Tap density

When determining bulk density, a distinction should be made between loose bulk density and tap density, eg, ASTM B527-81. The latter is a measure of the influence of settling on filler volume at constant mass. 

Tap Density. Tapping a mass of loose powder, or more specifically, the appHcation of vibration to the powder mass, separates the powder particles intermittently, and thus overcomes friction. This short-time lowering of friction results in an improved powder packing between particles and in a higher apparent density of the powder mass. Tap density is always higher than apparent density. The amount of increase from apparent to tap density depends mainly on particle size and shape (see Table 4). 

Table 4. Effect of Particle Shape on Apparent and Tap Density ...

Since these materials have significant microporosity, we expect their bulk densities to be low. For example, the tap density (100 taps) of BrlOOO was measured to be 0.81 g/cc, compared to 1.34 g/cc for the synthetic graphitic carbon powder, MCMB2700, measui ed by the same method. 

Considerable increases in the capacity density of the electrodes have been achieved through the use of high-density / -Ni(OH)2 with a uniform particle size, a narrow range of pore sizes, and a high tapping density (1.9-2.0gem"3) [15, 16]. 

As a consequence of the irregular and rough structure of the xylan particles, entanglements between particles are promoted and this fact may explain the poor flow properties of this polymer (Kumar et al., 2002 Nunthanid et al., 2004). Additionally, rheological parameters of xylan powder have also been studied, such as bulk and tapped densities, Hausner ratio, Carr s index, and angle of repose values, and they are summarized in Table 1. 

The bulk density of a powder is calculated by dividing its mass by the volume occupied by the powder (Abdullah Geldart, 1999). Tapped bulk density, or simply tapped density, is the maximum packing density of a powder achieved under the influence of well-defined, externally applied forces (Oliveira et al., 2010). Because the volume includes the spaces between particles as well as the envelope volumes of the particles themselves, the bulk and tapped density of a powder are highly dependent on how the particles are packed. This fact is related to the morphology of its particles and such parameters are able to predict the powder flow properties and its compressibility. 

Method Reaction temp. Induction time Particle size Tap density... 

As the previously shown in Table 1, the tap density of the mple obtained by using the ultrasonic method was relatively higher than that obtained by the conventional one. The reason is that the surface morphology and particle size of fee sample obtain by the ultrasonic method are much smooth and small as fee shown in SEM results, respectively. 

Tap density. The mass of particles divided by the volume after tapping the powder in a container. Also referred to as the drop density [61]. The volume measurement is similar to that of bulk density. 

Fig. 6 The different types of densities, (a) Bulk density, (b) Tap density, (c) Particle density, (d) True density (Adapted from Ref. 49.)...

The discussion in this section will focus on true, bulk, and tap densities. The procedure and instrumentation used for each type of density measurement will be outlined, and pharmaceutical applications involving density will be presented. 

Tap density (ptap) is an extension of bulk density measurements, and the procedure used to measure the tap density again varies from lab to lab and can affect the final results. To measure tap density, a graduated cylinder is filled with powder and the weight and volume are recorded. The difference observed between procedures is the number of taps used for the measurement. In some cases, a particular number of taps is used, such as 200 [65], 500 [66], or even 1000 taps [67]. Other procedures involve tapping the cylinder for a number of times, recording the volume, and repeating the procedure until the volume remains constant [68]. This method ensures more consistent results. 

A number of other parameters can be calculated from true, bulk, and tap density measurements. These include void volume, porosity, bulkiness, and compressibility. 

The bulk density, A, is measured by a widely used tap-density technique by weighing of a convenient known macroscopic volume (e.g., a barrel) of PS [55], A void between granules can be generally considered as macroscopic pores, and its specific volume can be determined as Ua=A 1-(5 1=(1-A/(5)/A. 

Figure 4. Density of the powder activated carbons (packing density ( ) and tap density ( )) versus the total micropore volume Vpp (N2).

Bulk powder properties are important in understanding the handling properties of an excipient or a granulated product. Common parameters measured are bulk and tap density. From these values the compressibility can be calculated using the following ... 

The tap density is another form of bulk density obtained by tapping or vibrating the container in a specified manner to achieve more efficient particle packing. The tap density is therefore usually greater than the bulk density. 

Influence of sieve mesh sizes (if sieves are used) on the granulation properties (e.g., particle size distribution, moisture content, poured density, tap density, and flow capacity)... 

Tapped density - Bulk density) Tapped density x 100%... 

Mesh size (percent retained) Bulk density (g/cm ) Tap density (g/cc )... 

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