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9.6 The Uses of Composite Materials

Composite material
■ Composite material

	►	Materials made from two or more constituent materials with significantly different physical or chemical properties. The two materials combined together to give the composite desirable properties,
	►	Consist of a mixture of two or more materials such as metals, alloys, ceramics, carbon and polymer.
	►	Generally, composite materials have better properties of the original material.

■ This video contains information on the composite material.

■ Types of composite materials and its uses.

	►	○ Compositions: mixture of cement, gravel, sand water, iron/steel to produce nets, rods or bars. ○ Properties: strong, high tensile ○ Uses: construction material for highways, buildings and bridges.
	►	Superconductor ○ Compositions: Mixture of various components such as niobium and germanium. ○ Properties: No electrical resistance(zero resistance). Only can function under an extremely low temperature. ○ Uses: Materials for transportation, telecommunication and astronomy, industry and medical.
	►	Fibre glass ○ Compositions: Mixture of silica, sodium carbonate and calcium carbonate. ○ Properties: Good insulator of heat and electricity. ○ Uses: Protective apparel materials for astronauts and fire-fighters.
	►	Fibre optic ○ Compositions: Mixture of glass, copper and aluminium. ○ Properties: Enables information to be transmitted in light form at high speeds. ○ Uses: Electrical cables in communication industry and cables used in medical field to observe internal organs without performing surgery.
	►	Photochromic glass ○ Compositions: Molten silica mixed with a little argentum chloride. ○ Properties: Dark-coloured when exposed to bright light and bright when in the dark. ○ Uses: Optical lenses and glass windows for vehicles.
	►	Ceramic glass ○ Compositions: Exposing glass that contains certain amount of metals to ultraviolet rays and heating it at a high temperature. ○ Uses: Cooking materials and rocket heads.
	►	Plastic strengthened with glass fibres ○ Compositions: Mixture of plastic and glass fibres ○ Properties: Very strong, light, easily formed and can withstand corrosion. ○ Uses: Make helmets, the body of cars and aeroplanes, rods and other parts of aeroplanes.

← 9.5 Uses of Glass and Ceramics

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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.

← 9.4 Synthetic Polymers and Their Uses

9.6 Uses of Composite Materials →

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9.4 Synthetic Polymers and Their Uses

Polymers
■ Polymer

	►	Long-chained molecules with a high relative molecular mass.
	►	Made up of many smaller units called monomers, which are joined through a process called polymerisation.
	►	Thus, the monomer is the repetitive unit of a long polymer chain.
	►	Types of polymer: ○ Natural polymer ○ Synthetic polymer
	►	The animation below shows the classification of polymers.

Natural polymers
■ Natural polymers

	►	Made up of carbon, hydrogen, nitrogen and oxygen.
	►	Occur naturally in living things.
	►	Examples: natural rubber, cellulose, fat, protein and carbohydrates.

■ Natural polymers and its monomer.

	►	Natural polymer and it monomer Structure of polymer Natural rubber ○ 2-methyl-1, 3-butadiene, also called isopropene, joined together to form a long chain Protein ○ amino acid molecules Carbohydrates ○ glucose molecule
	►	The animation below shows the polymerisation of isopropene into polyisoprena(rubber).

■ This video contains information about natural polymer.

Synthetic polymer
■ Synthetic polymers

	►	A polymer that is manufactured in industry from chemical substances through the polymerisation process.
	►	Examples: plastic, synthetic fibres and elastomer

■ Types of polymerisation

	►	Addition polymerisation
	►	Condensation polymerisation

■ Addition polymerisation

	►	Monomers with C=C bonding, join together to make a long chain without losing any simple molecules from it.
	►	Examples: polythene, PVC perspex and other plastics
	►	The animation below shows the addition polymerisation of synthetic polymer with their monomers.

■ Condensation polymerisation

	►	The elimination of small molecules like water, methanol, ammonia or hydrogen during polymerisation process.
	►	Examples: terylene and nylon 66.
	►	The animation below shows the condensation polymerisation of synthetic polymer with their monomers.

Uses of synthetic polymers
■ Plastics

	►	Light, strong and do not react with any chemical substances like acid and alkalis.
	►	Can be made into many shapes and sizes.
	►	Good insulators of heat and electricity.
	►	The following table shows the plastic types, structure and uses. Name Structure of monomer Structures of polymer Uses Properties Polythene (polyethylene) Plastic bags, containers and cups Light and cannot tear easily Polyvinyl chloride (PVC) Raincoat, pipes, wires insulators Heat and electricity resistant Teflon (Polytetrafluoroethene or PTFE) Non-stick pots and pans Hard, can withstand high temperatures and corrosives chemicals Polypropene Plastics, bottles,. Strong and light Polystyrene Packaging materials, toys Heat and electrics insulators, light and strong Perspex (Polymethyl 2-methyle propene) Aeroplane window panes, lenses, car lamp covers. Light, strong, translucent, stable towards sunlight

■ Synthetic Fibre

	►	Nylon and terylene are synthetic fibres which undergo the condensation polymerisation process.
	►	These fibres resemble natural fibres but more resistant to stress and chemicals, and more long-lasting.
	►	The following table shows the synthetic fibre, structure and uses. Name and structures of monomer → polymer Uses Nylon – polyamide polymer resulting from condensation of a diamine monomer and a dicarboxylic acid monomer To make umbrellas, socks, carpets, nylon string and rope, toothbrush, comb and so on. Terylene – polyester polymer produced by the condensation of a diol with a carboxylic acid as the monomers. To make fishing nets, clothes.

■ Synthetic Rubber

	►	Synthetic rubber is an elastomer or polymer which regains its size original shape after being pulled or pressed.
	►	The following table shows the synthetic rubber, structure and uses. Name and structures of monomer → polymer Uses Neoprene To make rubber gloves and to insulate electric wires Styrene-butadiene or SBR To make tyres, soles of shoes and mechanical belts

Effects of disposing items made from synthetic polymers on the environment
■ Synthetic polymers cause environmental pollution:

	►	Most polymers are not biodegradable. ○ Polymers cannot be decomposed biologically or naturally by bacteria or fungus as in the case of other garbage. ○ The disposal of polymers has resulted in environmental pollution because they remain in the environment forever.
	►	Careless disposing of synthetic polymers. ○ Plastic containers and bottles strewn around become good breeding places for mosquitoes which cause dengue fever, or malaria.
	►	Burning of synthetic polymers. ○ The open burning of plastics creates poisonous and acidic gases like carbon monoxide, hydrogen chloride and hydrogen cyanide. ○ Burning of plastics can also produce carbon dioxide, too much of this gas in the atmosphere leads to the “green house effect”.

■ This problem can be overcome by the following ways:

	►	Recycling polymer ○ Plastics can be decomposed by heating them without oxygen at 700°C. This process is called pyrolysis. The products of this process are then recycled into new products.
	►	Replacement of polymer with others material. ○ Example: Use paper bag instead of plastic bag.
	►	Reuse ○ Polymer can be reused and made into decorative items.
	►	Inventing biodegradable polymer. ○ Such polymers should be mixed with substances that decompose by bacteria or light.

← 9.3 Alloys

9.5 Uses of Glass and Ceramics →

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9.3.2 - Laboratory Activity : Comparing the rate of corrosion of iron, steel and stainless steel

Laboratory Activity 9.3.2: Comparing the rate of corrosion of iron, steel and stainless steel

Aim: To define the rates of rusting between iron, steel and stainless steel.
Problem statement: How does the rusting of iron compare to steel and stainless steel?
Hypothesis: Iron is easily corroded, followed by steel and stainless steel.
Variable:

	»	Fixed variable : Experimental conditions
	»	Manipulated variable : Types of nails
	»	Responding variable : Rate of corrosion

Material: » Iron nails » Steel nails » Stainless steel nails » Potassium hexacyanoferrate(III) » Jelly

Apparatus: » Beakers » Test tubes » Test tube rack » Sand paper

Procedure:

	►	The animation below shows the arrangement of apparatus and the observation of the experiment.
	►	(A) With chlorine 1. Each nail is cleaned with sand paper. 2. Iron nail is put into test tube A, steel nail is put into test tube B and stainless steel nail is put into test tube C. 3. 5g of jelly is dissolved in 100cm3 of boiling water. 1cm3 of potassium hexacyanoferrate(III) are added into the jelly. 4. The test tube A, B and C are filled with jelly until all nails are completely submerged. 5. The experiment set-up is put aside for three days, and the results are studied.

Results:

Test tube	Nails	Observation	Inferences
A	Iron nail	The jelly around the nail turn bluish	The iron nail has rusted
B	Steel nail	Small amount of jelly around the nail turn bluish	Iron nail has a slight rust
C	Stainless nail	No changes	No rusting occurred

Discussion:

	►	Iron will form iron(II) hydroxide. ○ 2Fe(s) + O2(g) + 2H2O(l) → 2Fe(OH)2(s)
	►	The potassium hexacyanoferrate is to detect the presence of the rust that has formed.
	►	The bluish colour detected in the test tube indicate that the iron has rusted.

Conclusion:

	►	Iron corrodes easily, steel corrodes slightly, while stainless steel does not corrode at all in the presence of water and air.
	►	The hypothesis is accepted.

↶ 9.3 Alloys

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9.3.1 - Laboratory Activity : Investigating the difference in hardness of an alloy and a pure metal

Laboratory Activity 9.3.1: Investigating the difference in hardness of an alloy and a pure metal

Aim: To understand the strength and hardness of alloys.
Problem statement: Is the hardness of alloys and pure metal are the same?
Hypothesis: Alloy is harder than pure metal.
Variable:

	»	Fixed variable : Height and mass of the weight and the steel ball bearing.
	»	Manipulated variable : Blocks of copper and brass.
	»	Responding variable : Diameter of the dent.

Material: » Copper block » Brass block

Apparatus: » Ruler » 1kg weight » Retort stand » Steel ball bearing » String

Procedure:

	►	The animation below shows the arrangement and the results of the experiment.
	►	1. A steel ball bearing is taped to a block of copper. 2. The weight is pulled to a height of 50 cm above the ball bearing. 3. The weight is released from the height of 50cm. 4. The diameter of the dent formed on the copper block is measured with a ruler and recorded. 5. Repeat step 1 – step 4 twice by using the different surface to get the average diameter rate. 6. The experiment is repeated by replacing the copper block with brass block.

Results:

Blocks	Test 1	Test 2	Test 3	Average
Copper	3.2cm	3.1cm	3.3cm	3.2cm
Brass	2.4cm	2.5cm	2.3cm	2.5cm

Discussion:

	►	Pure metal is soft. Therefore, the dent for copper is deeper and the diameter is bigger.
	►	Alloy is harder. Therefore, the dent for brass is shallow and the diameter is smaller.

Conclusion:

	►	Copper (pure metal) is softer than brass (alloy).
	►	The hypothesis is accepted.

↶ 9.3 Alloys

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