sieve analysis

Sieve analysis sizes a powder by shaking it through a stack of screens, much like sorting beach finds through a set of progressively finer kitchen sieves. The screens are arranged with the coarsest mesh on top and the finest at the bottom, so each particle settles on the screen whose holes it cannot pass through.

In practice a weighed powder is placed on the top sieve of a nest of standard sieves, and the stack is shaken or vibrated for a fixed time. Particles distribute themselves among the sieves by size, and weighing what is retained on each gives the mass in each size band. From these masses the cumulative distribution and values like the d50 are calculated.

It is simple, inexpensive, and widely used for coarse to moderately fine powders, roughly down to 38 to 45 micrometres with woven-wire sieves. Because it sorts by whether a particle can squeeze through a square opening, sieving effectively measures a particle's second-largest dimension, which suits roughly equant grains better than long needles or thin flakes.

Its limits are real. Very fine, cohesive, or electrostatic powders clog the mesh and resist passage, fragile granules may break during shaking, and sieving cannot reach the sub-micron sizes important for inhaled or micronized drugs. For those, laser diffraction or other methods are needed.