DENSITY

Density Measurement Lab Services

Density is an important physical characteristic of a material. Its defined as the ratio of an object mass to its volume. Density specifies how much of a substance occupies a defined volume at a stated temperature and pressure. The density of a substance can be used to define the substance and it performance character.

This measurement is vitally important for quality monitoring and process control to avoid costly over dosage of raw and intermediate products during manufacturing. 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.

Available Density Measurements:

Skeletal Density:

Sometimes called true density, is determined gas pcynometery.  We use an 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.

Mercury Density:

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.

Bulk Density or TAP Density:

Essentially, the difference between bulk and tapped density is a measure of the interparticle interactions that affect powder flow. This is especially important when combining ingredients to be used in a pharmaceutical capsule or tablet. Using a dual tap density tester, Micromeritics Analytical Services reports bulk density, tapped density, a compressibility index, and the Hausner Ratio.

Further discussion of these terms and equations are found in USP <61>

The following ASTM or USP standards can be specifically requested when submitting samples for density: USP <616> | USP <699> | ASTM D-2856 and ASTM D-6683 

Polymer Foam and Cellular Materials:

We can provide data to calculate, and report the percentage of open cell volume in blocks of foamed or cellular plastic, glass, rubber, or metal. These foamed materials have thin membranes or walls that separate internal cavities or cells. These cells can be open or interconnecting, closed or non-connecting, or a combination of open and closed. With this information, you can determine the percentage of sample volume occupied by open cells, as well as closed cells

Envelope Density:

Measured as 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 1365. 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.