Alloys

Question 1

What is an alloy?

Answer 1

Mixture of two or more elements where the main element is a metal

Question 2

Examples of alloys in everyday usage?

Answer 2

Duralumin : body of an aeroplane
Bronze : medals
Brass : keys
Pewter : souvenirs
Stainless steel : cutlery
Steel : body of car

Question 3

Difference between alloy and pure metal in physical properties?

Answer 3

Alloy : Shiny, resistant to corrosion, hard

Pure metal : Dull, easily corroded, less hard

Question 4

Why are pure metals ductile and easily pulled into fine wires?

Answer 4

A pure metal is made up of one type of atom that is of the same size and are arranged in an orderly arrangement. When force is applied, the layers of atoms in the metal easily slide over each other.

Question 5

Why are pure metals malleable and its shape can be easily changed?

Answer 5

There are empty spaces between the atoms in a pure metal. When force is applied, the layer of atoms in a metal will slide to fill the empty spaces and form a new structure.

Question 6

An alloy is formed when

Answer 6

foreign atoms are mixed with the pure metal.

Question 7

How does alloys make it hard for layers of atoms to slide over each other when force is applied?

Answer 7

The foreign atoms which are mixed with a pure metal are different in size. Hence, orderly arrangement of atoms in a pure metal is disrupted

Question 8

What is an example of an alloy used in electrical transportation such as the Maglev train?

Answer 8

superconductor

Question 9

How are various types of glass with different properties obtained?

Answer 9

silica is heated together with other chemicals

Question 10

Basic properties of glass?

Answer 10

• Chemically inert
• Hard but brittle
• Transparent
• Heat insulator
• Electrical insulator
• Waterproof

Question 11

Fused silica glass

Answer 11

Made from Silica (silicon dioxide, SiO2) without adding any other chemical

SiO2 needs high temperature (1800 C) to melt. Hence, fused silica glass has a high melting point. This glass doesn’t expand nor contract much when there is large change in temperature.

Suitable to be used in making telescope lens

Question 12

Soda-lime glass

Answer 12

made from silica SiO2, soda (sodium carbonate, Na2CO3) and limestone (calcium carbonate, CaCO3)

Soda, Na2CO3 lowers melting point of silica, SiO2. Hence, soda glass has a low melting point, around 1000C. This glass cannot withstand high temperatures and can easily crack when subjected to sudden temperature change

This glass is easily moulded and used to make glass containers such as bottles and jugs.

Question 13

Borosilicate glass

Answer 13

made from silica, soda, limestone, boron oxide, B2O3 and aluminium oxide, Al2O3

Resistant to heat. Do not crack easily when subjected to thermal stress because of its low expansion coefficient.

Borosilicate glass can be removed from the refrigerator and heated immediately without cracking

Many laboratory glassware such as beakers and flasks are made from borosilicate glass because of its resistance to heat

It is also chemically inert compared to other glass

Question 14

Lead crystal glass

Answer 14

made from silica, soda, lead (II) oxide, PbO

Lead, Pb replaces calcium, Ca to produce glass that is softer and denser.

Lead glass is heavier and has a high refractive index.

This glass is suitable to be used in making prisms

Question 15

What is a ceramic?

Answer 15

Solid made up of inorganic and non-metallic substances

Question 16

Ceramic is produced through process of

Answer 16

shaping and hardening by using heating technique at a high temperature

Question 17

Basic properties of ceramics

Answer 17

• High thermal resistance
• Heat insulator
• Break easily
• Chemically inert
• Electrical insulator
• Hard and strong

Question 18

Why are ceramics resistant to high temperatures and are hard and resistant to compression?

Answer 18

Atoms in ceramics are bonded by strong covalent bonds and ionic bonds. (temperature)

When force is applied, atoms in ceramics cannot slide over each other because these atoms are strongly bonded in indefinite arrangement

The energy from the force will be used to break the bonds between the atoms. Hence, ceramics are brittle and weak towards stretching.

The electrons in ceramics cannot move freely to conduct electricity or heat

Question 19

Two types of ceramics?

Answer 19

• Traditional

- Advanced

Question 20

Traditional ceramics

Answer 20

made from clay such as kaolin, Al2O3.2SiO.2H20.

Clay is mixed with water to produce a soft, mouldable mixture. The mixture is then heated at a very high temperature

Generally, traditional ceramics are used to make bricks, pottery and crockery

Question 21

Advanced ceramics

Answer 21

made from inorganic compounds such as oxides, carbides and nitrides

higher resistance to heat and abrasion, more chemically inert and have superconductivity properties

Eg : silicon carbide used to make cutting discs due to its hard and strong properties. Silicon carbide is also used to make brake discs because it can withstand thermal shocks and has high resistance to heat.

Advanced ceramics are also used to make carbide rings because it is hard and resistant to abrasion.

Question 22

Examples of ceramic uses?

Answer 22

Transportation :
-Engine components in jet planes are made from ceramics

Energy production :
-Ceramic is used to make electrical insulators in high voltage areas such as power stations

Medicine :

• Zirconia ceramic is used in dental implants
• Alumina ceramic is used to make knee bone
• Ceramic is used in Magnetic Resonance Imaging (MRI) machines because it has superconductivity properties.

Question 23

What is a composite material?

Answer 23

Composite materials are materials made from combining two or more non-homogenous substances, that is matrix substance and strengthening substance. The matrix substance surrounds and binds the strengthening substance together.

Question 24

Wood is made of

Answer 24

Lignin (matrix substance) + Cellulose fibres (Strengthening substance)

Question 25

How are reinforced concretes made?

Answer 25

Steel bars or wire mesh (strengthening substance) is immersed in concrete (matrix substance)

Used in construction of bridges, dams and buildings

Question 26

How are fibre glass made?

Answer 26

Plastic (matrix substance) is strengthened with glass fibres (strengthening substance).

Used to make helmets, car bumpers and printed circuit boards

Question 27

How are optical fibres made?

Answer 27

Three layers.
Innermost layer is the core that is made up of silica glass fibres (strengthening substance)

Second layer which is glass or plastic (matrix substance) encase the core

Outermost layer is made of plastic that acts as a protective jacket (matrix substance)

Question 28

Use of optical fibres?

Answer 28

Transmit information and data in the form of light. Light moves through the optical fibre (core section) in a series of total internal reflection. The core and cladding have different refractive indexes to enable them to carry data in large capacity and to not be influenced by electromagnetic disturbances.

Question 29

How are photochromic glass made?

Answer 29

Glass (matrix substance) is combined with silver chloride AgCl and copper (I) chloride, CuCl (strengthening substance).

When exposed to sunlight, photochromic glass darkens. This is due to the formation of silver atoms that prevents the passage of light.

In dim light, copper (I) chloride, CuCl in photochromic glass protects the user from UV rays and is suitable for use in car windows, building windows and camera lenses.

Question 30

Superconductors

Answer 30

yttrium barium copper oxide (YBCO) ceramic is a composite material that has superconductivity properties other than alloys.

This superconductor is used to make electromagnets that are superconductor magnets or supermagnets.

Supermagnets are light and have strong magnetic force. Superconductor magnets are used in particle accelerators and involved in Nuclear Magnetic Resonance (NMR) machines and Magnetic Resonance Imaging (MRI) machines