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Georg Agricola, author of De re metallica, an important early book on metal extraction

Metallurgy is a domain of materials science that studies the physical and chemical behavior of metallic elements, their intermetallic compounds, and their mixtures, which are called alloys. It is also the technology of metals: the way in which science is applied to their practical use. Metallurgy is commonly used in the craft of metalworking.

Contents

History

Gold headband from Thebes 750-700 BC

The first evidence of human metallurgy dates from the 5th and 6th millennium BC, and was found in the archaeological sites of Majdanpek, Yarmovac and Plocnik, Serbia. These examples include a copper axe from 5,500BC belonging to the Vincha culture.[1] Other signs of human metallurgy are found from the third millennium BC in places like Palmela (Portugal), Cortes de Navarra (Spain), and Stonehenge (United Kingdom). However, as often happens with the study of prehistoric times, the ultimate beginnings cannot be clearly defined and new discoveries are continuous and ongoing.

Mining areas of the ancient Middle East. Boxes colors: arsenic is in brown, copper in red, tin in grey, iron in reddish brown, gold in yellow, silver in white and lead in black. Yellow area stands for arsenic bronze, while grey area stands for tin bronze.

Silver, copper, tin and meteoric iron can also be found native, allowing a limited amount of metalworking in early cultures. Egyptian weapons made from meteoric iron in about 3000 B.C. were highly prized as "Daggers from Heaven".[2]. However, by learning to get copper and tin by heating rocks and combining those two metals to make an alloy called bronze, the technology of metallurgy began about 3500 B.C. with the Bronze Age.

The extraction of iron from its ore into a workable metal is much more difficult. It appears to have been invented by the Hittites in about 1200 B.C., beginning the Iron Age. The secret of extracting and working iron was a key factor in the success of the Philistines.[2][3]

Historical developments in ferrous metallurgy can be found in a wide variety of past cultures and civilizations. This includes the ancient and medieval kingdoms and empires of the Middle East and Near East, ancient Egypt, and Anatolia (Turkey), Ancient Nok, Carthage, the Greeks and Romans of ancient Europe, medieval Europe, ancient and medieval China, ancient and medieval India, ancient and medieval Japan, etc. Of interest to note is that many applications, practices, and devices associated or involved in metallurgy were possibly established in ancient China before Europeans mastered these crafts (such as the innovation of the blast furnace, cast iron, steel)[4]. However, modern research suggests that Roman technology was far more sophisticated than hitherto supposed, especially in mining methods, metal extraction and forging. They were, for example, expert in hydraulic mining methods well before the Chinese, or any other civilization of the time.

A 16th century book by Georg Agricola called De re metallica describes the highly developed and complex processes of mining metal ores, metal extraction and metallurgy of the time. Agricola has been described as the "father of metallurgy"[5]

Extraction

Furnace bellows operated by waterwheels, Yuan Dynasty, China.

Extractive metallurgy is the practice of removing valuable metals from an ore and refining the extracted raw metals into a purer form. In order to convert a metal oxide or sulfide to a purer metal, the ore must be reduced physically, chemically, or electrolytically.

Extractive metallurgists are interested in three primary streams: feed, concentrate (valuable metal oxide/sulfide), and tailings (waste). After mining, large pieces of the ore feed are broken through crushing and/or grinding in order to obtain particles small enough where each particle is either mostly valuable or mostly waste. Concentrating the particles of value in a form supporting separation enables the desired metal to be removed from waste products.

Mining may not be necessary if the ore body and physical environment are conducive to leaching. Leaching dissolves minerals in an ore body and results in an enriched solution. The solution is collected and processed to extract valuable metals.

Ore bodies often contain more than one valuable metal. Tailings of a previous process may be used as a feed in another process to extract a secondary product from the original ore. Additionally, a concentrate may contain more than one valuable metal. That concentrate would then be processed to separate the valuable metals into individual constituents.

Alloys

the maker of bronzes.

Common engineering metals include aluminium, chromium, copper, iron, magnesium, nickel, titanium and zinc. These are most often used as alloys. Much effort has been placed on understanding the iron-carbon alloy system, which includes steels and cast irons. Plain carbon steels is used in low cost, high strength applications where weight and corrosion are not a problem. Cast irons, including ductile iron are also part of the iron-carbon system.

Stainless steel or galvanized steel are used where resistance to corrosion is important. Aluminium alloys and magnesium alloys are used for applications where strength and lightness are required.

Copper-nickel alloys (such as Monel) are used in highly corrosive environments and for non-magnetic applications. Nickel-based superalloys like Inconel are used in high temperature applications such as turbochargers, pressure vessel, and heat exchangers. For extremely high temperatures, single crystal alloys are used to minimize creep.

Production

In production engineering, metallurgy is concerned with the production of metallic components for use in consumer or engineering products. This involves the production of alloys, the shaping, the heat treatment and the surface treatment of the product. The task of the metallurgist is to achieve balance between material properties such as cost, weight, strength, toughness, hardness, corrosion and fatigue resistance, and performance in temperature extremes. To achieve this goal, the operating environment must be carefully considered. In a saltwater environment, ferrous metals and some aluminium alloys corrode quickly. Metals exposed to cold or cryogenic conditions may endure a ductile to brittle transition and lose their toughness, becoming more brittle and prone to cracking. Metals under continual cyclic loading can suffer from metal fatigue. Metals under constant stress at elevated temperatures can creep.

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Metalworking processes

Metals are shaped by processes such as casting, forging, flow forming, rolling, extrusion, sintering, metalworking, machining and fabrication. With casting, molten metal is poured into a shaped mould. With forging, a red-hot billet is hammered into shape. With rolling, a billet is passed through successively narrower rollers to create a sheet. With extrusion, a hot and malleable metal is forced under pressure through a die, which shapes it before it cools. With sintering, a powdered metal is heated in a non-oxidizing environment after being compressed into a die. With machining, lathes, milling machines, and drills cut the cold metal to shape. With fabrication, sheets of metal are cut with guillotines or gas cutters and bent into shape.

Cold working processes, where the product’s shape is altered by rolling, fabrication or other processes while the product is cold, can increase the strength of the product by a process called work hardening. Work hardening creates microscopic defects in the metal, which resist further changes of shape.

Various forms of casting exist in industry and academia. These include sand casting, investment casting (also called the “lost wax process”), die casting and continuous casting.

Heat treatment

Metals can be heat treated to alter the properties of strength, ductility, toughness, hardness or resistance to corrosion. Common heat treatment processes include annealing, precipitation strengthening, quenching, and tempering. The annealing process softens the metal by allowing recovery of cold work and grain growth. Quenching can be used to harden alloy steels, or in precipitation hardenable alloys, to trap dissolved solute atoms in solution. Tempering will cause the dissolved alloying elements to precipitate, or in the case of quenched steels, improve impact strength and ductile properties.

Often, mechanical and thermal treatments are combined in what is known as thermo-mechanical treatments for better properties and more efficient processing of materials. These processes are common to high alloy special steels, super alloys and titanium alloys.

Plating

Electroplating is a common surface-treatment technique. It involves bonding a thin layer of another metal such as gold, silver, chromium or zinc to the surface of the product. It is used to reduce corrosion as well as to improve the product's aesthetic appearance.

Thermal spraying

Thermal spraying techniques are another popular finishing option, and often have better high temperature properties than electroplated coatings.

Microstructure

Metallography allows the metallurgist to study the microstructure of metals.

Metallurgists study the microscopic and macroscopic properties using metallography, a technique invented by Henry Clifton Sorby. In metallography, an alloy of interest is ground flat and polished to a mirror finish. The sample can then be etched to reveal the microstructure and macrostructure of the metal. The sample is then examined in an optical or electron microscope, and the image contrast provides details on the composition, mechanical properties, and processing history.

Crystallography, often using diffraction of x-rays or electrons, is another valuable tool available to the modern metallurgist. Crystallography allows identification of unknown materials and reveals the crystal structure of the sample. Quantitative crystallography can be used to calculate the amount of phases present as well as the degree of strain to which a sample has been subjected.

Education

Metals Engineering Merit Badge

Metallurgy applies engineering and technical skills in the development of industrial metals and manufacturing processes. Subjects such as mechanics and thermal physics, thermo science, applied thermodynamics, metal testing, quality control, instrument calibration and advanced mathematics are required.[6]

See also

References

  1. ^ Neolithic Vinca was a metallurgical culture Stonepages from news sources November 2007
  2. ^ a b W. Keller (1963) The Bible as History page 156 ISBN 0 340 00312 X
  3. ^ B. W. Anderson (1975) The Living World of the Old Testament page 154 ISBN 0-582-48598-3
  4. ^ R. F. Tylecote (1992) A History of Metallurgy ISBN 0-901462-88-8
  5. ^ Karl Alfred von Zittel (1901) History of Geology and Palaeontology page 15
  6. ^ Metallurgy Colleges and Universities


1911 encyclopedia

Up to date as of January 14, 2010
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From LoveToKnow 1911

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Simple English

Metallurgy is the study of metals. Alloys are also studied. People who study metals are called metallurgists.

Contents

How to make metals -or- get metals from rocks

The rocks are made of a metal with oxygen, called an oxide. Separating the oxygen off the metal is called smelting This is done with chemistry or electricity. It happens often in very high temperature. This is the first step in metallurgy. A rock containing enough metal to be profitable is called ore.

Iron is smelted from iron ore in large reactors called blast furnaces. A blast furnace is a tall vertical structure which is fed with coke, iron ore and limestone. When hot air is blown in the blast furnace, the coke will burn and reduce the oxygen off the ore, producing bare iron and carbon dioxide. The limestone will bind off any remaining bedrock. The iron melts in the hot temperature and is tapped off in liquid phase at the bottom. It is then worked into steel. The limestone and bedrock form a compound called slag. It can be used for making bricks, concrete or road topping.

Aluminum is smelted in electric ovens called electric arc furnaces. The aluminum ore is poured on the bottom of the furnace and electric current is led through the ore. The temperature rises so high that the oxygen separates, leaving metallic aluminum.

Copper is poured on naked flame which burns off sulfur and other impurities, leaving raw copper. The copper is then electrolyzed (that is: separated by electric current) in big pools, which contain water solution called electrolyte. An electric current is led in the pool, and all copper will gather on the electrode called cathode.

Metal parts

Another part of metallurgy is making parts from metals. These parts must be made so they will not break when they are used. Metallurgists work to make the metal good when they are used. Sometimes the metal must be strong. Other times it must be tough (not easily broken). The metallurgist must follow directions when making the part to know what metal to use. Steel has a low cost, but rusts. Choosing a good metal is sometimes hard.

Making metal parts

A metal starts as a block, called an ingot. Metallurgists must know how to make a metal part from an ingot. Parts are made from ingots different ways. When a big hammer is used, it is called forging. To make thin metals, a metal is put between two rolls and moved, called rolling.

When a metal part is made hot, the metal moves farther than when it is cold. Most metal parts are made hot, to make moving metal easier. This is hot work.

Two metal parts can be put together with much heat. This is called welding. Iron is easy to weld.

How to know what to do to the metal

Metallurgists use many tools to know what to do to the metal. The most useful is the microscope. The microscope gives much information about the way the metal moves. Metals are sometimes pulled until they break. This is the tension test. Some useful information can be gotten from this test.



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