Bulk Density by Tap Density Analysis

Bulk density is defined as the mass of the many particles of the material divided by the total volume they occupy. The tapped density is an increased bulk density attained after mechanically tapping a container containing the powder sample. Determination of Tapped Densities is a method to determine the bulk densities of powdered materials, usually drugs.

Bulk Density Introduction:

Bulk density is defined as the mass of the many particles of the material divided by the total volume they occupy. Bulk density is not an intrinsic property of a material; it can change depending on how the material is handled. Determination of Tapped Densities is a method to determine the bulk densities of powdered drugs under tapped packing conditions. Tapped packing is defined as the state obtained when the vessel containing the powder sample is to be repeatedly dropped at a specified distance at a constant drop rate until the apparent volume of sample in the vessel becomes almost constant.

How it works: 

Tapped bulk density is achieved by mechanically tapping a measuring cylinder containing a powder. After observing the initial volume, the cylinder is mechanically tapped, and volume readings are taken until little further volume change is observed (Figure 1).

Strength of tap density analysis:

1. Cost-effective.
2. Easily reproducible results.
3. Standardized procedures.

Limitations of tap density analysis:

Tap Density Analysis is sensitive to human errors. 

Uses of tap density analysis:

Tapped bulk density test is used to determine the required volume of small containers carrying a fixed mass of powder that has been compacted. The results of this test are primarily applicable to containers with volumes up to about one cubic meter. 

Data:

The tap density data is given in the following equation

TD = Weight of the sample/Volume of the sample in the cylinder after tapping

Sample requirements:
Samples can be powders, granules, or other “divided” solids. In general, the samples should be tested in the as-received condition. In certain instances, the powder may be dried. However, if the powder is susceptible to oxidation, the powder is dried in a vacuum or inert gas. Powders containing volatile substances are not dried at all.