Helium pycnometry aims to find volume and true density using Archimedes' fluid overflow principle and Boyle's Law. For maximum accuracy of measurements, the overflowing fluid must be an inert gas that can enter all but the smallest pores. Therefore, Helium gas with small atomic dimensions approaching recesses and pores with a diameter of 0.25 nm is considered suitable for measurements. Helium's behavior as an ideal gas is also a reason for preference. Even when other gases are used (such as nitrogen), there is usually no measurable difference. For structures with helium permeability (such as low-density polymers and plant-derived materials), nitrogen or SF6 gas must be used.

Instrument: Quantachrome Ultrapycnometer 1000

The Ultrapycnometer 1000 is a small system with 3 cells of different volumes (135, 50 and 10 cm3). The precision digital pressure gauge has a resolution of 0.0001 psi.

Specifications

Sample Requirements

Samples should be of the appropriate size for the cell volumes and in the form of pieces, powders or pellets. A sample of at least 20cc volume should be delivered.

Applications

• Volume and actual density measurements
• Determination of percentages of solids in a slurry