Glass in Materials Science

Glass in Materials
Science
By
Prof. A. Balasubramanian
Centre for Advanced Studies in Earth
Science
University of Mysore, India

Types of Ceramics
Whitewares
Refractories
Glasses
Abrasives
Cements

Amorphous Ceramics
(Glasses)
 Main ingredient is Silica (SiO2)
 If cooled very slowly will form crystalline structure.
 If cooled more quickly will form amorphous structure
consisting of disordered and linked chains of Silicon
and Oxygen atoms.
 This accounts for its transparency as it is the crystal
boundaries that scatter the light, causing reflection.
 Glass can be tempered to increase its toughness and
resistance to cracking.

 There are innumerable examples of
glass, both in public and private
collections, which are unquestionably
of ancient origin, yet because of the
lack of proper inscriptions it is
impossible to classify them in
chronological order.
 The paintings of the Theban
glassmakers reproduced herein were
discovered on the tombs of Beni
Hassan.

About 2000 B. C,
 Figure 1 represents
an ancient Theban
taking molten glass
from the foot of a
furnace.

 Figure 2
 shows two others
seated on the
ground, holding
pipes similar to
those used at the
present time. The
glass on the end of
the pipes, which
are pointed toward
the fire, is ready to
be blown.

Figure 3 illustrates the blowing of
a large glass vase by two men

 With the encouragement of
Constantine, and also of Theodosius III,
who reigned from 408 A. D. to 450 A.
D., the manufacture of glass became an
important industry.
 This monopoly of the East was not
overcome by the West until the
fourteenth century, when Venice
became a factor.
 For several centuries the Venetian
Republic maintained its leadership as
the principal producer of glass.
 The Germans, in spite of the attempted
monopoly of the Venetians, began at this
period to manufacture glass in their own
country.

Ancient use of glass
 Bottles, drinking
glasses, vases and
toilet articles, many
of which bear a
striking
resemblance to
those of the present
day, were produced
by these early
Roman glassmakers.
 It bears the name of
Maximianu
Herculius, a Roman
emperor (250 A. D.
—310 A. D.).

Bohemian glass
 About 1609 Gaspar
Lehmann, a Bohemian,
invented a new method of
decoration—that of
engraving on glass. This
new decoration
revolutionized the industry,
and while the Bohemian
glass of this time was clear
and light in weight, it

 When the Roman Emperor, Caesar
Augustus, conquered Egypt (26 B. C.) he
quickly recognized the commercial value of
glass and ordered that it should form part of
the tribute which he imposed upon the
conquered country.
 According to Pliny, the Romans began the
manufacture of glass in their own country'.
With characteristic intelligence and industry,
they assimilated the knowledge of the
Egyptians, and within a comparatively short
time Roman glass rivaled that of Egyptian
origin.

USA
 In 1607 the first glass furnace was
erected about a mile distant from
Jamestown. The product was confined to
bottles. The second plant was erected in
1620 to manufacture glass beads, which
were used extensively at that time in
trading with the Indians. Both works
were destroyed in the great massacre of
1622.
 The next attempt to make glass in
America was at Salem, Mass., where a
plant was built in 1639 to produce bottles
and other articles.

 It is generally
conceded that the
two most powerful
influences giving the
greatest impetus to
the manufacture of
glass during the last
fifty years were (1)
the substitution of
gas for coal and (2)
the invention of the
glass-blowing
machine.

 1869, at the foot of Gist Street, in that
part of Pittsburgh known as the Bluff,
Thos. Evans established a glass works
which marked the beginning of the
Macbeth-Evans Glass Company.
 The plant was operated under the name
of Reddick & Company.
 In 1872, three years later, Geo. A.
Macbeth, with several associates,
purchased the Keystone Flint Glass
Works, Second and Try Streets,
Pittsburgh, known as the "Dolly Varden."
The company operating the plant was
called Muzzy & Company.

Mega event marking the
manufacture

The Glassy State
 Glass is an inorganic product of fusion that
has cooled to a rigid condition without
crystallizing.
 Glass is typically hard and brittle, and has a
conchoidal fracture.
 A glass may be colorless or colored.
 It is usually transparent, but may be made
translucent or opaque (such as in white, opal
glass).
 Objects made of glass are loosely and
popularly referred to as glass; such as glass
for a tumbler, a barometer, a window, a
magnifier, or a mirror.

The glassy state
 Glass is a unique material that presents
many possibilities to designers and
engineers, as well as to artists.
 Many of the unique possibilities that
come with this material often are coupled
with a large set of limitations.
 The glassy state is a state of matter that
is amorphous or disordered like a liquid
in structure, hence capable of continuous
composition variation and lacking a true
melting point, but softening gradually
with increasing temperature.

Good control on glass
 Part of truly being able to control this
material, for both artists and
engineers, is to understand, the often
complex processes involved in the
heating, forming, and cooling of this
material.

Properties of Glass
 Strain Point
 Annealing Point
 Softening Point
 Working Range
 Melting Point
 Physical Properties Involved in Lampworking
 Gravity and Surface Tension
 Physical properties involved in the forming of molten
glass.
 Proper Spinning Technique
 Necessary to evenly distribute the effects of gravity on
the piece.
 Heat Base

Strain Point
 The most crucial part of the annealing
process.
 The strain point is right below the
annealing point, when the molecules can
no longer re-arrange.
 This is when the majority of stresses due
to improper cooling will be reintroduced
to the glass.
 With thicker glass this usually requires
long soak times to make sure that all
parts of the glass are cooling at the
same rate.

Annealing Point
 Relieves stresses induced by the
shaping/forming processes.
 There is inevitable stress due to the
rapid and often uneven heating and
cooling processes when forming glass at
the torch.
 This, coupled with mechanical stresses
due to sharp angles in your form or
inconsistent thicknesses, will be enough
to crack your piece if it is not properly
annealed.

Softening Point
 When the glass has a viscosity high
enough to prevent deformation under
its own weight (very dull red).

Working Range
 The variety of viscosities ranging from
very stiff to very fluid.
 Minute differences in viscosity caused
by slight temperature changes give
the artist a broad range of working
properties (dull red – bright yellow).

Melting Point
 This is the point at which the glass is
very fluid and moving almost
uncontrollably fast.
 The closer you are to the melting
point, glass becomes more fluid and
has a higher surface tension (bright
yellow – white).

Other properties
 Gravity and Surface Tension
 Physical properties involved in the
forming of molten glass.
 Proper Spinning Technique
 Necessary to evenly distribute the
effects of gravity on the piece.

Heat Base
 An even distribution of heat.
 Heat base allows for symmetrical
blowing and forming.
 If glass is allowed to cool slightly
before forming, the heat will start to
even out, allowing for more balanced
forms.

Importance of Glass
 Glass has countless uses. Food is preserved in
glass jars.
 People drink from glass containers called
glasses.
 Windows in homes, schools, and office buildings
are glass.
 Motor vehicles have glass windshields and
windows.
 People with vision problems wear eyeglasses.
 Scientists use glass test tubes, and microscopes
and telescopes with glass lenses.
 Glass optical fibers carry data all over the world
at the speed of light over the Internet, the
worldwide network of computers.

Glass can take many different
forms
 It can be spun finer than a spider web.
 Or it can be molded into a disk for a
telescope lens or mirror weighing
many tons.
 Glass can be stronger than steel, or
more fragile than paper.
 Most glass is transparent, but glass
can also be colored to any desired
shade.

Glass industries
 Most countries of the world have glass
industries.
 For many years, Germany was the major
world source for optical glass, laboratory
glassware, and glass Christmas tree
ornaments.
 Today, glass manufacturers in many
countries produce such objects on a
large scale.
 Beautiful art glassware is made in many
countries, including the Czech Republic,
France, Ireland, Italy, and Sweden.

Composition of Glass
 Glass can be generally divided into two
groups: oxide glass and non-oxide glass.
 The ingredients of oxide glasses
include oxides (chemical compounds that
include oxygen).
 Non-oxide glasses are made from
compounds that contain no oxides, and which
often instead contain sulfides or metals.
 Oxide glasses are much more widely used
commercially.
 The common types of glass discussed below
are all oxide glasses.

Soda-lime glass
 Soda-lime glass is the kind of glass used for flat
glass, most containers and electric light bulbs,
and many other industrial and art objects.
 More than 90 percent of all glass is soda-lime
glass.
 It has been made of almost the same materials
for hundreds of years.
 The composition is about 72 percent silica (from
sand), about 13 percent sodium oxide (from soda
ash), about 11 percent calcium oxide (from
limestone), and about 4 percent minor
ingredients.
 Soda-lime glass is inexpensive, easy to melt and
shape, and reasonably strong.

All glass containers
 All glass container manufacturers use
the same basic soda-lime
composition, making the containers
easy to recycle.
 Manufacturers sort the glass by color
and then later reuse it in the
production of new containers.

Soda-lead glass
 Soda-lead glass, commonly
called crystal or lead glass, is made by
substituting lead oxide for calcium oxide and
often for part of the silica used in soda-lime
glass.
 Soda-lead glass is easy to melt.
 It is much more expensive than soda-lime
glass.
 Soda-lead glass has such beautiful optical
properties that it is widely used for the finest
tableware and art objects.
 In addition, lead oxide improves the electrical
properties of glass.

Borosilicate glass
 Borosilicate glass is heat-shock resistant
and better known by such trade names
as Pyrex and Kimax.
 It contains about 80 percent silica, 4
percent sodium oxide, 2 percent
alumina, and 13 percent boric oxide.
 Such glass is about three times as heat-
shock resistant as soda-lime glass and is
excellent for chemical and electrical
uses.
 This glass makes possible such products
as ovenware and beakers, test tubes,
and other laboratory equipment.

Fused silica glass
 This glass is a highly heat-shock
resistant glass that consists entirely of
silica.
 It can be heated to extremely high
temperatures and then plunged into ice-
cold water without cracking.
 Fused silica is expensive because
exceptionally high temperatures must be
maintained during production.
 It is used in laboratory glassware and
optical fibers.

Glass resists heat
 96 percent silica glass resists heat
almost as well as fused silica, but it is
less expensive to produce.
 It consists of a special borosilicate
composition that has been made porous
by chemical treatment.
 The pores shrink when the glass is
heated, leaving a smooth, transparent
surface.
 The glass is sold under the trade name
Vycor.

Colored glass
 Colored glass gets its coloring from
certain oxides that are added to the
glass.
 For example, 1 part of nickel oxide in
50,000 produces a tint that may range
from yellow to purple, depending on the
base glass.
 One part of cobalt oxide in 10,000 gives
an intense blue.
 Red glasses are made with gold, copper,
or selenium oxides.
 Other colors can be produced in glass
with other chemicals.

Glass Material Properties
 Hard Glasses
 Your typical silica based glasses with
the coefficient of thermal expansions
lower than 6 ppm/C.
 They are most commonly used to form
matched seals with the likes
of Molybdenum, and Tungsten.
 Typical hard glasses are Alkali Barium
Borosilicate and Alkali Borosilicate.

Soft Glasses
 These are the glasses with the
coefficient of thermal expansions
above 6 ppm/C.
 The most common use for these
glasses is for forming hermetic seals
between Alloy 52 pins and Stainless
Steel housings.
 Soft glasses are also used for many
other compression sealing
applications.

Specialty Glasses
 glasses for specific uses such as
lithium battery sealing glasses,
titanium sealing glasses & aluminum
sealing glasses.

Glass Manufacture
 Glassmaking involves two main steps:
 (1) heating and mixing raw materials
to produce molten glass, and
 (2) forming the molten glass into the
desired shape.
 Most glass then receives further
treatment to produce the final product.

Making Molten Glass
 Glass manufacture begins with the careful
selection and measurement of raw materials.
 The most important raw material is sand.
 Other raw materials used depend on the type
of glass being made.
 Broken glass, called cullet, is usually added
to the raw materials.
 It promotes the melting of the raw materials
as they are heated.
 Most cullet is waste from glass-forming
operations; some is obtained from recycled
glass products.

Melting
 Melting is done by batches or as a
continuous process.
 With the continuous-tank furnace, the
most common type of furnace used for
melting, raw materials are fed into one
end and molten glass is withdrawn
continuously from the other end.

Raw materials and cullet are
heated
 The raw materials and cullet are heated until
they have melted into a spongy mass full of
bubbles.
 The temperature of the melt is then
increased to make it more fluid, allowing the
bubbles to rise to the surface and escape.
 The glass at this stage is clear and
homogeneous. Soda-lime glass, the most
common type of glass, is initially heated to
about 2,550 F. (1,400 C.) and then rapidly
heated to about 2,800 F. (1,540 C.).
 Most other kinds of glass must be heated to
higher temperatures.

Forming
 When the glass is withdrawn from the
furnace its viscosity is too low for it to
hold any form.
 As the glass is cooled, it flows less
easily and can be formed.

Any of several processes can be
used:
 Blowing.
 In machine blowing, blasts of compressed air are
used to force gobs or ribbons of glass into molds.
Bottles are made by machine blowing.
 In hand blowing, a mass of molten glass is
gathered on the end of a four- to five-foot (120-
to 150-cm) pipe called a blowpipe or blowing
iron.
 The glassmaker blows through the pipe, giving
the material a hollow, balloon-shaped form.
 The glass is further shaped with various metal
tools.
 It is usually reheated several times to keep it
pliable while it is being shaped.

Drawing
 In producing flat drawn glass, a horizontal
wire called a bait is lowered into the molten
glass and then raised.
 Glass adheres to the wire and is drawn
upward as a continuous sheet.
 Once hardened, the glass is cut into sheets
for use in windows and inexpensive mirrors.
 Flat drawn glass has a fire-finished surface
that forms naturally as the molten glass
cools.
 Drawn glass tubing is made by forcing molten
glass along a ceramic cone, called a
mandrel, that forms the glass into tubing.

Floating
 Molten glass is allowed to flow onto a
bath of molten tin and is then allowed
to cool.
 The tin has a low melting point and
remains liquid at temperatures at
which the glass hardens.
 The surface of the metal leaves the
glass with a very smooth surface.
 Float glass is used in windows and
other flat glass products.

Pressing
 A measured amount of molten glass is
placed, by machine, into a mold, and a metal
plunger presses the glass outward to fill the
mold.
 When the glass has cooled and is firm
enough to hold its shape, the mold is
removed.
 Pressing techniques are well-suited for rapid
mass production.
 Many of the glass objects made for everyday
use, such as drinking glasses and heat-
resistant glassware, are produced by
pressing.

Rolling
 As the molten glass leaves the
furnace, it flows between sets of large,
heavy rollers.
 This method is typically used for flat
glass that does not require a fine
finish, such as glass made with a
figured pattern on its surface.

Further Processing
 After forming, glass is usually heat-
treated, either by annealing or by
tempering.
 It may also be decorated.

Annealing
 Stresses build up in glass objects as
they are cooled from forming
temperatures to room temperature.
 These stresses greatly weaken the
objects and may cause them to
fracture spontaneously.
 In annealing, glass products are
reheated in ovens called lehrs, and
then allowed to cool slowly under
controlled conditions, so that the
stresses do not recur.

Tempering
 Tempered glass is tougher (more resistant to
breakage) than ordinary glass.
 In tempering, controlled, uniform stresses are
deliberately set up in the surface of a glass
object.
 The glass is heated to just below the
temperature at which it would begin to soften
and is then quenched (rapidly chilled) to
stress its entire surface uniformly. Tempered
glass cannot be cut or drilled.
 If a piece of tempered glass is pierced in any
way, the uniformity of the stress is destroyed
and the whole piece shatters into small
pieces.

Decorating
 Glass objects can be decorated in
many ways. Some glass objects are
painted or glazed.
 Others are etched with hydrofluoric
acid, either to produce an artistic
design or to frost the entire surface.
 Designs can also be cut or ground into
the surface.

Reversible transition
 Glass is an amorphous solid (non-
crystalline) material that exhibits a
glass transition, which is the reversible
transition in amorphous materials (or
in amorphous regions within
semicrystalline materials) from a hard
and relatively brittle state into a molten
or plastic state.
 Glasses are typically brittle and can be
optically transparent.

Soda -lime
 The most familiar type of glass is
soda-lime glass, which is composed of
about 75% silicon dioxide (SiO2),
sodium oxide (Na2O) from sodium
carbonate (Na2CO3), lime (CaO), and
several minor additives.

Silicate glass
 Silicate glass generally has the
property of being transparent.
 Because of this, it has many
applications.
 One of its primary uses is as a light-
transmitting building material,
traditionally as small panes set into
window openings in walls, but in the
20th-century often as the major
cladding material of many large

Make optical lenses
 Glass is both reflective and refractive of
light, and these qualities can be
enhanced by cutting and polishing to
make optical lenses, prisms, fine
glassware, and optical fibers for high
speed data transmission by light.
 Glass can be colored by adding metallic
salts, and can also be painted.
 These qualities have led to the extensive
use of glass in the manufacturing ofart
objects and in particular, stained glass
windows.

Glass is extremely durable
 Although brittle, glass is extremely durable, and many
examples of glass fragments exist from early glass-
making cultures.
 Because glass can be formed or molded into any
shape, and also because it is a sterile product, it has
been traditionally used for vessels: bowls, vases,bottles,
jars and drinking glasses.
 In its most solid forms it has also been used for
paperweights, marbles, and beads.
 When extruded asglass fiber and matted as glass wool
in a way to trap air, it becomes a thermal insulating
material, and when these glass fibers are embedded
into an organic polymer plastic, they are a key structural
reinforcement part of the composite material fiberglass.

Fused quartz
 Fused quartz is relatively chemically-pure silica, or SiO2,
which is not in crystalline form but rather in vitrified or glass
form, with no true melting point.
 It can be used for some special glass applications.
 However, this is not very common due to silica's high
glass transition temperature of over 1200 °C (2192 °F).
 Normally, other substances are added to simplify processing.
 One is sodium carbonate (Na2CO3, "soda"), which lowers the
glass transition temperature.
 However, the soda makes the glass water soluble, which is
usually undesirable, so lime (calcium oxide [CaO], generally
obtained from limestone), some magnesium oxide (MgO)
and aluminium oxide (Al2O3) are added to provide for a
better chemical durability.
 The resulting glass contains about 70 to 74% silica by weight
and is called a soda-lime glass.
 Soda-lime glasses account for about 90% of manufactured
glass.

 Most common glass contains other ingredients
to change its properties.
 Lead glass or flint glass is more 'brilliant'
because the increased refractive index causes
noticeably more specular reflection and
increased optical dispersion.
 Adding barium also increases the refractive
index.
 Thorium oxide gives glass a high refractive
index and low dispersion and was formerly
used in producing high-quality lenses, but due
to its radioactivity has been replaced
by lanthanum oxide in modern eyeglasses.
 Iron can be incorporated into glass to
absorb infrared energy, for example in heat
absorbing filters for movie projectors,
while cerium(IV) oxide can be used for glass
that absorbs Uv wavelengths .

Lead-oxide glass, crystal glass
 Silica 59% + lead oxide (PbO) 25% +
potassium oxide (K2O) 12% + soda
(Na2O) 2.0% + zinc oxide (ZnO) 1.5% +
alumina 0.4%.
 Because of its high density (resulting in a
high electron density) it has a high
refractive index, making the look of
glassware more brilliant (called "crystal",
though of course it is a glass and not a
crystal).
 It also has a high elasticity, making
glassware 'ring'. It is also more workable
in the factory, but cannot stand heating
very well.

Aluminosilicate glass:
 Silica 57% + alumina 16% + lime 10%
+ magnesia 7.0% + barium oxide
(BaO) 6.0% + boric oxide (B2O3)
4.0%. Extensively used for fiberglass,
used for making glass-reinforced
plastics (boats, fishing rods, etc.) and
for halogen bulb glass.

Oxide glass:
 Alumina 90% + germanium oxide
(GeO2) 10%.
 Extremely clear glass, used for fiber-
optic waveguides in communication
networks.
 Light loses only 5% of its intensity
through 1 km of glass fiber..
 However, most optical fiber is based
on silica, as are all the glasses above.

 Another common glass ingredient is
crushed alkali glass or "cullet" ready
for recycled glass.
 The recycled glass saves on raw
materials and energy. Impurities in the
cullet can lead to product and equipment
failure.
 Fining agents such as sodium
sulfate, sodium chloride, or antimony
oxide may be added to reduce the
number of air bubbles in the glass
mixture.
 Glass batch calculation is the method by
which the correct raw material mixture is
determined to achieve the desired glass
composition.

Physical properties
 Optical properties
 Glass is in widespread use largely due
to the production of glass
compositions that are transparent to
visible light.
 In contrast, polycrystalline materials
do not generally transmit visible light.
 The individual crystallites may be
transparent, but their facets (grain
boundaries) reflect or scatter light
resulting in diffuse reflection.

 Glass does not contain the internal
subdivisions associated with grain
boundaries in polycrystals and hence
does not scatter light in the same
manner as a polycrystalline material.
 The surface of a glass is often smooth
since during glass formation the
molecules of the supercooled liquid are
not forced to dispose in rigid crystal
geometries and can follow surface
tension, which imposes a microscopically
smooth surface.
 These properties, which give glass its
clearness, can be retained even if glass
is partially light-absorbing—i.e., colored.

Glass has the ability to refract,
reflect, and transmit light
 Glass has the ability to refract, reflect, and
transmit light following geometrical optics,
without scattering it. It is used in the
manufacture of lenses and windows.
Common glass has a refraction index around
1.5.
 This may be modified by adding low-density
materials such as boron, which lowers the
index of refraction (see crown glass), or
increased (to as much as 1.8) with high-
density materials such as (classically) lead
oxide (see flint glass and lead glass), or in
modern uses, less toxic oxides
of zirconium, titanium, or barium.

 These high-index glasses
(inaccurately known as "crystal" when
used in glass vessels) cause more
chromatic dispersion of light, and are
prized for their diamond-like optical
properties.

 According to Fresnel equations,
the reflectivity of a sheet of glass is
about 4% per surface (at normal
incidence in air), and
the transmissivity of one element (two
surfaces) is about 90%.
 Glass with high germanium oxide
content also finds application
in optoelectronics—e.g., for light-
transmitting optical fibers.

Other properties
 In the process of manufacture, silicate glass
can be poured, formed, extruded and molded
into forms ranging from flat sheets to highly
intricate shapes.
 The finished product is brittle and will
fracture, unless laminated or specially
treated, but is extremely durable under most
conditions.
 It erodes very slowly and can withstand the
action of water.
 It is resilient to chemical attack and is an
ideal material for the manufacture of
containers for foodstuffs and most chemicals.

Contemporary production
 Following the glass batch preparation
and mixing, the raw materials are
transported to the furnace.
 Soda-lime glass for mass production is
melted in gas fired units.
 Smaller scale furnaces for specialty
glasses include electric melters, pot
furnaces, and day tanks.
 After melting, homogenization and
refining (removal of bubbles), the glass
is formed.

 Flat glass for windows and similar applications
is formed by the float glass process, developed
between 1953 and 1957 by Sir Alastair
Pilkington and Kenneth Bickerstaff of the UK's
Pilkington Brothers, who created a continuous
ribbon of glass using a molten tin bath on
which the molten glass flows unhindered under
the influence of gravity.
 The top surface of the glass is subjected to
nitrogen under pressure to obtain a polished
finish.
 Container glass for common bottles and jars is
formed by blowing and pressing methods. This
glass is often slightly modified chemically (with
more alumina and calcium oxide) for greater
water resistance.

 Once the desired form is obtained, glass
is usually annealed for the removal of
stresses.
 Surface treatments, coatings
or lamination may follow to improve the
chemical durability (glass container
coatings, glass container internal
treatment), strength (toughened
glass, bulletproof glass, windshields), or
optical properties (insulated
glazing, anti-reflective coating).

Network glasses
 A CD-RW (CD). Chalcogenide
glasses form the basis of rewritable CD
and DVD solid-state memory technology.
 Some glasses that do not include silica
as a major constituent may have
physico-chemical properties useful for
their application in fiber optics and other
specialized technical applications.
 These include fluoride
glasses, aluminosilicates, phosphate
glasses, borate glasses,
and chalcogenide glasses.

 There are three classes of components
for oxide glasses:
 network formers,
 intermediates, and
 modifiers.
 The network formers (silicon, boron,
germanium) form a highly cross-linked
network of chemical bonds.
 The intermediates (titanium, aluminium,
zirconium, beryllium, magnesium, zinc)
can act as both network formers and
modifiers, according to the glass
composition.

 The modifiers (calcium, lead, lithium,
sodium, potassium) alter the network
structure; they are usually present as
ions, compensated by nearby non-
bridging oxygen atoms, bound by one
covalent bond to the glass network and
holding one negative charge to
compensate for the positive ion nearby.
 Some elements can play multiple roles;
e.g. lead can act both as a network
former (Pb4+ replacing Si4+), or as a
modifier.

Glass Types-
Three common types of glass:
 Soda-lime glass - 95% of all glass,
windows containers etc.
 Lead glass - contains lead oxide to
improve refractive index
 Borosilicate - contains Boron oxide,
known as Pyrex.

Glasses
 Flat glass (windows)
 Container glass (bottles)
 Pressed and blown glass (dinnerware)
 Glass fibres (home insulation)
 Advanced/specialty glass (optical
fibres)

Importance of Glass
 Glass is one of the most useful materials
in the world.
 Few manufactured substances add as
much to modern living as does glass.
 Yet few products are made of such
inexpensive raw materials.
 Glass is made chiefly from silica
sand (silica, also called silicon
dioxide), soda ash (sodium carbonate),
and limestone (calcium carbonate).

 Glass has countless uses. Food is
preserved in glass jars.
 People drink from glass containers called
glasses.
 Windows in homes, schools, and office
buildings are glass.
 Motor vehicles have glass windshields and
windows. People with vision problems
wear eyeglasses.
 Scientists use glass test tubes, and
microscopes and telescopes with glass
lenses.
 Glass optical fibers carry data all over the
world at the speed of light over the
Internet, the worldwide network of
computers.

 Glass can take many different forms.
 It can be spun finer than a spider web.
 Or it can be molded into a disk for a
telescope lens or mirror weighing many
tons.
 Glass can be stronger than steel, or
more fragile than paper.
 Most glass is transparent, but glass can
also be colored to any desired shade.

 Most countries of the world have glass
industries.
 For many years, Germany was the
major world source for optical glass,
laboratory glassware, and glass
Christmas tree ornaments.
 Today, glass manufacturers in many
countries produce such objects on a
large scale.
 Beautiful art glassware is made in many
countries, including the Czech Republic,
France, Ireland, Italy, and Sweden.

 Major glass companies spend millions
of dollars each year on research to
discover ways to make better glass and
to develop new uses for glass.
 Many of the revolutionary developments
in glass during the 1900's have come
from the laboratories of glass
manufacturers.

Types of Glass
When people speak of glass, they ordinarily
mean a transparent, shiny substance that
breaks rather easily. They may think of the
glass in windows and the glass used in
eyeglasses as being the same material.
Actually, they are not. There are many kinds of
glass. Several important kinds of glass are :

Flat glass , Glass containers
Optical glass, Fiberglass , Laminated
safety glass ,Bullet-resisting glass
Tempered safety glass, Colored
structural glass , Opal glass , Foam
glass,
Glass building blocks , Heat-resistant
glass

 Flat glass is used chiefly in windows.
 It is also used in mirrors, room dividers,
and some kinds of furniture.
 All flat glass is made in the form of flat
sheets.
 But some of it, such as that used in
automobile windshields, is reheated
and sagged (curved) over molds.

 Glass containers are used for
packaging food, beverages, medicines,
chemicals, and cosmetics.
 Glass jars and bottles are made in a
wide variety of shapes, sizes, and
colors.
 Many are for common uses, such as
soft-drink bottles or jars for home
canning.
 Others are made from special glass
formulas to make sure there will be no
contamination or deterioration of blood
plasma, serums, and chemicals stored
in them.

 Optical glass is used in eyeglasses,
microscopes, telescopes, camera
lenses, and many instruments for
factories and laboratories.
 The raw materials must be pure so that
the glass can be made almost flawless.
 The care required for producing optical
glass makes it expensive compared with
other kinds of glass.

 Fiberglass consists of fine but solid rods of
glass, each of which may be less than one-
twentieth the width of a human hair.
 These tiny glass fibers can be loosely packed
together in a woollike mass that can serve as
heat insulation.
 They also can be used like wool or cotton fibers
to make glass yarn, tape, cloth, and mats.
 Fiberglass has many other uses. It is used for
electrical insulation, chemical filtration, and
firefighters' suits.
 Combined with plastics, fiberglass can be used
for airplane wings and bodies, automobile
bodies, and boat hulls.
 Fiberglass is a popular curtain material because
it is fire-resistant and washable.

 Laminated safety glass is a “sandwich”
made by combining alternate layers of flat
glass and plastics.
 The outside layer of glass may break
when struck by an object, but the plastic
layer is elastic and so it stretches.
 The plastic holds the broken pieces of
glass together and keeps them from flying
in all directions.
 Laminated glass is used where broken
glass might cause serious injuries, as in
automobile windshields.

 Bullet-resisting glass is thick,
multilayer laminated glass.
 This glass can stop even heavy-caliber
bullets at close range.
 Bullet-resisting glass is heavy enough
to absorb the energy of the bullet, and
the several plastic layers hold the
shattered fragments together.
 Such glass is used in bank teller
windows and in windshields for military
tanks, aircraft, and special automobiles.

Tempered safety glass
 Tempered safety glass, unlike laminated
glass, is a single piece that has been given a
special heat treatment.
 It looks, feels, and weighs the same as
ordinary glass. But it can be several times
stronger.
 Tempered glass is used widely for all-glass
doors in stores, side and rear windows of
automobiles, and basketball backboards, and
for other special purposes.
 It is hard to break even when hit with a
hammer.
 When it does break, the whole piece of glass
collapses into small, dull-edged fragments.

Colored structural glass
 Colored structural glass is a heavy
plate glass, available in many colors.
 It is used in buildings as an exterior
facing, and for interior walls, partitions,
and tabletops.

Opal glass
 Opal glass has small particles in the
body of the glass that disperse the
light passing through it, making the
glass appear milky.
 The ingredients necessary to produce
opal glass include fluorides (chemical
compounds containing fluorine).
 This glass is widely used in lighting
fixtures and for tableware.

Foam glass
 Foam glass, when it is cut, looks like a
black honeycomb.
 It is filled with many tiny cells of gas.
 Each cell is surrounded and sealed off
from the others by thin walls of glass.
 Foam glass is so light that it floats on
water.
 It is widely used as a heat insulator in
buildings, on steam pipes, and on
chemical equipment.
 Foam glass can be cut into various
shapes with a saw.

Glass building blocks
 Glass building blocks are made from
two hollow half-sections sealed
together at a high temperature.
 Glass building blocks are good
insulators against heat or cold
because of the dead-air space inside.
 The blocks are laid like bricks to make
walls and other structures.

Heat-resistant glass
 Heat-resistant glass is high in silica
and usually contains boric oxide.
 It expands little when heated, so it can
withstand great temperature changes
without cracking.
 This quality is necessary in cookware
and other household equipment, and
in many types of industrial gear.

Laboratory glass
 Laboratory glassware includes
beakers, flasks, test tubes, and
special chemical apparatus. It is made
from heat-resistant glass to withstand
severe heat shock (rapid change in
temperature). This glass is also much
more resistant to chemical attack than
ordinary glass.

Glass for electrical uses
 Glass has properties that make it
useful in electrical applications: ability
to resist heat, resistance to the flow of
electric current, and ability to seal
tightly to metals without cracking.
 Because of these properties, glass is
used in electric light bulbs and for
picture tubes in television sets.

Glass optical fibers
 Glass optical fibers are glass fibers
used to transmit information as pulses
of light.
 Thin, extremely pure optical fibers are
used to carry telephone and television
signals and digital (numeric) data over
long distances.
 Glass optical fibers are also used in
control board displays and in medical
instruments.

Glass tubing
 Glass tubing is used to make
fluorescent lights, neon signs, glass
piping, and chemical apparatus.
 Glass tubing is made from many kinds
of glass and in many sizes.

Glass-ceramics
 Glass-ceramics are strong materials made
by heating glass to rearrange some of its
atoms into regular patterns.
 These partially crystalline materials can
withstand high temperatures, sudden
changes in temperature, and chemical
attacks better than ordinary glass can.
 They are used in a variety of products,
including heat-resistant cookware, turbine
engines, electronic equipment, and nose
cones of guided missiles.
 Glass-ceramics have such trade names as
Pyroceram, Cervit, and Hercuvit.

Radiation-absorbing and
radiation-transmitting glass
 Radiation-absorbing and radiation-
transmitting glass can transmit, modify, or
block heat, light, X rays, and other types of
radiant energy.
 For example, ultraviolet glass absorbs the
ultraviolet rays of the sun but transmits visible
light.
 Other glass transmits heat rays freely but
passes little visible light. Polarized glass cuts
out the glare of brilliant light.
 One-way glass is specially coated so that a
person can look through a window without
being seen from the other side.

Laser glass
 Laser glass is an optical glass containing small
amounts of substances that enable the glass to
generate laser beams efficiently.
 Such glass is used as the active medium in solid-
state lasers, a type of laser that sends light out
through crystals or glass (One substance
commonly used in laser glass is the element
neodymium.
 Researchers are using glass lasers in an attempt
to harnessnuclear fusion (the joining of atomic
nuclei) as a source of commercially useful
amounts of energy.
 In their experiments, powerful glass lasers heat
hydrogen atoms until hydrogen nuclei fuse,
releasing large amounts of energy.

Invisible glass
 "Invisible glass" is used principally
for coated camera lenses and
eyeglasses.
 The coating is a chemical film that
decreases the normal loss of light by
reflection.
 This allows more light to pass through
the glass.

Photochromic glass
 Photochromic glass darkens when
exposed to ultraviolet rays and clears
up when the rays are removed.
 Photochromic glass is used for
windows, sunglasses, and instrument
controls.

Photosensitive glass
 Photosensitive glass can be
exposed to ultraviolet light and to heat
so that any pattern or photograph can
be reproduced within the body of the
glass itself.
 Because the photographic print then
becomes an actual part of the glass, it
will last as long as the glass itself.

Photochemical glass
 Photochemical glass is a special
composition of photosensitive glass
that can be cut by acid.
 Any design can be reproduced on the
glass from a photographic film.
 Then when the glass is dipped in acid,
the exposed areas are eaten away,
leaving the design in the glass in three
dimensions.
 By this means, lacelike glass patterns
can be made.

Heavy metal fluoride glass
 Heavy metal fluoride glass is an
extremely transparent glass being
developed for use in optical fibers that
transmit infrared rays.
 Infrared rays are much like light waves
but are invisible to the human eye.
 In optical fibers, infrared light transmits
better over distance than visible light
does.

Chalcogenide glass
 Chalcogenide glass is made up of
elements from the chalcogen group,
including selenium, sulfur, and
tellurium.
 The glass is transparent to infrared
light and is useful as a semiconductor
in some electronic devices.
 Chalcogenide glass fibers are a
component of devices used to perform
laser surgery.

Sol-Gel glass
 Sol-Gel glass can be used as a protective
coating on certain solar collectors or as an
insulating material.
 It is also used to make short, thick tubes that are
drawn into optical fibers.
 To make Sol-Gel glass, workers dissolve the
ingredients in a liquid.
 They then heat the liquid.
 The liquid evaporates, leaving behind small
particles of glass. Heating these
particles fuses (joins) them to form a solid piece
of glass.
 The temperatures involved in Sol-Gel processes
are often lower than those needed to make
ordinary glass.

Pressed Glass Processing
Softened
Gob

Armoured Glass
 Many have tried to
gain access with golf
clubs and baseball
bats but obviously the
glass remains intact !
From time to time a
local TV station
intends to show videos
of those trying to get at
the cash!!

Tempered Glass
The strength of glass
can be enhanced by
inducing compressive
residual stresses at the
surface.
The surface stays in
compression - closing
small scratches and
cracks.
Small Scratches

Hardening Processes
 Tempering:
◦ Glass heated above Tg but below the softening point
◦ Cooled to room temp in air or oil
◦ Surface cools to below Tg before interior
◦ when interior cools and contracts it draws the exterior into
compression.
 Chemical Hardening:
◦ Cations with large ionic radius are diffused into the
surface
◦ This strains the “lattice” inducing compressive strains and
stresses.

Commercial glasses
 Commercial glasses are mainly
complex silicates (Si02) in chemical
composition with numerous other
oxide substances (e.g., Na2O, CaO,
Al2O3, B2O3).
 Glasses are made by melting the
source materials together, forming in
various ways while fluid, and allowing
to cool.

Crystalline solids
 Crystalline solids have a very ordered
structure; they crystallize into specific
forms such as cubes.
 When liquids crystallize, there is a
contraction in volume due to the
transition from an open, random
structure to an ordered structure.

 Most materials when cooled from the
liquid state will crystallize into a rigid
solid.
 Consider melting lead or solder to
form a liquid, when it cools it becomes
a solid.
 Liquids do not have an ordered
structure; they have a random, open
network.

Viscosity
 When glass cools from a liquid state at
high temperatures it does not
crystallize.
 First it becomes what we call a
supercooled liquid.
 As temperatures below the
supercooled phase, the glass
becomes very viscous (thick, stiff) and
becomes a rigid solid.

 Since glasses do not have distinct
melting or fusion points like solids, we
use viscosity to describe the various
states of glass.
 Viscosity is a property related to liquid
flow.
 The opposite of viscosity is fluidity.
 A liquid that pours easily has a low
viscosity (high fluidity); a liquid that is
thick and hard to pour has a high
viscosity (low fluidity).

Glass melting
 Glass melting is conducted at high
temperatures (1500oC, 2700oF)
where the viscosity is about 50 - 150
Poise.
 For comparison, heavy machine oil
and castor oil have viscosity values of
10 to 20 Poise at room temperature.
 Corn syrup has a viscosity of 200
Poise at room temperature which is
close to that of glass at melting

Glass melting
 Glass is normally formed or "worked" at
temperatures from 800 to 1100oC (1470
- 2000 oF) where viscosities range from
3,000 to 10,000 Poise.
 Glass at room temperature has a very
high viscosity of about 10 followed by 18
zeros.
 Thus we normally use the log of viscosity
since it is easier to write.
 We would then write the viscosity at
room temperature as 1018 Poise.

Colored Glass
There are three mechanisms of colored
glasses:
a) Ionic/Electronic transfer - transition metal
ions
b) Sulfides, selenides, and tellurides
c) Metallic (colloidal)
 Colored glass can be made by adding
small amounts of certain chemicals such
as cobalt (Co), manganese (Mn), copper
(Cu), and chromium (Cr).
 These materials cause specific
wavelengths of light to be absorbed,
creating a colored glass.

Color Formation in Glasses
Color Coloring Agents
Purple Manganese(III), Neodymium, Nickel in K2O glasses
Blue Cobalt, Copper(II), Sulfur in B2O3 glasses
Green Chromium, Copper with Ti, Cr, Fe
Iron with chromium-uranium-vanadium
Molybdenum in P2O5 glasses
Yellow Uranium, Cadmium sulfide*, Cerium , titanium-silver
Orange Cadmium sulfide plus cadmium selenide*
Amber Iron and sulfur* - manganese and sulfur*
Brown Manganese and iron-titanium and iron-nickel in Na2O glasses; iron and
selenium-manganese and titanium-manganese and cerium
Red Cadmium sulfide plus selenium* - gold-copper-uranium in PbO glasses
Black Combinations of cobalt, manganese, nickel, iron, copper, and chromium-
iron sulfide* - manganese and cobalt in PbO glasses

Some typical colors are:
Ion Color Comments
Co2+ Blue
Ni2+ Violet in glasses containing K2O
Yellow in glasses containing Na2O
Nd3+ Violet
Pr3+ Yellow-Green
Ce4+ Yellow Ce3+ is colorless
Cr3+ Green
Mn3+ Violet Mn2+ colors faintly yellow
Cu2+ Blue Cu1+ is colorless
Fe3+ Yellow-Brown
Fe2+ + Fe3+ Blue-Green total reduction to Fe2+ not possible
(UO4)2- Yellow-Green

 With our borax glass we will make a
copper blue glass.
 When we melt the borax glass on the
copper wire loop, some of the copper
metal will go into the glass.

 BACKGROUND
 Glass is the rigid metastable solid produced by
quenching a liquid form rapidly enough to prevent
crystallization.
 In most cases glass can be cooled very slowly without
worry of crystallization (except metallic glasses).
 Due to its extreme viscous nature at high temperature,
atomic mobility is low preventing orderly arrangement of
atoms upon cooling.
 Glass is characterized by an arrangement of amorphous
semi-periodic regions, and therefore lacks any long-term
crystalline order.
 Pure silicate glasses are transparent, and coloring is
determined by impurities.
 Therefore, silicate glasses are hard, brittle and
electrically insulating.
 In contrast, metallic glasses are opaque, corrosion
resistant, electrically conducting, very strong, flexible,
and some have useful magnetic properties.

 When glass is in its highly viscous
molten state, it is considered a
supercooled liquid. In its solid form,
glass is referred to as an amorphous or
vitreous solid.
 The temperature at which this transition
from a supercooled liquid state to a
vitreous state is referred to as the glass
transition temperature, Tg (fig. 7-1).

Transition paths for liquid to glass vs. liquid to
crystal in terms of specific volume

The glass transition
temperature
 The glass transition temperature is not
fixed for a particular glass
composition.
 Rather, the glass transition
temperature varies slightly and is
dependent on the cooling rate.
 Faster cooling rates promote glass
transitions at higher temperatures and
slower cooling rates promote glass
transitions at lower temperatures.

Cooling rate
dependence of
the glass
transition
temperature and
specific volume

Fast cooling
 Fast cooling yields a glass with a
relatively open structure, compared to
a slow cooled glass whose specific is
lower (density higher).
 For this reason, among others, it is
important to anneal glass artifacts in
the range of the glass transition
temperature to eliminate the effects
(residual internal stresses) of
differential cooling rates, which may
result from glass processing.

Glass Compositions
 Soda-lime-silica glass is a very
common glass which is used in
windows, bottles, canning jars,
drinking glasses, and other household
glass objects.
 Soda-lime-silica glass is also called
"flint" glass since its primary
component is sand (SiO2) and the
rock called "flint" is 100% SiO2.

 The basic composition of flint glass is
as follows.
 SiO2: 75 wt % NaO2: 15 wt %
CaO: 10 wt %

We only need to use three raw
materials to produce flint glass:
Common
Name
Chemical
Name
Chemical
Formula
Glass
Compone
nt
Wt %
Sand Silica or
Silicon
Dioxide
SiO2 SiO2 100
Soda Ash Sodium
Carbonate
Na2CO3 Na2O 58.5
Limestone Calcium
Carbonate
CaCO3 CaO 56

Let's calculate how much raw materials
(batch) would be required to make 100
pounds (lb.) of flint glass
Raw
Material
Wt %
Oxide
Glass
Calculatio
n
Pound
s
Oxide
Batch
Calculatio
n
Pounds
Batch
Sand 100% SiO2 0.75 x 100 75 lb. 75 / 1.00 75.0 lb.
Soda Ash 58.5%
Na2O
0.15 x 100 15 lb. 15 / 0.585 25.6 lb.
Limestone 56% CaO 0.10 x 100 10 lb. 10 / 0.56 17.9 lb.
Total 100 lb. 118.5 lb.

 As you can see, we require 118.5 pounds
of batch to produce 100 pounds of glass.
 What happens to the extra 18.5 pounds?
 It goes out the furnace chimney as carbon
dioxide (CO2) gas. Soda ash and
limestone are called carbonates.
 Upon heating or decomposition, they
release CO2.
 Na2CO3 (s) Na2O (s) + CO2 (g)
 CaCO3 (s) CaO (s) + CO2 (g)

 Another common commercial glass is
the borosilicate glass often referred to
as "Pyrex" or "Kimax" glass.
 This glass contains boron oxide
(B2O3) which makes it more resistant
to thermal shock (sudden heating or
cooling) than soda-lime-silica glass.

 Borosilicate glass is the type of glass
you find used in the beakers and test
tubes used in your chemistry
laboratory.
 It is also used at home in the kitchen
for ovenware.
 The major components is borosilicate
glass include:
 SiO2 : 81% Al2O3 : 2% B2O3 :
13% Na2O : 4%

 You can make a very simple glass using just a
Bunsen burner or propane torch.
 For this glass we will use a common household
ingredient, Borax, that you can buy at the grocery
store.
 Borax has the following chemical composition:
 Na2B4O7 - 10 H2O
 When we heat the borax, the water (H2O) is
released. We end up with a final glass composition
of 69.2 wt% B2O3 and 30.8 wt% Na2O.
 Ten grams (10 g) of borax would produce 5.3 g of
glass. Unfortunately, borax glass can easily react
with water and decomposes after awhile in water
atmospheres.
 Thus we can only use it to demonstrate the
formation of glass.

 Glasses are amorphous ceramic
materials.
 The amorphous (or glassy) state of matter
occurs when a substance has not been
given sufficient time to crystallize.
 Glasses are most commonly made by
rapidly quenching a melt.
 This means that the atoms making up the
glass material are unable to move into
positions which allow them to form the
crystalline regularity.
 This may be attributed to the fact that
each atom is strongly bonded to adjacent
atoms while in the liquid state, and that the
crystalline structures are very complex.

 The end result of all these factors is that
the glass structure is disordered and
therefore amorphous.
 One of the most notable characteristics of
glasses is the way they change between
solid and liquid states.
 Unlike crystals, which transform abruptly
at a precise temperature (i.e., their melting
point) glasses undergo a gradual
transition.
 Between the melting temperature (Tm) of a
substance and the so-called glass
transition temperature (Tg), the substance
is considered a supercooled liquid.

 When glass is worked between Tg and
Tm, one can achieve virtually any
shape.
 The glass blowing technique is a
fascinating demonstration of the
incredible ability of glass to deform.

Advantage Of The Glass
Forming
 A chief advantage of the glass forming
process is that the item remains one
single piece with continuous molecular
structure and without internal surfaces.
 That is why optical fibers are drawn from
glass. No scattering of light at grain
boundaries occurs. Certain glasses have
non-linear optical properties that can be
used for optical switches making the
development of optical computers more
likely.

 Properly doped with polyvalent
transition metals, glasses become
semiconducting.
 But, their semiconducting properties
can be altered by electrical fields,
making these glasses suitable for
information storage devices.
 Glasses of this kind are used for the
coatings on the printing drums in laser
printers or Xerox copiers.

 Some glasses exhibit very high ionic
conductivity, which makes them useful
as electrolytes in batteries or sensors.
 One commercial example can be found
in every chemistry laboratory, the pH
meter.
 While crystalline ceramics, for the most
part, have well defined chemical
compositions, the compositions of
glasses can be widely varied.
 Glass is made out of silica which has a
very high melting point.

 In the attempt to lower the melting
temperature, soda ash (a mixture of
Na2O, sodium oxide, and Na2CO3,
sodium carbonate), and limestone
(CaCO3) are added as fluxes.
 Other glass fluxes might include lead
oxides or lead carbonates (leaded
glass or flint glass) or borax/borax
oxides (borosilicate glass).

 Borax is a naturally occurring mineral that is
chemically hydrated sodium borate or Na2B4O7 ·
10 H2O.
 The material is a white powder that is sold in super
markets as a laundry aid. Borax is also used as a
flux in working some metals because it coats and
cleans the metal and allows soldering to take
place.
 When Borax is heated, the water of hydration is
driven off and the sodium, boron and oxygen form
a non-crystalline glass.
 This glass is clear but will take a color from the
various metal oxides such as cobalt or nickel.
 Thus the Borax beads can be used to identify
some metal ions as well as demonstrate materials
used to make colored glass.
 Borax Glass is also unstable in that it tends to
absorb moisture from the air and revert back to a
cloudy hydrated material.

Silicate glass
 Ingredients
 Silica (the chemical compound SiO2)
is a common fundamental constituent
of glass.
 In nature, vitrification of quartz occurs
when lightning strikes sand, forming
hollow, branching rootlike structures
called fulgurite.

More common types of silicate glasses, and
their ingredients, properties, and applications:
 Fused quartz, also called fused silica glass,
vitreous silica glass, is silica (SiO2) in
vitreous or glass form (i.e., its molecules are
disordered and random, without crystalline
structure). It has very low thermal expansion,
is very hard, and resists high temperatures
(1000–1500 °C). It is also the most resistant
against weathering (caused in other glasses
by alkali ions leaching out of the glass, while
staining it). Fused quartz is used for high
temperature applications such as furnace
tubes, lighting tubes, melting crucibles, etc.

 Soda-lime-silica glass, window glass:
 silica 72% + sodium oxide (Na2O) 14.2% +
lime (CaO) 10.0% + magnesia (MgO) 2.5% +
alumina (Al2O3) 0.6%. Is transparent, easily
formed and most suitable for window glass
(see flat glass).
 It has a high thermal expansion and poor
resistance to heat (500–600 °C). It is used for
windows, some low temperature incandescent
light bulbs, and tableware.
 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.

 Sodium borosilicate glass, Pyrex:
 silica 81% + boric oxide (B2O3) 12% + soda
(Na2O) 4.5% + alumina (Al2O3) 2.0%. Stands
heat expansion much better than window
glass. Used for chemical glassware, cooking
glass, car head lamps, etc. Borosilicate
glasses (e.g. Pyrex) have as main constituents
silica and boron oxide.
 They have fairly low coefficients of thermal
expansion (7740 Pyrex CTE is 3.25×10–6/°C as
compared to about 9×10−6/°C for a typical
soda-lime glass), making them more
dimensionally stable. The lower CTE also
makes them less subject to stress caused
by thermal expansion, thus less vulnerable
to cracking from thermal shock. They are
commonly used for reagent bottles, optical
components and household cookware.

Glass in Materials Science

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