Bronze
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Assorted ancient bronze castings found as part of a cache, probably intended for recycling. |
Bronze refers to a broad range of
copper alloys, usually with
tin as the main additive, but sometimes with other
elements such as
phosphorus,
manganese,
aluminum, or
silicon. (See
table below.) It is strong and tough, and has myriad uses in industry. It was particularly significant in antiquity, giving its name to the
Bronze Age.
The introduction of bronze was significant to any civilization that encountered it. Tools, weapons, armor, and various building materials like decorative tiles made of bronze were harder and more durable than their stone and copper ("
Chalcolithic") predecessors. In early use, the natural impurity
arsenic sometimes created a superior natural alloy; this is termed
arsenical bronze.
The earliest tin-alloy bronzes date to the late
4th millennium BC in
Susa (Iran) and some ancient sites in
Luristan (Iran) and
Mesopotamia (Iraq).
While copper and tin can naturally co-occur, the two
ores are rarely found together (although one ancient site in
Thailand and one in
Iran provide counterexamples). Serious bronze work has therefore always involved trade. In fact, archaeologists suspect that a serious disruption of the tin trade precipitated the transition to the
Iron Age. For Europe, the major source for
tin was
Great Britain.
Bronze was stronger than the era's
iron; quality
steels were not available until thousands of years later. But the Bronze Age gave way to the
Iron Age, perhaps because the shipping of tin around the
Mediterranean (or from Great Britain) became more limited during the major population migrations around
1200 –
1100 BC, which dramatically limited supplies and raised prices [
1]. Bronze was still used during the Iron Age, but for many purposes the weaker iron was found to be sufficiently strong. As ironworking improved, iron became both cheaper and stronger, eclipsing bronze in Europe by the early to mid-
Middle Ages.
When
steel is excluded from the discussion, bronze is superior to iron in nearly every application. Although bronze develops a
patina, it does not
oxidize beyond the surface. It is considerably less brittle than iron and has a lower casting temperature.
Copper-based alloys have lower
melting points than steel and are more readily produced from their constituent metals. They are generally about 10 percent heavier than steel, although alloys using
aluminium or
silicon may be slightly less dense. Bronzes are softer and weaker than steel, Bronze
springs are less stiff (and so store less energy) for the same bulk. It resists
corrosion (especially
seawater corrosion) and
metal fatigue better than steel and also conducts heat and electricity better than most steels. The cost of copper-base alloys is generally higher than that of steels but lower than that of
nickel-base alloys.
Copper and its alloys have a huge variety of uses that reflect their versatile physical, mechanical, and chemical properties. Some common examples are the high
electrical conductivity of pure copper, the excellent deep-drawing qualities of cartridge case brass, the low-friction properties of bearing bronze, the resonant qualities of bell bronze, and the resistance to corrosion by
sea water of several bronze alloys.
In the twentieth century,
silicon was introduced as the primary alloying element, creating an alloy with wide application in industry and the major form used in contemporary statuary. Aluminium is also used for the structural metal
Aluminium bronze.
Bronze is the most popular metal for top-quality
bells and
cymbals, and more recently,
saxophones. It is also widely used for cast metal
sculpture (see
bronze sculpture). Common bronze alloys often have the unusual and very desirable property of expanding slightly just before they set, thus filling in the finest details of a
mould.
Bronze also has very little metal-on-metal
friction, which made it invaluable for the building of
cannons where iron cannonballs would otherwise stick in the barrel. It is still widely used today for springs, bearings, bushings and similar fittings, and is particularly common in the bearings of small electric motors.
Phosphor bronze is particularly suited to precision-grade bearings and springs.
Bronze is typically 60%
copper and 40%
tin. Alpha bronze consists of the alpha solid solution of tin in copper. Alpha bronze alloys of 4-5% tin are used to make
coins,
springs,
turbines and
blades.
Commercial bronze (otherwise known as
brass) is 90% copper and 10% zinc, and contains no tin. It is stronger than copper and it has equivalent ductility. It is used for
screws and
wires.
Classification of Copper and Its Alloys - Wrought / Extruded[Machinery's Handbook, Industrial Press Inc, New York, ISBN 0-8311-2492-X, Edition 24, page 501]| Family | Principal alloying element | UNS numbers |
|---|
| Copper alloys, Brass | Zinc (zn) | C1xxxx–C4xxxx,C66400–C69800 |
| Phosphor bronzes | Tin (Sn) | C5xxxx |
| Aluminium bronzes | Aluminium (Al) | C60600–C64200 |
| Silicon bronzes | Silicon (Si) | C64700–C66100 |
| Copper nickel, Nickel silvers | Nickel (Ni) | C7xxxx |
*
Brass, a subset of the copper alloys in which
zinc is the principal additive
*
Gunmetal*
Cupronickel, an alloy used on ships
*
lost-wax casting*
Aluminum bronze*
Phosphor bronze *
Tiles*
Bronzing, a process by which an object is coated in bronze
*
Luristan bronze*
19th century bronze sculpture sand casting*
Flash animation of lost-wax casting*
Bronze Casting process explained - good pictures*
The source of tin for the ancient bronze production*
National Pollutant Inventory - Copper and compounds fact sheet*
Information about Bronze Tiles*
lost wax casting process
