en>Robinh: neutrality characterises the Dirichlet

2014-07-25T02:56:37Z

neutrality characterises the Dirichlet

en>Melcombe: tidy citation, display maths, split off lnon-tech ead

2011-08-08T12:48:53Z

tidy citation, display maths, split off lnon-tech ead

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The '''Carr index''' (also: Carr's index<ref>Bowker, Michael I. & P. Heinrich Stahl. 2008. "Preparation of Water-Soluble Compounds through Salt Formation." In Camille Georges Wermuth, ed. ''The Practice of Medical Chemistry'', pp. 747–766. Burlington, MA: Elsevier, p. 756.</ref> or Carr's Compressibility Index<ref name = "Podczeck">Podczeck, Fridun & Brian E. Jones, eds. 2007. ''Pharmaceutical Capsules''. London: Pharmaceutical Press, p. 111.</ref>) is an indication of the [[compressibility]] of a [[Powder (substance)|powder]]. It is named after the pharmacologist Charles Jelleff Carr (1910–2005).<ref name = "Podczeck"/><ref>[http://www.lsro.org/newsroom/jeff_carr.html In Memoriam: Charles Jelleff Carr, Ph.D., 1910–2005]</ref> It measures the relative significance of interparticle interactions.<ref>http://www.pharmacopeia.cn/v29240/usp29nf24s0_c616.html</ref>

The Carr index is calculated by the [[formula]] <math>C=100\frac{V_T-V_B}{V_T}</math>, where <math>V_B</math> is the volume that a given mass of power would occupy if let settled freely, and <math>V_T</math> is the volume of the same mass of powder would occupy after "tapping down". It can also be expressed as <math>C=100\times(1-\frac{\rho_B}{\rho_T})</math>, where <math>\rho_B</math> is the freely settled [[bulk density]] of the powder, and <math>\rho_T</math> is the tapped bulk density of the powder.

The Carr index is frequently used in [[pharmaceutics]] as an indication of the flowability of a powder. In a free-flowing powder, the bulk density and tapped density would be close in value, therefore, the Carr index would be small. On the other hand, in a poor-flowing powder where there are greater interparticle interactions, the difference between the bulk and tapped density observed would be greater, therefore, the Carr index would be bigger. <ref>http://www.pharmacopeia.cn/v29240/usp29nf24s0_c616.html</ref>A Carr index greater than 25 is considered to be an indication of poor flowability, and below 15, of good flowability.<ref>{{cite book |author=Kanig, Joseph L.; Lachman, Leon; Lieberman, Herbert A. |title=The Theory and Practice of Industrial Pharmacy |publisher=Lea & Febiger |location=Philadelphia |year=1986 |edition=3 |isbn=0-8121-0977-5}}</ref>

Another way to measure the flow of a powder is the [[Hausner ratio]], which can be expressed as <math>H=\rho_T/\rho_B</math>.

Both the Hausner ratio and the Carr index are sometimes criticized, despite their relationships to flowability being established [[empirical]]ly, as not having 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.

==References==
{{Reflist}}

==General Bibliography==
{{cite book |author=Mark Gibson |title=Pharmaceutical Preformulation and Formulation: A Practical Guide from Candidate Drug Selection to Commercial Dosage Form |publisher=CRC Press |location=Boca Raton |year=2001 |isbn=1-57491-120-1}}

[[Category:Particulates]]
[[Category:Pharmaceutics]]

{{pharmacology-stub}}

Neutral vector - Revision history

en>Robinh: neutrality characterises the Dirichlet

en>Melcombe: tidy citation, display maths, split off lnon-tech ead