pycnometrie

Pycnometry is a set of techniques used to determine the volume and, from mass, the density of materials by measuring how much space a sample occupies when surrounded by a known volume of gas or liquid. The basic approach relies on a calibrated pycnometer, a sealed chamber of known volume. In gas or liquid displacement, the resulting volume is used with the sample’s mass to compute density. For porous materials, pycnometry can distinguish true density from apparent density by accounting for pore volume.

Gas pycnometry uses a non-reactive gas, typically helium, to fill the volume around the sample. Pressure changes are recorded and, via Boyle’s law, the sample volume is calculated. Because helium can enter connected pores, this method yields the true density (skeleton volume) of the material, excluding open porosity under the measurement conditions. It is fast, requires small samples, and is non-destructive, but results can be affected by adsorption, surface roughness, and temperature.

Liquid pycnometry relies on Archimedes’ principle. A sample is weighed in air and then placed in a calibrated pycnometer filled with a reference liquid of known density; by measuring the displaced liquid and the sample’s mass, the sample volume is obtained and its density computed. This method is robust for liquids and for solids that do not react with the liquid, but care must be taken with solvent compatibility, temperature, and surface effects.

Applications include characterizing powders, ceramics, polymers, minerals, and pharmaceuticals; it provides densities, porosity estimates, and quality-control data. Pycnometry complements other methods and offers a relatively simple means to obtain accurate density values for a wide range of materials.