Alloys and their Composition
Alloys are homogeneous mixtures of metals and cannot be separated into their components by physical methods.Pure metals have poor mechanical properties. Hence, they are not used in their pure form in industry. Their properties are modified by adding other elements.
- Reasons for Alloying: To improve mechanical properties.Alloys are often made to alter the mechanical properties of the base metal.
- Characteristics of alloys: Alloys are harder and tougher than the base metal and are resistant to corrosion. They are inert to commonly used chemicals.
- An alloy is considered as a mixture because it shows the properties of its constituents and can have variable composition.
- Amalgams: Alloys of mercury with other metals like sodium, potassium, gold and zinc etc are called amalgams. Amalgams stored in iron bottles as iron cannot form an amalgam with mercury.
- Rold Gold is a metal, such as brass, coated with a thin layer of gold, usually of above 9 carat purity.
Some commonly Used Alloys and their composition:
- Composition- zinc 30%, copper 70%
- uses- In the making of utensils, pipes and radiator statues etc.
- Composition – Cu 67%, Zn 33%
- uses – Hardware items
- Composition – Copper 90%, Tin 10%
- uses – In the making of coins, ornaments, utensils and statues.
- Composition – Fe 82%,(Ni + Cr) 18
- uses – In the making of surgical instruments, watches and utensils etc.
- Composition- Al 95% ,Mg 5%
- uses – In making light articles and physical balance etc.
- Composition- Al 95%, Cu 4% ,Mn 0.5%
- uses -In making parts of aeroplane and ship etc.
- Composition – Al 8-12% , Ni 15-26% , Co 5-24% ,Cu 6%, Remaining: Fe, Tl
- uses – It is useful in making of magnets.
- Composition – Cu 60% ,Zn 20%, Ni 20%
- uses – It is useful in electroplating and making of utensils.
- Composition – silver 92.5%, copper 7.5%
- uses – jewellery, art object
- Composition – Cu 88%, Sn 10%,Zn 2%
- uses – It is useful in making of guns, machine parts and canons..etc
- Composition – Pb 50%, Sn 50%
- uses – It is mainly useful to join electric wires.
- Composition – copper – 77%, tin – 23%
- uses- casting of bells
- Composition – copper 75%, nickel 25%
- uses – U.S coins
- Composition – Bi 50%, Pb 25%, Sn 12.5%, Cd 12.5%
- Uses – fuse plugs, automatic sprinklers.
- Composition – Ni 67%, and copper, with small amounts of iron, manganese, carbon, and silicon.
- Uses – It is resistant to corrosion and acids and thus used for making valves, pumps, shafts, fittings, fasteners, and heat exchangers.
- Composition – Pb 67%, sn 33%
- uses- soldering joints.
Answer the following questions based on the above notes:
1.Which metal is used in fuse wire-
Ans: An alloy of tin and lead.
2.Which metal is used for the manufacturing of heating elements used in electric iron?
3.Which alloy is used in the manufacturing of the filament of an electric bulb?
Ans: Tungsten(because of high melting point)
4.Which amalgams are useful for the dental cavities.
5.The composition of dutch metal?
Ans: copper – 84% , zinc 16%
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