Metallurgy of Iron

Metallurgy is a domain of materials science and engineering that studies the physical and chemical behavior of metallic elements, their inter-metallic compounds, and their mixtures, which are called alloys. 

1.       Introduction

2.       Properties

3.       Occurrence

4.       Uses

5.       Metallurgy

1.       Introduction

   Iron or ferrum (latin word)

   Elemental symbol: Fe

   Atomic number:     26

   Elemental group:   Transition element

            Uses: 

            prehistoric ages: ornamental purposes and used as weapons (IRON AGE)

   earliest specimen still extant is a group of oxidized iron beads found in Egypt, dates from about 4000 BC.

2.       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.

3.       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).

·         Iron becomes corroded, forming a reddish-brown, flaky, hydrated ferric oxide (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.

4.       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, it 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.

·         The principal ore of iron is hematite, Fe₂O_3, which is mined in the United States in Minnesota, Michigan, and Wisconsin.

·         Other important ores:

   goethite - FeO(OH) Hydrated Iron Oxide

            magnetite

            siderite – FeCO₃

            limonite - mixture of hydrated iron oxides

·         Pyrite, FeS₂ (sulfide ore of iron)

·         Small amounts of iron occur in combination in natural waters, in plants, and as a constituent of blood.

5.             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.

·         Ferrous sulfate (FeSO₄), green vitriol or copperas.

·         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.

·         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.

·         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.

6.             Metallurgy of Iron

A.      Reduction of iron oxide in the Blast furnace.

B.       Materials:

1.       Concentrated iron ore

2.       Coke

3.       Blast of hot air

4.       Flux

C.       Reactions taking place in the Blast furnace

Combustion of Coke

                C_(s)  +  O_2(g)  ® CO_2(g)  + heat

                CO_2(g) +  C_(s) ® 2CO_(g)

 Reduction of Fe₂O₃

                      2Fe₂O_3(s)  + 3C_(s)  ® 4Fe_(l)  + 3CO_2(g)

                Fe₂O_3(s)  + 3CO_(g)  ® 4Fe_(l)  + 3CO_2(g)

 Calcination

                CaCO_3(s)  + heat  ® CaO_(s)  +  CO_2(g)

 Slag formation

                CaO_(s)  + SiO_2(s)  ® CaSiO_3(l)   (slag)

                CaO_(s)  + Al₂O_3(s)  ® Ca(AlO₂)_2(l)

D.      Products of the Blast furnace

1.       Pig iron  - 93-95% Fe, 3-5% C, 1% Si, 0.1-0.3% P, <1% S

2.       Waste gases – CO₂ and CO

3.       Slag – CaSiO₃ and Ca(AlO₂)₂

E.       Principal products of Iron

1.       Cast iron

2.        Wrought iron

3.        Steel

7.             Steel Making

·         Bessemer Process

·          Open-Hearth Method

·          Basic Oxygen Process

·          Electric-furnace method