particle size & size distribution

1. A presentation on
Particle size & Size distribution
Prepared by-
Mandakini Porwal
B.Pharm (4th sem.)
S.R.L.T group of institutions,Ekdil ,Etawah

2. Particle size,
Average particle size ,
Particle size distribution
• Methods for particle size distribution-
1. By determining numbers of particles
2. By determining weight of particle
• Methods of particle size determination
1. Microscopic technique
2. Sieving technique
3. Sedimentation technique

3. PARTICLE SIZE
• Size of spherical particles can be easily expressed in
terms of diameter.
• In case of non sphere particles particle size expressed
in term of equivalent spherical diameter by using
some measurable properties like –
Surface diameter-is the diameter of a sphere having
the same surface area as that of the asymmetric
particles.

4. METHODS OF PARTICLE SIZE
DETERMINATION
• Microscopic method
Used for particle measurement in the range of (0.2-
200µm).At least 300-500 particles counted to obtain
a good particle size distribution.

5. METHOD
 Dilute suspension of powder in suitable vehicle in which it is
insoluble.
 A drop of suspension mounted on a slide.
 Observe under a micro scope.
 Eye piece of microscope is attached with the micrometer to
obtain the particle size of powder sample.
 Particles are counted with the help of eye piece.
 A size frequency distribution curve is obtained with the help of
particle size & their number.
 In case of very small particle electron microscope is used.

6. ADVANTAGE
• Agglomerates as well as particles of more than one
component can be detected by this method.
Disadvantage
• The measured diameter of the particles represents two
dimensions only.i.e,length & breadth .

7. SIEVING TECHNIQUE-
• In this technique the particle
size of the powder determined
by place it on the next of
standard sieves which is stacked
over one another .
• Sieve of large aperture on the
top followed by sieves of
decreasing pore size .

8. METHOD-
 The powder is shaken for a definite period of time
using a mechanical sieve shaker.
 The material pass through a sieve & retain on a final
sieve is collected & weigh it.
 The data obtained is analysed & particle size is
calculated.
 The measurement of smaller particle size (<50µm) is
difficult by this method.

9. ADVANTAGE-
• This method is very useful for the measurement of
coarsed particles.
DISADVANTAGE
1. Particle may aggregate during sieving due to
electrostatic charge.
2. Powder moisture can also leads to aggregation of
particles by which actual particle size can not be
determine.
3. Attrition of particles during shaking may cause
reduction in particle size.
4. Sieve loading & duration of mechanical shaking can
influence the result

10. SEDIMENTATION TECHNIQUE
In this technique ANDREASON
Pipette is used to determine
particle size.
Andreason pipette-
It consist of 550ml Stoppard
cylindrical vessel of about
5.5cm internal diameter & a
scale graduated (0-20)cm on
it. It has a 10ml bulb pipette
fitted with a two way
stopcock & a side tube for
discharging the sample.

11. METHOD
 (1-2)% of powder sample suspension prepared.
 Deflocculating agent added in sufficient amount.
 To brake powder aggregate.
 Sample filling- powder sample is introduced into vessel
up to 550ml mark.
 The vessel is shaking to distribute particles uniformly.
 After that the whole assembly is kept undisturbed in a
constant temperature water bath.
 At various time interval 10ml of sample withdrawn
through stopcock & poured it into previously weighted
china disc.
 The sample are evaporated & weigh & necessary
correction is made for the deflocculating agent added

12. The particle diameter corresponding to the various time
periods is calculated by using the stokes law-
ADVANTAGE
It is in expensive.
It is a simple technique.
DISADVANTAGE
Method is laborious & complicated.
Very small particles can not be determined accurately.
𝑉 =
h
t
=
𝑑2
𝑠𝑡 𝜌 𝑠−𝜌0 𝑔
18𝔶0

13. AVERAGE PARTICLE SIZE-
• Average particle size of the powder may be calculated
as-
Average particle size
In the above calculation , the total number & the mean
size of particles have been considered.
=
∑𝑛𝑑
∑𝑛

14. METHODS FOR PARTICLE SIZE DISTRIBUTION-
It can be determine by following two methods-
1. Number distribution- based on counting method e.g.
Optical microscopy.
2. Weight distribution-based on weight distribution e.g.
Sieve analysis , andreason pipette sedimentation
technique .

15. When the number or
weight of particles
lying with in a
certain size range
is plotted against
the size range or
mean particle size
a frequency
distribution curve is
obtained.
(frequency distribution curve)

16. 1. when the number of particle is plotted against the
mean particle size, the curve is obtained is known as
number frequency distribution curve.
2. when the weight of particle is plotted against the
mean particle size ,the curve is obtained is known as
weight distribution frequency curve.