The document gives an overview of ceramics, covering their classification, raw materials, properties, and various specialized ceramic products. Ceramics are categorized into different classes, including heavy clay products and pottery, with key components like clay, feldspar, and silica. Specialized ceramics include composites, ferroelectric materials, biomaterials, and high-alumina ceramics, which serve various applications across construction, electronics, and medical fields.

1. Module: 6
Lecture: 26 Ceramic industries
Dr. N. K. Patel
N P T E L 175
Module: 6
Lecture: 26
CERAMIC INDUSTRIES
INTRODUCTION
Ceramic is an inorganic, nonmetallic solid prepared by the action of heat
and subsequent cooling. Ceramic materials may have a crystalline or partly
crystalline structure, or may be amorphous (e.g. glass). Because most common
ceramics are crystalline, the definition of ceramic is often restricted to inorganic
crystalline materials, as opposed to the non-crystalline glasses.
The earliest ceramics were pottery objects made from clay, either by itself or
mixed with other materials, hardened in fire. Later ceramics were glazed and fired to
create a coloured, smooth surface. Ceramics now include domestic, industrial and
building products and art objects. In the 20th century, new ceramic materials were
developed for use in advanced ceramic engineering; e.g., in semiconductors.
The word "ceramic" comes from the Greek word Keramos means burnt stuff.
Earlier the term ceramic was applied to products made from natural earth material
that was not exposed to heat. But nowadays the silicate mainly used in the
construction industries and prepared by burning the clay products are called as
ceramics.
CLASSIFICATION
A broad sense classification divides the ceramic products in to two classes
1. Heavy clay products e.g. bricks, roofing tiles, drain tiles, hollow tiles, stoneware
and refractories
2. Pottery products e.g. chinaware, wall tiles, electric insulation
Ceramic may also be classified as porous and non-porous. The porosity is
depends on particle size, moulding pressure and temperature of vitrification.
Further, ceramic may be classified based on the method of production and
its uses into following classes.
1. Whiteware
2. Structural clay products
3. Refractory material

2. Module: 6
Lecture: 26 Ceramic industries
Dr. N. K. Patel
N P T E L 176
4. Special ceramic products
5. Vitreous enamel
RAW MATERIAL
The raw materials for ceramics are divided into following groups.
a) Plastics material such as clay
b) Fluxes such as feldspar
c) Non-plastics materials such as silica
a) Clay
Clay gives the main body to the ceramics. The advantage of using clay are it
is plastic when mixed with water becomes hard after drying and finally it becomes
irreversibly solid after firing. Clay is chosen according to the requirements of
particular products and is often blended.
Impurities in common clay incorporate specific qualities as follows.
 Iron oxide in common clay gives red colour to the burnt material
 Lime, magnesia, iron oxide and alkali oxides act as flux which lowers the
fusion point of clay
 Silica increases its porosity and refractory nature, while decreases shrinkage
 Clay containing very little and good deals of silica known as fire clays
b) Feldspar
Feldspar is general name given to the group of minerals. Flux materials like
feldspar (Na2OAl2O3.6SiO2) which is easily melting material decreases the melting
point of sand or quartz present in the ceramic body. So, that after firing glass like
material is obtained called as vitrified material, which is highly impervious and stable
to the environment. Fluxes are used for adding vitrifications, reducing porosity, to
increase the strength of cold articles and for bonding. Feldspar is used as fluxing
constituent in ceramic formulations along with clay. The common fluxing agents
which lower the temperature are borax, boric acid, soda ash, sodium nitrate,
potassium carbonate, calcined bones, lead oxides, lithium & barium minerals.
Type of feldspar
 Potash feldspar K2O.Al2O3.6SiO2
 Soda feldspar Na2O.Al2O3.6SiO2
 Lime feldspar CaO.Al2O3.6SiO2

3. Module: 6
Lecture: 26 Ceramic industries
Dr. N. K. Patel
N P T E L 177
c) Silica or quartz
The non-plastic or leading admixture like sand or quartz gives strength to the
body. It is incorporated in ceramic formulation to reduce shrinkage and cracking
which is occurs during drying and firing.
PROPERTIES
The physical and chemical properties of ceramic depend upon component
present in it.
 The strength is mainly controlled by the factors like temperature, size and
shape, composition, surface condition and microstructure
 Mechanically they are brittle and highly resistant to compression
 Oxides and carbides which give high chemical and physical stability
 Electrical and magnetic properties are due to composition itself. E.g. oxides
are generally bad conductors where the non-oxides are semiconductors and
ceramics with transition metal ions shows the magnetic properties.
 Transparency depends upon the crystal lattice of ceramic which in turn is
dependent of composition, crystal structure, extent of polarization etc.
USES
Ceramic is one of the oldest materials used in construction with the time
quality and decoration has been added to its property and therefore they are at
present used in following
 Construction and decoration as bricks and tiles
 Metallurgy as construction material of furnace
 Chemical products as stoneware and porcelain
 In drainage of water
 In sanitation
The small uses includes pottery work, specialty ceramic like peuzo electric
and insulation material in electrical connections
Therefore, we conclude that ceramics deals with manufacture and technical
characteristics and raw material for article building.

4. Module: 6
Lecture: 29 Specialized ceramic products
Dr. N. K. Patel
N P T E L 193
Module: 6
Lecture: 29
SPECIALIZED CERAMIC PRODUCTS AND VITREOUS ENAMEL
4. SPECIALIZED CERAMIC PRODUCTS
Based on the specific requirements/application ceramic material having
special properties are developed and they are as follow
a) Ceramic composites
Materials with different combinations of properties are required in specific
applications like underwater, transportation and aerospace. E.g. in construction of
aircrafts, structural materials should have low densities. At the same time, they should
be strong, stiff, and resistant to abrasion, impact and corrosion. Ceramic composite
like cermet should fulfill such demands. Cermet is intimate mixture of ceramic and
metallic components in the form of powder, which are compacted and sintered.
Cemented carbide is probably the most common cermet which is composed of
extremely hard particles of a refractory carbide ceramic like tungsten carbide or
titanium carbide embedded in a matrix of a metal like cobalt or nickel which
increases toughness of the carbide particles. These carbides are widely used as
cutting tools for hardened steels. Cermet is also used in linings for brakes and
clutches and it is also used as heat shields, rocket nozzles and ram jet chambers in
aerospace application.
Ceramic metal composites can be produce by bonding of the two materials
which are heated below the melting point of individual components. Ceramic
catalyzes the conversion of metal into its oxide. As the metal oxide is formed, crystals
of the oxide grow into the crystal structure of the ceramic materials. Thus the bond
becomes strong between the two phases of the resultant cermet. Metals like Pt, Au,
and Ag exhibit the best bonding with the ceramic phase like Alumina, Magnesia,
Silica, Zirconia, or Beryllia. Their applications are gold coated ceramic wafers for
semiconductor chips, zirconia-lined steel for corrosion resistant uses, and ceramic
capped gold dental crowns. The process is also used for gem setting in gold.
b) Ferroelectric ceramics
Dielectric materials like insulators are known as ferroelectrics, which show
spontaneous polarization in the absence of an electric field e.g. Barium titanate
(BaTiO3) which have very high dielectric constants at relatively low applied field
frequencies and permanent electric dipoles. Another example of ferroelectrics is

5. Module: 6
Lecture: 29 Specialized ceramic products
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N P T E L 194
potassium dihydrogen phosphate (KH2PO4), Rochelle salt (sodium potassium
tartarate- NaK.C4H4O4.4H2O), KH2AsO4, NaTaO3, KTaO3, LiTiO3 etc.
BaTiO3 have piezoelectricity. For piezoelectric application poly crystalline
BaTiO3 is used which is cooled through the curie temperature in the presence of
strong electric field. This imparts permanent orientation to the dipoles in the resulting
ceramic materials.
Piezoelectric materials convert electrical energy into mechanical strains or
vies versa when employed in transducer. They are also employed in phonograph,
pick-ups, microphones and sonar detectors. They are employed in ultrasonic
generators which are used for mixing of powders and paints, homogenisation of
milk, aging of clays and the emulsifying of liquids etc.
High amount of voltage is generated because pressure is applied on
piezoelectric material. The spark that can be drawn from such a high voltage in
used for ignition in gas lighter, cooking stoves and cigarette lighters.
c) Ferromagnetic ceramic
Ferrites are an important class of compounds which having magnetic
properties. It formed by mixing of oxides of Iron with other metals. But they are poor
electrical conductors. Soft ferrites can be easily magnetized and demagnetized.
They are used in transformers, in capacitors, as microwave devices in
communicating radio signals, as memory devices in computers and tape recorders.
While hard ferrites are permanent magnets made from oxides of iron, barium and
strontium. Hard ferrites are used in motors and loudspeakers.
d) Ceramic biomaterials
Ceramics have many advantages as biomaterials. They are light weight,
more wear resistant and not attacked by enzymes and biochemical in the human
body. Ceramics are used in making artificial teeth, bone joints. It is also used in filling
the gaps in damaged bones which is facilitated by the similarity between natural
bone and calcium phosphate ceramics.
e) High alumina ceramic
They are mechanically strong dense and special ceramic material. They
possess good wear resistance, corrosion resistance and dimensional stability. So they
are used in insulators for electrostatic precipitators. It is also used in linings for mining
chutes and slides and in making of precision machine parts.
f) Sensors
When ceramic material is exposed to water vapour and certain gases it
transforms non-electrical signals into electrical ones. Humidity sensors are made from

6. Module: 6
Lecture: 29 Specialized ceramic products
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mixture of titanium oxide and magnesium chromates while gas sensors usually
ceramic semiconductors made from oxides of titanium, iron, tin, silver and zinc.
g) Ceramic superconductors
Ceramics which had been used as insulating materials could be better than
conductors. They are high temperature superconductors and show zero electrical
resistance. It can be prepared by fusing an oxide of barium and copper. Thus if
cables are made of superconducting material, one-fifth of the loss of electricity
during its transmission through aluminium or copper wires is avoided.
Super conductors can repel magnet and also applied in super-fast
magnetically levitated trains. It is also used in magnetic resonance imaging (MRI),
which is a modern diagnostic tool.
h) Ionic conduction
Ceramics materials are made into sodium-sulfur batteries which are used in
electric cars. Ions become mobile at high temperatures and able to carry electrical
charge across them is known as ionic conductivity.
5. VITREOUS ENAMEL
Besides flux and refractories, oxidizing agents such as pyrolusite, red lead and
nitre are included for the formation of enamel. In the formation of enamel colouring
agents, floating agents and free electrolytes are required. Lead oxide, boric acid,
potassium and sodium oxide are easily fusible compounds at lower temperature so
considered as fluxes. Refractories include feldspar; quartz and clay contribute to the
acidic part of the melt and give body to the glass. The basic part is supplied by the
flux.
MANUFACTURE
Raw materials
The raw materials used for the manufacture of enamel are feldspar quartz,
kaolin quartz and feldspar contribute to the hardness and resistance to the action of
acid of the enamel.
 Kaolin lends plasticity
 Fluxes: boric acid, borax
 Flux as well as oxidation agents: Red lead and lead carbonate
 Opacifiers: TiO2 SnO2, ZrO2, fluorspar, cryolite
 Floating agent: Clay and gums
 Colouring agents: Oxides, elements or frits
 Electrolytes: borax, Na2CO3, MgSO4 and MgCO3

7. Module: 6
Lecture: 29 Specialized ceramic products
Dr. N. K. Patel
N P T E L 196
Manufacture
The manufacture of enamel glass (frit) is similar to the first stage of
manufacture of ordinary glass. The finely powdered raw materials are mixed in
proper proportioned and charged into a melting furnace. After the batch has been
uniformly melted, the melt is poured into a quenching tank to granulate it. The cold
water shatters the melt to innumerable pieces, which are called frit. The frit is then
ground into ball mill with porcelain balls where plastic clay is added to prevent the
separation of water from the powdered material. Than colouring agents and
opacifiers are used for milling. After milling the product is discharged and in the form
of thick enamel slip.
Articles of high carbon steels and of cast iron can be enameled. But before
the application surface of these objects should be cleaned thoroughly of all foreign
matters so that the coating of enamel may adhere well.
Enamel may be applied to the metal by slushing, brushing or spraying. e.g.
Iron sheet, or iron pieces are coated by dipping or slushing. In slushing enamel slips is
poured over the metal surface to allow the excess run off.
PROPERTIES
Vitreous enamel is opaque seldom transparent, coloured or colourless flux. It is
easily fusible material
USES
It is used as protective or decorative agent to coat the surface of glass,
porcelain and metals particularly iron sheets.