Heliumpycnometers

Helium pycnometers are instruments used to determine the true density of solid materials. They operate on the principle of gas displacement, specifically using helium gas. Helium is chosen because it is an inert gas that can penetrate very small pores and cavities within a sample, allowing for the measurement of the skeletal volume of the material, excluding any internal voids or closed pores. The instrument works by measuring the pressure change in a chamber containing the sample when a known volume of helium is introduced. By applying Boyle's Law, which relates pressure and volume of a gas at constant temperature, the volume occupied by the helium after it expands into the interstitial spaces of the sample can be calculated. This volume is directly related to the volume of the solid material itself. Knowing the mass of the sample and its calculated solid volume, the true density can then be precisely determined. Helium pycnometry is a non-destructive technique and is widely used in materials science, chemistry, and geology for characterizing powders, porous materials, and dense solids.