Tap volume

Powder flow rate was determined using a glass funnel. The volume before and after tapping (AF=F10-F500) was measured with an Eberhard Bauer (J.Engelsmann AG) tapping volume meter [14-16]. 

Figure 10 Bulk volume/tapped volume (Formulation 1).

Given that the bulk volume associated with the particle mass is a mixture of air and solid material, the bulk density value is highly dependent on sample history prior to measurement. Calculation of the tapped density can then be achieved by tapping the bulk powder a specified number of times (to overcome cohesive forces and remove entrapped air) to determine the tapped volume of the powder. The tapped and bulk density values can be used to define the flowability and compressibility of a powder using Carr s index and the Hausner ratio. 

Primary particle size (in nm) Specific surface area h (in m-/g) Tap volumes-" (in niL/IOOg) porosity... 

One of the standard methods to evaluate the flowability of a particulate system is to calculate the Hausner ratio after tapping. The Hausner ratio is defined as the ratio of a powder system s initial (loose) bulk density to its tapped bulk density (i.e., the ratio of loose volume to tapped volume). It is easy to calculate the Hausner ratio and evaluate the flowability when the loose and tapped volumes of the test material are known. For a Hausner ratio of l.O-l.l, the powder is classified as free flowing 1.1-1.25, medium flowing 1.25-1.4, difficult flowing and >1.4, very difficult flowing (Hayes, 1987). 

The Hausner ratio and compressibility index are calculated from the measured bulk volume or poured volume (Vo) and tapped volume or settled volume (Vt) and are defined by Equations 8.4a and 8.4b, respectively. The bulk volume can be determined by filling a known amount of powder in a graduated cylinder, while the tapped volume is obtained by mechanically tapping a measuring cylinder containing a powder sample in a controlled way. A Hausner ratio close to 1 or a low-compressibility index indicates good flow properties, while a Hausner index >1.35 or a compressibility index >26% would indicate poor flow properties. For a more detailed classification. ... 

Various methods recommend a fixed mass (10-100 g) or a fixed volume (usually 50 mL) with a special density cup coupled with an extension to accommodate the extra powder that will eventually flow into the tapped volume and fill the fixed volume cup. 

Prepare the acetylating mixture by adding i volume of acetic anhydride to 4 volumes of pure anhydrous pyridine, and shaking thoroughly. Immediately before use, transfer the mixture to a clean dry burette having a welUfitting glass tap, and then close the top of the burette by means of a soda-lime tube. 

When the volume of mother liquor is large and the amount of crystals small, the apparatus of Fig. II, 32, 1 may be used. The large pear-shaped receiver is supported on a metal ring attached to a stand. When the receiver is about two-thirds fuU, atmospheric pressure is restored by suitably rotating the three-way stopcock the filtrate may then be removed by opening the tap at the lower end. The apparatus is again exhausted and the filtration continued. 

Determine the parts per million of F in the tap water, (b) For the analysis of toothpaste a 0.3619-g sample was transferred to a 100-mL volumetric flask along with 50.0 mL of TISAB and diluted to volume with distilled water. Three 20.0-mL aliquots were removed, and the potential was measured with an L ion-selective electrode using a saturated calomel electrode as a reference. Live separate 1.00-mL additions of a 100.0-ppm solution of L were added to each, measuring the potential following each addition. 

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. 

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