Pyknometri

Pyknometry (also referred to as pycnometry) is a set of methods for determining the density of solids by measuring the solid’s volume using a known reference volume, typically with a pycnometer. The approach relies on the principle that a solid’s mass divided by its volume yields its density. Pycnometric measurements are commonly used for powders, ceramics, metals, polymers, and porous materials to assess true or skeletal density and, when combined with bulk density, porosity.

In liquid-based pycnometry, a solid sample is weighed and then immersed in a liquid of known density inside a pycnometer of known volume. By comparing masses recorded before and after immersion and accounting for the liquid’s density, the true density of the solid can be calculated. Proper saturation and elimination of trapped air are important to ensure accurate results. This method is widely used to determine material density and, in turn, porosity and particle packing characteristics.

Gas pycnometry, or gas pycnometry, uses an inert gas (commonly helium) at controlled pressure to determine the sample’s volume by gas displacement. The technique can measure the skeletal or true density of a solid, often with pores that are inaccessible to liquids. Gas pycnometry is particularly useful for materials with surface roughness, moisture sensitivity, or complex porosity, where liquid methods may be problematic.

Standards and practice for pyknometry are provided by organizations such as ASTM and ISO and vary by method and material. Limitations include moisture, saturation state, and air entrapment, all of which can impact accuracy. The technique remains a standard tool in materials science, geology, and pharmaceuticals for characterizing density and porosity.