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Dry dispersion is ideal for dry, free-flowing and non-sticking materials. Especially coarse material can be measured with it very well and easily.
With the dry dispersion unit the sample material is transported continuously via a vibratory feeder through the measuring cell via an air flow, measured and then vacuumed off. The needed sample material amounts of < 1 – 100 cm3 are a clearly higher as with a wet dispersion.
With a high frequency feeder the sample material is continuously transported over the funnel-shaped opening of the dry measuring cell and then drops in the actual dispersion area. In an annular gap Venturi nozzle the powder is accelerated and passes with a high speed through the nozzle channel and the measurement of the particle size distribution in the laser beam takes place directly behind it. Then it passes a zone with aerodynamic wave generation at the nozzle outlet. The by the high turbulent current caused strong shearing forces, as well as blows between the particles lead to the breakdown of the agglomerates. No impact areas in the flight path of the particles exist in order to prevent soft sample materials from being ground during the dispersion process.
Compared with the wet dispersion is the dry dispersion not as efficient due to chemically-physical as well as rheological material properties of the sample material.
One of the main differences between dry and wet dispersion is based on the fact, that it is almost a solely mechanical dispersion in an air flow. Thereby, with a dry dispersion, a sensible measurable particle size and the associated complete primary particle dispersion is typically at approximately 1 - 10 µm. Depending on the material and its properties, below this range an incomplete dispersion can be expected. The utilization of the dry dispersion makes sense in areas where a wet dispersion in water or solvents has to be ruled out.
The dispersion pressure is set with the assistance of SOP’s with the software MaS control and then is carried out automatically. Measurement processes can therefore be freely programmed and the entire measurement takes place completely automatic.
Ideally, for the operation of the Dry Dispersion Unit, is an oil-, water- and particle-free supply of compressed air with a pressure of at least 5 bar and a flow rate of at least 125 l/min. An external exhaust system is necessary to vacuum the sample material, which can be ordered as a FRITSCH accessory together with the instrument.
In order to use the FRITSCH Dry Dispersion Unit you will need the ANALYSETTE 22 NanoTec plus Measuring Unit (Order No. 22.2400.00).