DENSITY MEASUREMENT

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The determination of sample density, also termed pycnometry, is undertaken at MCA Services through two different analytical techniques, each providing fundamentally different information about the sample density.

SC9 Test: Mercury Pycnometry (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 and may be performed alone or in conjunction with our mercury porosimetry analysis (SC11 test). The test may be conducted at any pressure from 50 μm Hg to 30000 psi. Wherever possible the optimum mercury pressure for the calculation of sample density is selected, ensuring the sample is fully enveloped by mercury without mercury 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:

·         Mercury displacement density of the sample (also termed envelope density or bulk density).

·         Skeletal density of the sample (in conjunction with the SC11 test).

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.

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

SC10 Test: Helium Pycnometry (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 instrument. The technique uses the principle of helium displacement for the determination of sample volume and is suited to the provision of highly accurate and reliable density measurement. It is the policy of MCA Services to average five analyses on a given sample and to ensure that results comply to an acceptable tolerance. 

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

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

SC8 Test: Total Pore Volume (TPV)

Since the pores within a material are excluded from the measurement of true density but are included in the measurement of bulk density, it is possible to combine these techniques 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) and is regularly performed by the staff at MCA Services on behalf of clients. 

Representation of total pore volume measurement, pore volume (in blue) reported as cm³ through combination of bulk density and true density measurements. 

For the accurate analysis of sample density it is imperative that samples are adequately degassed prior to analysis. MCA Services can accommodate a wide range of conditions for this purpose. Furthermore, these may be combined to suit the individual requirements of our clients. Degassing temperatures up to 200˚C under vacuum and 400˚C under flowing nitrogen or helium gas can be applied. Such activities are usually conducted at MCA Services immediately prior to analysis and form part of the analytical procedure.