This presentation discusses micromeritics, which involves the study of small particles around a few micrometers in size. It summarizes several key methods for analyzing particle size, shape, and distribution, including optical microscopy, sieving, sedimentation, and conductivity. It also covers techniques for measuring surface area, such as adsorption and air permeability methods. Derived powder properties like density, bulk density, tapped density, porosity and their importance are also highlighted.

1. Presented by:
Ibrahim Mussa.
PRESENTATION ON MICROMERETIS
SCHOOL OF PHARMACEUTICAL AND
HEALTH CARE SCIENCES

2. MICROMERITIES
Micromeritics involve the study of the science and
technology of small particles, and of the order of a
few micrometer size. Particle size is normally
denoted in micrometers called as microns. One
micrometer is equal to 10-3 mm (millimeters.
Applications
Release and dissolution
Absorption and drug action
Physical stability
Dose uniformity

3. In a collection of particles of more
than one size, two properties are
important namely:
i. The shape and the surface of the
individual particles
ii. The particle size and size
distributions(The size range and
number or weight of particles)

4. PARTICLE SIZE
The size of a sphere is readily expressed in terms of its
diameter or radius
The Surface diameter, ds is the diameter of a sphere
having the same surface area as the particle
The Volume diameter, dv, is the diameter of a sphere
having the same volume as the particle
The Projected diameter, dp, is the projected diameter of
a sphere having the same observed area as that of the
particle
The Stokes diameter, dst, is the diameter which
describes an equivalent sphere undergoing sedimentation
at the same rate as the asymmetric particle

5. PARTICLE SIZE DISTRIBUTION
Any collection of particles is usually polydisperse
.It is therefore necessary to know not only the size
of a certain particle but also how many particles of
the same size exist in the sample
Thus ,we need an estimate of the size range
present and the number or weight fraction of each
particle size
This is the particle size distribution and from it we
can calculate an average particle size for the
sample

6. Count ….
When the number or weight of particles lying
within a certain range is plotted against the size
range or mean particle size, a so called frequency
distribution curve is obtained
This is important because it is have two samples
with the same average diameter but different
distributions

7. Methods to estimate particle
sizes are:
i. Optical Microscopy
ii. Sieving Method
iii. Sedimentation Method
iv. Conductivity Method

8.  Optical Microscopy
Particle size in the range of 0.2-100 μm can be
measured by optical microscopy. This method directly
gives number distribution, which can be further
converted to weight distribution. The optical
microscope has a limited resolving power (of the lens)
Is used to determine:
 particle size analysis in suspensions
 globule size distribution in emulsions
 particle size analysis in aerosols
Depending on the amount of solids or
globules

9. Advantages:
Microscopy allows the observer to view the
particles.
Agglomeration of particles and any
contamination in the powder can be detected.
Preparation of sample is simple and easy
Disadvantages
Depth of the particles is not measureable
Large sample is required.

10. Sieving Method
Particles having size range
between 50 and 1500 um are
estimated by sieving method In
this method, This method is
also known as analytical
sieving. Normally 15% of fine
powder (passed through mesh
100) should be present in
granulated mass to get a proper
flow and achieve good
compaction in tableting.

11. Advantages
sieving method is inexpensive, simple and
rapid with reproducible result
Disadvantages:
 Lower limit of the particle size is 50 μm.
 If powder is not dry, apertures become
clogged with particles, reproducible results.
leading to improper sieving.

12. Sedimentation Method
Sedimentation method may be
used over a size range of 1
(one) to 200 micrometer In
this method Sedimentation of
particles may be evaluated by
different methods. Some of
these are Andreasen pipette
method, balance method and
hydrometer method

13. The procedure is as follow
One or two percent suspension of the powder is
prepared in a suitable medium A deflocculating
agent will help in uniform dispersion of the
suspension. The suspension is transferred into the
Andreasen The stopper is placed and the vessel is
shaken to distribute the suspension uniformly. The
stopper is removed and two-way pipette is placed
and securely suspended the vessel in a constant
temperature water Bath At different time intervals,
10 mL samples are withdrawn using two-way
stopcock and collected in a watch-glass. Samples
are evaporated and weighed
13

14. Advantages
sizing is carried out rapidly
Disadvantages
it is difficult to automate, evaluation can be
automated , if the fluid is replaced by gas
The weight or the amount of particles obtained in
each time interval is referred to as weight
undersize. The weights are converted into
cumulative percent weight undersize. Particle
diameter is calculated from Stokes' law,
14

15. Conductivity Method
Particle size ranging from 0.5 to 500 μm is
measured by conductivity method. This method
gives number distribution. In fact, particle
volume is measured and converted into particle
diameter. Coulter counter is used to measure the
particle volume. Thus, size is expressed as
volume diameter, dv
15

16. CONDUCTIVITY METHOD
This method find the application in study of :
Particle growth in suspension and solution
Dissolution of drugs in desired medium
Effect of antibacterial agents
16

17. PRINCIPLE
The particles are suspended in conducting
electrolyte NaCl , This dispersion is filled in the
sample cell that has an orifice and maintain
contact with the external medium Electrode are
placed in solution.
When the suspend particle travel through the
orifice it displace its own volume of electrolyte
into beaker . The net result is a change in
electrical resistance.
17

18. ADVANTAGES
It is quick and gives accurate result
It takes short period of time
DISADVANTAGES
Unsuitable for polar and highly water soluble
materials
The instrument is expensive
18

19. Particle Shape
Particle shape will influence the
surface area, flow of particles,
packing and compaction
properties of the particles.
The surface area per unit weight
and unit volume are important
in the studies of adsorption and
dissolution. Spherical particle
exhibit better flow than
irregularly shaped particles use
surface roughness interlock with
each other, resulting in poor
flow and bridging with hopper.

20. Methods for determination
of surface area
There are several methods of determining the
surface area of a powder sample depending on the
nature of the particle whether it is porous or non
porous.
For non porous particles;
Specific surface area is defined as the surface area
per unit weight(sw) or unit volume(sv) of the
material.
Sv= surface area of particles÷ 𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑝𝑎𝑟𝑡𝑐𝑙𝑒𝑠

21. For porous particles,
There are two commonly used methods. These are
I. Adsorption method
II. Air permeability
ADSORPTION
An instrument used to obtain data for calculation of
surface area is quintasorb.
The adsorption and desorption is measured with
thermal conductivity detector.
A mixture of helium and nitrogen is passed through
the cell containing the powder at a specific pressure
and temperature

22. Adsorption Method
Principle :
A large specific surface allows good adsorption of
gas or solutes from a solution. The volume of gas (in
m3) adsorbed per gram of adsorbent (solid) can be
plotted against the pressure of gas introduced at
constant temperature. At low pressure, the gas (or
solute)adsorb on the surface of adsorbent and form a
monolayer .At saturation, the amount of adsorbed is a
function of surface area of powder. At high pressures,
the adsorbed layer becomes multi-molecular. The
completion of mono-molecular film can be identified
using BET equation. At that stage, the volume Ym)
adsorbed per one gram can be obtained.
22

23. Procedure
A known weight of powder is introduced into the
sample tube. The sample is mounted to the out-
gassing station to remove gas. Then the sample tube
is mounted to the analysis station. A mixture of
helium and nitrogen are used as adsorbate gas.
Nitrogen gas adsorbs on the powder and helium
does not adsorb (inert). Vapor dosing options are
available with the instrument. A mixture of gases is
passed through sample tube (containing powder) at
a specific pressure and temperature (thermostat
facility). 23

24. The amount of nitrogen gas adsorbed and desorbed is
measured using a thermal conductivity detector. The
signal height is proportional to the rate of adsorption or
desorption of nitrogen gas. The area under the curve is
proportional to the gas adsorbed on the particles. The
adsorption is measured, at several pressure
The bell shape curve is formed.
24

25. Here the nitrogen is adsorbate gas and helium is inert
and is not adsorbed on surface.
With the help of mathematical calculations and graph
studies the amount of nitrogen adsorbed and therefore
surface area is calculated.
p/y(po-p)=
1
𝑦𝑚 𝑏 +
𝑏−𝑝
𝑦𝑚 𝑏 . 𝑝/𝑝𝑜
Where p= pressure of adsorbate
y= vol of gas per gram
po= vapour pressure at saturation
ym =amount of vapour adsorbed per unit mass
when surface is covered with b= constant monolayer

26. Air permeability method
Air is passed through the dryer to remove any
moisture. Air is then allowed to flow through the
packed powder in the sample tube.
The flow of air is measured by manometer. The
level of the fluid in the manometer is related to the
average diameter of the particles.
The higher the surface area the greater the resistance
to the flow of air, the pressure drop is higher and
manometer level decreases.

27. Method
Assemble of the apparatus. It consists of a sample
tube containing the packed powder sample with
one connected to an air pump through a constant
pressure regulator .The other end is attached to a
calibrated manometer containing a suitable liquid
of low viscosity and negligible vapour pressure.
The air pump builds up air pressure and is
connected to a constant pressure regulator. Air is
passed through the dryer to remove any moisture
27

28. Cont….
Air is then allowed to flow through the packed
powder in the sample tube. The flow of air is
measured by the manometer. The level of the
fluid in the manometer is related to the average
diameter of the particles. The higher the surface
area, the greater is the resistance, the pressure
drop is higher and manometer level decreases.
28

29. Air permeability
29

30. DERIVED PROPERTIES OF
POWDER
These are the properties which are obtained from
fundamental properties such particle size and
diameter of the powder.
Such derived properties are like:
Flow properties= help to maintain a uniform
weight of tablet or capsule
Bulk Density=help in selecting container for
packing a dosage
Porosity= influence the dissolution of the drugs
30

31. Density
True density
This is the of the material itself. It is given as
True density =
𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑝𝑜𝑤𝑑𝑒𝑟
𝑡𝑟𝑢𝑒 𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑝𝑜𝑤𝑑𝑒𝑟
This density excludes the volume of the pores and
voids(space) within the powder sample.
Eg. Lactose=1.55 g/cm3
Starch=1.43 g/cm3
Sucrose=1.6 g/cm3
Talc =2.7 g/cm3
31

32. Method of determining true
density
True density can be determined by two methods
• Gas / helium pycnometer
• Liquid displacement method
32

33. Gas / helium pycnometer
In this method the gas is used because it does not adsorb on solid
sample and also penetrate into small pores
It consists of:-
 Sample cell which is sealed when sample is placed into it.
 Valve which is attached to sample cell. It is used to remove the air
from sample cell and also introduce helium gas
 A pressor detector
 A variable volume piston used to read pressure which is related to
volume of powder
33

34. procedure
 Volume of empty pycnometer is measured. Air in a
sample is removed by vacuum, helium gas is
introduced through valve , pressure is adjusted with
movable piston .Reading on the scale U1 represent
volume of empty cell
 Pycnometer is calibrated by putting sample of known
true volume Vc in sample cell. Air in sample cell is
removed and sealed. Same amount of helium gas is
introduced. Pressure is adjusted with removable piston
.reading on scale U2 represent is measured now.
34

35.  The different between U1 and U2 represent volume occupied by
sphere
 Lastly ,volume of a sample is determined. The stainless is
replaced by test sample powder, air in sample cell is removed
and sealed. Some amount of helium gas is introduced .
Pressure is adjusted with movable piston. Reading on the scale
(Us) is measured
 The different between U1 and Us represent volume occupied
by sample.
The resulting equation will be
Vt=
𝑉𝑐
𝑈1−𝑈2
(𝑈1 − 𝑈2)
Where Vt is true volume of sample
35

36. Liquid displacement Method
In this method, Solvent such as ethyl alcohol, water, mercury etc
Pycnometer or specific gravity bottle is used,
true density=
𝑊2
𝑊4−𝑊2
true density=
𝑊2−𝑊1
𝑊4−𝑊2
Where,
W1 =wt of Pycnometer
W2=wt of Pycnometer +sample
W4=wt of Pycnometer with powder and filled with solvent
W=W2-W1 = Wt of sample
W4-W2= Volume of liquid displaced by thee solid
36

37. Bulk density
This value includes the volume of all of the
pores within the powder sample.
It is defined mathematically as ;
Bulky density =
𝑚𝑎𝑠𝑠 𝑜𝑓 𝑝𝑜𝑤𝑑𝑒𝑟(𝑤)
𝑏𝑢𝑙𝑘 𝑣𝑜𝑙𝑢𝑚𝑒 (𝑣𝑏)
The bulk volume is obtained by using a
mechanical tapped density apparatus.
37

38. When particles are packed loosely, lots of gap
between the particles are observed., hence the
bulk volume increases making the powder light.
Light powders have high bulk volume while
heavy power have low bulk volume.
38

39. Applications of bulk density.
1. It is used to check the uniformity of bulk
chemicals
2. In determination of size of capsules for a
given dose of material.
3. Selecting proper size of container, packing
material mixing apparatus in the production
of tablets and capsules.
39

40. TAPPED DENSITY
Its obtained by mechanically tapping a graduated measuring
cylinder containing a powder sample
PROCEDURE
 Accurately measure a quantity of sample , M.
 Introduce the sample in 100ml measuring cylinder
 Cylinder was tapped mechanically at approximate time and
tapped density is measured by using the following equation
tapped density =
𝑀
𝑉
Where M= mass of test sample
V= final tapped volume
40

41. Porosity.
Porosity is the quality of being porous, or full of tiny holes.
It is given by:
Porosity or void=
𝑣𝑜𝑖𝑑 𝑣𝑜𝑙𝑢𝑚𝑒
𝑏𝑢𝑙𝑘 𝑣𝑜𝑙𝑢𝑚𝑒
Void volume= bulk volume - true volume
=
𝑏𝑢𝑙𝑘 𝑣𝑜𝑙𝑢𝑚𝑒−𝑡𝑟𝑢𝑒 𝑣𝑜𝑙𝑢𝑚𝑒
𝑏𝑢𝑙𝑘 𝑣𝑜𝑙𝑢𝑚𝑒
Ɛ =
𝑣𝑏−𝑣𝑝
𝑣𝑏
In percentage: Ɛ =[1-
𝑣𝑝
𝑣𝑏
]×100
41

42. Applications of porosity
It influences the rate of disintegration and
dissolution.
The higher the porosity, the faster the rate of
dissolution.
Also used in the study of adsorption and
diffusion of drug materials.
42

43. Packing arrangements.
 The arrangement of particles in a powder influences
the volume occupied by it.
 If the particles are uniform size of spheres, the
following can be used;
i. Closet or rhombohedral packing
ii. Most open loosest or cubic packing
43

44. If the particles in a powder are neither spherical
or uniform in size, the following arrangement is
possible.
Porosity of powder about 26% means closed
packing
Porosity of powder about 48% means loose
packing.
44

45. Flow properties
Flowability is the ability of a powder to flow through
easily.
Flow properties influence mixing and de-mixing of
powders. They also influence the design of formulation
and selection of process equipment. It can be evaluated
by,
Compressibility index and hausner Ratio
They measure the relative importance of intraarticular interaction . A
volume of powder is filled into graduated glass cylinder and
repeatedly measured and calculated as follow:
45

46. Flow chart of Carr’s index hausner’s
ratio
46
Compressible index% =
𝑡𝑎𝑝𝑝𝑒𝑑 𝑑𝑒𝑛𝑠𝑖𝑡𝑦−𝑏𝑢𝑙𝑘 𝑑𝑒𝑛𝑠𝑡𝑦
𝑡𝑎𝑝𝑝𝑒𝑑 𝑑𝑒𝑛𝑠𝑖𝑡𝑦
X100
hausner’s ratio =
𝑡𝑎𝑝𝑝𝑒𝑑 𝑑𝑒𝑛𝑠𝑖𝑡𝑦
𝑏𝑢𝑙𝑘 𝑑𝑒𝑛𝑠𝑖𝑡𝑦

47.  Nature of particles
smooth surface of particles improves the flow. Surface
roughness leads to poor flow, due to friction and
cohesiveness. particles having high density and low
internal porosity tends to posses good flow properties.
 Particle size
if the particle size is small (fine powder 100μm), the
powder flow is restricted, owing to cohesion of particles
by surface tension forces. Coarse powder (>1000μm
particle diameter)is free flowing and is governed by
gravitational forces which depend on diameter.
47
Factor affect flow properties of a powder.

48. Moisture content; the higher the moisture
content, the greater the risk of cohesion and
adhesion. It promotes liquid bridges and packing
of powders leading to poor flow.
Angle of repose; the flow characteristics are
measured by angle of repose. Improper flow of
powder is due to frictional forces between the
particles.
Angle of repose is defined as maximum angle
possible between the surface of pile of powder
and the horizontal plane.
48

49. • Formulation additives: flow activator are
commonly known as glidants. They improve
flowability of powder by reducing adhesion
and cohesion
49

50. Angle of repose;
Is the maximum angle
possible between the surface
of the pile of powder and
horizontal plane
It is used to measure the flow
property of the powder
50

51. Procedure
Weigh accurately 5-10g of powder sample.
Take a clean and dry funnel and attach it to
the burette stand at a height of about 2-3cm
from the surface.
Place a graph below funnel to draw the circle
around pile and gently pour sample from top
till a heap is formed.
51

52. Using pencil draw a circle around the heap
Repeat the procedure 3-4 times to obtain the
average radius.
Precautions
The peak of the pile of the powder can be
distorted care is not taken and this can lead to
errors in the height of the pile.
52

53. tan ϴ = ℎ/( 𝑟)
ϴ=(𝑡𝑎𝑛−)^1 ℎ/𝑟
Where;
h= height of pile, cm
r= radius of the base of the pile, cm
ϴ= angle of repose
The lower the angle of repose the better the
flow property of the powder and vice versa.
53

54. ANGLE OF REPOSE FLOW PROPERTY
25-30 Excellent
31-35 good
36-40 Fair, aid is not needed
41-45 Passable
46-55 poor
56-65 Very poor
>66 Very very poor.
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