Particle Size Measurement Technique
There are numerous techniques of particle size measurement
which have been discussed below in detail. The more common
techniques employed in P/M and their range of applicabil i ty are
given in Table1.
Table1. Common methods of particle size measurement and
Their limit of useful size range.
M e t h o d o f An a l ys i s
A p p r o x i ma t e u s e f u l
Particle size range
( mi c r o n s )
1. Sieving Analysis
(i) Sieving, using mechanical shaking,
(ii) micromesh sieve
44
--
840
1
--
1
5
--
44
C11ARACNIUSTICS AND TBSTINGS Of MBRAT
M e t h o d o f An a l ys i s
POWDER
A p p r o x i ma t e
Particle size range
( mi c r o n s )
2.Microscopic analysis
(i) Light Microscopy
0.1
(ii) Electron microscopy
0.001
3.Sedimenlution method.
(i)Sedimentation and
2
(ii)decantation Method
(iii)Pipette Method
2
(iv)Gravitational
1
(v)Turbidimetry
0,05
Centrifugal
0,05
4.Elutriation Method,
( i ) El u t r ia ti on
5
( i i ) R o ll e r Ai r An a l yz e r
5
5 . P e r me a b i l it y M e t ho d .
( i ) P e r me a b i li t y
0 .5
( i i ) F i sh e r Su b -s i ev e si z e
0 .2
6 . ...Ad s o r pt io n M e t hod .
( i ) Ad s o rp ti on ( g a s es )
0 .0 02
7 . El e c t r ol yt i c R e s is ti vi t y M e t ho d
( i ) C o ul t er c ou nt e r
0 .3
1) Sieving Method
Sieving is the most popular and the simplest method particle size
testing Sieves are employed for classifying powder different systems of
serves
are used in various, countries determination
of, sieve size
powders. In America the Tyler of U.S. standard System, in U.K mainly
the B.S system, in Geri usually the DIN system and in France the .
AFNOR system widely prevalent. Among these, Tyler series of testing
has been almost, universally. Accepted as the standard opening of a
screen is expressed in either inch or mm. or number of meshes per
linear inch.
In most cases , mesh numb. known by the number of
apertures per linear Inch.
Woven-wire sieves arc made or copper, brass, bronze, nickel,
monel metal or stainless steel and in recent years nylon woven sieve
clothes have been employed ; each of them has n specific use,, for
example, bronze aleves are chiefly used for hard alloy powders. Sieves
vary In size of aperture and thickness of the wire or thread front which
they have been made.
Sieve size particles are usually denoted by the mesh size through which
till of the powders in tile batch will pass, for example, between amount
and size15. Particle, size distribution Is also of fundamental importance
as it affects pressing and sintering behaviour as well as the physical and
mechanical properties of the sintered material. Size distribution is based
oil the percentage by weight of sample powder which is retained on a
screen of given mesh size from a given weight of starting material after
passing through the just coarser sieve
Thus, with the help of its knowledge, .1he properties of the green
and final products can be controlled,"Fine metal powders resultin poor
apparent apparent density , poor flow rate and Maximum sinterability
while Coarser powders cause good apparent density, good flow rate but
minimum sinterability. if we use the mixed sized and uniform sized
particles, optimum packing, with optimum sinterability with lower
packing density can he achieved respectively.
2) Microscopic method Microscopic sizing or counting technique is the
most direct, simple and well known of the many method which are
employed for the measurement of the many size and its distribution 19. It
involves actual counting of particles and individual examination of a
large number of particles on a slid sample of powder by an operator 12.
This furbishes the operator an indication of particles shape, size range
quality of fractious and stale of dispersion or extent of agglomeration of
the sample Though this is a long time-taking and tedious process. it is
regarded as the most reliable and standard method used for checking the
accuracy of other methods.
Optical Microscopic is employed for. The determination of particle
diameters down to about 0.3μ while the electron microscope is used for
the measurement of metal particles in the range of 10 to 0.001μ in
diameter20.
1) Sedimentation Method.
Sedimentation sizing is the classification of powder particle according to
their settling velocitics in a fluid and is the most important method for
particle size analysis in the sub-sieve range Sedimentation involves
spending the powder sample by means of proper agitation in a fluid
medium and allowing it to settle for a suitable time thereby measuring the
settling velocity in suspensions.
Sloke's law establishes the relationship between the settling velocity of
falling particles and particles size which states that the settling velocity
of falling spherical particle at low velocity in a quiescent homogeneous
fluid of infinite extent is proportional to the square of the particle
diameter. The law may be expressed by
ν = (pρ – pt) d2
g
18η
where ν is the terminal velocity of the particle in cm/sec, p ρ and pt the
density of the particle and fluid respectively in gm/cc, d the stoke's
diameter of spherical particle in cans, η the viscosity of the fluid in poises
and g the gravitational accelerant lion in cm/sec on this basis irregularly
shaped size is defined as the diameter of a sphere of same material having
the same settling velocity under the same controlled conditions. In order
to achieve consistent results for Irregularly shaped particles the Reynold
number which may be expressed by the formula.
R=
Would be less than 0.2.
V . d pt
η