Ceramic materials are inorganic,
non-metallic materials made from
compounds of a metal and a non metal.
Ceramic materials may be crystalline or partly crystalline.
They are formed by the action of heat and subsequent
cooling. clay was one of the earliest materials used to
produce ceramics, but many different ceramic materials are
now used in domestic, industrial and building products.
Ceramic materials tend to be strong, stiff, brittle,
chemically inert, and non-conductors of heat and electricity,
but their properties vary widely. For example, porcelain is
widely used to make electrical insulators, but some ceramic
compounds are superconductors.
Crystalline ceramic materials are not amenable to a great
range of processing. Methods for dealing with them tend to fall
into one of two categories - either make the ceramic in the
desired shape, by reaction in situ, or by "forming" powders into
the desired shape, and then sintering to form a solid
body. Ceramic forming techniques include shaping by hand
(sometimes including a rotation process called "throwing"), slip
casting, tape casting (used for making very thin ceramic
capacitors, etc.), injection moulding, dry pressing, and other
variations. (See also Ceramic forming techniques. Details of these
processes are described in the two books listed below.) A few
methods use a hybrid between the two approaches.
Non-crystalline ceramics,
being glasses, tend to be
formed from melts. The glass is
shaped when either fullymolten,
by casting, or when in a state
of toffee-like viscosity, by
methods such as blowing to a
mold. If later heat-treatments
cause this glass to become
partly crystalline, the resulting
material is known as a glassceramic.
The important mechanical properties affecting
the selection of a material are:
(i) Tensile Strength: This enables the material to
resist the application of a tensile force. To
withstand the tensile force, the internal
structure of the material provides the internal
resistance.
(ii) Hardness: It is the degree of resistance to
indentation or scratching, abrasion and wear.
Alloying techniques and heat treatment help to
achieve the same.
(iii) Ductility: This is the property of a metal by
virtue of which it can be drawn into wires or
elongated before rupture takes place. It depends
upon the grain size of the metal crystals.
(iv) Impact Strength: It is the energy required per
unit cross-sectional area to fracture a specimen, i.e.,
it is a measure of the response of a material to shock
loading.
(v) Wear Resistance: The ability of a material to
resist friction wear under particular conditions, i.e.
To maintain its physical dimensions when in sliding or
rolling contact with a second member.
(vi) Corrosion Resistance: Those metals and alloys
which can withstand the corrosive action of a
medium, i.e. corrosion processes proceed in them
at a relatively low rate are termed corrosionresistant.
(vii) Density: This is an important factor of a
material where weight and thus the mass is
critical, i.e. aircraft components.

Conductivity, resistivity, dielectric strength
are few important electrical properties of a material. A
material which offers little resistance to the passage
of an electric current is said to be a good conductor of
electricity.

Some ceramics are semiconductors. Most of these
are
transition
metal
oxides
that
are
II-VI
semiconductors, such as zinc oxide.

While there are prospects of mass producting
blue LEDs from zinc oxide, ceramicists are most
interested in the electrical properties that show grain
boundary effects.

Insulators have very high resistivity. Ceramic
insulators are most common examples and are used on
automobile spark plugs, Bakelite handles for electric
iron, plastic coverings on cables in domestic wiring

In general metals are good conductors.
 Materials in which a state of magnetism can be
induced are termed magnetic materials. There are
five classes into which magnetic materials may be
grouped: (i) diamagnetic (ii) paramagnetic (iii)
ferromagnetic (iv) antiferromagnetic and (v)
ferrimagnetic.
Diamagnetic materials have a weak,
negative susceptibility to magnetic fields.
Diamagnetic materials are slightly repelled by a
magnetic field and the material does not retain
the magnetic properties when the external field
is removed. In diamagnetic materials all the
electron are paired so there is no permanent net
magnetic moment per atom. Diamagnetic
properties arise from the realignment of the
electron paths under the influence of an external
magnetic field. Most elements in the periodic
table, including copper, silver, and gold, are
diamagnetic.
Diamagnetism is a fundamental property of all matter, although it
is usually very weak. It is due to the non-cooperative behavior of
orbiting electrons when exposed to an applied magnetic field.
Diamagnetic substances are composed of atoms which have no net
magnetic moments (ie., all the orbital shells are filled and there
are no unpaired electrons). However, when exposed to a field, a
negative magnetization is produced and thus the susceptibility is
negative. If we plot M vs H, we see:
Note that when the field is
zero the magnetization is
zero.
The
other
characteristic behavior of
diamagnetic materials is
that the susceptibility is
temperature
independent.
Some
well
known
diamagnetic substances, in
units
of
10-8
m3/kg,
include:
quartz (SiO2)
-0.62
Calcite (CaCO3) 0.48
water
-0.90
Paramagnetic materials have a small, positive
susceptibility to magnetic fields. These materials are
slightly attracted by a magnetic field and the material
does not retain the magnetic properties when the external
field is removed. Paramagnetic properties are due to the
presence of some unpaired electrons, and from the
realignment of the electron paths caused by the external
magnetic field. Paramagnetic materials include magnesium,
molybdenum, lithium, and tantalum.
This class of materials, some of the atoms or ions in the material have a net
magnetic moment due to unpaired electrons in partially filled orbitals. One of
the most important atoms with unpaired electrons is iron. However, the
individual magnetic moments do not interact magnetically, and like
diamagnetism, the magnetization is zero when the field is removed. In the
presence of a field, there is now a partial alignment of the atomic magnetic
moments in the direction of the field, resulting in a net positive
magnetization and positive susceptibility.
Montmorillonite (clay)
13
Nontronite (Fe-rich clay)
Biotite (silicate)
79
Siderite(carbonate) 100
Pyrite (sulfide)
30
65
Ferromagnetic materials have a large, positive
susceptibility to an external magnetic field. They exhibit a
strong attraction to magnetic fields and are able to retain
their magnetic properties after the external field has been
removed. Ferromagnetic materials have some unpaired
electrons so their atoms have a net magnetic moment. They
get their strong magnetic properties due to the presence of
magnetic domains. In these domains, large numbers of atom's
moments (1012 to 1015) are aligned parallel so that the
magnetic force within the domain is strong. When a
ferromagnetic material is in the unmagnitized state, the
domains are nearly randomly organized and the net magnetic
field for the part as a whole is zero. When a magnetizing
force is applied, the domains
When you think of magnetic materials, you probably think of iron, nickel or
magnetite. Unlike paramagnetic materials, the atomic moments in these
materials exhibit very strong interactions. These interactions are produced
by electronic exchange forces and result in a parallel or antiparallel
alignment of atomic moments. Exchange forces are very large, equivalent to
a field on the order of 1000 Tesla, or approximately a 100 million times the
strength of the earth's field.
The exchange force is a quantum
mechanical phenomenon due to the
relative orientation of the spins of
two electron.
Two distinct characteristics of
ferromagnetic materials are
their:
(1) spontaneous magnetization
and the existence of
(2) magnetic ordering
temperature
In ionic compounds, such as oxides, more
complex forms of magnetic ordering can occur as a
result of the crystal structure. One type of magnetic
ordering is call ferrimagnetism. A simple representation
of the magnetic spins in a ferrimagnetic oxide is shown
here.
The magnetic structure is composed of two
magnetic sublattices (called A and B) separated by
oxygens. The exchange interactions are mediated by
the oxygen anions. When this happens, the
interactions are called indirect or superexchange
interactions.
The
strongest
superexchange
interactions result in an antiparallel alignment of spins
between the A and B sublattice.
In ferrimagnets, the magnetic moments of the A and B
sublattices are not equal and result in a net magnetic
moment. Ferrimagnetism is therefore
similar to
ferromagnetism. It exhibits all the hallmarks of
ferromagnetic behavior- spontaneous magnetization, Curie
temperatures, hysteresis, and remanence. However, ferroand ferrimagnets have very different magnetic ordering.
If the A and B sublattice moments are exactly equal but
opposite, the net moment is zero. This type of magnetic
ordering is called antiferromagnetism.
The clue to antiferromagnetism is the behavior of
susceptibility above a critical temperature, called the Néel
temperature (TN). Above TN, the susceptibility obeys the
Curie-Weiss law for paramagnets but with a negative
intercept indicating negative exchange interactions.

These properties includes atomic weight, molecular
weight, atomic number, valency, chemical composition, acidity,
alkalinity, etc. These properties govern the selection of
materials particularly in Chemical plant.

Optically transparent materials focus on the
response of a material to incoming lightwaves of a range of
wavelengths. Frequency selective optical filters can be
utilized to alter or enhance the brightness and contrast of
a digital image. The optical properties of materials, e.g.
refractive index, reflectivity and absorption coefficient
etc. affect the light reflection and transmission,

Ceramic processing is used to produce commercial
products that are very diverse in size, shape, detail,
complexity, and material composition, structure, and cost.The
purpose of ceramics processing to an applied science is the
natural result of an increasing ability to refine, develop, and
characterize ceramic materials.
Ceramics are typically produced by the application of
heat upon processed clays and other natural raw materials to
form a rigid product. Ceramic products that use naturally
occurring rocks and minerals as a starting material must
undergo special processing in order to control purity, particle
size, particle size distribution, and heterogeneity. These
attributes play a big role in the final properties of the
finished ceramic.
The next step is to form the ceramic particles
into a desired shape. This is accomplished by the
addition of water and/or additives such as binders,
followed by a shape forming process. Some of the most
common forming methods for ceramics include
extrusion, slip casting, pressing, tape casting and
injection molding. After the particles are formed,
these "green" ceramics undergo a heat-treatment
(called firing or sintering) to produce a rigid, finished
product. Some ceramic products such as electrical
insulators, dinnerware and tile may then undergo a
glazing process. Some ceramics for advanced
applications may undergo a machining and/or polishing
step in order meet specific engineering design criteria.
 Milling is the process by which materials are reduced
from a large size to a smaller size. Milling may involve
breaking up cemented material (in which case individual
particles retain their shape) or pulverization (which
involves grinding the particles themselves to a smaller
size). Milling is generally done by mechanical means,
including attrition (which is particle-to-particle collision
that results in agglomerate break up or particle
shearing), compression (which applies a forces that
results in fracturing), and impact (which employs a milling
medium or the particles themselves to cause fracturing).
Attrition milling equipment includes the wet scrubber
(also called the planetary mill or wet attrition mill), which
has paddles in water creating vortexes in which the
material collides and break up.
 Batching is the process of weighing the oxides
according to recipes, and preparing them for
mixing and drying.
 Mixing occurs after
batching and is performed
with various machines,
such as dry mixing ribbon
mixers (a type of cement
mixer),
Mueller
mixers, and pug mills. Wet
mixing generally involves
the same equipment.
 Forming is making the mixed material into
shapes, ranging from toilet bowls to spark plug
insulators. Forming can involve: (1) Extrusion, such
as extruding "slugs" to make bricks, (2) Pressing
to make shaped parts, (3) Slip casting, as in
making toilet bowls, wash basins and ornamentals
like ceramic statues. Forming produces a "green"
part, ready for drying. Green parts are soft,
pliable, and over time will lose shape. Handling the
green product will change its shape. For example,
a green brick can be "squeezed", and after
squeezing it will stay that way.
 Drying is removing the
water or binder from the
formed material. Spray
drying is widely used to
prepare
powder
for
pressing
operations.
Other dryers are tunnel
dryers
and
periodic
dryers. Controlled heat is
applied in this two-stage
process.
First,
heat
removes water. This step
needs careful control, as
rapid
heating
causes
cracks
and
surface
defects.
 Firing is where the
dried
parts
pass
through a controlled
heating process, and
the
oxides
are
chemically changed to
cause sintering and
bonding. The fired
part will be smaller
than the dried part.

In recent years, the number and variety of materials,
which are of particular interest to an engineer have increased
tremendously. Each type of material has a specific
composition possessing specific properties for a specific use.
It is not possible for one to explain the properties of all types
of these materials. A knowledge of the structure of the
material helps students and engineers to study the properties
of the material. Material structure can be classified as:
macrostructure,
microstructure,
substructure,
crystal
structure, electronic structure and nuclear structure
Macrostructure of a material is examined by
low-power magnification or naked eye. It deals with the
shape, size and atomic arrangement in a crystalline
material. In case of some crystals, e.g., quartz,
external form of the crystal may reflect the internal
symmetry of atoms. Macrostructure may be observed
directly on a fracture surface or on a forging specimen.
The individual crystals of a crystalline material can be
visible, e.g. in a brass doorknob by the constant
polishing and etching action of a human hand and sweat.
Macrostructure can reveal flaws, segregations, cracks
etc. by using proper techniques and one can save much
expenses by rejecting defective materials at an early
stage.
 This generally refers to the structure of the material
observed under optical microscope. Optical microscopes can
magnify a structure about 1500 to 3000 times linear, without loss
of resolution of details of the material structure. We may note
that optical microscopes can resolve two lines separately when
their difference of separation is 10-7 m (= 0.1 m). Cracks,
porosity, non-metallic insclutions within materials can be revealed
by examining them under powerful optical microscope.
 This refers to the electrons in
the outermost shells of individual
atoms that form the solid.
Spectroscopic
techniques
are
commonly used for determining the
electronic structure.

When crystal imperfections such as dislocation in a
structure are to be examined, a special microscope having
higher magnification and resolution than the optical microscope
is used. Electron microscope with magnifications 10 are used
for this purpose. Another important modern microscope is field
ion microscope, which can produce images of individual atoms as
well as defects in atomic arrangements.

This is studied by nuclear spectroscopic techniques,
e.g., nuclear magnetic resonance (NMR) and Mössbauer spectroscopy.

This reveals the atomic arrangement within a
crystal. X-ray diffraction techniques and electron
diffraction method are commonly used for studying
crystal structure. It is usually sufficient study the
arrangement of atoms within a unit cell. The crystal is
formed by a very large number of unit cells forming
regularly repeating patterns in space.
Compressive strength makes ceramics good structural
materials (e.g., bricks in houses, stone blocks in the
pyramids)
• High voltage insulators and spark plugs are made from
ceramics due to its electrical conductivity properties
Good thermal insulation has ceramic tiles used in ovens and
as exterior tiles on the Shuttle orbiter Some ceramics are
transparent to radar and other electromagnetic waves and
are used in radomes and transmitters
• Hardness, abrasion resistance, imperviousness to high
temperatures and extremely caustic conditions allow
ceramics to be used in special applications where no other
material can be used.
• Chemical inertness makes ceramics
ideal for biomedical applications like
orthopaedic prostheses and dental
implants
• Glass-ceramics, due to their high
temperature capabilities, leads to
uses in optical equipment and fiber
insulation

Thousands of engineering gears have used from
advanced ceramics solutions for wear resistance, corrosion
resistance & thermal resistance, providing significant
lifetime added to over conventional metal gears. It is not
always the best possible design solution, commonly advanced
ceramics can be benefited as direct substitutes for available
designs.
Typical gears include wear plates & thermal
barriers, bearings for high speed and high stiffness
spindles, bushes, gears and many others. Dynamic-Ceramic
can provide now hundreds of case histories on the
successful and cost effective application of advanced
ceramics solutions in mechanical engineering applications.
Although ceramics have been used by man
for many centuries, until recently their
applications have been limited by their mechanical
properties. Unlike metals, most ceramics materials
do not exhibit a non-linear plastic region before
failure. Instead, ceramics are known to be brittle
and fail catastrophically. Their application in
engineering applications has certainly been limited
by their lack of toughness.