Carr index

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The Carr index is an indication of the compressibility of a powder. It is calculated by the formula C=100\frac{V_B-V_T}{V_B}, where VB is the freely settled volume of a given mass of powder, and VT is the tapped volume of the same mass of powder. It can also be expressed as C=100\times(1-\frac{\rho_B}{\rho_T}), where ρB is the freely settled bulk density of the powder, and ρT is the tapped density of the powder.

The Carr index is frequently used in pharmaceutics as an indication of the flowability of a powder. A Carr index greater than 25% is considered to be an indication of poor flowability, and below 15%, of good flowability.[1]

The Carr index is related to the Hausner ratio, another indication of flowability, by the formula C=100\times(1-1/H).

Both the Hausner ratio and the Carr index are sometimes criticized because their relationships to flowability was established empirically and do not have a strong theoretical basis. Use of these measures persists, however, because the equipment required to perform the analysis is relatively cheap and the technique is easy to learn.

[edit] References

Mark Gibson (2001). Pharmaceutical Preformulation and Formulation: A Practical Guide from Candidate Drug Selection to Commercial Dosage Form. Boca Raton: CRC Press. ISBN 1-57491-120-1. 

  1. ^ Kanig, Joseph L.; Lachman, Leon; Lieberman, Herbert A. (1986). The Theory and Practice of Industrial Pharmacy, 3, Philadelphia: Lea & Febiger. ISBN 0-8121-0977-5. 
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