05 powder charzterization 2

05 powder charzterization 2 - Electrical Sensing techniques...

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Electrical Sensing techniques - Coulter Counter Measurement principle: Resistance of electrolyte current path through narrow orifice between two electrodes increases when particles pass through. The pulse in resistance is proportional to the olume of electrolyte displaced volume of electrolyte displaced. Working range is 2-40% of aperture size or 0.3 to 400 micron using several aperture tubes
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lectrozone Sensing lectrozone Sensing - oulter Counter) Electrozone Sensing Electrozone Sensing (Coulter Counter) (Coulter Counter) Problems z Must measure in an ELECTROLYTE z Requires regular calibration z Poor dynamic size range z owest ze set by orifice selected-~ 300 nm Lowest size set by orifice selected 300 nm z Porous particles give problems
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Sieves Very old technique but has the advantage that it is cheap and is readily usable for large particles such as are found in the mining industries. llows eparation f materials Allows separation of materials.
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ieves Sieves isadvantages… Disadvantages… Measurement of dry powders below 00#(38 ) very difficult 400#(38 μ m) very difficult Cohesive, agglomerated difficult aterials as small as 1 impossible to Materials as small as 1 μ m impossible to resolve ow resolution and low precision Low resolution and low precision The longer you measure the smaller is our answer your answer Second smallest dimension is measured
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Sieves
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Mesh sizes and microns
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Schematic Drawing of Sieving m Δ Q m j j j j n = = 1 QQ ij i = Δ j = 1 m i : amount retained by sieve Q i : amount retained by sieve divided by total amount Aspect ratio important – elongated particles have no characteristic size for sieving Low frequ. shaking, high frequ. air pulse Wet sieving with vacuum pump
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Sieving - a common question “I sieved my material to 110 μ m but Laser diffraction tells me I still have particles larger than 110 μ m.” How can this be so?”
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Sieving - a common question
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05 powder charzterization 2 - Electrical Sensing techniques...

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