metals

Metal
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Metals Alkali Metals
Lithium, Sodium, Potassium
Rubidium, Caesium, Francium
Alkaline Earth Metals
Beryllium, Magnesium, Calcium
Strontium, Barium, Radium
Transition Metals
Scandium, Titanium, Vanadium
Chromium, Manganese, Iron
Cobalt, Nickel, Copper
Yttrium, Zirconium, Niobium
Technetium, Ruthenium, Rhodium
Palladium, Silver, Hafnium
Tantalum, Tungsten, Rhenium
Osmium, Iridium, Platinum
Gold, Rutherfordium, Dubnium
Seaborgium, Bohrium, Hassium
Meitnerium, Darmstadtium/Ununnilium
Roentgenium
Poor Metals
Aluminium, Gallium, Indium
Tin, Thallium, Lead, Bismuth
Ununbium, Ununtrium, Ununquadium
Ununpentium, Ununhexium
Lanthanoids
Lanthanum, Cerium, Praseodymium
Neodymium, Promethium, Samarium
Europium, Gadolinium, Terbium
Dysprosium, Holmium, Erbium
Thulium, Ytterbium
Actinoids
Actinium, Thorium, Protactinium
Uranium, Neptunium, Plutonium
Americium, Curium, Berkelium
Californium, Einsteinium, Fermium
Mendelevium, Nobelium, Lawrencium
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In chemistry, a metal (Greek: Metallon Μέταλλο ) is defined as an element that readily loses electrons to form positive ions (cations) and forms metallic bonds between other metal atoms[1] (forming ionic bonds with non-metals).

[edit] Definition
Periodic table showing the various types of metals and nonmetals.
Periodic table showing the various types of metals and nonmetals.

Metals are sometimes described as a lattice of positive ions surrounded by a cloud of delocalized electrons. They are one of the three groups of elements as distinguished by their ionization and bonding properties, along with the metalloids and nonmetals. On the periodic table, a diagonal line drawn from boron (B) to polonium (Po) separates the metals from the nonmetals. Most elements on this line are metalloids, sometimes called semi-metals; elements to the lower left are metals; elements to the upper right are nonmetals (see the periodic table showing the metals).
Contents
[hide]

* 1 Definition
* 2 Chemical properties
* 3 Physical properties
o 3.1 Density
o 3.2 Malleability
o 3.3 Conductivity
o 3.4 Electric charge
* 4 Alloys
* 5 Categories
o 5.1 Base metal
o 5.2 Ferrous metal
o 5.3 Noble metal
o 5.4 Precious metal
* 6 Extraction
* 7 Metallurgy
* 8 Applications
* 9 Trade
* 10 Astronomy
* 11 See also
* 12 References
* 13 External links

An alternative definition[citation needed][unreliable source?] of metals is that they have overlapping conduction bands and valence bands in their electronic structure. This definition opens up the category for metallic polymers and other organic metals, which have been made by researchers and employed in high-tech devices. These synthetic materials often have the characteristic silvery-grey reflectiveness (luster) of elemental metals.

[edit] Chemical properties

Metals are usually inclined to form cations through electron loss,[1] reacting with oxygen in the air to form oxides over changing timescales (iron rusts over years, while potassium burns in seconds). The alkali metals are the most volatile[unreliable source?], followed by the alkaline earth metals, found in the leftmost two groups of the periodic table. Examples:

4Na + O2 → 2Na2O (sodium oxide)
2Ca + O2 → 2CaO (calcium oxide)
4Al + 3O2 → 2Al2O3 (aluminium oxide)

The transition metals (such as iron, copper, zinc, and nickel) take much longer to oxidize. Others, like palladium, platinum and gold, do not react with the atmosphere at all. Some metals form a barrier layer of oxide on their surface which cannot be penetrated by further oxygen molecules and thus retain their shiny appearance and good conductivity for many decades (like aluminium, some steels, and titanium). The oxides of metals are basic (as opposed to those of nonmetals, which are acidic), although this may be considered a rule of thumb, rather than a fact.

Painting, anodising or plating metals are good ways to prevent their corrosion. However, a more reactive metal in the electrochemical series must be chosen for coating, especially when chipping of the coating is expected. Water and the two metals form an electrochemical cell, and if the coating is less reactive than the coatee, the coating actually promotes corrosion.

[edit] Physical properties
Gallium crystals
Gallium crystals

Metals in general have superior electric and thermal conductivity, high luster and density, and the ability to be deformed under stress without cleaving.[1] While there are several metals that have low density, hardness, and melting points, these (the alkali and alkaline earth metals) are extremely reactive, and are rarely encountered in their elemental, metallic form[1].

[edit] Density

The majority of metals have higher densities than the majority of nonmetals[1]. Nonetheless, there is wide variation in the densities of metals; lithium is the least dense solid element and osmium is the densest. The metals of groups I A and II A are referred to as the light metals because they are exceptions to this generalization[1]. The high density of most metals is due to the tightly-packed crystal lattice of the metallic structure. The strength of metallic bonds for different metals reaches a maximum around the center of the transition series, as those elements have large amounts of delocalized electrons in a metallic bond. However, other factors (such as atomic radius, nuclear charge, number of bonding orbitals, overlap of orbital energies, and crystal form) are involved as well.[1]

[edit] Malleability

The nondirectional nature of metallic bonding is thought to be the primary reason for the malleability of metal. Planes of atoms in a metal are able to slide across one another under stress, accounting for the ability of a crystal to deform without shattering.
Hot metal work from a blacksmith.
Hot metal work from a blacksmith.

When the planes of an ionic bond are slid past one another, the resultant change in location shifts ions of the same charge into close proximity, resulting in the cleavage of the crystal. Covalently bonded crystals can only be deformed by breaking the bonds between atoms, thereby resulting in fragmentation of the crystal.[unreliable source?]

[edit] Conductivity

The electrical and thermal conductivity of metals originate from the fact that in the metallic bond, the outer electrons of the metal atoms form a gas of nearly free electrons, moving as an electron gas in a background of positive charge formed by the ion cores. Good mathematical predictions for electrical conductivity, as well as the electrons' contribution to the heat capacity and heat conductivity of metals can be calculated from the free electron model, which does not take the detailed structure of the ion lattice into account.

[edit] Electric charge

When considering the exact band structure and binding energy of a metal, it is necessary to take into account the positive potential caused by the specific arrangement of the ion cores - which is periodic in crystals. The most important consequence of the periodic potential is the formation of a small band gap at the boundary of the brillouin zone. Mathematically, the potential of the ion cores is treated in the nearly-free electron model.

[edit] Alloys

Main article: Alloy

An alloy is a mixture of two or more elements in solid solution in which the major component is a metal. Most pure metals are either too soft, brittle or chemically reactive for practical use. Combining different ratios of metals as alloys modifies the properties of pure metals to produce desirable characteristics. The aim of making alloys is generally to make them less brittle, harder, resistant to corrosion, or have a more desirable color and luster. Examples of alloys are steel (iron and carbon), brass (copper and zinc), bronze (copper and tin), and duralumin (aluminium and copper). Alloys specially designed for highly demanding applications, such as jet engines, may contain more than ten elements.

[edit] Categories

[edit] Base metal

Main article: Base metal

In chemistry, the term 'base metal' is used informally to refer to a metal that oxidizes or corrodes relatively easily, and reacts variably with dilute hydrochloric acid (HCl) to form hydrogen. Examples include iron, nickel, lead and zinc. Copper is considered a base metal as it oxidizes relatively easily, although it does not react with HCl. It is commonly used in opposition to noble metal.

In alchemy, a base metal was a common and inexpensive metal, as opposed to precious metals, mainly gold and silver. A longtime goal of the alchemists was the transmutation of base metals into precious metals.

In numismatics, coins used to derive their value primarily from the precious metal content. Most modern currencies are fiat currency, allowing the coins to be made of base metal.

[edit] Ferrous metal

Main article: Ferrous and non-ferrous metals

The term "ferrous" is derived from the latin word meaning "containing iron". This can include pure iron, such as wrought iron, or an alloy such as steel. Ferrous metals are often magnetic, but not exclusively.

[edit] Noble metal

Main article: Noble metal

Noble metals are metals that are resistant to corrosion or oxidation, unlike most base metals. They tend to be precious metals, often due to perceived rarity. Examples include tantalum, gold, platinum, and rhodium.

[edit] Precious metal

Main article: Precious metal

A gold nugget
A gold nugget

A precious metal is a rare metallic chemical element of high economic value.

Chemically, the precious metals are less reactive than most elements, have high luster and high electrical conductivity. Historically, precious metals were important as currency, but are now regarded mainly as investment and industrial commodities. Gold, silver, platinum and palladium each have an ISO 4217 currency code. The best-known precious metals are gold and silver. While both have industrial uses, they are better known for their uses in art, jewelry, and coinage. Other precious metals include the platinum group metals: ruthenium, rhodium, palladium, osmium, iridium, and platinum, of which platinum is the most widely traded. Plutonium and uranium could also be considered precious metals.

The demand for precious metals is driven not only by their practical use, but also by their role as investments and a store of value. Palladium was, as of summer 2006, valued at a little under half the price of gold, and platinum at around twice that of gold. Silver is substantially less expensive than these metals, but is often traditionally considered a precious metal for its role in coinage and jewelry.

[edit] Extraction

Main articles: Ore and Mining

Metals are often extracted from the Earth by means of mining, resulting in ores that are relatively rich sources of the requisite elements. Ore is located by prospecting techniques, followed by the exploration and examination of deposits. Mineral sources are generally divided into surface mines, which are mined by excavation using heavy equipment, and subsurface mines.

Once the ore is mined, the metals must be extracted, usually by chemical or electrolytic reduction. Pyrometallurgy uses high temperatures to convert ore into raw metals, while hydrometallurgy employs aqueous chemistry for the same purpose. The methods used depend on the metal and their contaminants.
Please help improve this section by expanding it. Further information might be found on the talk page or at requests for expansion. (June 2008)


[edit] Metallurgy

Main article: Metallurgy

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.

[edit] Applications

Some metals and metal alloys possess high structural strength per unit mass, making them useful materials for carrying large loads or resisting impact damage. Metal alloys can be engineered to have high resistance to shear, torque and deformation. However the same metal can also be vulnerable to fatigue damage through repeated use, or from sudden stress failure when a load capacity is exceeded. The strength and resilience of metals has led to their frequent use in high-rise building and bridge construction, as well as most vehicles, many appliances, tools, pipes, non-illuminated signs and railroad tracks.

The two most commonly used structural metals, iron and aluminium, are also the most abundant metals in the Earth's crust.[2]

Metals are good conductors, making them valuable in electrical appliances and for carrying an electric current over a distance with little energy lost. Electrical power grids rely on metal cables to distribute electricity. Home electrical systems, for the most part, are wired with copper wire for its good conducting properties.

The thermal conductivity of metal is useful for containers to heat materials over a flame. Metal is also used for heat sinks to protect sensitive equipment from overheating.

The high reflectivity of some metals is important in the construction of mirrors, including precision astronomical instruments. This last property can also make metallic jewelry aesthetically appealing.

Some metals have specialized uses; Radioactive metals such as Uranium and Plutonium are used in nuclear power plants to produce energy via nuclear fission. Mercury is a liquid at room temperature and is used in switches to complete a circuit when it flows over the switch contacts. Shape memory alloy is used for applications such as pipes, fasteners and vascular stents. However they are very good at conducting electricity and heat.

[edit] Trade
Metal and ore imports in 2005
Metal and ore imports in 2005

The World Bank reports that China was the top importer of ores and metals in 2005 followed by the U.S.A. and Japan.

[edit] Astronomy

Main article: Metallicity

In the specialised usage of astronomy and astrophysics, the term "metal" is often used to refer to any element other than hydrogen or helium, including substances as chemically non-metallic as neon, fluorine, and oxygen. Nearly all the hydrogen and helium in the Universe was created in Big Bang nucleosynthesis, whereas all the "metals" were produced by nucleosynthesis in stars or supernovae. The Sun and the Milky Way Galaxy are composed of roughly 70% hydrogen, 30% helium, and 2% "metals" by mass.[3]Metallurgy
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Jump to: navigation, search
Georg Agricola, author of De re metallica, an important early book on metal extraction
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 compounds, 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
[hide]

* 1 History
* 2 Extractive metallurgy
* 3 Properties of metals
* 4 Important common alloy systems
* 5 Production engineering of metals
o 5.1 Metal working processes
o 5.2 Joining
+ 5.2.1 Welding
+ 5.2.2 Brazing
+ 5.2.3 Soldering
o 5.3 Heat treatment
o 5.4 Surface treatment
+ 5.4.1 Plating
+ 5.4.2 Thermal spray
+ 5.4.3 Case hardening
* 6 Electrical and electronic engineering
* 7 Metallurgical techniques
* 8 Chemical properties of metals
* 9 See also
* 10 References
* 11 External links

[edit] History

Main article: History of ferrous metallurgy
See also: Chalcolithic, Bronze Age, Iron Age, Metallurgy in pre-Columbian Mesoamerica, and History of metallurgy in the Indian subcontinent

An illustration of furnace bellows operated by waterwheels, from the Nong Shu, by Wang Zhen, 1313 AD, during the Chinese Yuan Dynasty.
An illustration of furnace bellows operated by waterwheels, from the Nong Shu, by Wang Zhen, 1313 AD, during the Chinese Yuan Dynasty.

The earliest recorded metal employed by humans appears to be gold which can be found free or "native". Small amounts of natural gold have been found in Spanish caves used during the late Paleolithic period, c. 40,000 BC.[1]
Gold headband from Thebes 750-700 BC
Gold headband from Thebes 750-700 BC

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 copper and tin 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[3][4]

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), 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, hydraulic-powered trip hammers, etc.)[5]. 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[citation needed].

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"[6]

[edit] Extractive metallurgy

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 either 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 a 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.

[edit] Properties of metals

The five metals most used by the human species are:

1. Iron
2. Aluminum
3. Copper
4. Zinc
5. Magnesium

The general physical properties of metals are:

* They are strong and hard.
* They are solids at room temperature (except for Mercury, which is the only metal to be liquid at room temperature)
* They have a shiny luster when polished.
* They make good heat conductors and electrical conductors.
* They are dense
* They produce a sonorous sound when struck.
* They have high melting points
* They are malleable

The properties of metals make them suitable for different uses in daily life.

* Copper is a good conductor of electricity and is ductile. Therefore Copper is used for electrical cables.
* Gold and Silver are very malleable, ductile and very nonreactive. Gold and silver are used to make intricate jewelery which does not tarnish. Gold can also be used for electrical connections.
* Iron and Steel are both hard and strong. Therefore they are used to construct bridges and buildings. A disadvantage of using Iron is that it tends to rust, whereas most steels rust, they can be formulated to be rust free.
* Aluminum is a good conductor of heat and is malleable. It is used to make saucepans and tin foil, and also aeroplane bodies as it is very light.

Pure elemental metals are often too soft to be of practical use which is why much of metallurgy focuses on formulating useful alloys.

[edit] Important common alloy systems

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 are 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.

Cupro-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 vessels, and heat exchangers. For extremely high temperatures, single crystal alloys are used to minimize creep.

[edit] Production engineering of metals

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.

[edit] Metal working 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 compressed into a die at high temperature. 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.

[edit] Joining

[edit] Welding

Main article: Welding

Welding is a technique for joining metal components by melting the base material. A filler material of similar composition may also be melted into the joint.

[edit] Brazing

Main article: Brazing

Brazing is a technique for joining metals at a temperature below their melting point. A filler with a melting point below that of the base metal is used, and is drawn into the joint by capillary action. Brazing results in a mechanical and metallurgical bond between work pieces.

[edit] Soldering

Main article: Soldering

Soldering is a method of joining metals below their melting points using a filler metal. Soldering results in a mechanical joint and occurs at lower temperatures than brazing, specifically below 450 C (840 F)[7].

[edit] Heat treatment

Main article: 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.

[edit] Surface treatment

[edit] Plating

Main article: 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.

[edit] Thermal spray

Main article: Thermal spray

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

[edit] Case hardening

Main article: Case hardening

Case hardening is a process in which an alloying element, most commonly carbon or nitrogen, diffuses into the surface of a monolithic metal. The resulting interstitial solid solution is harder than the base material, which improves wear resistance without sacrificing toughness.

[edit] Electrical and electronic engineering

Metallurgy is also applied to electrical and electronic materials where metals such as aluminium, copper, tin, silver, and gold are used in power lines, wires, printed circuit boards and integrated circuits.

[edit] Metallurgical techniques
Metallography allows the metallurgist to study the microstructure of metals.
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. A metallurgist can then examine the sample with an optical or electron microscope and learn a great deal about the sample's 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 allow the 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.

The physical properties of metals can be quantified by mechanical testing. Typical tests include tensile strength, compressive strength, hardness, impact toughness, fatigue and creep life.

[edit] Chemical properties of metals
The black surface is lead oxide. The white surface is the lead viewed when the lead oxide is scratched.
The black surface is lead oxide. The white surface is the lead viewed when the lead oxide is scratched.

Substances on the Earth's surface will come in contact with air, water or acids. A major concern for the use of metals is their corrosion. The shiny surface of many metals becomes dull in time. This is due to a slow chemical reaction between the surface of the metal and oxygen in the air, this is typically a surface coating of the metal oxide. The general word equation is:

metal+oxygen → metal oxide

For example: The dull appearance of the metal lead is due to a coating of lead oxide.

lead+oxygen → lead oxide

If the surface is scratched then the shiny lead metal can be seen underneath.

Heating can speed up the reaction with oxygen. If a piece of copper is heated it quickly becomes coated in black copper oxide. The word equation is:

copper + oxygen → copper oxide