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→Types of Ferrous Materials
The overall reaction for the production of iron in a blast furnace is as follows:
The overall reaction for the production of iron in a blast furnace is as follows:
'''Fe<sub>2</sub>O<sub>3</sub>(s)+3C(s)−Δ→2Fe(l)+3CO(g)'''
'''Fe<sub>2</sub>O<sub>3</sub>(s)+3C(s)−Δ→2Fe(l)+3CO(g)'''
Where Fe<sub>2</sub>O<sub>3</sub>(s) stands for Hematite ore (Ferrous Oxide, s = solid), C stands for Carbon (in the form of solid coke), Δ represents the energy requirement for the reaction to take place, Fe stands for Ferrum (elemental Iron, l = liquid) and CO stands for Carbon monoxide (g = gaseous state)[[File:Blast furnace .png|381x381px|Blast Furnace for Converting Iron Oxides to Iron Metal. Courtesy: General Chemistry (Libre Texts)|alt=|thumb]]
Where Fe<sub>2</sub>O<sub>3</sub>(s) stands for Hematite ore (Ferrous Oxide, s = solid), C stands for Carbon (in the form of solid coke), Δ represents the energy requirement for the reaction to take place, Fe stands for Ferrum (elemental Iron, l = liquid) and CO stands for Carbon monoxide (g = gaseous state)
Iron compounds in the ores could be reduced by carbon; and for a long time, charcoal was the form of carbon used in the reduction process. Charcoal was replaced by Coke, a form of carbon formed by heating coal in the absence of air to remove impurities, improving the reduction process. As seen in the equation above, the actual reductant is CO, which reduces Fe<sub>2</sub>O<sub>3</sub> to give Fe(l) and CO<sub>2</sub>(g).
Iron compounds in the ores could be reduced by carbon; and for a long time, charcoal was the form of carbon used in the reduction process. Charcoal was replaced by Coke, a form of carbon formed by heating coal in the absence of air to remove impurities, improving the reduction process. As seen in the equation above, the actual reductant is CO, which reduces Fe<sub>2</sub>O<sub>3</sub> to give Fe(l) and CO<sub>2</sub>(g).
==== Steps in the Extraction of Iron ====
==== Steps in the Extraction of Iron ====
The extraction of iron involves following steps.
The extraction of iron involves following steps.<ref name=":3" />
# Collection of raw materials
# Collection of raw materials
# Washing and concentration or dressing of the ore
# Washing and concentration or dressing of the ore
# Preliminary roasting and calcinations
# Preliminary roasting and calcinations
# Reduction or smelting in a Blast Furnace
# Reduction or smelting in a Blast Furnace
'''Collection of raw materials''': Iron is the most abundant metal in the earth's crust. Because of its strong affinity to oxygen, it is not found in the elemental state but predominantly in its combined forms such as oxides, and much less as sulphide and carbonate.
'''Collection of raw materials''': Iron is the most abundant metal in the earth's crust. Because of its strong affinity to oxygen, it is not found in the elemental state but predominantly in its combined forms such as oxides, and much less as sulphide and carbonate. Iron is predominantly extracted from its oxide ore, hematite.
'''Ore Dressing''': After washing with water, ore is subjected to magnetic separation. This way the ore is rich in oxide of iron. Washing removes the silicious impurities, concentrating the ore.
'''Preliminary roasting and calcinations''': The concentrated ore is roasted and calcined with little coal and excess air in a shallow furnace. Following changes take place during roasting and calcinations.
(i) Moisture escapes as steam and organic matter present burns off to give CO<sub>2</sub> Sulphur and arsenic are oxidized to form their volatile oxides SO<sub>2</sub> and As<sub>2</sub>O<sub>3</sub> respectively.
(ii) Ferrous oxide is converted to ferric oxide which avoids formation of ferrous silicate in the slag during smelting. The reactions that happen in the furnace at various temperatures are elaborated in the image. [[File:Blast furnace .png|381x381px|Blast Furnace for Converting Iron Oxides to Iron Metal. Courtesy: General Chemistry (Libre Texts)|alt=|thumb]](iii) The mass becomes porous and thus makes it more suitable for reduction to metallic iron.
Reduction or smelting in a blast furnace: The roasted and calcined ore ( 8 parts ) is mixed with coke ( 4 parts ) which acts as a reducing agent and limestone ( 1 part ) which acts as a flux. The mixture is introduced in a tall Blast Furnace. The blast furnace has two functions (i) to reduce the ore to metallic iron and (ii) to remove the impurities in the form of slag.
==== Products of the Blast furnace ====
The products obtained from the blast furnace include Pig Iron, Slag and Flue gasses.<ref name=":3" /> Pig iron is the most impure form of iron having impurities. Slag is mostly calcium silicate and some amount of aluminum silicate. Gasses produced in the extraction process are called flue gasses containing CO (carbon monoxide), Nitrogen and hyderogen.
==== Commercial forms of Iron ====
# '''Pig iron''' - The most impure form of iron, it contains about 1.5% to 4.5% Carbon. Other impurities like Si, P, Mn and S are present up to about 1.5 %.
# '''Cast Iron''' - Pig iron when is remelted in a vertical furnace can be poured into moulds. It is then called cast iron. When the pig iron is suddenly cooled, crystalline cast iron is obtained called as white cast iron. In this form carbon is present combined with iron as iron carbide. However, if the molten pig iron is cooled gradually in sand moulds, a graphite coloured iron is formed called grey cast iron. Major part of cast iron is used to manufacture steel and other heavy machinery.
# '''Wrought or Malleable iron''' – It is the purest form of iron. It contains about 0.2 % carbon.
# '''Steel''' – It is an alloy of iron with carbon and other elements like manganese, silicon and phosphorus. It is midway between cast and wrought iron as far as impurities are concerned. It contains 0.1 to 1.5 % carbon.
== Types of Ferrous Materials ==
== Types of Ferrous Materials ==
The Rasaratnasamucchaya describes three types of ferrous materials
The Rasaratnasamucchaya describes three types of ferrous materials.
{| class="wikitable"
|+Classification of iron and its properties as given in Rasa Ratna Samucchaya<ref name=":6">Prakash, B. ''Ancient Iron Making in India'' in Iron & Steel Heritage of India Ed. S. Ranganathan, ATM 97, Jamshedpur</ref>
!Kinds of Iron
(Loha)
!Sub-categories
!Properties
|-
| rowspan="5" |Kanta Loha (Soft Iron)
|Bhramaka
|Very soft magnetic iron
|-
|Chumbaka
|Mildly magnetic, sticks to iron pieces
|-
|Karsaka
|It can attract iron objects
|-
|Dravaka
|Very strong magnetic iron
|-
|Romaka
|Permanent magnet, develops strong magnetic field around it. Itmay be Ekmukh or sarva mukh
|-
| rowspan="6" |Tikshna Loha (Carbon steel)
|Khara
|Develops good cutting edge, breaks on bending
|-
|Sara
|Softer iron and it has fibrous fracture
|-
|Hrnnala
|Hard and tough having fibrous fracture
|-
|Travaratta
|Develops good cutting edge
|-
|Vajra
|Has good hardening and tempering property, has bluish color and hard cutting edge
|-
|Kala
|Develops hard cutting edge after blue tempering
|-
| rowspan="3" |Munda Loha (Cast Iron)
|Mrdu
|Soft brittle iron may be grey cast iron, has low melting point
|-
|Kunda
|Mottled grey iron
|-
|Kadara
|White cast iron
|}
== Extraction Process in Ancient Times ==
== Extraction Process in Ancient Times ==
Iron ores were widely distributed in Indian subcontinent. However they were delayed to smelt Iron. The reason is that the primitive condition of furnace has produced temperature about 1100°C which is required for Copper smelting. But Iron needs a high temperature almost above 1500°C for the ore to smelt into a liquid. Little solid grains of Iron have obtained by low temperature as 800°C. Iron is a soft and spongy material which had to be admixed with carbon in proper proportion to obtain sufficient sharpness and hardness. It was obtained from ores at high temperature. Iron has more impurities than Copper. This impurity is removed by using a catalytic flux such as lime to produce the slag. Iron produced by smelting is of 3 kinds:
Iron ores were widely distributed in Indian subcontinent. However they were delayed to smelt Iron. The reason is that the primitive condition of furnace has produced temperature about 1100°C which is required for Copper smelting. But Iron needs a high temperature almost above 1500°C for the ore to smelt into a liquid. Little solid grains of Iron have obtained by low temperature as 800°C. Iron is a soft and spongy material which had to be admixed with carbon in proper proportion to obtain sufficient sharpness and hardness. It was obtained from ores at high temperature. Iron has more impurities than Copper. This impurity is removed by using a catalytic flux such as lime to produce the slag. Iron produced by smelting is of 3 kinds based on its carbon content:
* wrought iron (Kanta Loha)
* wrought iron (Kanta Loha)
''How happy I feel,'' ''The chokh boy beats with the hammer''
''How happy I feel,'' ''The chokh boy beats with the hammer''
''The hammer whistles as he swings it round,'' ''And I feel very happy.''</blockquote>As it appears from the above mentioned song the whole operation was a family affair controlled by the headman and his wife and the technology was maintained as a secret, passed on from generation to generation. The younger generation participated in the activities and when by the age of 17 to 20 they were trained in all the skills of the trade, they were permitted to marry and operate their own furnace. The actual practice of iron making can be divided into the following six steps-<ref name=":2" /><ref name=":4">A.K. Vaish, P.K. Biswas, S.P. Chaudhuri, M.M. Humane, R.K. Minz, B.A. Lakra, S.K. Sinhababu, P.K.De, N.G. Goswami, C. S. Sivaramakrishnan and P. Ramachandra Rao. ''Iron making in ancient India - A critical assessment'' in Tradition and Innovation in the History of Iron Making - An Indo-European Perspective eds., Girijā Pāṇḍe, Jan af Geijerstam (2002) Nainital: Pahar Parikarma</ref>
''The hammer whistles as he swings it round,'' ''And I feel very happy.''</blockquote>As it appears from the above mentioned song the whole operation was a family affair controlled by the headman and his wife and the technology was maintained as a secret, passed on from generation to generation. The younger generation participated in the activities and when by the age of 17 to 20 they were trained in all the skills of the trade, they were permitted to marry and operate their own furnace. The actual practice of iron making can be divided into the following six steps-<ref name=":2" /><ref name=":6" /><ref name=":4">A.K. Vaish, P.K. Biswas, S.P. Chaudhuri, M.M. Humane, R.K. Minz, B.A. Lakra, S.K. Sinhababu, P.K.De, N.G. Goswami, C. S. Sivaramakrishnan and P. Ramachandra Rao. ''Iron making in ancient India - A critical assessment'' in Tradition and Innovation in the History of Iron Making - An Indo-European Perspective eds., Girijā Pāṇḍe, Jan af Geijerstam (2002) Nainital: Pahar Parikarma</ref>
# '''Collection of raw material''' '''i.e. iron ore, wood and refractory clay''': In spite of the abundantly available hematite deposits, ancient smelters preferred to use low grade magnetite ore. The ore was concentrated by panning in the water stream. Ore is calcined to remove moisture and associated organic matter and broken to small pieces. The charcoal used for heating the ore and generating the reducing gas (CO) was produced from a variety of woods depending upon their availability in the region, and generally no basic flux was used to adjust the properties of the FeO rich fayalite (2FeO.SiO<sub>2</sub>) slag formed during smelting. Refractory clay and stiff mud are used for making the furnace.[[File:Iron Smelting Furnace.PNG|thumb|Megalithic iron smelting furnace at Naikund (near Nagpur, Maharashtra)|327x327px]]
# '''Collection of raw material''' '''i.e. iron ore, wood and refractory clay''': In spite of the abundantly available hematite deposits, ancient smelters preferred to use low grade magnetite ore. The ore was concentrated by panning in the water stream. Ore is calcined to remove moisture and associated organic matter and broken to small pieces. The charcoal used for heating the ore and generating the reducing gas (CO) was produced from a variety of woods depending upon their availability in the region, and generally no basic flux was used to adjust the properties of the FeO rich fayalite (2FeO.SiO<sub>2</sub>) slag formed during smelting. Refractory clay and stiff mud are used for making the furnace.[[File:Iron Smelting Furnace.PNG|thumb|Megalithic iron smelting furnace at Naikund (near Nagpur, Maharashtra)|327x327px]]
# '''Removal of slag and handling of red hot sponge iron bloom''': In case of bowl furnaces, generally the slag was allowed to get collected and solidified at the bottom of the furnace. In the case of other furnaces, it was tapped out through the slag hole known as 'Hagan.' After the smelting period was over, the bellows along with blow pipes were removed and the temporary wall for closing the front opening was removed and the partially melted tuyere was taken out with the help of a tong and a wooden pole. It was placed on a large granite stone anvil and hammered to consolidate and remove the molten slag filled in the pores.
# '''Removal of slag and handling of red hot sponge iron bloom''': In case of bowl furnaces, generally the slag was allowed to get collected and solidified at the bottom of the furnace. In the case of other furnaces, it was tapped out through the slag hole known as 'Hagan.' After the smelting period was over, the bellows along with blow pipes were removed and the temporary wall for closing the front opening was removed and the partially melted tuyere was taken out with the help of a tong and a wooden pole. It was placed on a large granite stone anvil and hammered to consolidate and remove the molten slag filled in the pores.
# '''Secondary refining of the bloom''': This most important and exclusive Indian practice was carried out to remove the slag trapped inside the iron block. For this, the iron bloom was reheated in a smithy forge to almost white hot (>1250°C) condition and silica sand was sprinkled upon it. This reacted with the remaining FeO and helped in forming fluid 2FeO.SiO<sub>2</sub> slag which flowed out of the iron block. The iron block was taken out of the furnace and forged to increase its density. This process was repeated till the bloom was converted into 12 to 15mm square/circular rod. This refined rod containing 0.2 to 0.4% SiO<sub>2</sub> almost free from the slag inclusion was cut into 150 to 180mm long pieces and sold to the blacksmiths or 'Lohars' for reshaping them into useful objects.
# '''Secondary refining of the bloom''': This most important and exclusive Indian practice was carried out to remove the slag trapped inside the iron block. For this, the iron bloom was reheated in a smithy forge to almost white hot (>1250°C) condition and silica sand was sprinkled upon it. This reacted with the remaining FeO and helped in forming fluid 2FeO.SiO<sub>2</sub> slag which flowed out of the iron block. The iron block was taken out of the furnace and forged to increase its density. This process was repeated till the bloom was converted into 12 to 15mm square/circular rod. This refined rod containing 0.2 to 0.4% SiO<sub>2</sub> almost free from the slag inclusion was cut into 150 to 180mm long pieces and sold to the blacksmiths or 'Lohars' for reshaping them into useful objects.
National Metallurgical Laboratory, Jamshedpur, in India made great strides in improving the ancient iron making process and made significant contributions to the iron industry.<ref name=":4" />
== Wootz Steel ==
Wootz is the anglicized version of 'ukku' in the language of the states of Karnataka and Andhra Pradesh, a term denoting steel. Ample literary references suggest that the steel from southern India was the finest and once exported to Europe, China, Arab countries and the Middle East.<ref>Srinivasan. S and Ranganathan. S. ''Wootz steel: An advanced material of the ancient world'' in Iron & Steel Heritage of India Ed. S. Ranganathan, ATM 97, Jamshedpur</ref>
#
#
== References ==
== References ==
[[Category:Shastras]]
[[Category:Shastras]]