View Sample Chapter

ASM Specialty Handbook: Magnesium and Magnesium Alloys Copyright © 1999 ASM International® M. Avedesian and H. Baker, Editors All rights reserved www.asminternational.org Introduction: History, Production, Applications, and Markets l.j. Polmear, Department of Materials Engineering, Monash University, Victoria, Australia MAGNESIUM is the lightest of all structural many using a modification of Bunsen's cell (Ref heating in air, after which further heating is dis metals. As such, it forms the basis for commer 3-5). In 1896, this process was jointly taken advantageous because it leads to formation of cial alloys that have found successful use in a up by Chemische-Fabrik Griesheim-Elektron undesirable oxides and oxychlorides. The Dow wide variety of applications. It is a plentiful and Aluminium und Magnesium Fabrik as the sole Chemical Company relies on flashing off the element, comprising 2.7% of the earth's crust significant producer of magnesium metal in remaining water by adding small quantities of (Ref 1). Although magnesium does not occur the world untill914-1915 (Ref6). the partially dehydrated chloride directly into in nature in the metallic form, magnesium By 1900, worldwide production had only reached a large mass of a liquid mixture of magnesium, compounds occur worldwide, and commercial approximately 10 tonnes per annum. and by 1915, sodium, and calcium chlorides contained in amounts of magnesium ores are found in most yearly production had risen to only 350 tmmes. the electrolytic cell. Norsk Hydro, the major countries. The most common ores are the car At that time, however, several other countries European producer, employs complete dehydra bonates: dolomite (MgC03·CaC03) and magne (notably the United States) began production, tion by heating in an atmosphere of dry hydro site (MgC03). The double chloride carnallite and worldwide annual output jumped to more than chloric acid (HCI). Plants in the Commonwealth (MgC12·KC1·6H20) is found to form salt depos 3000 tonnes by the last year of the First World its in natural brines and evaporites, such as in the War, only to fall again to 330 tonnes in 1920. Raw materials Great Salt Lake in Utah. However, the major By 1939, production was 32,000 tonnes per source of magnesium is ocean water. Magne annum; under the impetus of the Second World Seawater Oyster shells sium constitutes 0.13% of the world's oceans War it again increased nearly tenfold, only to fall (calcium carbonate) Natural gas (Ref 2); therefore, seawater provides a virtually again in the late 1940s. During the 1990s, pro inexhaustible supply of the metal. duction in the Western world has been close to 250,000 tonnes per annum, which represents ap c$==J proximately 90% of productive capacity. In ad Calcium oxide History dition, the annual estimated capacity of the (unslaked lime) Hydrochloric Commonwealth of Independent States is 50,000 acid In 1808 Sir Humphrey Davy established that tonnes, and that of The People's Republic of magnesium oxide was the oxide of a newly rec China is 50,000 tonnes (Ref7). ognized metal. Magnesium metal was first iso lated in 1828 by the French scientist Antoine Alexander Bussy, who fused magnesium chloride Production Processes with metallic potassium to obtain metallic mag ' Calcium Magnesium hydroxide chloride nesium. The first production of magnesiwn by Currently, two basic processes are used to pro ! solution electrolytic reduction from the chloride was ac duce magnesium metal; the electrolysis of fused Neutralizer complished by Michael Faraday in 1833 (Ref anhydrous magnesium chloride (MgC12) derived 3-5). from magnesite, brine, or seawater, which ac Magnesium chloride solution Corrnnercial production commenced in Paris counts for about 80% of the output, and thermal in the middle of the nineteenth century with the reduction of magnesium oxide (MgO) by fer Deville-Caron process, which uses potassium to rosilicon derived from carbonate ores. A third reduce magnesium chloride in a heated closed process has been· recently developed that uses container. For several years, the world produc electrolysis of fused anhydrous MgCI2 derived Sol$ide tion of magnesium metal was used almost en from serpentine ores. tirely in wire or powder form for photographic The electrolytic process used by many of the purposes. About 1860, Johnson Matthey & Co. producers is similar to the Dow seawater process Dry magnesium chloride in Manchester, England began British produc (Fig. 1), the differences residing mainly in the tion using a similar process. methods used to produce the anhydrous MgCI2 Chloride gas In 1852, Robert Bunsen, a German, construct (Ref 7, 8). While it is comparatively easy to ed a small laboratory cell for the electroly extract MgC12·6H20, complete removal of the Magnesium Ingots sis of the fused chloride (Ref 3--5). In 1886, water of crystaUization has proven to be diffi commercial production also commenced in Ger- cult. The first four moles can be evaporated by Fig. 1 The Dow Process 4 I Metallurgy and Alloys of Independent States have a different approach; for night aerial photography, miscellaneous fire lubricating oils; in the purification of argon and it involves the use of a cell feed of dehydrated works, high-energy fuels, and incendiary de hydrogen gases; as a "getter" in the manufacture carnallite, which is easier to reduce to the anhy vices. of vacuum tubes; for the production of boron, drous form (Ref7). Metallurgical Applications. In the metallur lithium, and calcium hydride; and for deoxygen Recently, a completely new process for pro gical field, magnesium is used in the manufac ating and dechlorinating boiler water. ducing the basic feedstock of anhydrous MgCI2 ture of nodular cast iron where the magnesium Electrochemical- applications of magnesium has been developed by the Australian Magne removes some of the sulfur and spheroidizes the and magnesium-alloy cast and wrought products sium Corporation. Gylcol is added to a MgC12 graphite to provide greatly improved ductility include cathodic protection, batteries, and photo solution, water is removed by distillation, and and strength. It also is used extensively to desul engraving. Sacrificial galvanic anodes of mag magnesium chloride hexammoniate is fonned furize steel. In addition, it is useful as a deoxidizer, nesium are used to extend the life of household by sparging with ammonia. Calcining then pro or "scavenger," in the manufacture of copper and industrial water heaters; underground struc duces a high-quality anhydrous MgC12; solvents base alloys, such as brass and bronze, and in the tures such as cables, pipelines, well casings, tanks, and ammonia can be recycled. manufacture of nickel alloys. Magnesium used and tower footings; and seawater condensers, The Magnola process (Fig. 2), an electrolytic in combination with calcium is indispensable in ship hulls, ballast tanks, and steel piling in process that uses magnesium chloride derived the Betterton-Kroll process used to remove bis marine environments. Magnesium has also been from serpentine ore, was developed in Canada to muth from lead. used in the construction of batteries, both dry take advantage of the magnesium silicate con By far, the largest use of magnesium is as an cell and reserve-cell types such as seawater tained in the tailings from asbestos mines (Ref alloying element in aluminum where it is added activated cells, and its good etching qualities 9). The tailings are leached with a strong hydro to improve strength and corrosion resistance. In combined with good mechanical properties and chloric acid in a novel process to produce MgClz addition, magnesium is added to zinc dieMcasting ability to withstand wear have contributed to its solution, which is purified by pH adjustment and alloys to improve mechanical properties and di use as photoengraving plate. ion exchange techniques to generate a concen mensional stability. Magnesium is also a con Structural Applications. Due to its many at trated ultra-high-purity brine for dehydration stituent in other zinc products, such as roofmg tractive properties, magnesium has been suc and electrolysis. sheet, photoengraving plate, the sheet used in cessfully used in various structural applications. The thermic-reaction processes are batch op dry-cell batteries, and galvanizing baths. Nickel, Its extreme lightness alone makes it attractive in erations carried out under a vacuum and gener nickel-copper, and copper-nickel-zinc alloys also all parts that are moved or lifted during their ally use dolomite as the ore and ferrosilicon as benefit from the use of magnesium additives. manufacture or use. Low inertia, which results the reductant. Volatile magnesium is produced, Chemical Applications. In the chemical from the low density of magnesium, is especially which distills off and is collected in a container. field, magnesium is used in the well-known The oldest of these thermic-reaction processes Grignard process for the production of complex was developed in 1941 by the Canadian scien and specialized organic and organometallic Raw materials tist Lloyd Montgomery Pidgeon. The Pidgeon compounds. It is also used in the production of Volomlte ore Slllca ore Coke + process (Ref 8) uses externally heated retorts magnesium alkyls and aryls; as a neutralizer in (magnesium carbonate + (quartizite) scrap iron of relatively small diameter, each producing calcium carbonate) about 120 kg (265 !b) of magnesium per day (Fig. 3). Plants are located in Canada, China, Raw materials and India. Natural gas ll~i-11 Asbestos tailings c$=J The Magn6thenn process (Fig. 4) of France's (serpentine, magnesium Calcined dolomite Pechiney Electrometallurgie, which was devel silicate) (magnesium oxide + Ferro-silicon oped shortly after the Second World War, differs calcium ox!de) from the Pidgeon process in that it produces a molten slag that can be tapped off without t breaking the vacuum (Ref 8, 10). The furnace is Magnesium electrically heated internally, and alumina is chloride brine Calcined used as a flux to reduce the melting point of the Hydrochloric dolomite powder Ferro-silicon slag.

Load more