size. Deconvolution of
the sample scattering pattern with an optical model such as Mie or Fraunhofer results in the
particle size distribution.
The technique is especially applicable for particle size analysis of samples with a
broad or bimodal distribution and for information on size trends in series of samples.
Materials can be characterized in the range of 0.04 to 2000 µm and dispersion can be made in
water, organic liquids as well as in air (dry).
1. particle
