Heliumpyknometrie

Helium pyknometry, written here as heliumpyknometrie, is a gas-based method used to determine the volume and density of solid materials. It employs a pycnometer filled with helium gas to measure the solid’s volume with high precision. Because helium atoms are very small and diffuse readily into connected pores, the technique yields the skeletal or true volume of the solid, excluding open porosity. From the measured mass and this volume, the skeletal density can be derived. When combined with a separate measurement of bulk density, helium pycnometry also supports porosity estimates.

The principle rests on gas displacement and the ideal gas behavior of helium. A sample is placed in a fixed-volume chamber, and the pressure changes of the contained helium are recorded as the gas is allowed to fill the chamber around the sample. Using the known reference volume and the measured pressures, the sample’s volume is calculated. Because helium can access most open pores, the computed volume corresponds to the solid portion of the material, not including pores accessible to the gas. This allows the determination of density that reflects the material’s skeletal framework.

Typical procedures involve drying or degassing the sample to remove adsorbed moisture, weighing the sample, and performing measurements in a controlled temperature environment. The method is widely used in materials science, ceramics, catalysts, polymers, and geology to characterize density, porosity, and pore structure. Limitations include sensitivity to open porosity that is not accessible to gas, the need for dry samples, and careful calibration of the instrument. Overall, heliumpyknometrie provides a fast, non-destructive means to obtain accurate skeletal volumes and densities.