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Gas Displacement Pycnometry System

Link to Principle of Operation Video! »

Gas pycnometry is recognized as one of the most reliable techniques for obtaining true, absolute, skeletal, and apparent volume and density. This technique is non-destructive as it uses the gas displacement method to measure volume. Inert gases, such as helium or nitrogen, are used as the displacement medium. Density calculations using the gas displacement method are much more accurate and reproducible than the traditional Archimedes water displacement method.

The AccuPyc II 1340 Series Pycnometers are fast, fully automatic pycnometers that provide high-speed, high-precision volume measurements and true density calculations on a wide variety of powders, solids, and slurries. The instrument completes most sample analyses in less than three minutes without sacrificing accuracy. After analyses are started with a few keystrokes, data are collected, calculations are performed, and results displayed. A minimal amount of operator intervention is required.


Maintain product integrity with this non-destructive test

Eliminate error with programmable automatic repeat and data acquisition set to your tolerances to comply with your SOPs

Ability to use a variety of gases

Maximize your investment-Adaptive configuration to meet your sample size needs

Low-cost, minimal maintenance, and small footprint

Increase efficiency and compliance with barcoding compatibility

Speed of analysis, accuracy, repeatability, and reproducibility

Versatility of keypad or Windows software operation

Eliminate procedural steps with direct input from an analytical balance

Principle of Operation

This technique uses the gas displacement method to measure volume accurately. Inert gases, such as helium or nitrogen, are used as the displacement medium. The sample is sealed in the instrument compartment of known volume,the appropriate inert gas is admitted, and then expanded into another precision internal volume. The pressures observed upon filling the sample chamber and then discharging it into a second empty chamber allow computation of the sample solid phase volume. Helium molecules rapidly fill pores as small as one angstrom in diameter; only the solid phase of the sample displaces the gas. Dividing this volume into the sample weight gives the gas displacement density.

Inert gas flows into a sample chamber
valve a opens then closes

Equilibrium is reached yet again

Equilibrium is reached

Volume divided into sample weight determines density

Gas flows into second chamber for volume measurement - valve b opens

Pressure vented off to atmosphere
- valve c opens

Density Measurement

On an elementary level, the volume of a solid material can be calculated by measuring its length, width, and thickness. However, many materials have within their structure surface irregularities, small fractures, fissures, and pores. Some of these voids or pores are open to the surface or closed within the structure of the solid material. Therefore, differences in the material volume depend on the measurement technique, measurement method, and the conditions under which the measurements were performed.


Density TypeDefinitionMaterial VolumeOpen-PoreVolumeClosed-PoreVolumeInter particle VolumeExternal Void VolumeAddressed by
True (Absolute)The mass of a substance divided by its volume, excluding open and closed (or blind) poresAccuPyc II
Skeletal(Apparent)The ratio of the mass of the solid material to the sum of the volume including closed (or blind) pores

AccuPyc II
EnvelopeThe ratio of the mass of a substance to the envelope volume (imaginary boundary surrounding the particle)
BulkMass of the material divided by the volume occupied that includes interstitial spaceGeoPyc
TAPApparent powder density obtained under stated conditions of tapping GeoPyc with T.A.P. function

Instrument Demonstration Video

AccuPyc II Interactive Brochure


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