BALL MILLING
MECHANISM OF GRAIN SIZE
REDUCTION
MECHANICAL ATTRITION
SUBMITTED TO:
DR. MANDEEP SINGH
SUBMITTED BY:
ADITYA BHARDWAJ
(12025101)
M.TECH NANO 5 YRS
CONTENTS
• Ball milling-Introduction, use , principle and
construction, method, application, merits and
de-merits and conclusion.
• Mechanism of grain size reductionintroduction, grain growth and its rules,
mechanism, principle and various size
reducing instruments.
• Mechanical attrition- introduction, principle
and process, attrition devices and conclusion.
BALL MILLING
INTRODUCTION
• Ball milling is a method of production of nano
materials.
• This process is used in producing metallic and
ceramic nano materials.
• These mills are equipped with grinding media
composed of wolfram carbide or steel.
• Ball mills rotate around a horizontal axis,
partially filled with the material to be ground
plus the grinding medium.
USE OF BALL MILLING
• Generation of curved or closed-shell carbon
nanostructures , carbon scrolls by ball-milling
of graphite
• Nanoporous carbon by ball milling
• Carbon nanotubes and carbon microspheres
by high energy ball milling of graphite.
• Highly curved carbon nanostructures
produced by ball-milling.
PRINCIPLE & CONSTRUCTION
PRINCIPLE
• It works on the principle of impact, i.e., size reduction is
done by impact as the balls drop from near the top of the
shell.
Construction
• A ball mill consists of a hollow cylindrical shell rotating
about its axis. The axis of the shell may be either
horizontal or at a small angle to the horizontal. it is
partially filled with balls. The grinding media is the balls
which may be made of steel (chrome steel), stainless steel
or rubber. The inner surface of the cylindrical shell is
usually lined with an abrasion-resistant material such as
manganese steel or rubber. less wear takes place in the
rubber lined mills. The length of the mill is approximately
equal to its diameter.
METHOD
• The method consist of loading graphite powder
(99.8% purity) into a stainless steel container
along with four hardened steel balls. The
container is purged and argon gas (300 kPa) is
introduced. The milling is carried out at room
temperature for up to 150 hours.
• Following milling, the powder is annealed under
a nitrogen (or argon) gas flow at temperatures
of 1400 degree Celsius for six hours. The
mechanism of this process is not known but it is
thought that the ball milling process forms
nanotube nuclei and the annealing process
activates the nanotube growth.
• Multi-walled nanotubes are formed but single –
walled nanotubes are more difficult to prepare .
ILLUSTRATIONS
APPLICATIONS
• The ball mill is used for grinding materials
such as coal, pigments, and felspar for pottery.
• Widely used in production lines for powders
such as cement, silicates, refractory material,
fertilizer, glass ceramics, etc. as well as for ore
dressing of both ferrous non-ferrous metals.
MERITS AND DE-MERITS
• Advantages
The cost of installation, Power required and grinding
medium is low; it is suitable for both batch and
continuous operation, similarly, it is suitable for
open as well as closed circuit grinding and is
applicable for materials of all degrees of hardness.
• Disadvantages
Bulky size ,running a strong vibration and noise,
there must be a solid foundation ,low efficiency,
energy consumption is relatively large ,greater
friction loss.
CONCLUSION
• The significant advantage of this method is
that it can be readily implemented
commercially.
• Ball milling can be used to make carbon
nanotubes and boron nitride nanotubes.
• It is a preferred method for preparing metal
oxide nano crystals like Cerium(CeO2) and Zinc
Oxide (ZnO).
MECHANISM OF GRAIN SIZE
REDUCTION
INTRODUCTION
• Grain- portion of material
within which arrangement
of atoms is identical,
however, orientation of
atom or crystal structure is
different for each grain.
• Grain Boundary- surface
that seperates individual
grains, is a narrow zone in
which atoms are not
properly spaced.
GRAIN GROWTH
• Grain growth is the increase in size of grains
(crystallites) in a material at high temperature. This
occurs when recovery and recrystallisation are
complete and further reduction in the internal
energy can only be achieved by reducing the total
area of grain boundary. The term is commonly used
in metallurgy but is also used in reference to
ceramics and minerals.
RULES OF GRAIN GROWTH
• Grain growth occurs by the movement of grain boundaries
and not by coalescence (i.e. like water droplets)
• Boundary movement is discontinuous and the direction of
motion may change suddenly.
• One grain may grow into another grain whilst being
consumed from the other side
• The rate of consumption often increases when the grain is
nearly consumed
• A curved boundary typically migrates towards its centre of
curvature
• When grain boundaries in a single phase meet at angles
other than 120 degrees, the grain included by the more
acute angle will be consumed so that the angles approach
120 degrees.
SIZE REDUCTION
Smaller particle size and increased surface
area leads to:
• More uniformity of weight and drug content
• More impalpability and spreading of dusting
and cosmetic powders
• More stability of suspensions, increasing
rates of reaction, drying, extraction, ..etc
DISADVANTAGE OF GRAIN SIZE
REDUCTION
•
•
•
•
•
Possible change in polymorphic form
Possible degradation by heat
Less flowability
Static charge problems
Air adsorption, hence, less wetting
PRINCIPLE
• Strengthening by grain size reduction is based
on the fact that crystallographic
orientation changes abruptly in passing from
one grain to the next across the grain
boundary. Thus it is difficult for a dislocation
moving on a common slip plane in one crystal
to pass over to a similar slip plane in another
grain, especially if the orientation is very
misaligned.
MECHANISM OF SIZE REDUCTION
•
•
•
•
Compression: positive pressure, e.g., nut
crusher
Impact: material is stationary and hit by an
object ,e.g., hammer mill
Shear: cutting force, e.g., scissors
Attrition: breaking the edges of the solid
either by impact or particle collisions
SIZE REDUCTION INSTRUMENTS
• Hammer mill
• Ball mill
• Fluid energy mill
• Colloid mill
HAMMER MILL
• Intermediate crusher
Feed P.S. 5-50mm,
Product P.S. 0.1-5 mm
Size control: Hammer speed,
screen size, feed size
Use of deflectors to present
the particles into hammer impact
Advantages: Ease of cleaning,
Minimum scale-up problems
Disadvantages: Clogging of
screen, heat build up on milling,
Mill and screen wear
FLUID ENERGY MILL
Ultra-fine particle size production
Feed P.S. :5OO microns
Product P.S. :1-10 microns (Ultra-fine)
Grinding medium: superheated steam or
compressed air
Mechanism of size reduction: shear and
impact
Built in classifier
Advantages: 6000 kg feed milled per hour,
no contamination.
Disadvantages: quite expensive, not
suitable for soft, tacky& fibrous
materials.
COLLOID MILL
• Reduce size of a solid in
suspension
• Reduce the droplet size of a
liquid suspended in another
liquid
• This is done by applying high
levels of hydraulic shear.
• It is frequently used to
increase the stability of
suspensions and emulsions
COLLOID MILL CONTD.........
• The mill consists of a rotor
and stator
• Clearance from zero
to1.25mm
• Thin film of material is
passed between working
surfaces, subjected to high
shear
GENERAL CHARACTERISTICS OF
VARIOUS TYPES OF MILLS
S.NO
NAME OF MILL
MECHANISM
OF ACTION
USES
1.
HAMMER MILL
IMPACT
USED FOR ALMOST
ALL DRUGS
2.
ROLLER MILL
ATTRITION AND
COMPRESSION
SOFT MATERIALS
3.
COLLOID MILL
IMPACT AND
ATTRITION
FOR ALL DRUGS
AND BRITTLE
MATERIALS
4.
FLUID ENERGY MILL
IMPACT AND
ATTRIRION
FOR ALL DRUGS
5.
BALL MILL
IMPACT AND
ATTRITION
MODERATELY HARD
AND FRIABLE
MATERIALS
MECHANICAL ATTRITION
INTRODUCTION
• It is a Top-Down process.
• This process produces nanocrystalline nanoparticles and
coarser particles that contain nanocrystals and used in
fields, such as ,material classes, including metals, ceramics,
and polymers. metallurgy industries for many years.
• The objectives of milling include : particle size reduction
(comminution or grinding); shape changing (flaking);
agglomeration; solid-state blending (incomplete alloying);
modifying, changing, or altering properties of a material
(density, flowability, or work hardening); and mixing or
blending of two or more materials or mixed phases.
However, the primary objective of milling is often purely
particle size reduction.
PRINCIPLE & PROCESS
• The fundamental principle of
size reduction in mechanical
attrition devices lies in the
energy imparted to the
sample during impacts
between the milling media.
This model represents the
moment of collision, during
which particles are trapped
between two colliding balls
1 Model of impact event at a time of maximum
within a space occupied by a FIG
impacting force,
the formation of a microcompact. Reprinted
dense cloud, dispersion, or showing
with permission
[28], E. Kuhn, ASM Handbook, Vol. 7, Materials
mass of powder particles. from
Park, OH, 1984.
© 1984, ASM.
• Figure 2 shows the process of trapping an
incremental volume between two balls.
Compaction begins with a powder mass that is
characterized by large spaces between particles
compared with the particle size. The first stage
of compaction starts with the rearrangement
and restacking of particles. Particles slide past
one another with a minimum of deformation
and fracture, producing some fine, irregularly
shaped particles. The second stage of
compaction involves elastic and plastic
deformation of particles. The third stage of
compaction, involving particle fracture, results
in further deformation and/or fragmentation of
the particles.
FIG 2 Process of trapping an incremental volume of powder
between two balls in a randomly agitated charge of balls and powder.
(a–c) Trapping and compaction of particles. (d) Agglomeration. (e)
Release of agglomerate by elastic energy. Reprinted with permission
from [28], E. Kuhn, ASM Handbook, Vol. 7, Materials Park, OH, 1984.
© 1984, ASM.
ATTRITION DEVICES
• Attrition Mill Also known as the
attritor or stirred ball mill. The
balls are set in motion by rotation
of the central shaft on which
secondary arms are fixed. The
cylinder itself is fixed.
Horizontal Mill. The cylinder rotates
around its horizontal axis. The
combined effects of the centrifugal
force induced by this rotation and
gravity cause the balls to rise and
fall onto the powder particles.
1D Vibratory Mill. Also known as a
shaker mill. The vessel is set in vertical
oscillatory motion. Under this action,
the 1-kg ball rises then falls back onto
the powder particles.
Planetary Mill. The containers are fixed
on a table which rotates until the
centrifugal acceleration reaches 30 to 50
times the acceleration due to gravity.
The containers themselves also rotate in
modern mills, this rotation being either
coupled or uncoupled with respect to
the rotation of the table.
3D Vibratory Mill. Also
known as a three-axis
shaker. These operate
according to the same
principle as the 1D
vibratory mill, but this time
in a more complex way due
to the 3 vibrational degrees
of freedom. The balls
collide with the side walls
of the container (friction
and impacts), but also with
its floor and ceiling.
PROBLEMS OF MECHANICAL
ATTRITION
The problem of milling atmosphere is also
serious and has been found to be a major cause
of contamination. It has been observed that if
the container is not properly sealed, the
atmosphere surrounding the container, usually
air, leaks into the container and contaminates
the powder. This is particularly problematic for
oxidation-sensitive materials, such as pure
metals.
CONCLUSION
• It is a simple and useful processing technique
that is being employed in production of
nanomaterials or nanocrystals from all
material classes.
• Despite the difficulties of contamination, MA
is more widely used than ever and continues
to be applied to the formation of
nanoparticles and nanocrystalline structures
in an ever-increasing variety of metals,
ceramics, and polymers.
REFERENCES
• Wikipedia.org
• www.slideshare.net
• The science of engineering and materials book by
Donald Askeland, Pradeep Fulay and Wendelin
Wright.
• Callister’s material science book.
• Nanoparticles from Mechanical Attrition by Claudio
L. De Castro, Brian S. Mitchell, Department of
Chemical Engineering, Tulane University, New
Orleans, Louisiana, USA
THANK YOU