Milena Velba Feree-ones

IRON

Iron is the metal most used, with 95% by weight of the world's metal. Pure iron (purity 99.5% apartir not have too many applications, with exceptions to use your magnetic potential. The iron has a great application to form the steel products , using this as an array to accommodate other alloying elements both metallic and nonmetallic, which confer different properties to the material. It is believed that iron is an alloy of steel if it contains less than 2% carbon , if the percentage is higher, called Foundry . Steel is indispensable due to its low price and toughness, especially in automobiles, boats and structural components of buildings. ferrous alloys have a wide range of mechanical properties depending on their composition or treatment has been carried out.

Steel
The steels are ferrous alloys with a maximum carbon content of 2%, which can be as insertion alloyed ferrite and austenite forming iron carbide. This may have other alloying and impurities.

Depending on carbon content are classified as:

Carbon steel : less than 0.25% C by weight. They are soft but ductile. They are used in vehicles , pipes, structural elements , etcetera. There are also high-strength steels, low alloy, which contain other alloying elements up to 10% by weight have a higher mechanical strength and can be worked easily.

medium carbon steel : between 0.25% and 0.6% C by weight. To improve its properties are heat treated. Are stronger than low carbon steels, but less ductile, are used in engineering components requiring high strength and wear.

high carbon steel : between 0.60% and 1.4% C by weight. Are still stronger, but less ductile. Adding other elements to form carbides, for example, tungsten forms tungsten carbide, WC, these carbides are very hard. These steels are used primarily in tools.

alloy steels: With non alloy steel, or carbon, it is impossible to meet current industry demands. To achieve certain characteristics of resilience, wear resistance, hardness and resistance to certain temperatures we use these. By the action of one or more alloying elements in appropriate proportions introduce chemical and structural changes that affect the resistance, mechanical properties, oxidation and other properties

The technical and accurate classification for carbon steel (not alloyed) according to their content Carbon:

• hypoeutectoid steels , whose carbon content ranges between 0.02% and 0.8%.
• steels r eacción eutectoid , whose carbon content is 0.8%.
• hypereutectoid steels with a carbon content of 0.8% to 2%
• stainless steels : One of the drawbacks of iron is that it rusts easily. Adding 12% chromium is considered stainless steel, because this creates an alloying chromium oxide layer that protects the steel surface of the corrosion or rusting of iron. You may also have other alloying elements such as n iquel to prevent the formation of chromium carbides, which contribute fragility and enhance intergranular oxidation.

Foundries
When the carbon content exceeds 2% by weight, the alloy is called cast. This carbon can be dissolved to form cementite or in free form. They are very hard and brittle. There are different types of castings:

• Grey
  White
• Atruchada
• American Malleable
• European Malleable
• Esfeoridal or ductile

Their characteristics vary from one type to another, depending on the type used for different applications: other , valves, gears , etc. Furthermore, iron oxides have varied applications: in paintings, acquisition of iron, magnetite (Fe3O4) and iron III oxide in magnetic applications, etc. The Fe (OH) 3, is used for concentrating actinides radiochemistry by co-precipitation.

History
is no evidence of use of iron, four millennia BC by the Sumerians and Egyptians. In the second and third millennium BC, are appearing increasingly iron objects (distinguishable from iron meteorites by the absence of nickel) in Mesopotamia , Anatolia and Egypt . However, their use appears to be ceremonial, to be a very expensive metal, more than gold. Some sources suggest that it was obtained as a by-product of copper . Between 1600 BC C. and 1200 BC C. increasing its use in Middle East, but does not replace the predominant use of bronze . Between the ages XII a. C. and X a. C. is a rapid transition in the Middle East since bronze weapons of iron. This rapid transition may be due to the lack of tin, rather than improved technology in the iron work. In this period, which occurred on different dates depending on location, is called the Iron Age , replacing the Bronze Age . In Greece began to be used around the year 1000 BC C. and did not Western Europe until the seventh century C. The replacement of bronze by iron was gradual, it was difficult to make pieces of iron ore find, then melt at high temperatures to finally shape it.

In Central Europe, emerged in ninth century BC C. the Hallstatt culture (replacing the culture fields polls, called the early Iron Age, as it coincides with the introduction of this metal. Around 450 BC . developed the culture of La Tene , also called second Iron Age. The iron is used in tools, weapons and jewelry, although they bronze objects found. Along with this transition from bronze to iron was discovered carburization process, to add carbon iron. The iron was obtained as a mixture of iron and slag with some carbon or carbons, and was forged , removing the slag and oxidizing the carbon, creating the product and with a form. This wrought iron had a very low carbon content and is not easily hardened by quenching. It was noted that one could obtain a much harder by heating the piece of wrought iron in a bed of charcoal , then quenched in water or oil. The resulting product, which had a surface of steel, was harder and less brittle than the bronze it began to replace.

In China the first iron that was used also meteoric, having wrought iron objects found in the northwest, near Xinjiang, in the eighth century C. The procedure was the same as that used in the Middle East and Europe. In recent years Zhou Dynasty (550 BC C) it manages to cast iron (fusion product of pig iron ). The ore found there has a high phosphorus content, which melts at temperatures lower than in Europe and elsewhere. But for quite some time, until the Qing Dynasty (to 221 BC), had no major impact. Cast iron took over in Europe because the temperature is not getting enough. Some of the earliest examples of cast iron have been found in Sweden in Lapphyttan and Vinarhyttan of 1150 to 1350 .

In Middle Ages, and until the late nineteenth century , many European countries used as a method of steel farga Catalan. Was obtained iron and mild steel using charcoal and iron ore . This system was already in place in the XV century , and managed to reach up to 1200 ° C. This procedure was replaced by the employee in the blast furnaces. At first charcoal was used to obtain iron as a heat source and reducing agent. In the eighteenth century in England, began to dwindle and become more expensive charcoal, and this made the start to be used coke, a fossil fuel as an alternative. It was first used by Abraham Darby in the early eighteenth century , he built a Coalbrookdale blast furnace . Also, the coke was used as an energy source in the Industrial Revolution . In this period iron demand was increasing, for example for application railways in .

The blast furnace was developed over the years. Henry Cort in 1784 , applied new production techniques improved. In 1826 German Friedrich Harkot build a masonry furnace without smoke. By the late eighteenth century and early nineteenth began widely used as an iron structural (in bridges, buildings , etc.). Between 1776 to 1779 the first bridge constructed of iron, built by John Wilkinson and Abraham Darby. In England, first used in the construction of buildings, by Matthew Boulton and James Watt in the early nineteenth century . They are also known other works of that century, such Crystal Palace built for the Universal Exhibition of 1851 in London the architect Joseph Paxton, who has an iron frame, or the Eiffel Tower in Paris, built in 1889 for the Universal Exhibition, where he used thousands of tons of iron.

Occurrence
is the most abundant transition metal in the earth's crust, and a quarter of all items. Also abundant throughout the universe , meteorites have been found that contain it. Is part of many minerals, most notably the hematite (Fe2O3), the magnetite (Fe3O4), the limonite (FeO (OH)), the siderite (FeCO3), the pyrite (FeS2), the ilmenite (FeTiO3), and so on.

can be obtained from iron oxides more or less impurities. Many minerals are iron oxides, and that can not be oxidized to obtain the corresponding oxides. The reduction of iron oxides to get done in a furnace called commonly blast furnace (also blast furnace). It added iron ore in the presence of coke and calcium carbonate, CaCO3, which acts as a slag forming. The gases undergo a series of reactions, the coke can react with oxygen to form carbon dioxide:

C + O2 → CO2
turn carbon dioxide, carbon monoxide can be reduced to give Carbon:
CO2 + C → 2CO
Although also be given the reverse the oxidation of carbon monoxide with oxygen to give carbon dioxide re- Carbon:
2CO + O2 → 2CO2
The oxidation process of coke with oxygen and releases energy used to heat (reaching about 1900 ° C at the bottom of the oven.) First iron oxides can be reduced, partially or completely, carbon monoxide, CO, for example: Fe3O4 + 3CO →
3FeO
FeO + CO2 + CO → Fe + CO2
Later, as low in the oven and the temperature increases, react with coke (carbon mostly), reducing the oxides. For example:
Fe3O4 + C → CO
3FeO + calcium carbonate ( limestone) decomposes:
CaCO3 → CaO + CO2
And carbon dioxide is reduced with coke to carbon monoxide as we have seen before. Below carburizing processes occur:
3Fe + 2CO + CO2 → Fe3C

Finally occurs combustion and desulphurization (removal of sulfur ) through the air inlet. And finally separate two fractions: the slag and pig iron : cast iron, which is the raw material which is then used in the industry. The Cast iron usually contains many undesirable impurities, and must submit to a process of refining in furnaces called converters.


In 2000 the five largest producers of iron were China, Brazil , Australia, Russia e India, with 70% of world production.

compounds
States most common oxidation are +2 and +3. The best-known iron oxides are iron oxide (II), FeO, iron oxide (III), Fe2O3, and Fe3O4 mixed oxide. Also formed numerous salts and complexes in these oxidation states. The hexacyanoferrate (II) iron (III), used in paints, has been called Prussian blue or Turnbull blue, were thought to be different substances.

compounds are known in the oxidation state +4, +5 and +6, but are rare, and in the case of +5, is not well characterized. Potassium ferrate, K2FeO4, in which the iron is in oxidation state +6, is used as an oxidant. The +4 oxidation state is in a few compounds and in some enzymatic processes. The Fe3C is known as cementite , which contains 6.67% carbon, iron is known as α ferrite, and the mixture of ferrite and cementite, pearlite or ledeburita depending on carbon content. The austenite is a solid solution of carbon in iron interstitial γ (Gamma).