The density of a solid particle can assume different values depending on the method used to measure the volume of the particle. It is useful to distinguish three levels of expression of density:
— the crystal density which only includes the solid fraction of the material; the crystal density is also called true density
— the particle density also includes the volume due to intra particulate pores and this density can be determined by helium pycnometry
— the bulk density further includes the inter particulate void volume formed in the powder bed; the bulk density is also called apparent density.
For Material Experts:
Gas pycnometric density Instrument and measuring principles
Measures the volume occupied by a known mass of powder/particles, which is equivalent to the volume of gas displaced by the powder using a gas displacement pycnometer. The volume determined excludes the volume occupied by open pores. It includes the volume occupied by sealed pores or pores inaccessible to the gas. Helium is used as a test gas due to its high diffusivity into small open pores. With other gases, different values are obtained.
|Accupyc 1330 from Micromeritics
|USP 699 / Ph. Eur. 2.2.42 Density of Solids (non-GMP)
|The volume of gas (helium) displaced by a known mass of substance is measured. The density of particles is expressed in grams per cubic centimetre (g/cm3)
|1-5 g – volume preferably 7.5-75 cm³.
|Drying conditions have to be determined
Blake GR, Hartge KH (1986) Particle density. Methods of soil analysis: Part 1 physical and mineralogical methods. 1986 5:377-82.
Viana M, Jouannin P, Pontier C, Chulia D (2002) About pycnometric density measurements. Talanta. 57(3):583-93.