Lab 7– Powder Micromeritrics Physical Pharmacy Lab 7– Powder Micromeritrics

Particle size analysis Powder flow

Particle Size Analysis Microscopy Sieving Sedimentation techniques Optical and electrical sensing zone method Laser light scattering techniques (Surface area measurement techniques)

Particle size

Sieve method Sieve analysis is performed using a nest or stack of sieves where each lower sieve has a smaller aperture size than that of the sieve above it. aperture size or mesh size (or sieve number). The mesh size is the number of wires per linear inch.

Sieve method Sieve diameter dA: The width of the minimum square aperture through which the particle will pass (see text and

Advantages Easy to perform Wide size range Inexpensive Disadvantages Known problems of reproducibility Wear/damage in use or cleaning Irregular/agglomerated particles Rod-like particles : overestimate of under-size Labour intensive

Procedure Instruments Analytical Sieves Analytical balance Weigh about 50 gm of the given granules on analytical balance. Switch on the analytical sieve machine, set the amplitude at 1 and the time of mechanical vibration on 5 minutes. Add the given amount of the powder granules to the coarsest sieve on the top and push start to initiate mechanical vibration.

4. After the vibration have stopped, weigh the granules or powder in each of the sieves with recording its corresponding number and particle size. 5. Calculate the percentage weight of powder at each of the size ranges by the following equation: % Retained = weight in the sieve number x X 100 total weight

6. Make a table as follows 7. Build a histogram using Microsoft Excel or graph paper, between particle size of different sieves and % retained

Powder Micrometrics & Flow General factors that affect flow powders Size Shape porosity Density Humidity

Angle of Repose The maximum angle possible between the surface of pile of non-cohesive (free-flowing) material and the horizontal plane. Related to the interparticulate friction and resistance to flow

Different angles of reposes can be obtained for the same powder because of the differences in the way the samples were handled.

Procedure ( Angle of repose) Take a certain amount of powder and Form the angle of repose on a fixed base, the base should be free of vibration Vary the height of the funnel to carefully build up a symmetrical cone powder. Care should be taken to avoid vibration as the funnel is moved. The funnel height should be maintained approximately 2-4 cm from the top of the powder pile as its us being formed in order to minimise the impact of falling powder on the tip of the cone. Determine the angle of repose by measuring the height of the cone of the powder and calculating the angle of repose from the following equation: