Section 5: Compressibility Index & Packing Geometry

Carr's Compressibility Index Theory

Reports that the more a powder material compacts during a tapping test, the poorer its overall flow properties are.

Carr's Compressibility Index Equation

Calculated using the formula: C.I. = [(ρ_tapped - ρ_bulk) / ρ_tapped] * 100.

Excellent Flow Carr's Index

Indicated by a Carr's Compressibility Index strictly less than 10% (< 10%).

Good Flow Carr's Index

Indicated by a Carr's Compressibility Index ranging from 11% to 15%.

Fair Flow Carr's Index

Indicated by a Carr's Compressibility Index ranging from 16% to 20%.

Passable Flow Carr's Index

Indicated by a Carr's Compressibility Index ranging from 21% to 25%.

Poor Flow Carr's Index

Indicated by a Carr's Compressibility Index ranging from 26% to 31%.

Very Poor Flow Carr's Index

Indicated by a Carr's Compressibility Index ranging from 32% to 37%.

Very, Very Poor Flow Carr's Index

Indicated by an extremely high Carr's Compressibility Index exceeding 38% (> 38%).

Porosity (ε) Definition

A direct measure of the collective air spaces or voids present within a bulk bed of powder material.

Void Volume Formula (V_void)

Calculated mathematically as V_void = V_bulk - V_true.

Porosity Percentage Equation

Calculated mathematically as Porosity (ε) = (V_void / V_bulk) * 100.

Rhombohedral / Closest Packing

An extremely tight powder packing arrangement where angles of 60° and 120° dominate, resulting in a low porosity of 26%.

Cubic / Loosest Packing

An open powder packing arrangement where particles sit at 90° to one another, resulting in a high porosity of 47% to 48%.

Feret's Diameter (I)

The absolute distance between two imaginary parallel lines tangent to a randomly oriented particle and perpendicular to the ocular scale.

Martin's Diameter (II)

The diameter value calculated at the precise point that divides a randomly oriented particle into two equal projected surface areas.

Projected Area Diameter (III)

The diameter calculated from a theoretical perfect circle that possesses the exact same projected area as the asymmetrical particle.