comminution

Comminution is the general term for reducing the size of solid particles by mechanical force, the umbrella word that covers crushing, grinding, milling and pulverising. Where milling usually names a specific machine operation, comminution names the underlying process of making solids smaller, whatever equipment achieves it.

Physically it works by applying stress until particles fracture. Brittle materials crack along internal flaws under compression or impact, while tougher materials need shear or attrition to wear them down. As particles shrink they become stronger and harder to break further, because there are fewer flaws to propagate cracks, so finer grinding takes disproportionately more energy.

This energy relationship is summarised by classic laws. Rittinger's law holds that the energy needed is proportional to the new surface area created and suits fine grinding; Kick's law relates energy to the size reduction ratio and suits coarse crushing; Bond's law sits between them. These are empirical guides rather than exact predictions.

In pharmacy comminution serves the same ends as milling: faster dissolution through greater surface area, the fine sizes required for inhalation and suspensions, and uniform mixing of small drug doses. The same caution applies too, that excessive size reduction can heat-degrade, charge, or partly amorphise sensitive drugs.