Sangam Sharma & Shristika Thapa

SILICATE INDUSTRIES
Silicate Industries is a sector encompassing various businesses that produce and
utilize silicate-based materials. Silicates are compounds composed of silicon and
oxygen, forming the largest and most essential group of minerals in the Earth's crust.
These industries are integral to numerous applications in manufacturing, construction,
and technology.

The production of silicate-based materials involves processing raw materials like

quartz, sand, and soda ash to create various forms, including sodium silicate,
potassium silicate, and calcium silicate. These materials find applications in diverse
industries, such as:

Glass Manufacturing: Silica-based glass is widely used in windows, bottles, and

various types of containers.

Ceramics: Silicates are essential components in ceramic materials used in pottery,

tiles, and other ceramic products.

Cement: Silicates are crucial in cement production, forming the main ingredient,
known as calcium silicate hydrate, responsible for the strength and durability of
concrete structures.

GLASS

INTRODUCTION
Glass is a non-crystalline, amorphous solid that is often transparent and has
widespread practical, technological, and decorative usage in, for example, window
panes, tableware, and optoelectronics. The most familiar, and historically the oldest,
types of manufactured glass are "silicate glasses" based on the chemical compound
silica (silicon dioxide, or quartz), the primary constituent of sand. The term glass, in
popular usage, is often used to refer only to this type of material, which is familiar
from use as window glass and in glass bottles.

When crystalline quartz is heated in a specially designed electric furnace to a

temperature of about 1650°C, it melts to a colourless liquid. On the other hand, if this
liquid is cooled rapidly, the quartz can be obtained as a clear, colourless, glassy mass,
called supercooled liquid and appears like ordinary glass and is much more
transparent. This fused quartz glass expands and contracts only very slightly with
change in temperature. As a result of this property, it can, unlike ordinary glass be
rapidly heated or rapidly cooled without cracking. Quartz glass is, therefore, widely
used in the manufacture of various kinds of laboratory apparatus, specially those wher
rapid changes of temperature are encountered. The glassy quartz also passes into
crystalline form when heated for some time at a temperature of about 1150°C.

Unlike fused glass or silica glass, ordinary glass is not a single substance, but a
homogeneous mixture of substances. When quartz or silica is heated with sodium
carbonate, a compound known as sodium silicate is obtained. When it is allowed to
cool, it solidifies to a glassy mass called water glass (because it is soluble in water). If
sand or quartz is heated with other metal oxides or carbonates (other than sodium or
potassium carbonate) such as lime, alumina or oxide of lead etc., mixture of silicates
are obtained. When allowed to cool, they solidify to glasses but do not dissolve in
water, and constitute what is known as glass Glass, has, therefore, no definite
composition. Physically glass may be defined as a hard, rigid, undercooled, brittle, non
crystalline substance having no definite melting point and sufficiently high viscosity to
prevent crystallization. It is usually transparent, but sometimes opaque or translucent.
Chemically glass may be defined as a fused mixture of silicates, alkali and alkaline
earth compounds and other glass constituents, such as calcium oxide, magnesium
oxide, tin oxide, barium oxide, lead oxide. Glass is completely vitrified product. As
seen above, glass has no definite composition. However, the major ingredients are
sand, lime and soda ash, and any other raw material may be considered to be minor
ingredient. Lime, silica and soda ash still form over 90 per cent of all the glasses of
the world. Other ingredients, such as borax, boric acid, potash, zine oxide etc, are
added to give certain other properties to glass. So these are called minor ingredients.
GLASSY STATE AND IT'S PROPERTIES
Glassy state is a state of matter that combines the rigidity of crystals with the random
molecular structure of liquids. Glass is defined as 'an inorganic product of fusion
which has been cooled to a rigid condition without crystallization'. More specifically,
the term is used to relate to a state of inorganic matter which may be likened to a
solid, but which has the properties of a very highly viscous liquid, exhibiting neither
crystalline structure nor a distinct melting point, i.e. a super-cooled liquid.

PROPERTIES
1) Glass is usually transparent and amorphous:

This means that most glass materials allow light to pass through them, making them
see-through. Additionally, glass lacks a regular crystalline structure, which is
characteristic of amorphous solids. Instead, the atoms in glass are arranged in a
disordered manner.

2) Glass is a completely vitrified product:

Vitrification refers to the process of transforming a material into a non-crystalline,

glassy state by heating and cooling it rapidly. When the raw materials are melted and
then rapidly cooled, they solidify into the amorphous structure we recognize as glass.

3) Glass is hard and rigid with no definite melting point:

Glass is known for its hardness and rigidity, making it less prone to scratching or
deformation compared to other materials. It doesn't have a clear-cut melting point like
crystalline materials. Instead, it softens over a range of temperatures, known as the
glass transition temperature.

4) Glass has sufficiently high viscosity:

Viscosity refers to the resistance of a material to flow. Glass has a very high viscosity,
greater than 10^13 paise (Poise), at room temperature. This high viscosity contributes
to its solid-like behavior, even though it is an amorphous material.

5) Glass is an insulator of heat and electricity:

Due to its non-crystalline structure, glass does not have free-moving electrons, making
it a poor conductor of both heat and electricity. This property is beneficial for various
applications, like electrical insulators and thermal barriers.
6) Glass can incorporate coloring material while preserving transparency:

One of the unique features of glass is that it can incorporate various colorants during
its manufacturing process, allowing it to display a wide range of colors while still
maintaining its transparent or translucent nature. This makes glass versatile for
decorative and artistic purposes.

CLASSIFICATION OF GLASS
1) Silicate Glass:
Silicate glasses are the most common type of glass and are composed primarily of
silica (silicon dioxide). Silica is the main ingredient in sand, and when heated at high
temperatures, it melts and forms a glassy material. Silicate glasses make up around
90% of all commercial glasses. They have a unique amorphous structure, meaning
their atoms are arranged in a random pattern without a long-range order.

Here are some specific types of silicate glasses:

a) Soda Lime Glass: This is the most widely used type of glass for windows,
containers, and everyday objects. It contains silica, sodium oxide (Na2O), and calcium
oxide (CaO). Soda lime glass is inexpensive and has good transparency.

b) Borosilicate Glass: This type of glass contains a higher percentage of boron oxide
(B2O3) in addition to silica, which makes it more resistant to thermal expansion and
thermal shock. Borosilicate glass is commonly used in laboratory glassware and
cookware.

c) Photosensitive Glass: Photosensitive glasses contain compounds that respond to

light exposure, leading to a change in their properties. They are used in the production
of holograms and optical components.
2) Non-Silicate Glass:
Non-silicate glasses are made from different chemical compositions that do not
contain silica as their primary component. These glasses are less common than
silicate glasses and often have specific properties that make them useful for
particular applications.

Here are some specific types of non-silicate glasses:

a) Lead Glass: Also known as lead crystal, this glass contains lead oxide (PbO), which
gives it a higher refractive index and a brilliant sparkle. Lead glass is commonly used
in fine glassware and decorative items.

b) Armoured Glass: Armoured or bulletproof glass is a type of safety glass made by

sandwiching layers of glass and plastic materials. It provides enhanced protection
against impacts and is used in security applications and vehicle windows.

c) Safety Glass: Safety glass is designed to be less hazardous when broken. There are
two main types:

• Tempered Glass: Tempered glass is heated and then rapidly cooled, making it
stronger and shatter into small, granular pieces when broken.

• Laminated Glass: Laminated glass is made by sandwiching a layer of plastic (usually

polyvinyl butyral) between two glass layers, creating a strong, transparent, and impact-
resistant material.

d) Colored Glass: Colored glass is achieved by adding metal oxides or other

compounds to the glass mixture during production. Different colors can be obtained,
making it useful for decorative purposes and artistic glasswork.

e) Fluorosilicate Glass: This glass contains fluorine in addition to silica and is known
for its gexcellent chemical resistance. It is used in specialized applications requiring
resistance to harsh chemicals.
 MANUFACTURE AND PROCESSING OF
GLASS

1. Collection of raw materials:

The raw materials such as silica in the form of white sand or quartz (SiO2), soda ash
(Na2CO3), lime stone (CaCO3) and cullet (broken pieces) are ground separately and
mixed in proper proportion. The fusion of cullet or broken glass is to bring down
melting point of the charge. The process is made economical.

Some other raw materials used:

Sodium as Na2CO3 (used in soft glass)

Potassium as K2Co3 (used in hard glass)

Calcium as lime stone , chalk and lime .

Lead as litharge , red lead (flint glass)

Zinc is zinc oxide (heat and shock proof glass)

Borates are borax , Boric acid(heat and shock proof glass)

2. Preparation of batch:

The raw materials, cullet and decolouriser are finely powdered in grinding machines.
These materials are accurately weighed in correct proportions before they are mixed
together. The mixing of these materials is carried out in mixing machines until a
uniform mixture is obtained. Such a uniform mixture is known as the batch or frit and
it is taken for further process of melting in a furnace.

Note:

The batch of the starting materials (is called a charge) to be melted and loading it into
the furnace is called charging the furnace. The intimate homogeneous mixture of raw
materials is called batch.

3. Melting or Heating of charge:

The Glass batch is melted either in a pot furnace or in a tank/ open hearth furnace
furnace made of fireclay or platinum. The heating is continued until the evolution of
carbon dioxide, oxygen, sulphur dioxide and other gases stops.
 FIG-1

Heating is done by burning producer gas mixed with air over the charge. The cullet (or
broken glass) melts first and helps in the fusion of the rest of the charge. A high
temperature of 1500 – 1800 °C is maintained to reduce the viscosity of glass melt and
to obtain a homogeneous liquid.

The following reactions take place in the manufacture of glass:

Heating is continued till the glass melt is free from gas bubbles like CO2, SO2 etc.
Undecomposed raw materilas and impurities form a scum called glass gall which is
skimmed off. The clear liquid is now allowed to cool after adding the necessary
decolorisers or colouring agents. It is cooled to 700-1200 °C, so that it will have the
proper viscosity for shaping.

Note:

Pot furnace:

Small scale preparation of high grade glass is carried out in a pot furnace. Glass of
uniform quality is possible in a pot furnace. These pots are placed in specially
prepared holes in the furnace. The charging and collecting doors are kept projecting
outside so that raw materials may be added and molten glass may be taken out
conveniently.

The pots are filled with raw materials. The furnace is heated by means of producer
gas. When the mass has melted down, it is removed from the pot and it is taken for
the next operation of fabrication. The melting of glass by pot furnace is an intermittent
process. It is used to melt small quantities of glass at a time or to prepare special
types of glass.

Tank Furnace:

This furnace resembles the reverberatory furnace adopted for puddling of the wrought
-iron. Fig. 1 shows the section of a tank furnace adopted for the melting of glass. It is
constructed with reinforced masonry. The roof is given special shape to deflect the
flames of heated gas. The ports are provided for the entry of preheated producer gas.
The doors are provided for charging and for taking out the molten glass. A bridge
separates the tank into two unequal compartments. The batch is heated in large
compartment and it contains somewhat impure glass. It flows through opening of
bridge into small compartment. The gall or floating impurities are collected at the top
of large compartment. The refractory lining is provided to the interior surface of tank.

The tank is filled with raw materials. The furnace is heated by allowing producer gas
through ports. The charging of raw materials and taking out of molten mass are
simultaneous. This is a continuous process and it is adopted to melt large quantities
of glass at a time.
Salt cake Na2SO4 is added to remove the scum from tank furnace and also to enable
ready escape of bubbles.

4. Processing of glass:

Shaping:

The molten glass is run into moulds and automatic machines turn them into desired
shapes such as sheets, tubes, rods, wires etc.The molten glass is given suitable shape
or form in this stage. It can either be done by hand or by machine. The hand
fabrication is adopted for small scale production and machine fabrication is adopted
for large scale production.

Annealing:

After shaping, the glass articles need to be cooled gradually and slowly. Rapid cooling
causes fracture. Annealing is carried out in special chambers, where temperature is
brought down slowly. The entire process of annealing may require a few days glass
may crystalline if cooled very slowly.

The glass articles, after being manufactured, are to be cooled down slowly and
gradually. This process of slow and homogeneous cooling of glass articles is known
as the annealing of glass.

The annealing of glass is a very important process. If glass articles are allowed to cool
down rapidly, the superficial layer of glass cools down first as glass is a bad
conductor of heat. The interior portion remains comparatively hot and it is therefore in
a state of strain. Hence, such glass articles break to pieces under very slight shocks or
disturbances.
Finishing:

After annealing the glass articles are subjected to finishing such as cleaning, grinding,
polishing and cutting etc. Certain decolorizing agents such as cerium oxide,
neodymium oxide etc., are added to neutralize an undesired colour present in glass.

PROPERTIES AND COMPOSITION OF THE

FOLLOWING TYPE OF GLASSES

1) Soda Lime Glass-

PROPERTIES:
It is also known as Soda-lime-silica glass or soda glass or soft glass or window glass.
It Is transparent, easily formed and most suitable for window glass. It has a high
thermal expansion and poor resistance to heat (500–600 °C). Container glass is a
soda-lime glass that is a slight variation on flat glass, which uses more alumina and
calcium, and less sodium and magnesium, which are more water-soluble. This makes
it less susceptible to water erosion.

COMPOSITION:
• About 90% of all glass is sodalime glass made with silica(sand) , Carbonate and
soda ash.

• The approximate composition is Na2CO3.CaO.6SiO2.

• They are low cost , resistant to water but not to acids. They can melt easily and
hence can be hot worked.

• The composition of soda-lime glass varies marginally depending on the

manufacturer. The typical composition of soda-lime glass is 73% SiO2 – 15% Na2O −
7% CaO − 4% MgO − 1% Al2O3 Refractive index - 1.46 Density, 2.5 ρ (g/cm3)

USES:
Window glass, Electric bulbs, Plate glass, Bottles, Jars, Cheaper tablewares, Test
tubes, Reagent bottles etc.
2) Lead Glass-
PROPERTIES:
• It is made up of lead oxide fluxed with silica and K2CO3

• Its approximate composition is K2CO3.PbO. SiO2

• Lead glasses has lower softening temperature than soda glass and higher refractive
index and good electrical properties . It is bright lustrous and possess high specific
gravity.

COMPOSITION:
Lead glass contains typically 18–40% (by weight) lead(II) oxide (PbO), while modern
lead crystal, historically also known as flint glass due to the original silica source,
contains a minimum of 24% PbO. Lead glass is often desirable for a variety of uses
due to its clarity.

USES:
High quality table wares, optical lenses, Neon sign tubing, Cathode ray tubes, Electrical
insulators, Crystal art objects or cut glass, Windows and Shields for protection against
X-rays and Gamma rays in medical and atomic energy fields etc.
3) Armoured Glass-
PROPERTIES:
It is also known as bullet resistant glass or bullet-proof glass. It is obtained by
pressing together several layers of glass with vinyl resins in a alternate layers. A
thickness of 12-76 mm is common. It is usually 70-76 mm thick. More is the thickness
more is its resistance. Glasses of different thickness are needed to withstand
penetration from different types of bullets.

COMPOSITION:
The composition of armoured glass can vary depending on its intended level of
protection, but it usually consists of layers of tempered glass, polycarbonate, and
sometimes additional interlayers like PVB (Polyvinyl butyral) or EVA (Ethylene-vinyl
acetate). The combination of these materials helps to dissipate and absorb the energy
of incoming projectiles, preventing them from penetrating the glass.
USES:
Armoured glass is used to provide enhanced protection and safety in various
applications. It is commonly used for military and defense purposes, law enforcement
and security applications, bank security, vehicles for diplomats and VIPs, and in high-
security buildings to guard against potential threats like bullets, explosives, and high-
impact projectiles.

4) SAFETY GLASS:
PROPERTIES:
It is classified into laminated safety glass and heat strengthened or tempered safety
glass. Laminated safety glass is made by bonding two sheets of ordinary glass with a
thin layer of vinyl plastic between them. Poly vinyl butyral (PVB) is used as a bonding
agent between two or more layers of glass. An important property of safety glass is
that when it is broken, the fragments are held in place by the interlayer. The glass
pieces do not fly off that is it is shatter-proof. Tempered safety glass is obtained by
heating a single sheet of glass to just below its fusion point and then quenching in oil,
air or molten salt.It does not get fractured easily and is capable of withstanding
mechanical and thermal shocks. If the outer surface breaks the pieces does not fly
and the broken pieces have no sharp edges.

COMPOSITION:
Laminated glass: Laminated glass is composed of multiple layers. The most common
configuration is two layers of glass with a layer of polyvinyl butyral (PVB) interlayer
sandwiched between them. The approximate percentage composition of laminated
glass can be broken down as follows:

Glass layers: Around 88% (44% per glass layer)

PVB interlayer: Around 12%

Tempered glass:

Tempered glass is typically made up of 100% glass. The tempering process involves
heating the glass and then rapidly cooling it, but no additional layers are added during
this process.The percentage composition of tempered glass typically consists of
approximately 70-80% silica (SiO2), 10-15% soda ash (Na2CO3), and 5-10% lime (CaO),
along with other minor additives and impurities.

USES:
Laminated Glass:

1. Automotive windshields

2. Safety glass for buildings

3. Glass doors and partitions

4. Bullet-resistant glass

5. Glass flooring and stairs

 6. Hurricane-resistant windows

Tempered Glass:

1. Shower doors and enclosures

2. Glass table tops

3. Glass shelves and cabinets

4. Building facades and curtain walls

5. Oven doors and refrigerator shelves

6. Safety glass for skylights and balconies

5) Borosilicate Glass-
PROPERTIES:
• It is common hard glass containing silica and boron with small amount of alumina
and less alkaline solids.

• These equipments are mainly known for resistant to thermal shock as compared to
other ordinary glasses.

• The borosilicate glass is made by adding the boric oxide to the traditional
glassmaker frit of the silicate soda , sand or to the ground lime .

• The glass normally requires a higher temperature to melt and thus for the industrial
productions of borosilicate glass.

COMPOSITION:
The borosilicate glass composition includes silicon dioxide (SiO2) in a range from
about 60% to 74% by total composition weight; boric oxide (B2O3) in a range from
about 9% to 25% by total composition weight; aluminum oxide (Al2O3) in a range from
about 7% to 17% by total composition weight; and at least one alkali oxide in a range
from about 2% to 7% by total composition weight.

USES:
Kitchen wares, Chemical Plants, Electrical insulators, Superior Laboratory apparatus,
Industrial pipeline for corrosive liquids, Gauge glass etc.
6) Fluorosilicate Glass-
PROPERTIES:
It is composed of mainly fluorite and silica. They have good mechanical properties. It
has low dielectric constant and used in semiconductor fabrication. They have good
resistance to chemicals and can be used in microwave ovens.

COMPOSITION:
Fluorosilicate glass, also known as fluoride glass, is a type of optical glass composed
of fluorine (F) and silicon (Si), with small amounts of other elements such as
aluminum (Al) and rare earth elements like erbium (Er) or neodymium (Nd).

USES:
It's commonly used in optical fibers and laser applications due to its unique optical
properties, including low dispersion and high infrared transmittance.

7) Coloured Glass-
Coloured galsses are made by the addition of appropriate amounts of a colouring
agent to the batch.

USES:
Used for window panels, fancy articles, decorative tiles etc.
8) Photosensitive Glass-
PROPERTIES:
It has high strength, good stability, grain free image, accurate reproducibility.

COMPOSITION:
Photosensitive glass, also known as photosensitive optical glass or photosensitive
silica glass, typically consists of a combination of silicon dioxide (SiO2) and other
elements such as silver (Ag) or other photosensitive compounds. A potash- alumina
glass, mixed with LiSiO3, Cerium and Silver in appropriate proportions have also been
used as photosensitive glass.

USES:
It is used in printing, and reproducing process. It finds its use in military. It is possible
to burn images and words that are hidden in photosensitive glass by heating at high
temperatures.
References:

1) Industrial Chemistry- BK Sharma

2) OpenAI
https://chat.openai.com
ChatGPT
3) tumkuruniversity.ac.in
http://tumkuruniversity.ac.in › ...PDF
Chapter 2 Glass Glass can be defined as a rigid
super cooled liquid having ...
4) Centurion University of Technology and
Management
https://courseware.cutm.ac.in › ...PDF
INTRODUCTION TO GLASS , TYPES OF GLASS AND
THEIR COMPOSITION