Section 4: Density Types & Bulk Volume Metrics

True Density Definition

The actual density of the solid material itself, exclusive of all internal interparticle and intraparticle voids.

Helium Densitometer

The official instrument used to determine the true density of a powder material.

Granule Density Definition

The density of the combined granule structure; includes internal intraparticle pores but excludes external interparticle voids.

Granule Density Determination

Determined via the displacement of mercury, which resists penetrating pores smaller than about 10 micrometers under standard pressure.

Bulk Density Definition

The macro-density of the bulk powder mass; includes all intraparticle and interparticle voids combined.

Bulk Density Instruments

Determined using a bulk density apparatus (graduated cylinder method) or a pycnometer.

Relative Density Definition

The ratio of the bulk density of a powder or compact to the absolute true density of that same material.

Bulk Density Equation (ρ_bulk)

Expressed mathematically as ρ_bulk = grams of sample / mL of untapped volume.

Scott Volumeter

An apparatus using a sieve no. 18, powder funnel, loading funnel, baffle assembly, and receiving cup to find bulk density.

Tapped Density Mechanism

Achieved by mechanically raising a graduated cylinder and allowing it to drop under its own weight for a fixed duration.

Tapped Density Equation (ρ_tapped)

Expressed mathematically as ρ_tapped = grams of sample / mL of tapped volume.

Starch Powder Math Sample Data

A 10-gram sample of starch powder displays an untapped bulk volume of 23 mL and a final tapped volume of 17 mL.

Starch Bulk Density Calculation

Yields a bulk density value of exactly 0.43478 g/mL when dividing 10 grams by 23 mL.

Starch Tapped Density Calculation

Yields a tapped density value of exactly 0.58824 g/mL when dividing 10 grams by 17 mL.

Bulkiness Definition

Specific bulk volume, which is the direct mathematical reciprocal of bulk density (Bulkiness = 1 / Bulk density).