Digital Microscopes
Observation and Measurement of Powders Using Digital Microscopes
Granular material is a collective term for aggregations of solid particles including powder materials. Generally, granular materials larger than 1 mm (0.039″) are called grains and those smaller than 1 mm (0.039″) are called powders. Its shape and volume can be freely changed. Therefore, it can be said that powders are solids with liquid and gas properties. This section provides an overview of powders, explains their properties, and introduces examples of their observation and measurement using digital microscopes.
Particle Size Distribution of Powders
The particle diameter of a powder varies and the degree of variation is called the particle size distribution.
Particle size distributions are usually expressed graphically with the particle diameter [μm] on the horizontal axis and the frequency [%] on the vertical axis.
Particle size distribution and typical powder examples
Normal distribution
Typical example : Powdered activated carbon
Large particle diameter and small particle diameter (two peaks)
Typical example : Powders that clump easily
Even diameter
Typical example : Toners
Large particle diameter
Typical example : Sand, sugar, salt
Small particle diameter
Typical example : Titanium oxide, pigments, dyes
Fluidization of Powders
Powders that exhibit a normal particle size distribution are likely to retain air and thus are easy to fluidize. On the other hand, powders composed of particles with similar diameters are hard to fluidize because air passes between the particles.
Powders that are easy to fluidize
Powders that are difficult to fluidize
Fluidity of Powders
The angle between the horizontal plane and the sloping plane is called the angle of repose. Powders with a high fluidity have a small angle of repose, while those with a low fluidity have a large angle of repose.
A : Angle of repose
Powders with a high fluidity often have large particles, such as sand. These powders spread on the horizontal plane and slump when piled in a conical shape.
Powders with a low fluidity, such as wheat flour, do no spread on the horizontal plane, maintaining their shapes when piled in a conical shape. Powders with a low fluidity are hard to discharge from hoppers and silos, and may form bridges or ratholes.
A : Angle of repose
A : Bridge B : Rathole
Observation and Measurement Examples of Powders Using Digital Microscopes
These are the latest examples of observation and measurement of powders using KEYENCE’s VHX Series 4K Digital Microscope.
Observation of crude drug powder
500×, ring illumination + with/without depth composition
500×, ring illumination + depth composition, with depth composition
The depth composition function allows for observation of all particle surfaces in focus.
Automatic area measurement of powder
ZS-200, 1000×, ring illumination, before measurement
ZS-200, 1000×, ring illumination, after automatic area measurement
The automatic area measurement function makes analysis efficient.
Observation of powder
VH-Z20, 20×, ring illumination
Observation of powder
VHX-E300, 200×, ring illumination
Observation of finely ground powder
VH-Z100, 1000×, ring illumination
Observation of powder used for drug manufacturing
VHX-E500, 500×, transmitted illumination
