Granulometry, Fraunhofer diffraction, laser diffraction, and static light scattering are all terms used to describe the same technique. In this process, the light of a coherent light source is scattered at particles to create a characteristic, angle-dependent, intensity distribution, the exact course of which is determined by the size of the particles. Therefore, to create a particle sizing instrument, the particles are placed at a defined position in a laser beam (coherent light) and a suitable detector is also correctly positioned.
Details are of Paramount Importance
It is important to consider various questions including how and where the particles should be placed in the laser beam; how the laser beam should be shaped; where the detectors should be positioned and what geometry the detector elements should have. It is imperative to prepare the particles so that they are available in the desired mode (singly or bound in agglomerates) and in the required concentration. This process is known as the dispersion process.
Different manufacturers of particle sizing instruments address these considerations differently. The ISO standard 13320 provides basic orientation and discusses general requirements for appropriate instruments and the quality of measuring results with standardized samples systems, as well as the basic optical design of the measuring systems.
One of the variants is the Reverse Fourier design, invented in the 1980s by FRITSCH GmbH and developed to market maturity. This design is the basis for the newest generation of the ANALYSETTE 22 from FRITSCH, and this has now been adopted by numerous suppliers.
Keep it Simple
The current instrument is based on 35 years of experience and is characterized by the central approach: keep it simple!
Unlike many other suppliers, FRITSCH uses a single light source with a single wavelength. Theoretically, several wavelengths from very fine materials offer the advantage of being able to obtain more information from the scattering processes for the Mie theory to be used.
However, these theoretical advantages are often associated with immense practical difficulties which, in turn, negate the advantages. With the Mie theory, the absorption coefficient and the refraction index of the sample material must be known for the respective wavelength of the light used. This can often present a challenge, even for a single wavelength. With multiple different wavelengths, this can quickly become unmanageable.
Therefore, FRITSCH only applies one wavelength. A fiber-coupled green laser is used as this provides the ideal wavelength for the reliable detection of both the finest particles well below one-tenth of a micrometer and large particles down to the millimeter range. Additionally, only a single beam is used, rather than several beams from different directions at different points in the measuring cell, as this single beam is easy to control.
The ANALYSETTE 22 NeXT Nano provides a possible measurement range from 10 nm to 3800 mm when it is in the full expansion stage. The slightly simpler NeXT Micro allows particle size measurements between 0.5 and 1500 mm and is equipped for multiple applications.
The dispersion unit for measurement is also based on the principle of maximum simplicity. Therefore, this component of the ANALYSETTE 22 NeXT, which is imperative for daily work and the success of measurements, works innovatively and entirely without valves in the sample circulation system.
To date, all wet dispersion units available on the market have relied either on clamping elements or rotating multi-port valves. Here, a hose branching in the circuit is squeezed in either one direction or the other which causes plugging. Rotating systems are slow and can be damaged by particles that get stuck and jam in the sealing surfaces.
This causes sluggishness and sometimes leakage. On the other hand, clamping systems usually have dead spaces where particles can settle during a measurement. Particles can also get stuck in sealing surfaces. FRITSCH elegantly avoids these issues by dispensing without valves in the sample circulation system. The result is a fast, reliable, compact and highly flexible dispersion system.
Ultrasonic Flexible Application
Laser Particle Sizer ANALYSETT 22 NeXT with ultrasonic box.
The use of ultrasonic is often the method chosen when agglomerates from the sample require degrading. However, there are always situations where ultrasonic is either unnecessary or harmful. Sometimes, it is sensible to use an ultrasonic treatment before the actual measurement and then to dispense completely in the main measuring circuit.
The powerful and variably programmable ultrasonic box from FRITSCH is innovative. It is offered as an independent module, which can be inserted simply into the sample circuit system. Therefore, it is possible to configure a system completely without an ultrasonic chamber, if the application requires it.
The ANALYSETTE 22 NeXT represents a powerful and flexible system for particle size determination. It is also available as an entry-level version as the NeXT Micro model which comes at an extremely attractive price. Furthermore, a later expansion with respect to dispersion (for example using the optional ultrasonic box) or an upgrade of the Micro-version to the NeXT Nano is possible.
This information has been sourced, reviewed and adapted from materials provided by FRITSCH GmbH - Milling and Sizing.
For more information on this source, please visit FRITSCH GmbH - Milling and Sizing.