Carr index
Template:Short description The Carr index (Carr's index[1] or Carr's Compressibility Index[2]) is an indicator of the compressibility of a powder. It is named after the scientist Ralph J. Carr, Jr.
The Carr index is calculated by the formula , where is the freely settled bulk density of the powder, and is the tapped bulk density of the powder after "tapping down". It can also be expressed as .
The Carr index is frequently used in pharmaceutics as an indication of the compressibility 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 larger.[3] A Carr index greater than 25 is considered to be an indication of poor flowability, and below 15, of good flowability.[4]
Another way to measure the flow of a powder is the Hausner ratio, which can be expressed as .
Both the Hausner ratio and the Carr index are sometimes criticized, despite their relationships to flowability being established empirically, 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
General Bibliography
- ↑ 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.
- ↑ Podczeck, Fridun & Brian E. Jones, eds. 2007. Pharmaceutical Capsules111.
- ↑ Template:Cite web
- ↑ Template:Cite book