Thursday, 19 February 2015

9.5 The Uses of Glass and Ceramics

Glass and Ceramics
■ Electrolyte

The raw materials used in the making of glass and ceramic are obtained from the earth's crust.

Silica or silicon(IV) dioxide, SiO2, form the most important component of glass and ceramics.

Both glass and ceramic are used widely in our daily life because of the low production cost. It it used in industry to make bottles, cooking utensils, plates and bowls, laboratory apparatus, window panes, bulbs and others.
■ Structure of silicon (IV) oxide

Molecule of each silicon atom held in a tetrahedral structure by four oxygen atoms.

Each oxygen atom is held by two silicon atoms to form a gigantic covalent molecule.
■ Properties of glass and ceramics

Hard and brittle

Do not conduct heat and electricity

Inactive towards chemical reactions

Weak when pressure is applied

Can be cleaned easily


Types, compositions, characteristics and uses of glass
■ Glass

A mixture of two or more types of metallic silicates but the main component is silicon(IV) dioxide.
■ Properties of glass

Transparent and not porous

Hard and brittle

Do not conduct heat and electricity

Inactive towards chemical reactions

Can withstand compression but not pressure

Can be cleaned easily
■ Types of glass

Different types of glass can be obtained depending on the compositions of substances in it.

Types of glass Properties Uses
Soda lime glass
■ Limestone (CaCO3) and sodium carbonate(Na2CO3) are mixed with molten silica and cooled down.
■ Low melting point
■ Easily to be shaped(soft glass)
■ Easily broken
■ Transparent
Bottle, glass container, electrical bulb.
Lead glass
■ A mixture of lead(II) oxide, sodium oxide and silica, Lead glass of better quality contains a higher percentage of PbO.
■ High refractive index and density.
■ Glittering and attractive surface.
■ Very transparent.
Decorative items, crystal glass-wares, lens, prism.
Borosilicate glass
■ Boron oxide (B2O3) and sodium carbonate is added to molten silica.
■ Able to withstand high temperature and chemical reaction.
■ It does not break easily.
■ High melting point.
■ Transparent to light and infra red ray but no to ultraviolet ray.
Laboratory apparatus, cooking utensils and ultraviolet column.
Fused silicate glass (Quartz glass)
■ Sand is heated until it melts at 1700°C, and the viscous liquid is cooled immediately which produces a transparent solid with an uneven arrangement of atoms
■ Cannot expand or contract easily when there are temperature changes.
■ Difficult to be made into different shapes.
■ High melting point.
Mirrors, lenses and laboratory wares.
Compositions, properties and uses of ceramics
■ Ceramics

A substance that is made from clay and hardened by heat in a furnace maintained at a high temperature.
■ Clay

Composed of aluminosilicate with sand and iron(III) oxide as impurities.

Kaolin, or clay in its pure form, is white in colour. It consists of crystals of hydrated aluminosilicate with the formula Al2O3•Si2O3•2H2O

Red clay contains iron(III) oxide, Fe2O3
■ Properties of ceramics

Hard and brittle

Do not conduct heat and electricity

Inactive towards chemical reactions

High melting point – heat resistant

Cannot be compressed easily
■ The preparation of ceramic objects involves 3 stages:

Step 1: A layer of water exists between the aluminosilicate crystals. This gives it a plastic-like property when wet. Thus, the clay is first wet to make it soft before it is shaped

Step 2: The shaped object is then dried. At this stage, the product can still be reshaped by adding more water.

Step 3; The dried object is heated to a temperature of 1000°C in a furnace. The product of this stage cannot be softened with water or reshaped.


The uses of special purpose glass and ceramics
■ Photochromic glass

A type of glass that is very sensitive to light.

It darkens in the presence of bright light and lightens when the amount of sunlight lessens.

The glass is produced by adding silver chloride and some copper(II) chloride to normal glass.

Silver halides decompose to silver and its halogen when exposed to ultraviolet rays.
AgCl(s) → Ag(s) + ½ Cl2(g) . It is the silver which makes the glass become dark.

When there is a decrease in light, silver chloride is formed again.
AgCl(s) → Ag(s) + ½ Cl2 Therefore, the glass lightens.

Used in windows, sunglasses and instrument control.
■ Conducting glass

A type of glass which can conduct electricity. It is obtained by coating a thin layer of a conducting material around the glass, usually indium tin (IV) oxide or ITO. Used in the making of LCD.

Another type of conducting glass can be obtained by embedding thin gold strips into a piece of glass. This is used to make the front windows of aeroplanes which tend to mist at very high heights. By passing an electric current through this glass, the water of condensation will dry up.
■ Superconductor

Electrical conductors which have zero electrical resistance.

Perovsite is a type of ceramic superconductor composed of itrium oxide, copper oxide and barium oxide.

Used to make magnets which are light but thousands of times stronger than the normal magnet.
■ Ceramic block

When clay is heated with magnesium oxide, the ceramic that is produced has a high resistance to heat.

Used to build the engine blocks in cars as they can withstand high temperatures.


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