Carr’s Index or Compressibility Index

Carr’s index is an indicator of the compressibility of powders. It can be determined by measuring both the bulk volume and the tapped volume of a powder.

The basic procedure is to measure the unsettled apparent volume (V0), and the final tapped volume (Vf) of the powder after tapping the material until no further volume changes occur. The compressibility index can calculated as follows:

Compressibility Index = 100 × [(V0 – Vf)/ V0]

Alternatively, the compressibility index can be calculated using measured values for bulk density (ρ bulk) and tapped density (ρ tapped) as follows:

Compressibility Index = 100 × [(ρ tapped – ρ bulk)/ ρ tapped]

Compressibility Index (%) – Flow Character

  • ≤10 = Excellent
  • 11–15 = Good
  • 16–20 = Fair
  • 21–25 = Passable
  • 26–31 = Poor
  • 32–37 = Very poor
  • >38 = Very, very poor

Related Topics:

Partition CoefficientDissociation ConstantsBuffer Capacity
MicromeriticsAngle of ReposeRheology

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