bronze

bronze, in art: see bronze sculpture.

bronze, in metallurgy, alloy of copper, tin, zinc, phosphorus, and sometimes small amounts of other elements. Bronzes are harder than brasses. Most are produced by melting the copper and adding the desired amounts of tin, zinc, and other substances. The properties of the alloy depend on the proportions of its components. Aluminum bronze has high strength and resists corrosion; it is used for bearings, valve seats, and machine parts. Leaded bronze, containing from 10% to 29% lead, is cast into heavy-duty bushings and bearings. Silicon bronze is used for telegraph wires and chemical containers. Phosphor bronze is used for springs. Bronze is used for coins, medals, steam fittings, and gunmetal and was formerly employed for cannon. Because of its particularly sonorous quality, bell metal, containing from 20% to 24% tin, is used for casting bells. Bronze has long been used in art, e.g., for castings, engravings, and forgings.

Alloy traditionally composed of copper and tin. Bronze was first made before 3000 BC (see Bronze Age) and is still widely used, though iron often replaced bronze in tools and weapons after about 1000 BC because of iron's abundance compared to copper and tin. Bronze is harder than copper, more readily melted, and easier to cast. It is also harder than iron and far more resistant to corrosion. Bell metal (which produces pleasing sounds when struck) is bronze with 20–25percnt tin content. Statuary bronze, with less than 10percnt tin and an admixture of zinc and lead, is technically a brass. The addition of less than 1percnt phosphorus improves the hardness and strength of bronze; that formulation is used for pump plungers, valves, and bushings. Also useful in mechanical engineering are manganese bronzes, with little or no tin but considerable amounts of zinc and up to 4.5percnt manganese. Aluminum bronzes, containing up to 16percnt aluminum and small amounts of other metals such as iron or nickel, are especially strong and corrosion-resistant; they are cast or wrought into pipe fittings, pumps, gears, ship propellers, and turbine blades. Most “copper” coins are actually bronze, typically with about 4percnt tin and 1percnt zinc, or copper plating over base metal.

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Third phase in the development of material culture among the ancient peoples of Europe, Asia, and the Middle East, following the Paleolithic and Neolithic periods and preceding the Iron Age. The term also denotes the first period in which metal was used. The date at which the age began varied by region; in Greece and China it began before 3000 BC, in Britain not until circa 1900 BC. The beginning of the period is sometimes called the Chalcolithic (Copper-Stone) Age, referring to the initial use of pure copper (along with its predecessor, stone). By 3000 BC the use of copper was well known in the Middle East, had extended westward into the Mediterranean area, and was beginning to infiltrate Europe. Only in the 2nd millennium BC did true bronze come to be widely used. The age was marked by increased specialization and the invention of the wheel and the ox-drawn plow. From circa 1000 BC the ability to heat and forge iron brought the Bronze Age to an end.

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Bronze is any of 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 was particularly significant in antiquity, giving its name to the Bronze Age. "Bronze," in turn, is perhaps ultimately taken from the Persian word "berenj," meaning "brass".

History

Bronze was significant to any culture that encountered it. It was one of the most innovative alloys of mankind. Tools, weapons, armour, 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 impurity arsenic sometimes created a superior 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).

The two ores are rarely found together (exceptions include one ancient site in Thailand and one in Iran), so serious bronze work has always involved trade. In Europe, the major source for tin was Great Britain's deposits of ore in Cornwall. Phoenician traders visited Great Britain to trade goods from the Mediterranean for tin.

Though bronze is stronger (harder) than wrought iron, the Bronze Age gave way to the Iron Age; this happened because iron was easier to find. Bronze was still used during the Iron Age, but for many purposes the weaker wrought iron was found to be sufficiently strong. Archaeologists suspect that a serious disruption of the tin trade precipitated the transition. The population migrations around 1200 – 1100 BC reduced the shipping of tin around the Mediterranean (and from Great Britain), limiting supplies and raising prices. As ironworking improved, iron became cheaper, and cultures learned how to make steel, which is stronger than bronze and holds a sharper edge longer.

Properties

With the exception of steel, bronze is superior to iron in nearly every application. It is considerably less brittle than iron. Bronze only oxidizes superficially; once the surface oxidizes, the thin oxide layer protects the underlying metal from further corrosion. Copper-based alloys have lower melting points than steel or iron, and are more readily produced from their constituent metals. They are generally about 10 percent heavier than steel, although alloys using aluminum or silicon may be slightly less dense. Bronzes are softer and weaker than steel, e.g. 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 such as stainless steel.

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. Aluminum is also used for the structural metal aluminum bronze.

It is also widely used for cast metal sculpture (see bronze sculpture). Many common bronze alloys have the unusual and very desirable property of expanding slightly just before they set, thus filling in the finest details of a mould. Bronze parts are tough and typically used for bearings, clips, electrical connectors and springs.

Bronze also has very little metal-on-metal friction, which made it invaluable for the building of cannon where iron cannonballs would otherwise stick in the barrel. It is still widely used today for springs, bearings, bushings, automobile transmission pilot bearings, 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. It is also used in guitar and piano strings.

Bronze is typically 88% copper and 12% 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.

Unlike steel, bronze struck against a hard surface will not generate sparks, so it (along with beryllium copper) is used to make hammers, mallets, wrenches and other durable tools to be used in explosive atmospheres or in the presence of flammable vapours.

Musical instruments

Bronze is the most popular metal for top-quality bells, and more recently, saxophones. Nearly all professional cymbals are made from bronze. Cymbal bronze is unique in that a balance of durability and timbre is needed.

In 1623, an Armenian man in Turkey named Avedis Zildjian, an alchemist, was attempting to form base metals into gold. Upon dropping an ingot on the ground, he was amazed at how well it rang. He was given the title Zildjian (Son of Cymbal Maker) by the Turkish Sultan. Today, the Avedis Zildjian Corporation is the largest maker of cymbals in the world.

Modern cymbals consist of several types of bronze, the most common being B20 bronze, which is roughly 20% tin, 80% copper, with traces of silver. Zildjian and Sabian use this alloy for their professional lines. A Swiss Company, Paiste, uses a softer B8 bronze which is made from 8% tin and 92% copper in nearly all of their cymbals. (Zildjian and Sabian use this metal too, in their budget priced cymbals).

Generally speaking, as the tin content goes up, the pitch becomes lower. Meinl uses 16% tin 84% copper cymbals, which has a pitch roughly in between B8 and B20.

Bronze is also used for strings of various instruments such as the piano and the guitar.

See also

• Aluminum bronze
• Brass, a subset of the copper alloys in which zinc is the principal additive
• Bronze medal
• Bronze sculpture, the use of bronze for artistic representations
• Bronzing, a process by which an object is coated in bronze
• Chinese bronze inscriptions‎, in various scripts since Shang Dynasty onward
• Cupronickel, an alloy used on ships
• Florentine bronze, an alloy which is not standardised (in proportions) worldwide
• Gunmetal, various copper-zinc-tin alloys, some including phosphorus
• Lost-wax casting
• Luristan bronze - Bronze Age artifacts recovered from areas of present day Iran
• Phosphor bronze, with properties useful in making corrosion-resistant springs
• Seagram Building, with a record 3.2 million pounds of bronze used in its façade
• Speculum metal, a high-tin bronze

References

External links

• 19th-century bronze sculpture sand casting
• Casting process explained with pictures
• Flash animation of lost-wax casting process
• "Lost Wax, Found Bronze": lost-wax casting explained
• various bronze alloys
• Viking Bronze - Ancient and Early Medieval bronze casting