METAL ALLOYS
•By mixing a metal with other metals or some non metals, we can change its properties. This process is called alloying and the resulting metal is an alloy.
•For example pure gold (24 carat) is a relatively soft element and is easily deformed. The alloy 18 carat gold is used in jewellery. This alloy contains 75 % by mass gold and 25% of silver and copper. This makes the alloy stronger and more durable.
SUBSTITUTIONAL ALLOYS
•If the atoms of the metals being used to form an alloy are about the same size, they can replace each other in the metal crystals. This type of alloy is called a substitutional alloy.
•Example: Sterling silver is a substitutional alloy made from silver and copper.
Image- wikimedia commons
•By mixing a metal with other metals or some non metals, we can change its properties. This process is called alloying and the resulting metal is an alloy.
•For example pure gold (24 carat) is a relatively soft element and is easily deformed. The alloy 18 carat gold is used in jewellery. This alloy contains 75 % by mass gold and 25% of silver and copper. This makes the alloy stronger and more durable.
SUBSTITUTIONAL ALLOYS
•If the atoms of the metals being used to form an alloy are about the same size, they can replace each other in the metal crystals. This type of alloy is called a substitutional alloy.
•Example: Sterling silver is a substitutional alloy made from silver and copper.
Image- wikimedia commons
INTERSTITIAL ALLOYS
•Sometimes the atomic sizes of the metals in the alloy differ greatly. The smaller atoms may then fit into the spaces between the larger atoms, forming an interstitial alloy.
•Example: Steel is an interstitial alloy made from iron and carbon.
Image- wikimedia commons
•Sometimes the atomic sizes of the metals in the alloy differ greatly. The smaller atoms may then fit into the spaces between the larger atoms, forming an interstitial alloy.
•Example: Steel is an interstitial alloy made from iron and carbon.
Image- wikimedia commons
Common metals and their alloys
MODIFYING METALS
Most materials, including metals are polycrystalline. They are composed of huge numbers of crystals called grains. Each grain contains the regular array of cations and sea of electrons. The properties of a metal rely on both the properties of the grains and the size, arrangement and interaction between grains. Grain structure can be modified by various heat treatments. Quenching- heating metal to a point just below melting temperature and then cooling rapidly by plunging into water at room temperature. This results in grains being close together and difficult to move- these metals are hard but brittle. Annealing- heating a metal to a point just below its melting temperature, and then allowing it to cool slowly back to room temperature. This results in larger grains- softer more malleable metal. Tempering- heating a quenched metal to a point just below its melting temperature, then cooling it slowly. This results in a hard but less brittle metal. EXTRACTION OF METALS |