picnometria

Picnometria, also known as pycnometry in English, is a set of methods used to determine the volume and thus the density of a material by means of a pycnometer. The term comes from Greek roots meaning “dense” and “measure.” It is applied to solids such as ceramics, metals, polymers, rocks, and powders, as well as to liquids where precise density measurements are needed for formulation and quality control.

Two principal approaches are gas pycnometry and liquid pycnometry. Gas pycnometry measures the true solid volume by introducing a known gas into a fixed-volume chamber containing the sample and applying Boyle’s law to relate pressure changes to volume. Helium is commonly used because it penetrates fine pores, providing a volume that closely reflects the solid framework. Liquid pycnometry determines volume by the displacement of a calibrated liquid: the sample is weighed in a liquid-filled pycnometer, and the difference in mass and the liquid’s density yield the sample’s volume. Porosity, moisture, and pore filling must be considered, particularly for porous materials.

Applications include characterizing material density, calculating porosity, quality control in manufacturing, and aiding in material design and research. Temperature control and buoyancy corrections are important for accurate results, and samples often require degassing or careful drying. The method provides a relatively quick, precise measure of volume and, from mass, density, enabling comparisons across samples and processes. See also density measurement, Archimedes’ principle, and porosity assessment.