Hausner ratio

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Hausner ratio

  1. 1. Particle & Powder Density, Hausner Index and Carr RatioIntroduction The smaller the Carr’s Index the betterThe measurement of individual particle the flow properties. For example 5-15and bulk powder density is a process indicates excellent, 12-16 good, 18-21 faircritical measurement for many industrial and > 23 poor flow.sectors. This short note presents detailsabout two commonly used techniques. Examples Data measured and determined for aBulk Density range of household products are shownThe density of a powder is often in Table I. It can be seen from thedetermined using a jolting volumeter. A Hausner ratio and the Carr’s Index thatknown weight of sample is placed into a the bath salts and washing powder aremeasuring cylinder and ‘tapped’ free flowing, whereas the talcs are(mechanically raised and lowered a set cohesive.distance) until a consistent volume is Bulk Tapped Hausner Carr’sreached which corresponds to the Material Density Density Ratio Indexmaximum packing density of the material. BlueBy measuring both the untapped volume Bath 1.100 1.175 1.068 6.383and the tapped volume the following can Saltsbe determined: Peach Bath 0.713 0.723 1.014 1.351 SaltsPour (or Bulk) density = mass / untapped Washingvolume 0.666 0.730 1.097 8.824 Powder OwnTapped density = mass / tapped volume Brand 0.673 0.886 1.316 24.000 Talc BrandHausner ratio = tapped density / pour Talc 0.585 0.843 1.440 30.556density Table I: Typical density and flowability dataCarr’s Index = (tapped density – bulk determined for household products.density) x 100 / tapped density PycnometryIt is well known that particle size Pycnometry is used to measure theinfluences flowability. For example fine skeletal (or true) density of solids (andparticles (< 100µm) tend to be more some liquids) by measuring changes incohesive and therefore less free-flowing, pressure with gas displacement. Heliumwhereas larger denser particles tend to is typically used as it is a small inertbe free flowing. molecule that easily permeates the smallest of voids and open pores (butThe Hausner ratio and Carr’s index are does not permeate any closed porosity).both measures of the flow properties of It is an ideal technique to measurepowders. A Hausner ratio of <1.25 particle density.indicates a powder that is free flowingwhereas >1.25 indicates poor flow ability.AN006 Particle & powder density hausner index and carr ratio rev 0.doc
  2. 2. Propan-2-olA pycnometer contains two chambers. In 5the first chamber the volume is calibrated 4.5 Washing Powder 4and then filled with a known weight of 3.5 Talc Bath Saltssample. Prior to analysis the sample Washing Up Liquid 3 Density g/ccchamber is purged with helium to remove Clay Milk Powder Toothpaste 2.5 Body Lotionany water and gases. During the analysis 2 Waterhelium is filled into the second chamber 1.5 1(known as the reference chamber) to a 0.5specified pressure. From here the helium 0flows into the sample chamber and when Materialthe pressure has stabilised the change inpressure is recorded. The analysis is Figure 2: Pycnometer density results forrepeated until consistent results are a range of samplesobtained and the volume of the sample isthen calculated. From the volume the Escubed Ltddensity can then be determined, and Leeds Innovation Centretypical values are shown in figure 1. 103 Clarendon Road Leeds LS2 9DF UK tel +44 (0)870 126 3200 fax +44 (0)870 126 3201 www.escubed.co.ukAN006 Particle & powder density hausner index and carr ratio rev 0.doc Page 2 of 2

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