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Thread: POWTECH 2004: L.O.T.-Oriel

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    POWTECH 2004: L.O.T.-Oriel

    Particle Size Analysis using modern Disc Centrifuges

    At PowTech Hall / booth No. 7-622 in Nürnberg L.O.T.-Oriel introduces the new disc for particle size measurements in aggressive solvents. The particles sizes can be in the measurement range of 10 nm to 50 µm. In addition to the capabilities of the CPS disc centrifuge to analyze particles in aqueous or less demanding liquids now it is even possible to use solvents like DMF, DOP, Methanol, Ethanol, Toluene, MEK, MIBK, Methylchloroform and Xylene. These solvents are aggressive to the measurement environment however are very often used to disperse particles in the daily laboratory work. So far such liquids destroyed the disc in the disc centrifuge.
    But with a new disc made of a special resin the stability against such aggressive solvents can be guaranteed also for long measurement runs. The great advantage is that from now on nearly all samples can be measured in a solvent which is optimal to the production process or the laboratory work.
    Although changing discs in the CPS Disc Centrifuge is not time consuming at all you can of course measure also water based samples with the new solvent resistant disc.

    For some years now the CPS Disc Centrifuge as an up-to-date development of the proved technique of Ultracentrifuges is available.

    This modern Disc Centrifuge takes advantage of the sedimentation technique in terms of the high accuracy but eliminates the disadvantage of old disc centrifuges and ultracentrifuges which needed a very long time to measure a sample.

    Unlike old disc centrifuges which only allows rotation speeds of hundreds to a few thousands the technique of this new disc centrifuge takes advantage of rotation speeds of up to 24000 rpm.
    That results in the ability of the CPS Disc Centrifuge to measure samples with a broad distribution also in a short time as well even to measure particles in the size range of 10 nm with a high accuracy.
    With a lower speed small particles need several hours to sediment to the detector and the effect of Brownian Motion leads to an inaccurate result whereas a high sampling speed allows high accuracy in a short time of measurement.
    Only the high rotation speed allows to measure small particles with a disc centrifuge but also makes such instruments interesting for routine measurements with a need for fast and accurate results.

    In general the CPS Disc Centrifuge offers measurements with a high resolution compared to other particle sizers.

    A disc centrifuge uses the effect of sedimentation of particles in liquids. Particles sediment in a time which is dependant on their size and density. Big and heavy particles sediment fast, whereas small, light particles take a long time to settle on the ground. The speed of sedimentation increases with the square of the size. This leads to the effect that only a small difference in size results in a remarkable difference in sedimentation speed. This is why sedimentation is a favoured method for accurate and highly resolved particle size analysis.
    On the other hand sedimentation is a slow process. To shorten the time of sedimentation the disc centrifuges have been developed. They increase the speed of sedimentation as they support sedimentation by the centrifugal force.
    That results in an exact separation even of small particles in a short time.
    Using the time the particles need to sediment the size of the particles can be accurately calculated.
    The absorption of the particles in addition give the fraction and concentration the particles have in the sample.

    After only few minutes of measurement time one gets an output that shows even small differences in the particle size distribution. The resolution of the CPS Disc Centrifuge measurement is 5%. That means that particles can be shown in separate peaks although their size difference could be less than 5%. That is a far higher resolution than other measurement techniques.

    As the measurement result is based on a measurement of time also the repeatability of the result is very good. Typically the measurement accuracy can be 0.25%.

    One disadvantage of a disc centrifuge measurement had been so far that big particles could not be measured with high sedimentation speeds. The reason is that big particles only travel a short time to sediment and reach the detector very fast. If the disc is rotating fast, this time even becomes shorter and a measurement is impossible.
    This is why particles above a size of about 5 µm need to be measured using a relatively slow disc speed. On the other hand having a broad distribution would lead to the fact that the small particles need a very long time to reach the detector and beside the long duration of the measurement Brownian Motion becomes relevant.
    But a development by CPS allows to measure both together big and small particles. The so call Speed Ramping Disc is the reason that such samples can be measured easily and accurately nowadays.
    The Speed Ramping Disc does not use a constant speed of rotation but starts with a few hundreds of rotations per minute in order to measure big particles accurate and then accelerates to 24000 rpm and measures the smallest particles in a short time of measurement. This innovation allows a high resolution and a broad dynamic of a factor of about 1000 between the smallest and largest particles in one run.

    The Disc Centrifuge typically is used in applications in chemical, pharmaceutical, biological and print and paint laboratories to measure particles like lattices, fillers, dispersions, emulsions, proteins, cells, abrasives, ink, carbon black, pigments, magnetic iron oxyds and many others.
    The number of applications seems not to be limited today.

    For more information, please visit:
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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