Metallurgy of Iron • Introduction • Properties • Occurrence • Uses • Metallurgy
Introduction Iron or ferrum (latin word) Elemental symbol: Fe Atomic number: 26 Elemental group: Transition element Metallic iron was known and used for ornamental purposes and weapons in prehistoric ages. The earliest specimen still extant, a group of oxidized iron beads found in Egypt, dates from about 4000 BC. The archaeological term Iron Age properly applies to the period when iron was used extensively for utilitarian purposes, as in tools, as well as for ornamentation.
Physical Properties • Iron is soft, malleable, and ductile. • Iron is easily magnetized at ordinary temperatures; it is difficult to magnetize when heated, and at about 790° C (about 1450° F) the magnetic property disappears. • Pure iron melts at about 1535° C (about 2795° F), boils at 2750° C (4982° F), and has a specific gravity of 7.86. • The atomic weight of iron is 55.847.
Chemical Properties • It combines with the halogens (fluorine, chlorine, bromine, iodine, and astatine), sulfur, phosphorus, carbon, and silicon. • It displaces hydrogen from most dilute acids. • It burns in oxygen to form ferrosoferric oxide, Fe3O4 (magnetite).
Chemical Properties • When exposed to moist air, iron becomes corroded, forming a reddish-brown, flaky, hydrated ferric oxide commonly known as rust. • When iron is dipped into concentrated nitric acid, it forms a layer of oxide that renders it passive—that is, it does not react chemically with acids or other substances. The protective oxide layer is easily broken through by striking or jarring the metal, which then becomes active again.
Occurrence • Metallic iron occurs in the free state in only a few localities, notably western Greenland. It is found in meteorites, usually alloyed with nickel. • In chemical compounds the metal is widely distributed and ranks fourth in abundance among all the elements in the earth's crust; next to aluminum it is the most abundant of all metals.
Occurrence • The principal ore of iron is hematite, which is mined in the United States in Minnesota, Michigan, and Wisconsin. • Other important ores are goethite, magnetite, siderite, and limonite (bog iron).
Occurrence • Pyrite, FeS, the sulfide ore of iron, is not processed as an iron ore because it is too difficult to remove the sulfur. • Small amounts of iron occur in combination in natural waters, in plants, and as a constituent of blood.
Uses of Iron • Iron is used in processed forms, such as wrought iron, cast iron, and steel. • Commercially pure iron is used for the production of galvanized sheet metal and of electromagnets. • Iron compounds are employed for medicinal purposes in the treatment of anemia. • Iron is also used in tonics.
Uses of Iron • The most important ferrous compound is ferrous sulfate (FeSO4), called green vitriol or copperas. It usually occurs as pale-green crystals containing seven molecules of water of hydration. It is obtained in large quantities as a by-product in pickling iron and is used as a mordant in dyeing, as a tonic medicine, and in the manufacture of ink and pigments.
Uses of Iron • Ferric oxide or hematite, an amorphous red powder, is obtained by treating ferric salts with a base or by oxidizing pyrite. It is used both as a pigment, known as either iron red or Venetian red; as a polishing abrasive, known as rouge; and as the magnetizable medium on magnetic tapes and disks. • Ferric chloride, obtained as dark-green, lustrous crystals by heating iron in chlorine, is used in medicine as an alcoholic solution called tincture of iron.
Uses of Iron • Ferric ferrocyanide (Fe4[Fe(CN)6]3), a dark-blue, amorphous solid formed by the reaction of potassium ferrocyanide with a ferric salt, is called Prussian blue. It is used as a pigment in paint and in laundry bluing to correct the yellowish tint left by the ferrous salts in water. • Potassium ferricyanide (K3Fe(CN)6), called red prussiate of potash, is obtained from ferrous ferricyanide (Fe3[Fe(CN)6] 2; also called Turnbull's blue), and is used in processing blueprint paper.
Metallurgy of Iron • Reduction of iron oxide in the Blast furnace. • Materials: • Concentrated iron ore • Coke • Blast of hot air • Flux
Reactions taking place in the Blast furnace • Combustion of Coke C(s) + O2(g) CO2(g) + heat CO2(g) + C(s) 2CO(g) • Reduction of Fe2O3 2Fe2O3(s) + 3C(s) 4Fe(l) + 3CO2(g) Fe2O3(s) + 3CO(g) 4Fe(l) + 3CO2(g)
Reactions taking place in the Blast furnace • Calcination CaCO3(s) + heat CaO(s) + CO2(g) • Slag formation CaO(s) + SiO2(s) CaSiO3(l) (slag) CaO(s) + Al2O3(s) Ca(AlO2)2(l)
1. A blast furnace forces in extremely hot air through a mixture of ore, coke, and limestone, called the charge. 2. Carts called skips dump the charge into the top of the furnace, where it filters down through bell-shaped containers called hoppers. Iron Blast furnace
4. The waste metal, called slag, floats on top of the molten pig iron. Both of these substances are drained, or tapped, periodically for further processing. 3. Once in the furnace, the charge is subjected to air blasts that may be as hot as 870° C (1600° F). Iron Blast furnace
Products of the Blast furnace • Pig iron - 93-95% Fe, 3-5% C, 1% Si, 0.1- 0.3% P, <1% S • Waste gases – CO2 and CO • Slag – CaSiO3 and Ca(AlO2)2 Principal products of Iron • Cast iron • Wrought iron • Steel
CAST IRON • This is pig iron melted with scrap Iron. It is the least pure of all forms of iron containing 93% Fe & 5% C. WROUGHT IRON • The purest form of iron produced when impurities are removed. It contains 0.5% impurities. STEEL • A form of iron which usually contains 0.1 to 2% carbon.
Carbon steels Carbon content Uses Low carbon steel < 0.3% Rivets, wires, nails Medium carbon steel 0.3% to 0.8% Railroad rails, axles High carbon steel 0.8% to 2% Tools, springs, files STEEL
Steel Making • Bessemer Process • Open-Hearth Method • Basic Oxygen Process