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Viewpoint - the nature of powders
Talcum, coffee, salt, flour, sand, cement! All are commonplace powders that have two things in common - they are made of lots of small particles or granules, and the spaces between the particles are normally filled with air. Sometimes liquid may also be present, so the powder is a complex blend of solids, liquid and gas. Understandably, this leads to widely varying flow behaviours.
The individual particles within powders may differ significantly in their size distribution, shape and texture. They may be hard, brittle, soft, friable, rounded, angular, plate or needle-like, for example, with the result that no two powders are identical. The very act of moving or vibrating a powder is likely to cause it to change by removing or adding air, causing wear between particles which generates fines, and by promoting segregation of larger and smaller particles.
Even doing nothing can result in change, as often happens when powders are stored, and may become consolidated or caked. With such variability it is not surprising that powders are the most difficult materials to characterise.
Reg Freeman, Managing Director |
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From Nuremberg to Nashville... New small volume shear cell takes to the road!
Leading the introduction of a number of new accessories for the FT4 Powder Rheometer is the fully automated, small volume shear cell - a unit that can measure volumes down to 3 ml or less, depending on the characteristics of the powder. With this completely new module, users can extend the range of shear testing applications on the FT4 to include those for which only very small amounts of sample are available. See it in action at Powtech 2005 and the AAPS Annual Meeting and Exposition.
For more on shear cells click here |
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And there's Mohr......
The latest addition to the FT4 data analysis suite allows automated Mohr Circle construction, enabling users to get even more information from shear cell data. Yield locus profiles can now be analysed easily to provide unconfined yield stress, major principal stress, angle of internal friction, flow function and cohesion values.
To find out about Mohr circles click here |
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New Aeration Control Unit refines a critical measurement
Powders always contain air and the amount significantly affects the flowability of the powder bulk. The new Aeration Control Unit for the FT4 Powder Rheometer allows fine control of air flow through a powder under test, enabling automated measurement of flow properties as a function of increasing levels of aeration.
Click here to find out more |
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Comparative flow data presented
'Measuring powder flow properties - a comparison of empirical dynamic measurements with single plane shear data'. This comparative study of powder flowability, presented at Particulate Systems Analysis 2005 in September, examines two techniques to evaluate a number of different powders.
Click here to view the abstract of the paper |
