GLASS

What is glass?History of glass.

How is glass made? Uses of glass.

What is Glass?• “An inorganic product of fusion which has cooled

to a rigid condition without crystallizing” • Uniform amorphous solid– will only have ONE refractive index– have atoms randomly arranged throughout the sample

• No specific m.p.• Softens over a temperature range

What is Glass?• Glass combines some properties of crystals and some of liquids but glass is distinctly

different from both.• Glass is rigid like a crystal but the molecules that make up glass are arranged

randomly like liquids. • In general glass is formed by melting crystalline substances and then cooling the liquid

before the molecules can form a crystal. • Properties of glass include:• Mechanically Strong – Glass has great inherent strength and is weakened only by surface

imperfections• Hard surface – Glass resists scratches and abrasions• Elastic – Glass “gives” under stress – up to a breaking point – but rebounds exactly to its

original shape• Chemical corrosion-resistant – Glass is affected by few chemicals. It resists most

industrial and food acids.• Thermal shock-resistant – Glass withstands intense heat or cold as well as sudden

temperature changes.• Heat-absorbent – Glass retains heat, rather than conducts it. Glass absorbs heat better

than metal.• Optical Properties – Glass reflects, bends, transmits and absorbs light with great

accuracy.

History of Glass• May date to 5000 BC when sailors, carrying soda ash

as cargo on their ships, used the blocks of soda ash on which to rest their cooking vessels. The heat produced soda glass.

• Bottles were used in Egypt and Babylon as early as 1500 BC.

• Glassblowing began around 250 BC, within 150 years glass replaced metals as status symbols in the Roman culture.

History of Glass• Flat glass was produced in the 13th century, but it was

not until the early 1800’s that flat glass could be produced at reasonable cost for everyday use in windows.

• In 1883 Pittsburgh Plate Glass Company became the first successful manufacturer of plate glass in the United States.

• Until the early 20th century, glass was made by hand in America, making glass products a luxury. In 1903, Michael Owens invented the first automated glass bottle-blowing machine.

The Composition of Glass

• Because glass is used in so many different ways, there is no one chemical composition for each glass sample.

• There are thousands of different glass compositions BUT only 3 categories of substances in ALL glass – Formers– Fluxes– Stabalizers

The Composition of Glass

• The former makes up the bulk of the glass.– silicon dioxide, SiO2, in the form of sand – most

common. – Other possible formers include B2O3 and P2O5.

• The fluxes change the temperature at which the formers melt during the manufacturing of glass. – sodium carbonate, Na2CO3, and potassium carbonate,

K2CO3.

•

The Composition of Glass

• The stabilizers strengthen the glass and make it resistant to water. – Calcium carbonate, CaCO3, most frequently used

What’s in Glass?

• Network Components-Formers:SiO2, B2O3, P2O5, GeO2, V2O5, As2O3, Sb2O5

• Fluxes–Softeners [lowers melting point]:Na2O, K2O, LiO, Al2O3, B2O3, Cs2O

• Stabilizers–Chemical/Corrosion Resistance:CaO, MgO, Al2O3, PbO, SrO, BaO, ZnO, ZrO

What do they all have in common?!

The Composition of Glass• The raw materials for making glass are all

oxides. • The composition of any sample of glass can be

given in terms of the percent of each oxide used to make it.

• There are six basic types of glass based on composition

Common Types

Soda-lead-- fine table ware and art objects

Borosilicate—heat resistant, like Pyrex

Tempered—used in side windows of cars

Laminated—used in the windshield of most cars

Soda-lime—used in plate and window glass, glass containers, and electric light bulbs

Common Types

Soda-lime—used in plate and window glass, glass

containers, and electric light bulbs

Soda-lead—fine table ware and art objects

Borosilicate—heat resistant, like Pyrex

Tempered—used in side windows of cars

Laminated—used in the windshield of most cars

Kendall/Hunt Publishing Company 12

Soda-Lime Glass

• SiO2 + Na2O / K2O + CaO / Al2O3 / MgO

• The most common (90% of glass made)• least expensive form of glass• It usually contains 60-75% silica, 12-18% soda,

5-12% lime• Resistance to high temperatures and sudden

changes of temperature are not good • Resistance to corrosive chemicals is only fair.

Lead Glass

• High percentage of lead oxide PbO (between 20% and 80% of the batch)

• It is relatively soft, and its refractive index gives a brilliance that may be exploited by cutting

• Somewhat more expensive than soda-lime glass • Favored for electrical applications because of its

excellent electrical insulating properties. • This glass will not withstand high temperatures or

sudden changes in temperature.

Borosilicate Glass

• B2O3 (replaces Na2O)

• Any silicate glass having at least 5% of boric oxide in its composition.

• High resistance to temperature change and chemical corrosion.

• Cost is moderate when measured against its usefulness.

Tempered Glass

• Tempered(Safety glass) – treatment involves heating the glass so

that it begins to soften (about 620 C) and then rapidly cooling it.

– Produces a glass which, if broken, breaks into small pieces without sharp edges

Laminated Glass

• Laminated glass – glass is made up of a sandwich of two or

more sheets of glass (or plastic), bonded together by a flexible, normally transparent material.

– if cracked or broken, the flexible material is designed to hold the glass fragments in place

Ways Glass is Made• Rolled Glass– 'Ordinary' sheet glass –made by passing the molten

glass through rollers– process gives an almost flat

finish but with distortions. – glass is used in glazing

greenhouses and garden sheds

Ways Glass is Made

• Float glass (plate) –molten glass is 'floated'

onto a bed of molten tin– produces a glass which is

flat and distortion free– process imparts a

fluorescence to the glass [UV light]

Ways Glass is Made• Tempered(Safety glass) • Heating:

– the glass begins a heat treatment process in which it travels through a tempering oven

– The oven heats the glass to a temperature of more than 600 degrees Celsius.

• Cooling:– The glass then undergoes a high-pressure cooling procedure

called "quenching." – High-pressure air blasts the surface of the glass for 5 seconds.– Quenching cools the outer surfaces of the glass much more

quickly than the center. which gives tempered glass its strength.

Video Of Tempered Glass

Ways Glass is Made• Laminated glass• Two layers of glass with a thickness of about 0.12 inches (3 mm) are

placed on either side of the PVB layer which is 0.015 inches (.38 mm) thick.

• Rollers press the layers together to expel any air pockets. • The glass is then heated to 158 degrees Fahrenheit (70 degrees C) in a

pressurized oil bath to permanently bond all the layers together.• Additional layers of glass and PVB will increase the strength of laminated glass.

Video Of Laminated Glass

Other Glass

Bullet Proof Glass• A thicker version of laminated glass • Armored cars have a thickness of 2.8-3 inches• Armored Hummers (war) have thickness of 4-

5 inches• VERY HEAVY

Other Glass

Plexiglas• Not glass at all, but a synthetic thermoplastic

polymer • Chemical name is polymethyl methacrylate

(PMMA)• Sold as Plexiglas, Acrylite and Lucite. • Less dense than glass, does not shatter, is

easily shaped, transmits visible light readily and does not block UV radiation.

Additives and Color

• Color can be added to glass as a result of impurities in the substances used to make the glass.

• Color can also be added by dissolving one or more metal oxides, by dispersing a colloid throughout the mix or by suspending pigments to create opaque areas. Oxide – Color Oxide - ColorIron - green, brown Antimony - whiteManganese – amethyst Cobalt - deep blueGold – red Copper - light blueLead - yellow