VIEWS: 0 PAGES: 5 POSTED ON: 11/3/2012
NON-IUPAC CLASSIFICATION OF METALS Coinage Metals A Group 11 element is one in the series of elements in group 11 in the periodic table, consisting of transition metals which are the traditional coinage metals of copper (Cu), silver (Ag), and gold (Au). They are also known as the "noble metals." The name "coinage metals" can be somewhat misleading as various nations have used probably dozens of metals (including stainless steel, lead, and zinc) in coins. They are all relatively inert, corrosion-resistant metals which have been used for minting coins, hence their name. These metals, especially silver, have unusual properties that make them essential for industrial applications outside of their monetary or decorative value. They are all excellent conductors of electricity. The most conductive of all metals are silver, copper and gold in that order. Silver is also the most thermally conductive element, and the most light reflecting element. Silver also has the unusual property that the tarnish that forms on silver is still highly electrically conductive. Copper is used extensively in electrical wiring and circuitry. Gold contacts are sometimes found in precision equipment for their ability to remain corrosion-free. Silver is used widely in mission-critical applications as electrical contacts, and is also used in photography (because silver nitrate reverts to metal on exposure to light), agriculture, medicine, audiophile and scientific applications. Gold, silver, and copper are quite soft metals and so are easily damaged in daily use as coins. Precious metal may also be easily abraded and worn away through use. In their numismatic functions these metals must be alloyed with other metals to afford coins greater durability. The alloying with other metals makes the resulting coins harder, less likely to become deformed and more resistant to wear. Gold coins: Gold coins are typically produced as either 90% gold (e.g. with pre-1933 US coins), or 22 carat (92%) gold (e.g. current collectible coins and “Krugerrands”), with copper and silver making up the remaining weight in each case. Bullion gold coins are being produced with up to 99.999% gold (in the Canadian Gold Maple Leaf series). Silver coins: Silver coins are typically produced as either 90% silver - in the case of pre 1965 US minted coins (which were circulated in many countries), or sterling silver (92.5%) coins for pre-1967 British Commonwealth and other silver coinage, with copper making up the remaining weight in each case. Copper coins: Copper coins are often of quite high purity, around 97%, and are usually alloyed with small amounts of zinc and tin. Because the face value of coins has fallen below the hard currency value of the historically used metals, this had led to most modern coins being made of base metals - Cupro-nickel (around 80:20, silver in color) is popular as are nickel-brass (copper (75), nickel (5) and zinc (20), gold in color), manganese-brass (copper, zinc, manganese, and nickel), bronze, or simple plated steel. Heavy Metals Types Characteristics Uses Effects Lead (Pb) -metallic and cubic close-packed -protective shield from -mental retardation among -soft bluish white metal radioactivity children exposed to lead in -non combustible solid (except as -lead acid accumulator water resulting from lead dust) -manufacture antiknock, pipes and solders in older -routes of exposure: inhalation, tetraethyl lead Pb(C2H5)4 in water systems ingestion, skin and/or eye contact petrol -exhibit weakness, general -target organs: gastrointestinal -pigments e.g., white basic disability, nervous tract, central nervous system, lead carbonate, Pb(OH)2 disorders and eventual kidneys, blood and gingival tissue orange pigment ‘red lead’, death Pb3O4 Mercury (Hg) -electrodes in the -carcinogenic, typically -silver colored liquid transition amalgamation of cause cancer or are metal electrolysis of brine mutagenic -non-combustible liquid -thermometers -cause for kidney damage -routes of exposure: inhalation, skin -barometers -cause for neurological absorption, ingestion, skin and/or -fluorescent lamps disorder eye contact -cause for blindness -target organs: eyes, skin, -associated with birth respiratory system, central defects nervous system, kidneys -damaging to aquatic life Arsenic (As) -metalloid and gray brittle non- -deadly poison in shotgun -carcinogenic metal flake pellets -associated with lung cancer -routes of exposure: inhalation, -metal for mirrors -results in skin cancer ingestion, skin and/or eye contact. -glass -damage to intestines and -target organs: skin, respiratory -lasers liver, as it is found in system, kidneys, central nervous -light emitting diodes (LED) pesticides, wood system, liver, gastrointestinal tract, -semiconductors preservatives and naturally reproductive system occurring in many household products -toxic when ingested Cadmium (Cd) -silvery white transition metal -nickel-cadmium batteries -toxic and poisonous -non-combustible solid (except as -nuclear reactor regulator dust) -red/yellow pigments -route of exposure: inhalation, ingestion target organs: respiratory system, kidneys, blood, prostate Platinum Group The platinum group (alternatively, the platinum group metals or platinum metals) is a collective name sometimes used for six metallic elements clustered together in the periodic table. These elements are all transition metals, lying in the d-block (groups 8, 9, and 10, periods 5 and 6. The six platinum group metals are ruthenium, rhodium, palladium, osmium, iridium, and platinum. They have similar physical and chemical properties, and tend to occur together in the same mineral deposits. The platinum metals have outstanding catalytic properties. They are highly resistant to wear and tarnish, making platinum, in particular, well suited for fine jewelry. Other distinctive properties include resistance to chemical attack, excellent high-temperature characteristics, and stable electrical properties. All these properties have been exploited for industrial applications. Platinum Sperrylite (platinum arsenide, PtAs2) ore is a major source of this metal. A naturally occurring platinum-iridium alloy, platiniridium, is found in the mineral cooperite (platinum sulfide, PtS). Platinum in a native state, often accompanied by small amounts of other platinum metals, is found in alluvial and placer deposits in Colombia, Ontario, the Ural Mountains, and in certain western American states. Platinum is also produced commercially as a by-product of nickel ore processing. The huge quantities of nickel ore processed makes up for the fact that platinum makes up only two parts per million of the ore. South Africa, with vast platinum ore deposits in the Merensky Reef of the Bushveld complex, is the world's largest producer of platinum, followed by Russia. Osmium Iridiosmium is a naturally occurring alloy of iridium and osmium found in platinum-bearing river sands in the Ural Mountains and in North and South America. Trace amounts of osmium also exist in nickel-bearing ores found in the Sudbury, Ontario region along with other platinum group metals. Even though the quantity of platinum metals found in these ores is small, the large volume of nickel ores processed makes commercial recovery possible. Iridium Metallic iridium is found with platinum and other platinum group metals in alluvial deposits. Naturally occurring iridium alloys include osmiridium and iridiosmium, both of which are mixtures of iridium and osmium. It is recovered commercially as a by-product from nickel mining and processing. Ruthenium Ruthenium is generally found in ores with the other platinum group metals in the Ural Mountains and in North and South America. Small but commercially important quantities are also found in pentlandite extracted from Sudbury, Ontario and in pyroxenite deposits in South Africa. Ruthenium is commercially isolated through a complex chemical process in which hydrogen is used to reduce ammonium ruthenium chloride yielding a powder. The powder is then consolidated by powder metallurgy techniques or by argon-arc welding. Rhodium The industrial extraction of rhodium is complex as the metal occurs in ores mixed with other metals such as palladium, silver, platinum, and gold. It is found in platinum ores and obtained free as a white inert metal which is very difficult to fuse. Principal sources of this element are located in river sands of the Ural Mountains, in North and South America and also in the copper-nickel sulfide mining area of the Sudbury Basin region. Although the quantity at Sudbury is very small, the large amount of nickel ore processed makes rhodium recovery cost effective. However, the annual world production of this element is only 7 or 8 tons and there are very few rhodium minerals. Palladium Palladium is found as a free metal and alloyed with platinum and gold with platinum group metals in placer deposits of the Ural Mountains, Australia, Ethiopia, South and North America. However it is commercially produced from nickel-copper deposits found in South Africa and Ontario. The huge volume of nickel-copper ore processed makes this extraction profitable in spite of its low concentration in these ores. Applications Platinum, platinum alloys, and iridium are used as crucible materials for the growth of single crystals, especially oxides. The chemical industry uses a significant amount of either platinum or a platinum-rhodium alloy catalyst in the form of gauze to catalyze the partial oxidation of ammonia to yield nitric oxide, which is the raw material for fertilizers, explosives, and nitric acid. In recent years, a number of platinum-group metals have become important as catalysts in synthetic organic chemistry. Ruthenium dioxide is used as coatings on dimensionally stable titanium anodes used in the production of chlorine and caustic. Platinum supported catalysts are used in the refining of crude oil, reforming, and other processes used in the production of high-octane gasoline and aromatic compounds for the petrochemical industry. Since 1979, the automotive industry has emerged as the principal consumer of platinum-group metals. Palladium, platinum, and rhodium have been used as oxidation catalyst in catalytic converters to treat automobile exhaust emissions. A wide range of platinum-group metal alloy compositions are used in low-voltage and low-energy contacts, thick- and thin- film circuits, thermocouples and furnace components, and electrodes. Poor Metals (or Post-Transition Metals). Applied to the metallic elements in the p-block of the periodic table. They have lower melting and boiling points, a higher electronegativity value, and are softer than transition metals. The grouping includes aluminum, gallium, indium, lead, thallium, and tin. Sometimes antimony, germanium, and polonium are included in this group of poor metals but these three are really properly considered metalloids. Radioactive Metals Rare Earth Metals Rare earth elements and rare earth metals are a collection of sixteen chemical elements in the periodic table, namely scandium, yttrium, and fourteen of the fifteen lanthanoids (excluding promethium), which naturally occur on the Earth. Scandium, yttrium are included as they tend to occur with the lanthanoids in the same ore deposits. Some definitions additionally include the actinoids. The terms "rare earth" and "rare earth metal" fall outside the official IUPAC nomenclature system, however, the terms retain their usability in the classification of metal alloys and other compounds, as well as distinguishing rare-earth magnets from other types of magnet. Rare earth elements became known to the world with the discovery of the black mineral gadolinite by Lieutenant Karl Arrhenius in the year 1887, in a quarry in the village of Ytterby, Sweden. Many of the rare earths are named in honor of the scientists who discovered the elemental properties, geographical discovery, Latin or Greek, or mythology: Cerium (after Greek deity of fertility, Ceres.) Dysprosium (from the Greek "dysprositos" meaning hard to get.) Gadolinium (Johan Gadolin (1760-1852), to honor his investigation of rare earths.) Lanthanum (from the Greek "lanthanon" meaning I am hidden.) Neodymium (from a Greek word "neo" which means new-one.) Praseodymium (from the Greek "praso" which means leek-green.) Promethium (after Prometheus who brought fire to mortals.) Samarium (V.E. Samarsky, discovered the rare-earth ore called samarskite.) Thulium (refers to the mythological land of Thule.) Ytterbium (named after the Ytterby, Sweden, where the first rare earth ore was discovered.) "Earth" is an obsolete term for oxide; it is a translation from the French terre as French was the lingua franca when these elements were discovered at the beginning of the 19th century. "Rare" was used because some of these elements were believed to be scarce in abundance as minerals. However these elements are (except highly-unstable promethium) relatively abundant in the Earth's crust; the most abundant, cerium, at 68 parts per million, is the 25th most abundant element in the crust, more common than lead, while even the least abundant "rare" earth element, lutetium, is 200 times more abundant than gold. The principal economic sources of rare earth elements are the rare-earth minerals bastnasite, monazite, and loparite and the lateritic ion-adsorption clays. Despite their relative abundance, however, these are more difficult to mine and extract than the sources of transition metals (due in part to their very similar chemical properties), making them relatively expensive. Their industrial use was very limited until efficient separation techniques were developed, such as ion exchange, fractional crystallization and liquid-liquid extraction during the late 50's and early 60's. The following abbreviations are often used: REE = rare earth elements LREE = light rare earth elements (La-Sm) HREE = heavy rare earth elements (Eu-Lu) TOXIC METALS Toxic metals are metals that form poisonous soluble compounds and have no biological role (are not essential minerals). Often heavy metals are thought of as synonymous, but lighter metals also have toxicity, as exemplified by beryllium, and not all heavy metals are particularly toxic and some are even essential (such as iron). The definition may also include trace elements when considered in abnormally high, toxic doses. A difference is that there is no beneficial dose for a toxic metal with no biological role. Toxic metals imitate the action of an essential element in the body, distorting the metabolic process to cause illness. Many metals, particularly heavy metals are toxic, but some heavy metals are essential, have a low toxicity, and bismuth is even non-toxic. Most often the definition includes at least cadmium, lead, mercury and the radioactive metals. Metalloids (arsenic, polonium) may be included in the definition. Radioactive metals have both radiation toxicity and chemical toxicity. Metals in an oxidation state abnormal to the body may also become toxic: chromium (III) is an essential trace element, but chromium (VI) is a carcinogen. The toxicity is a function of solubility, so that as insoluble salts or even in the metallic form, toxic metals may have negligible toxicity. On the other hand, organo- metallic forms, such as dimethyl mercury and tetraethyl lead, are extremely toxic. Toxic metals bioaccumulate in the body and in the food chain. The exceptions are barium and aluminum. Therefore, a common characteristic of toxic metals is the chronic nature of their toxicity. Toxic metals: Barium, Beryllium, Aluminum , Cadmium, Lead - lead poisoning, Mercury - mercury poisoning, Thallium, Antimony; Radioactive metals: Thorium, Uranium; The transuraniums, such as plutonium, americium, etc. Polonium (a metalloid); Radioactive isotopes of lighter elements, e.g. cobalt-60. Arsenic (see arsenic poisoning) is a metalloid. Trace elements with toxicity: Chromium as hexavalent Cr(VI); Nickel; Copper; Iron.
Pages to are hidden for
"Non Traditional Groupings of Metals"Please download to view full document