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Principles of Metallurgy

P.C. Ray was born on August 2, 1861 at Raruli - Katipara now in Bangladesh, in a wealthy and cultured family.
In 1888 when Ray returned from Edinburg, he began to wear Khaddar and decided to do something to industrialise the country with cattle bones experiment he succeeded to produce Sulphuric acid which is the mother of industries. Ray is the father of India's Chemical industry. Ray did not marry. He died in 1944.

 

KEYWORDS - EXPLANATION 
 

* Metallurgy

* Minerals
* Ores * Concentration of ore
* Activity Series * Froth flotation
* Thermite Process * Refining of the metal
* Distillation * Poling
* Liquation * Electrolytic refining
* Slag * Corrosion
* Smelting * Roasting
* Calcination * Furnace
* Blast furnace * Reverberatory furnace

KEYWORDS - EXPLANATION

Metallurgy: It is the process of extraction of metals from their ores.
Minerals: The elements or compounds of the metals which occur in nature in the earth crust are called minerals.
Ores: The minerals from which the metals are extracted without economical loss are called ores.
Concentration of ore: Concentration or dressing of ore means, simply getting rid of as much of the unwanted rocky material as possible from the ore.
Activity series: Arrangement of metals in descending order of their reactivity is called activity series.
Froth flotation: The ore with impurities is finely powdered and kept in water taken in a flotation cell. Air under pressure is blown to produce froth in water. Froth so produced, takes the ore particles to the surface where as impurities settle at the bottom. Froth is separated and washed to get ore particles.
Thermite Process: It involves the reaction of metal oxides with Aluminium. When highly reactive metals such as Sodium, Calcium, Aluminium etc., are used as reducing agents, they displace metals of lower reactivity from the compound.
Refining of metal: The process of obtaining the pure metal from the impure metal is called refining of the metal.
Distillation: Distillation is a refining process used in purification of low boiling point metals, containing high boiling point metals as impurities.
Poling: This is a refining process in which the molten metal is stirred with logs (poles) of green wood. The impurities are removed either as gases or they get oxidized and form scum (Slag) over the surface of the molten metal.
Liquation: In this method of refining a low melting metal like tin can be made to flow on a sloppy surface to separate it from high melting impurities.
Electrolytic refining: In this method, the impure metal is made to act as anode. A strip of the same metal is in pure form is used as cathode. They are put in a suitable electrolytic bath containing soluble salt of the same metal. The required metal gets deposited on the cathode in the pure form.
Slag: The impurities found from molten metal during polling process of refining are called slag.
Corrosion: In metallic corrosion, a metal is oxidized by loss of electrons generally to oxygen and results in the formation of oxides.

Smelting: Smelting is a pyro chemical process, in which the ore is mixed with flux and fuel and strongly heated.
Roasting: Roasting is a pyrochemical process in which the ore is heated in the presence of oxygen or air below its melting point.
Calcination: Calcination is a pyrochemical process in which the ore is heated in the absence of air.
Furnace: Furnace is the one which is used to carry out pyrochemical process in metallurgy.
Blast furnace: In blast furnace both fire box and hearth are combined in a big chamber which accommodates both ore and fuel.
Reverberatory furnace: Reverberatory furnace has both fire box and hearth separated, but the vapours (flame) obtained due to the burning of the fuel touch the ore in the hearth and heat it.

 

SYNOPSIS
* Metallurgy is the process of extraction of metals from their ores.
* Human history in terms of materials had the bronze age and iron age pertaining to the metals they started to use the bronze and iron.
* The earth's crust is the major source of metals. Sea water also contains same soluble salts such as sodium chloride and magnesium chloride etc. Some metals like Gold (Au), Silver (Ag) and Copper(Cu) are available in nature in free state (native) and they are least reactive.

* The elements or compounds of the metals which occur in nature in the earth's crust are called minerals.
* At some places, minerals contain a very high percentage of a particular metal and the metal can be profitably extracted from it.
* The minerals from which the metals are extracted without economical loss are called ores.
* Aluminium metal is present in the ore Bauxite: (Al2O. 2 H2O).
* Zinc metal is present in the ore Zinc blend (ZnS).
* Magnesium is present in Epsom Salt. (MgSO. 7 H2O)
* Silver is present in Horn Silver (AgCl).
* Manganese is present in Pyrolusite (MnO2).
* Mercury (Hg) is present in Cinnabar (HgS).
* Calcium is present in Gypsum (CaSO4. 2 H2O).
* Magnesium is present in Carnallite (KCl . MgCl2  6 H2O).
* Ores of many metals are oxides and sulphides. So Oxygen-Sulphur (16th group) group is called Chalcogen family. (Chalco = ore, genus = Produce)

* Based on reactivity we can arrange metal in descending order of their reactivity as shown below.


* The extraction of a metal from its ore involves mainly in three stages. they are
    1) Concentration or Dressing
    2) Extraction of Crude metal
    3) Refining or Purification of the metal.
* Concentration or Dressing means simply getting rid of as much of the unwanted rocky material as possible from the ore.
* Extraction of the metal from its ore depends on the reactivity of the metal.
* The process of obtaining the pure metal from the impure metal is called refining of the metal.
* Refining of the metal involves several types of process like distillation, poling, liquation, electrolysis etc.
* Concentration of the ore: Ores that are mined from the earth are usually contaminated with large amount of impurities such as soil and sand etc.

* The impurities like clay are called gangue.
* Various physical methods are used to enrich the ore. Froth flotation is one of the physical means to separate the metal compound from unwanted rocky material by physical means.
* Hand picking, washing, froth flotation, Magnetic separation are some methods for the concentration of the ore.
* Arrangement of the metals in descending order of their reactivity is known as activity series.
* The method used for a particular metal for reduction of its ore to the metal depends mainly on the position of the metal in the activity series.
* Simple chemical reduction methods like heating with C, CO etc., to reduce the ores of these metals namely K, Na, Ca, Mg and Aare not feasible.
* The temperatures required for the reduction is too high and more expensive.
* The only method viable is to extract these metals by electrolysis of their fused compounds.
* For electrolysis of the above, a large quantity of electricity is required to keep the ore is molten state. Suitable impurities are added to the ore to decrease its melting point.
* Zinc, lron, Tin, Lead and Copper are metals in the middle of the activity series. The ores of these metals are generally present as sulphides or carbonates in nature.

* Therefore prior to reduction of ores of these metals, they must be converted into metal oxides.
* Sulphide ores are converted into oxides by heating them strongly is excess of air. This process is called roasting.
* Reduction of ores (compounds) by more reactive metals: Thermite process involves the reaction of metal oxides with Aluminium.
* When highly reactive metals such as Sodium, Calcium, Aluminium etc., are used as reducing agents, they displace metals of lower reactivity from the compound.
* These displacement reactions are highly exothermic. The amount of heat evolved is so large that the metals produced are in molten state.
* The reaction of iron (III) oxide (Fe2O3) with Aluminium is used to join railing of railway tracks or cracked machine parts. This reaction is known as the thermite reaction
       2 A+ Fe2O3  Al2O3 + 2 Fe + Heat
       2 A+ Cr2O3  Al2O3 + 2 Cr + Heat
* Extraction of metals from the bottom of the activity series (Ag, Hg etc).
* Metals at the bottom of the activity series are often found in free state. Their reactivity with other atoms is very low.

* The oxides of these metals can be reduced to metals by heat alone and sometimes by displacement from their aqueous solutions.
* Purification of the crude metal: The metal obtained by the reduction of the ore is usually contaminated with impurities like unchanged ore, other metals present in the ore and non metals from the anions in the ore.
* Refining of the metal involves several types of process. Some methods are
    a) Distillation     b) Poling     c) Liquation     d) Electrolysis.
* Distillation - method is very useful for purification of low boiling metals like Zinc and Mercury containing high boiling metals as impurities.
* In poling the molten metal is stirred with logs (poles) of green wood. The impurities are removed either as gases or they get oxidized and form scum (slag) over the surface of the molten metal.
* Liquation is the method in which a low melting metal like Tin can be made to flow on sloppy surface to separate it from high melting impurities.
* In electrolytic refining the impure metal is made to act as anode. A strip of the same metal in pure form is used as cathode. They are put in a suitable electrolytic bath containing soluble salt of the same metal. The required metal gets deposited on the cathode in the pure form.

* The rusting of iron (iron oxide), tarnishing of silver (silver sulphide) development of green coating on Copper (Copper carbonate) and Bronze are some of the examples of corrosion.
* In metallic corrosion, a metal is oxidized by loss of electrons generally to Oxygen and results in the formation of oxides.
* Corrosion of iron (rusting) occurs in the presence of water and air.
* Prevention of corrosion is of prime importance. It not only saves money but also helps in preventing accidents such as a bridge collapse or failure of a key component due to corrosion.
* One of the simplest methods of preventing corrosion is to prevent the surface of the metallic object to come in contact with the atmosphere.
* This can be done by covering the surface with paint or by some chemicals (e.g.: bisphenol).
* Another simple method is to cover the surface by other metals (Sn, Zn etc) that are inert or react themselves with atmosphere to save the object. This is generally done by electroplating.
* Few important processes used in metallurgy are smelting, roasting, calcination.
* Smelting is a pyrochemical process, in which the ore is mixed with flux and fuel and strongly heated . The heat is so strong that the ore is reduced to even metal as in the case of iron (Fe) and the metal is obtained in the molten state.

* The smelting is carried out in a specially built furnace known as blast furnace.
* Roasting is a pyrochemical process in which the ore is heated in the presence of oxygen or air below its melting point. The products obtained are also in solid state. Generally reverberatory furnace is used for roasting.
* Calcination is a pyrochemical process in which the ore is heated in the absence of air. The ore is generally decomposed in the process.

Posted Date : 28-05-2021

గమనిక : ప్రతిభ.ఈనాడు.నెట్‌లో కనిపించే వ్యాపార ప్రకటనలు వివిధ దేశాల్లోని వ్యాపారులు, సంస్థల నుంచి వస్తాయి. మరి కొన్ని ప్రకటనలు పాఠకుల అభిరుచి మేరకు కృత్రిమ మేధస్సు సాంకేతికత సాయంతో ప్రదర్శితమవుతుంటాయి. ఆ ప్రకటనల్లోని ఉత్పత్తులను లేదా సేవలను పాఠకులు స్వయంగా విచారించుకొని, జాగ్రత్తగా పరిశీలించి కొనుక్కోవాలి లేదా వినియోగించుకోవాలి. వాటి నాణ్యత లేదా లోపాలతో ఈనాడు యాజమాన్యానికి ఎలాంటి సంబంధం లేదు. ఈ విషయంలో ఉత్తర ప్రత్యుత్తరాలకు, ఈ-మెయిల్స్ కి, ఇంకా ఇతర రూపాల్లో సమాచార మార్పిడికి తావు లేదు. ఫిర్యాదులు స్వీకరించడం కుదరదు. పాఠకులు గమనించి, సహకరించాలని మనవి.

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