Alloys
Category : JEE Main & Advanced
A metallic product containing two or more metals or sometimes one of the ingredients a non–metal provided that the mixture is homogenous and possesses metallic properties, is known as an alloy. Alloys are usually prepared by melting two or more metals together in the proportions and then allowing the melting to solidify. If one of the metals is mercury the alloy is known as amalgam.
Alloys are prepared with a view to impart some desirable properties which the individual metals do not possess. These are,
(1) Change in the chemical reactivity : Sodium acts vigorously with water, but Na–Hg amalgam reacts slowly to suit the requirement of a number of chemical reactions.
(2) Hardness : Silver, gold and soft metals but become hard when alloyed with copper.
(3) Melting Points : Melting points of an alloy may be higher or lower than any of its components. Wood-metal, which is an alloy of Bi, Pb, Sn and Cd fuses at \[{{60.5}^{o}}C\]., while none of these metals fuses at this low temperature.
(4) Change of colour : Aluminium bronze is an alloy of aluminium and copper. It is of golden, yellow colour and is used in making decoration articles, jewellery and coins while the colour of aluminium is white and that of copper is red.
(5) Corrosion resistance : Iron gets corroded soon whereas stainless Steel, an alloy of iron and chromium, resists corrosion.
(6) Casting : An alloy of lead and antimony is known as type metal is used for casting type required in printing works.
Alloys of Al
| Alloy | Percentage | Important Properties | Uses | |
| Aluminium bronze |
Al Cu |
95% 5% |
Light, strong alloy with golden lustre, resistant to corrosion | Coins, utensils, jewellary picture frames etc. |
| Magnalium |
Al Mg |
95% 5% |
Light, tough and strong | Light instruments, balance beam, pressure cookers etc. |
| Duralumin |
Al Cu Mg Mn |
95% 4% 0.5% 0.5% |
Light, tough, ductile, resistant to corrosive action | Making aeroplanes automobile parts pressure cookers etc. |
Alloys of Ag
| Alloy | Percentage composition | Uses |
| Coinage silver | Ag = 90, Cu = 10 | For making silver coins. |
| Silver solder | Ag = 63, Cu = 30, Zn = 7 | For soldering and joining metals |
| Dental alloy | Ag = 33, Hg = 52, Sn = 12.5, Cu = 2.0, Zn = 0.5 | For filling teeth |
| Silver palladium | Ag = 40, Pd = 60 | Potentiometers and winding of some special instruments. |
Alloys of Pb and Sn
| Alloy | Percentage Composition | Uses |
| Solder | Pb = 50, Sn = 50 | For soldering. |
| Pewter | Pb = 20, Sn = 80 | In making cups, mugs and other utensils. |
| Type metal | Pb = 70, Sb = 20 and Sn = 10 | For making printing type. |
| Rose metal | Pb = 22, Sn = 28, Bi = 50 | For making electric fuses. |
| Britannia metals | Sn = 90, Sb = 8, Cu = 2 | For making table wares. |
Alloys of Copper
| Alloy | Percentage Composition | Uses |
| Brass | Cu = 80, Zn = 20 | For making utensils, condenser tubes, wires parts of machinery etc. |
| Bronze or Copper bronze | Cu = 80, Zn = 10, Sn = 10 | For making cooking utensils, statues, coins etc. |
| Aluminium bronze | Al = 95, Cu = 5 | Coins, picture frames, cheap jewellery |
| Gun metal | Cu = 90, Sn = 10 | For making gun barrels. |
| Bell metal | Cu = 90, Sn = 20 | For making bells, gongs etc. |
| Constantan | Cu = 60, Ni = 40 | For electrical apparatus |
| German silver | Cu = 60, Zn = 20, Ni = 20 | For making silver wire, resistance wires etc. |
| Monel metal | Cu = 30, Ni = 67, Fe and Mn = 3 | For making acid pumps and acid containers. |
| Phosphor bronze | Cu = 95, Sn = 4.8, P = 0.2 | For making springs, electrical equipment |
| Gold-copper alloy | Au = 90, Cu = 10 | For making gold coins, jewellery, watch cases, spectacle rims etc. |
Alloys of Iron
| Name | Percentage | Properties | Uses |
| Stainless steel | Fe = 73%, Cr = 18%, Ni = 8% and carbon | Resists corrosion | For making utensils, cutlery and ornamental pieces. |
| Manganese steel | Fe = 86%, Mn = 13% and carbon | Very hard, resistant to wear and tear. | For Making rock drills, safes etc. |
| Tungsten steel | Fe = 94%, W = 5% and carbon | Retains hardness even at high temperatures | For making high speed cutting tools. |
| Invar | Fe = 64%, Ni = 36% | Practically no coefficient of expansion. | For making watches, meter scales, pendulum rods etc. |
| Nickel steel | Fe = 98?96%, Ni = 2?4% | Resistant to corrosion, hard and elastic. | For making wire cables, gears, drive shafts etc. |
| Permalloy | Fe = 21%, Ni = 78% and carbon | Strongly magnetised by electric current, loses magnetism when current is cut off. | For making electromagnets, ocean cables etc. |
| Chrome steel | Fe = 98?96%, Cr = 2?4% | High tensile strength | For making axles, ball bearings and cutting tools such as files. |
| Alnico | Fe = 60%, Al =12%, Ni = 20%, Co = 8% | Highly magnetic | For making permanent magnents. |
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