There are several definitions for density and it is important to understand how each is determined in order to choose the one that suits your needs best. The following densities are specifically determined and reported: skeletal density, bulk density, TAP density, T.A.P. density, mercury density, and envelope density.
The following ASTM or USP standards can be specifically requested when submitting samples for density: USP <616> | USP <699> | ASTM D-2856 ASTM D-6683
Skeletal Density, sometimes called true density, is determined by the Accupyc II 1340 which uses a gas displacement technique to determine the volume of sample under test. The density is calculated using the sample weight which was determined using a balance. The instrument measures the volume of the sample, excluding interstitial voids in bulk powders and any open porosity in the individual particles, to which the gas has access. Internal (closed) porosity is still included in the volume. This test is normally performed at room temperature, but can be performed at a customer-specified temperature in the range of 0C to 50C. Almost any solid samples as well as some fluid samples can be measured by this technique. Open cell content of rigid foams can also be measured using the Accupyc 1330 using ASTM Standard -D-2856. - Example Report
Mercury density is defined as the total volume of material including any interstitial volume AND any open or closed pore volume. Micromeritics Analytical Services uses a Mercury porosimeter (AutoPore Series) for this analysis.
Tap density (using Micromeritics’ T.A.P. method) is determined by applying a controlled packing force to the sample. As with bulk density, T.A.P. density includes the interstitial volume and pore volume in its calculations. T.A.P. density is measured using the GeoPyc 1360.
Envelope density is the mass of an object divided by its volume where the volume includes that of its pores and small cavities. This density is measured using the Geopyc 1360.
The specific pore volume and percent porosity of a sample can be determined by subtracting the skeletal volume from the envelope volume prior to doing the remaining computations.
Bulk density or TAP density is measured according to USP <616> which uses a graduated cylinder to determine the bulk volume of the powder, followed by a series of automated taps to compress the sample. Bulk density, TAP density, compressibility index and a Hausner Ratio are typically reported.
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