What is Metallurgy? – History, Definition, Classification, Extraction and Uses of Metals and Alloys

The major historical eras are distinguished according to the metals that dominated the development during the relevant period. For instance, the Neolithic era includes the Chalcolithic or Copper Age. Europe's civilizations advanced because of the development of copper manufacturing technology. Excavations have revealed copper jewellery from Turkmenistan and related South Asian civilizations. Similar to this, there are various significant ages, like the Bronze age. Remember that the earliest known evidence of copper processing dates from 5000 BCE. Nevertheless, 7000 years later, this process is still evolving. Metals are indispensable in our world and are used in everything from cooking utensils to the creation of priceless jewellery, making their study incredibly fascinating.

Let's explore these ideas further, which have been developed over many years on this concept page.

TABLE OF CONTENTS

• Metallurgy – History
• Metallurgy – Definition
• Uses of Metals and alloys
• Metallurgy – Classification
• Extraction of Metals
• Manufacturing and Production
• Practice Problems
• Frequently Asked Questions – FAQ

Metallurgy – History

The oldest metal that seems to have been utilised by humans is gold, which can be found in either the free or native condition. Spanish archaeological finds from the late Palaeolithic period, around 40,000 BC, had a little amount of natural gold in them. Thanks to the accessibility of local forms of meteoric iron, copper, silver and tin,, early cultures were able to perform a small amount of metalworking.

Some metals, mainly copper, lead and tin can be extracted in a blast or fire furncae ffrom their ores by simply heating the rocks in a fire or blast furnace, a procedure known as smelting. The earliest indications of this extractive metallurgy date back to the fifth and sixth millennia BC and were found at ancient finds in Plonik, Jarmovac and Majdanpek, all of which are located in what is now Serbia. The earliest indications of copper smelting have been found in Plocnik at the Belovode site by archaeologists. At this area, a 5500 BC copper axe of Vina culture was discovered.

The first traces of lead use can be found at the late Neolithic Arpachia Yarim Tepe and Arpachiyah sites in Iraq. These artefacts suggest that copper smelting followed lead smelting. Copper smelting from the same period (briefly after 6,000 BC) is visible at this site, while lead use seems to have existed earlier. Early metallurgy is also documented at the neighbouring Tell Maghz Aaliyah site, that looks to date far earlier and is entirely absent of that pottery. The Balkan peninsula has notable Neolithic cultures.

Around 3,500 BC, it was discovered in the Near East that combining copper and tin could result in bronze, an alloy that was a superior metal. As a result, the known Bronze Age experienced a substantial technological development. Compared to copper or tin, iron is much more hard to extract out of its ore and refine into a useful metal. The technique is thought to have been created by the Hittites around 1200 BC, beginning the Iron Age. The Philistines' capacity to acquire and refine iron had a considerable impact on their success. It is known that many ancient cultures and civilizations contributed to the development of ferrous metallurgy throughout history. 

Metallurgy – Definition

A procedure used to extract metals in their pure state is referred to as metallurgy. Minerals are made up of soil, rocks, limestone, sand, and metal complexes. Commercial metals are easily and cheaply mined from minerals called ores. Flux is a material that is added to the furnace charge to eliminate the gangue (impurities). The purification of metals and the creation of alloys are the subjects of metallurgy.

Uses of Metals and Alloys

• Engineering metals typically include zinc, titanium, nickel, magnesium, iron, copper, chromium, aluminium and silicon. These metals are typically utilised in alloys, with the notable exception being silicon. There has been a lot of focus on studying the iron-carbon alloys, which comprises cast irons and steels.

• Plain carbon steels (those that essentially just include carbon as an alloying element) are used in applications that call for high strength and low cost since they are weight and corrosion resistant.  Cast iron is a part of the iron-carbon system that includes ductile iron. Iron-manganese-chromium alloys are used in directional drilling, a non-magnetic application (Hadfield-type steels).

• Materials like copper alloys, titanium alloys, nickel alloys, galvanised and austenitic stainless steel and stainless steel are used to resist corrosion.

• Aluminum and magnesium alloys are often utilised when a strong, lightweight component is required, like in aerospace and automotive applications. Monel and other copper-nickel alloys are used in non-magnetic applications and very corrosive environments. Nickel-based superalloys like Inconel are used in high-temperature applications such as heat exchangers, pressure vessels, turbocharges and gas turbines.

• To lessen creep, single crystal alloys are employed at very high temperatures. Integrated circuits and Metal-oxide-silicon transistors (MOS) in modern electronics require high purity single crystal silicon.

Metallurgy – Classification

Chemical metallurgy and physical metallurgy are two further divisions of the science of metallurgy.

• The primary areas of research in chemical metallurgy include reduction, oxidation, and the chemical behaviour of metals. Chemical metallurgy includes the study of themes like chemical deterioration (corrosion), electrochemistry, thermodynamics, metal extraction and mineral processing.

• On the other hand, physical metallurgy is interested in the performance, physical and mechanical properties of metals. Physical metallurgy covers a variety of topics, including crystallography, material characterization, phase transitions, failure mechanisms and mechanical metallurgy.

Extraction of Metals

In the process of extractive metallurgy, precious metals are removed from an ore and refined into a purer form. A metal oxide or sulphide must be reduced physically, chemically, or electrolytically to provide a purer metal. 

A mineral is a naturally occurring material extracted from the earth's crust that contains metal in either its native or combined state. An ore is a mineral from which metal can be extracted easily and cheaply.  While not all minerals are ores, all ores are minerals. Gangue or matrix refers to the earthly and undesirable impurities associated with the ore.

Some important ore used for the extraction of metals are: 

A few important ores of iron are:

a. Haematite (Fe₂O₃) (red oxide of iron)
b. Iron pyrites (FeS₂) 
c. Siderite (FeCO₃)
d. Magnetite (Fe₃O₄) (Magnetic oxide of iron)

A few important ores of zinc are: 

a. Zinc blende (ZnS)
b. Zincite (ZnO)
c. Calamine (ZnCO₃)

The common ore of copper is Copper pyrite (CuFeS₂)

The most abundant metal in the earth's crust is aluminium. Bauxite is its most important ore with the formula Al₂O₃.2H₂O.

The processes involved in the extraction of metal include:

Step 1 – Crushing and Grinding of Ore: The ores are found in bulk forms in nature. Using crushers or grinders, they are reduced to little fragments. These fragments are subsequently processed in a stamp mill or ball mill to create a fine powder. Pulverization is the term for this.

Step 2 – Concentration of Ore: The ores frequently contain non-metallic impurities such as felspar, limestone, micasand, mica, limestone, felspar, earthy, and rocky impurities. Before the metals can be recovered, these undesirable impurities, sometimes referred to as gangue or matrix, must be eliminated. Ore benefaction, ore dressing or ore concentration are the terms used to describe the process of removing unwanted impurities (gangue) from ore. Froth flotation, levigation, magnetic separation, hydraulic washing, manual picking, gravity separation, leaching, and other techniques are used to concentrate ore. 

Step 3 – Extraction of Metals from the Concentrated Ore: The concentrated ore is further converted  into its oxide form by the processes such as calcination and roasting. Once the metal is converted into the oxide form, it is converted from oxide form to metal by methods such as smelting, hydrometallurgy, electrolytic reduction and auto reduction.

Step 4 – Refining of Ore: Metals that are impure are refined or purified. Refining is the process of purification of impure metal. It differs from other methods such as smelting and calcining in that both these two involve a chemical change to the raw material, whereas refining usually results in a final material that is chemically identical to the original, but purer.  Refining of metal takes place by methods such as distillation, zone refining, vapour phase refining, electrolytic refining, poling and liquation. 

Manufacturing and Production

A metallurgist's goal is to strike a balance between a material's performance in extreme temperatures, fatigue resistance, corrosion resistance, hardness, toughness, strength, weight and cost. To do this, significant consideration must be given to the operational environment. In a saltwater environment, the majority of non-ferrous alloya and ferrous metals corrode quickly. Extreme cold or cryogenic environments may cause metals to lose their toughness  and change from ductile to brittle. When cyclic loading is done to metals continuously, metal fatigue may develop. Continuously strained metals exposed to high temperatures can creep.

Metals are shaped by the following processes:

1. Casting: Casting is a procedure used in metalworking and jewellery manufacturing where a liquid metal is supplied into a mould that has the desired shape. Through a sprue, which is a hollow conduit, metal is poured into the mould. The metal component (the casting) is then removed after the metal and mould have cooled. Casting is most frequently used to create intricate shapes that would be challenging or expensive to create using alternative techniques. Since ancient times, casting techniques have been frequently utilised to create sculpture (particularly in bronze), jewellery made of precious metals, as well as tools and weaponry. 90 percent of durable goods, such as cars, appliances, pipes, wind turbines, nuclear power plants, defence goods, toys, and more, use highly designed castings.

Expendable casting and non-expendable casting are the two basic divisions of the contemporary casting process. It is further broken down by the pouring technique, such as gravity, vacuum, or low pressure, as well as the mould material, such as sand or metal.

2. Forging: The metal is shaped utilising localised compressive stresses during the forging manufacturing process. A hammer, frequently a power hammer, or a die is used to strike the target. Forging is frequently categorised into three categories namely, cold forging, warm forging, and hot forging. The metal is heated for the later two, typically in a forge. Weights of forged components can range from a few grams to hundreds of metric tonnes. Since ancient times, smiths have been forging items including kitchenware, metalwork, hand tools, edged weapons, cymbals, and jewellery. Since the Industrial Revolution, forged components have been utilised extensively in mechanisms and machines whenever a component needs to be highly durable; these forgings typically require additional processing to produce a completed part.

3. Rolling: In the metalworking business, rolling is a method of metal forging. The goal is to impart a desired mechanical feature, make thickness uniform and to reduce thickness by passing a metal stock between one or more pairs of rolls. The concept is analogous to rolling out dough. The type of rolling depends on the rolled metal's temperature. The process of heating a metal to a temperature above its recrystallization temperature is known as hot rolling. When the metal is warmer than its recrystallization temperature, cold rolling is the technique employed. In terms of tonnage, hot rolling is the most popular manufacturing method. Roll supports hold pairs of rolls in rolling mills, which may quickly process metal, typically steel, into products like rails, bar stock, and structural steel (channel stock, angle stick and I-beams). The majority of steel mills convert casting materials that are semi-finished into finished commodities in their rolling mill divisions. Among the several rolling procedures are controlled rolling, profile rolling, roll shaping and roll bening.

4. Extrusion: By forcing material through a die with the desired cross-section, the extrusion process produces objects with set cross-sectional profiles. Its ability to produce extremely intricate cross-sections and its ability to deal with brittle materials because the material only experiences compressive and shear stresses are two of its key benefits over other production procedures. Additionally, it produces exceptional surface finishes and allows for a great deal of form freedom during the design phase. A comparable procedure is drawing, which involves pulling the material through the die utilising the material's tensile strength. It can only be used for simpler shapes since it restricts the amount of change that can be made in a single step; numerous steps are typically required. Wire, bars, and tubes are typically produced through drawing.

Extrusion can be continuous or semi-continuous, theoretically yielding endless lengths of material (producing many pieces). Either hot or cold materials can be used. Metals, polymers, ceramics, concrete, modelling clay, and edibles are among the items that are frequently extruded. “Extrudates” are the broad term for the products of extrusion. Hollow cavities inside extruded material, often known as "hole flanging," cannot be generated with a straightforward flat extrusion die because there would be no means to maintain the centre barrier of the die. Instead, starting with a shape profile that supports the central section, the die takes on the form of a block with depth. The hanging centre parts are supported from the back of the die as the internal die shape changes along its length into the final shape. Oftentimes, extrusion is associated with an increase in the physical strength of the material.

5. Machining: By carefully controlling the removal of material, metals are cut into the appropriate final shape and size during the machining process. The procedures that share this characteristic are collectively referred to as subtractive manufacturing, which makes use of machine tools, as opposed to additive manufacturing (such as 3D printing), which adds material gradually. Many metal goods are manufactured with machining, but it can also be used on materials including wood, plastic, ceramic, and composites. A machinist is a person who focuses on machining. The term "machine shop" refers to a space, edifice, or business where machining is carried out. Computer numerical control (CNC), which uses computers to control the movement and operation of mills, lathes, and other cutting equipment, is used for a large portion of modern machining. This improves efficiency because the CNC machine operates without a human operator, which lowers labour costs for machine shops.

6. Sintering: Sintering, also known as frittage, is the process of compacting and producing a solid mass of material under pressure or heat without completely melting it. Sintering is a step in the production of materials such as metals, ceramics, polymers, and others. As atoms in the materials diffuse across particle borders, they fuse the individual particles to form a single, solid piece. Sintering is frequently selected as the shaping method for materials with exceptionally high melting points, such as tungsten and molybdenum, because the sintering temperature does not have to reach the melting point of the material. Powder metallurgy is the study of sintering in metallurgy processes that involve powder.

Ice cubes in a glass of water adhering to one another due to the temperature difference between the water and the ice is an example of sintering. The compacting of snowfall to produce a glacier or the creation of a hard snowball by packing loose snow together are two examples of pressure-driven sintering.

7. Fabrication: By means of procedures like cutting, bending, and assembly, metal structures are created in the process of fabrication. A fabrication shop often submits a bid for a task, typically based on engineering designs, and if the bid is accepted, constructs the product. Numerous value-added procedures, including welding, cutting, forming, and machining, are used in large fabrication facilities. Both manual labour and automated procedures are frequently utilised in production. Fabrication is a made item, and fab shops are businesses that specialise in this kind of labour. Although the final outputs of other popular metalworking operations, such as machining, metal stamping, forging, and casting, may be similar in form and purpose, they are not considered fabrication.

8. Cladding: Cladding is the joining of metals that are not compatible. This process of joining the metals is distinct from fusion welding or glueing. Extruding two metals via a die, pressing or rolling sheets together under high pressure, and other methods are frequently used to create cladding. The United States Mint makes coins out of various metals using cladding. This enables the use of a less expensive metal as a filler. By using a high power, multi-mode optical fibre laser, laser cladding is an additive manufacturing technique for metal coatings or exact piece repairs. In the process of coating a portion of a substrate or creating a part with a near-net shape, a powdered or wire feedstock material is melted and solidified using a laser (additive manufacturing technique).

9. 3D Printing: Additive manufacturing, also referred to as 3D printing, is the technique of creating a three-dimensional object from a CAD (Computer Aided Design) model or digital 3D model. It can be done using a variety of procedures in which the material is brought together, frequently layer by layer, and then computer-controlled deposition, joining, or solidification. At the time, 3D printing was regarded to be primarily beneficial for generating aesthetically beautiful or functional prototypes, therefore the term "rapid prototyping" was more appropriate. Because of advancements in 3D printing's accuracy, repeatability, and material diversity in 2019, the phrases 3D printing and additive manufacturing can be used interchangeably. Some 3D printing processes are now considered to be viable as industrial production technologies. One benefit of 3D printing is its ability to produce exceedingly complex geometries that would be impossible to make by hand, such as hollow components or parts with internal truss structures to reduce weight. FDM (Fused Deposition Modeling), which uses a continuous filament made of a thermoplastic material, is the most popular 3D printing method currently in use.

Practice Problems

Q 1. What is corrosion?

Solution: A refined metal undergoes natural corrosion, which changes it into a more stable oxide. By reacting chemically or electrochemically with their surroundings, materials (often metals) slowly deteriorate. The discipline of corrosion engineering is focused on managing and avoiding corrosion.

Q 2. What are some examples and uses of alloys?

Solution: The following are some common alloys and their uses.

• Iron and chromium-nickel are the main ingredients in stainless steel, which is mostly used to make cutlery, watches, and surgical tools.

• Coins are constructed with coin metal, which is composed of copper and nickel.

• Tin and lead are combined to make solder, which is used for soldering.

• Bell Metal, which is made of copper and tin, is employed both in the production of statues and the casting of bells.

• Duralumin, which is made of aluminium, copper, and manganese, is used to make wires, bars, ships, aeroplanes, and other things.

• Bronze, which is made of copper and zinc, is used to make sculptures, window frames, bearings, and bushings.

• Sterling silver, which is created from silver and copper, is used to create jewellery, kitchenware, art, medals, coins, and even medical equipment.

Q 3. Select the correct statement with respect to the extraction of metal? 

a. Gangue or matrix refers to the earthly and undesirable impurities associated with the ore.
b. Ore is a mineral from which metal can be extracted easily and profitably.
c. Steps involved in the extraction of  includes concentration of ore, reduction of concentrated ore into metal and refining of metal.
d. All of the above

Answer: D

1. Gangue or matrix refers to the earthly and undesirable impurities associated with the ore which is removed during the concentration of ore.

 2. Ore is a mineral from which metal can be extracted easily and profitably. 

 3. The steps involved in the extraction of  includes concentration of ore, reduction of concentrated ore into metal and refining of metal. 

Thus, the statements given in option A, B and C are correct.

So, option D is the correct answer. 

Q 4. Which of the following options is correct with respect to concentration of ores? 

 a. It is the process of removal of undesirable or unwanted impurities present in the ore. 
b. It is the process of conversion of large lumps of naturally occurring ore into smaller pieces. 
c. It refers to the extraction of metal from its metal oxide. 
d. It is the process in which the ore is heated below its melting point in a limited supply of air. 

Answer: A

Concentration of ore is defined as process of removal of undesirable or unwanted impurities present in the ore. Concentration of ore takes place after the conversion of large lumps of naturally occurring ore into smaller pieces by the crushing and grinding the ore. Once the ore is concentrated, the ore is converted into its oxide form by the process of either roasting or calcination depending on the type of ore present. Calcination is a process in in which the ore is heated below its melting point in a limited supply of air.

So, option A is the correct answer.

Frequently Asked Questions – FAQ

Q 1. What is the heat treatment of a metal?
Answer: Heat treatment is a technique used to modify the strength, ductility, toughness, hardness, and corrosion resistance of metals. Annealing, precipitation strengthening, quenching, and tempering are typical heat treatment procedures. For superior characteristics and more effective material processing, mechanical and thermal treatments are frequently combined to create what is known as thermo-mechanical treatments. High-alloy special steels, superalloys, and titanium alloys all go through these procedures.

Q 2. What is the difference between roasting and calcination?
Answer: Calcination is the method of heating the ore below its melting point in a limited supply of air. This method is used for oxide and carbonate ores. For example, when the concentrated ore of zinc carbonate is heated, it produces zinc oxide and carbon dioxide is released. 

ZnCO₃ZnO+CO₂

Roasting, on the other hand, is the process of heating the ore in an excess supply of air below its melting point. This method is applied to sulphide ores. For example, when the zinc sulphide ore is heated in the presence of oxygen, it is converted into zinc oxide and sulphur dioxide gas is produced. 

ZnS+O₂ZnO+SO₂

Q 3. What is hydrometallurgy?
Answer: The extraction of metals from ores using aqueous solutions is the subject of hydrometallurgy. Leaching, the initial stage of the hydrometallurgical process, entails dissolving the precious metals in an appropriate solvent or aqueous solution. After the extract is separated from the ore solids, it is frequently put through a number of purification and concentration procedures in order to recover the valuable metal, either in its metallic condition or as a chemical compound. Precipitation, distillation, adsorption, and solvent extraction are a few examples of this. Precipitation, cementation, or an electrometallurgical procedure may be used in the final recovery step.

There are occasions when hydrometallurgical procedures can be performed directly on the ore without any prior preparation. The ore must frequently undergo multiple stages of mineral processing as a pretreatment.

Q 4. What is the Ellingham diagram?
Answer: A graph illustrating the temperature dependence of a compound's stability is known as an Ellingham diagram. This study is typically used to gauge how easily metal oxides and sulphides can be reduced. Harold Ellingham created these diagrams for the first time in 1944. The Ellingham diagram is used in metallurgy to forecast the temperature at which a metal, its oxide, and oxygen are in equilibrium, and consequently, the reactions that a metal will have with sulphur, nitrogen, and other non-metals. The diagrams can be used to forecast the circumstances in which an ore will be converted into its metal. Reaction kinetics are disregarded in favour of the thermodynamic nature of the analysis. Therefore, processes that the Ellingham diagram predicts to be advantageous may nevertheless be delayed.

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