Gaspyknometrie

Gaspyknometrie, also known as gas pycnometry, is a method for determining the volume and density of solid materials by measuring the displacement of a gas in a calibrated chamber. The technique relies on Boyle’s law at controlled temperature: inserting a sample into the reference volume changes the gas pressure, from which the sample’s volume can be calculated.

A typical gas pycnometer consists of a reference cell with a known volume and a sample cell into which the material is placed. The system is evacuated and filled with a high-purity test gas, usually helium. The pressure is measured with the reference cell alone (P1) and then with the sample in place (P2). The sample volume V is derived from V = (P1/P2 − 1) × V_ref, assuming constant temperature. Temperature stability, gas purity, and precise calibration are important for accuracy. The method is well suited for powders and solids and can be used with various geometries and sample types.

Gas pycnometry yields the true or skeletal density by determining the volume that the solid matter occupies, including porosity accessible to the test gas. Helium is preferred because its small size allows diffusion into open pores; other gases such as nitrogen or argon may be used in certain instruments. The technique is fast, non-destructive, and requires only small samples, making it common in ceramics, minerals, polymers, catalysts, and other material science applications. Limitations include limited sensitivity to closed porosity, potential adsorption effects, and the need for careful temperature control and calibration.