Alloys Flashcards
(30 cards)
What is an alloy?
Mixture of two or more elements where the main element is a metal
Examples of alloys in everyday usage?
Duralumin : body of an aeroplane Bronze : medals Brass : keys Pewter : souvenirs Stainless steel : cutlery Steel : body of car
Difference between alloy and pure metal in physical properties?
Alloy : Shiny, resistant to corrosion, hard
Pure metal : Dull, easily corroded, less hard
Why are pure metals ductile and easily pulled into fine wires?
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.
Why are pure metals malleable and its shape can be easily changed?
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.
An alloy is formed when
foreign atoms are mixed with the pure metal.
How does alloys make it hard for layers of atoms to slide over each other when force is applied?
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
What is an example of an alloy used in electrical transportation such as the Maglev train?
superconductor
How are various types of glass with different properties obtained?
silica is heated together with other chemicals
Basic properties of glass?
- Chemically inert
- Hard but brittle
- Transparent
- Heat insulator
- Electrical insulator
- Waterproof
Fused silica glass
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
Soda-lime glass
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.
Borosilicate glass
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
Lead crystal glass
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
What is a ceramic?
Solid made up of inorganic and non-metallic substances
Ceramic is produced through process of
shaping and hardening by using heating technique at a high temperature
Basic properties of ceramics
- High thermal resistance
- Heat insulator
- Break easily
- Chemically inert
- Electrical insulator
- Hard and strong
Why are ceramics resistant to high temperatures and are hard and resistant to compression?
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
Two types of ceramics?
- Traditional
- Advanced
Traditional ceramics
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
Advanced ceramics
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.
Examples of ceramic uses?
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.
What is a composite material?
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.
Wood is made of
Lignin (matrix substance) + Cellulose fibres (Strengthening substance)
