MCA Services - Bulk Density and True Density Measurement

DENSITY MEASUREMENT - Mercury & Helium Pycnometry

(bulk density, skeletal density & true density / absolute density)

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The measurement of sample density by pycnometry is undertaken at MCA Services through two different analytical techniques, each providing fundamentally different information.

Mercury pycnometry is used to measure the bulk density and skeletal density of a sample (also termed the envelope density or mercury displacement density) whereas helium pycnometry is applied to the measurement of the absolute density of a sample (also termed the true density or helium displacement density). These techniques may be combined for the measurement of the total pore volume of a sample.

The following text provides more information on the techniques available and their possible attributes for given applications.

SC10 Test: Helium Pycnometry (helium density, true density or absolute density)

Helium pycnometry is used to measure the absolute density of a material, also termed the helium displacement density or true density, and is performed at MCA Services using a Micromeritics Accupyc 1330 instrument, yielding highly accurate and reliable density measurement.

The true density, or absolute density, of a sample excludes the volume of the pores and voids within the sample.

helium pycnometry for true density measurement, helium density or absolute density measurement, effectively bulk density excluding pores

Representation of true density measurement by helium pycnometry, showing helium (in red) intrusion to sample pores.

SC9 Test: Mercury Pycnometry (mercury density, bulk density or envelope density)

Mercury pycnometry is used to measure bulk density, also termed mercury displacement density or envelope density and is performed using a state-of-the-art Micromeritics AutoPore mercury porosimeter. This may be performed alone or in conjunction with our mercury porosimetry analysis (SC11 test). The technique allows for the selection of the optimum mercury pressure for the calculation of sample density is selected, ensuring the sample is fully enveloped by mercury without intrusion to the sample pores. This ensures that the most accurate bulk density value is generated for any given sample. Two density values are reported for this test:

· Bulk density of the sample (also termed envelope density or mercury density).

· Skeletal density of the sample (when in conjunction with full mercury porosimetry).

Since the calculation of bulk density is undertaken at a point whereby no mercury has been intruded to the sample pores, the bulk density value includes the volume of all of the pores within the sample.

mercury density or mercury displacement density for bulk density testing, skeletal density, envelope density or absolute density testing

Representation of bulk density measurement by mercury pycnometry, showing exclusion of mercury (in grey) from sample pores

SC8 Test: Total Pore Volume (TPV)

It is possible to combine mercury pycnometry and helium pycnometry to calculate the total volume of pores within a sample. The SC8 test applies the values obtained from the measurement of true density and bulk density to calculate Total Pore Volume (TPV).

total pore volume by combination of true density and bulk density by helium pycnometry and mercury pycnometry

Representation of total pore volume measurement, pore volume (in blue) reported as cm³through combination of bulk density and true density measurements.