Tap Density Testers

The bulk density of a powder is expressed in terms of grams per mL by dividing the weight of a given "untapped" powder sample by its volume. It is important to ensure that no settlement occurs during preparation such that the density of the powder concerned is "as poured" and therefore includes the contribution made by the volume of the interparticulate void. Tap Density, on the other hand, is the density attained after "tamping down". This is normally measured using an instrument that lifts and the drops a measuring cylinder or similar vessel containing the powder through a fixed distance. The Tap Density in grams per mL can now be calculated by dividing the sample weight by the final tapped volume. 

Compressibility Index and Hausner Ratio - Measures of the ability of the powder to flow and its compressibility can now be given in the form of (a) the Hausner Ratio or (b) the Compressibility Index. In a free-flowing powder, inter-particulate interaction is less significant and unsettled and tapped densities will be closer in value. In poorly flowing powders, the inverse is to be expected. It follows that the closer the Hausner ratio is to 1, the better the flow. Powders with poor flow generally have a ratio of greater than 1.25.