What is sieving Technique and Disadvantages of sieving technique

Sieving technique

In this technique the powder whose particle size is to be determined is placed on a nest of standard sieves stacked over one another with the sieve of largest aperture on top followed by sieves of gradually decreasing pore sizes. The powder is shaken for a definite period of time using a mechani- cal shaker and the material that passes through a particular sieve and is retained on the next finer sieve is collected and weighed. The data obtained is analysed and the particle size and size distribu- tion is recalculated.

Sieving technique is generally useful for coarse particles since the technique is limited by the smallest size of sieve that can be produced and hence measurement of sizes smaller than 50 um are difficult.

Disadvantages of sieving technique:

(i Particles may aggregate during sieving due to generation of electrostatic charge. 

(ii) Moisture can also lead to aggregation of powders and the actual particle size may not be obtained. 

(iii) Attrition of particles during sieving may lead to size reduction.. 

iv) Sieve loading and duration of mechanical shaking can influence the results.