Bulk Density

Measures of Powder Compressibility

Because the interparticulate interactions influencing the bulking properties of a powder are also the interactions that interfere with powder flow, a comparison of the bulk and tapped densities can give a measure of the relative importance of these interactions in a given powder. Such a comparison is often used as an index of the ability of the powder to flow, for example the Compressibility Index or the Hausner ratio as described below.

The Compressibility Index and Hausner Ratio are measures of the propersity of a powder to be compressed as described above. As such, they are measures of the powder’s ability to settle, and they permit an assessment of the relative importance of interpaticulate interactions. In a free-flowing powder, such interactions are less significant, and the bulk and tapped desities will be closer in value. For poorer flowing materials, there are frequently greater interparticle interactions, and a greater difference between the bulk and tapped densities will be observed. These differences are reflected in the Compressibility Index and the Hausner Ratio.

Compressibility Index –  Calculate by the formula:


V0=unsettled apparent volume

Vf=final tapped volume

Hausner Ratio – V0/Vf

epending on the material, the compressibility indexcan be determined using V10 instead of V0.

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