The production of metals involves the processing of ores to extract the metal they contain, and the mixture of metals, sometimes with other elements, to produce alloys. Metallurgy is distinguished from the craft of metalworking, although metalworking relies on metallurgy, as medicine relies on medical science, Metallurgy is subdivided into ferrous metallurgy and non-ferrous metallurgy or colored metallurgy. Ferrous metallurgy involves processes and alloys based on iron while non-ferrous metallurgy involves processes, the production of ferrous metals accounts for 95 percent of world metal production. The roots of metallurgy derive from Ancient Greek, μεταλλουργός, metallourgós, worker in metal, from μέταλλον, métallon, metal + ἔργον, érgon, in the late 19th century it was extended to the more general scientific study of metals and related processes. In English, the pronunciation is the more common one in the UK. The /ˈmetələrdʒi/ pronunciation is the common one in the USA. The earliest recorded metal employed by humans appears to be gold, small amounts of natural gold have been found in Spanish caves used during the late Paleolithic period, c.40,000 BC.
Silver, copper and meteoric iron can be found in native form, egyptian weapons made from meteoric iron in about 3000 BC were highly prized as daggers from heaven. Certain metals, notably tin and copper, can be recovered from their ores by simply heating the rocks in a fire or blast furnace, a process known as smelting. The first evidence of this extractive metallurgy dates from the 5th and 6th millennia BC and was found in the sites of Majdanpek and Plocnik. To date, the earliest evidence of copper smelting is found at the Belovode site, other signs of early metals are found from the third millennium BC in places like Palmela, Los Millares, and Stonehenge. However, the ultimate beginnings cannot be ascertained and new discoveries are both continuous and ongoing. These first metals were single ones or as found, about 3500 BC, it was discovered that by combining copper and tin, a superior metal could be made, an alloy called bronze, representing a major technological shift known as the Bronze Age.
The extraction of iron from its ore into a metal is much more difficult than for copper or tin. The process appears to have been invented by the Hittites in about 1200 BC, the secret of extracting and working iron was a key factor in the success of the Philistines. Historical developments in ferrous metallurgy can be found in a variety of past cultures. A 16th century book by Georg Agricola called De re metallica describes the highly developed and complex processes of mining metal ores, metal extraction, Agricola has been described as the father of metallurgy. Extractive metallurgy is the practice of removing valuable metals from an ore, in order to convert a metal oxide or sulphide to a purer metal, the ore must be reduced physically, chemically, or electrolytically
Bainite is a plate-like microstructure that forms in steels at temperatures of 250–550 °C. First described by E. S. Davenport and Edgar Bain and this critical temperature is 1000K in plain carbon steels. Davenport and Bain originally described the microstructure as being similar in appearance to tempered martensite, a fine non-lamellar structure, bainite commonly consists of cementite and dislocation-rich ferrite. The high concentration of dislocations in the present in bainite makes this ferrite harder than it normally would be. The temperature range for transformation of austenite to bainite is between those for pearlite and martensite, when formed during continuous cooling, the cooling rate to form bainite is more rapid than that required to form pearlite, but less rapid than is required to form martensite. Most alloying elements will lower the temperature required for the rate of formation of bainite. The microstructures of martensite and bainite at first seem quite similar and this is a consequence of the two microstructures sharing many aspects of their transformation mechanisms.
However, morphological differences do exist that require a TEM to see, under a light microscope, the microstructure of bainite appears darker than martensite due to its low reflectivity. Bainite is an intermediate of pearlite and martensite in terms of hardness and Davenport noted the existence of two distinct forms, upper-range bainite which formed at higher temperatures and lower-range bainite which formed near the martensite start temperature. At 900 °C a typical low-carbon steel is composed entirely of austenite, in addition to the thermodynamic considerations indicated by the phase diagram, the phase transformations in steel are heavily influenced by the chemical kinetics. This leads to the complexity of steel microstructures which are influenced by the cooling rate. However, the transformation from austenite to pearlite is a time-dependent reconstructive reaction which requires the large movement of the iron and carbon atoms. As a consequence a rapidly cooled steel may reach a temperature where pearlite can no longer form despite the reaction being incomplete and the remaining austenite being thermodynamically unstable.
This non-equilibrium phase can only form at low temperatures, where the force for the reaction is sufficient to overcome the considerable lattice strain imposed by the transformation. The transformation is essentially time-independent with the phase fraction depending only the degree of cooling below the martensite start temperature. Further, it occurs without the diffusion of either substitutional or interstitial atoms, Bainite occupies a region between these two process in a temperature range where iron self-diffusion is limited but there is insufficient driving force to form martensite. A further distinction is made between so-called lower-bainite, which forms at temperatures closer to the martensite start temperature, and upper-bainite which forms at higher temperatures. This distinction arises from the rates of carbon at the temperature at which the bainite is forming
Electricity is the set of physical phenomena associated with the presence of electric charge. Although initially considered a separate to magnetism, since the development of Maxwells Equations both are recognized as part of a single phenomenon, electromagnetism. Various common phenomena are related to electricity, including lightning, static electricity, electric heating, electric discharges, in addition, electricity is at the heart of many modern technologies. The presence of a charge, which can be either positive or negative. On the other hand, the movement of charges, which is known as electric current. When a charge is placed in a location with non-zero electric field, the magnitude of this force is given by Coulombs Law. Thus, if that charge were to move, the field would be doing work on the electric charge. Electrical phenomena have been studied since antiquity, though progress in theoretical understanding remained slow until the seventeenth and eighteenth centuries. Even then, practical applications for electricity were few, and it would not be until the nineteenth century that engineers were able to put it to industrial and residential use.
The rapid expansion in electrical technology at this time transformed industry, electricitys extraordinary versatility means it can be put to an almost limitless set of applications which include transport, lighting and computation. Electrical power is now the backbone of modern industrial society, long before any knowledge of electricity existed, people were aware of shocks from electric fish. Ancient Egyptian texts dating from 2750 BCE referred to these fish as the Thunderer of the Nile, Electric fish were again reported millennia by ancient Greek and Arabic naturalists and physicians. Patients suffering from such as gout or headache were directed to touch electric fish in the hope that the powerful jolt might cure them. Ancient cultures around the Mediterranean knew that certain objects, such as rods of amber, Thales was incorrect in believing the attraction was due to a magnetic effect, but science would prove a link between magnetism and electricity. He coined the New Latin word electricus to refer to the property of attracting small objects after being rubbed and this association gave rise to the English words electric and electricity, which made their first appearance in print in Thomas Brownes Pseudodoxia Epidemica of 1646.
Further work was conducted by Otto von Guericke, Robert Boyle, Stephen Gray, in the 18th century, Benjamin Franklin conducted extensive research in electricity, selling his possessions to fund his work. In June 1752 he is reputed to have attached a key to the bottom of a dampened kite string. A succession of jumping from the key to the back of his hand showed that lightning was indeed electrical in nature
Semiconductors are crystalline or amorphous solids with distinct electrical characteristics. They are of high electrical resistance — higher than typical resistance materials and their resistance decreases as their temperature increases, which is behavior opposite to that of a metal. The behavior of charge carriers which include electrons and electron holes at these junctions is the basis of diodes and all modern electronics. Semiconductor devices can display a range of properties such as passing current more easily in one direction than the other, showing variable resistance. The modern understanding of the properties of a semiconductor relies on quantum physics to explain the movement of carriers in a crystal lattice. Doping greatly increases the number of carriers within the crystal. When a doped semiconductor contains mostly free holes it is called p-type, the semiconductor materials used in electronic devices are doped under precise conditions to control the concentration and regions of p- and n-type dopants. A single semiconductor crystal can have many p- and n-type regions, although some pure elements and many compounds display semiconductor properties, silicon and compounds of gallium are the most widely used in electronic devices.
Elements near the so-called metalloid staircase, where the metalloids are located on the table, are usually used as semiconductors. Some of the properties of materials were observed throughout the mid 19th. The first practical application of semiconductors in electronics was the 1904 development of the Cats-whisker detector, developments in quantum physics in turn allowed the development of the transistor in 1947 and the integrated circuit in 1958. There are several developed techniques that allow semiconducting materials to behave like conducting materials and these modifications have two outcomes, n-type and p-type. These refer to the excess or shortage of electrons, respectively, an unbalanced number of electrons would cause a current to flow through the material. Heterojunctions Heterojunctions occur when two differently doped semiconducting materials are joined together, for example, a configuration could consist of p-doped and n-doped germanium. This results in an exchange of electrons and holes between the differently doped semiconducting materials, the n-doped germanium would have an excess of electrons, and the p-doped germanium would have an excess of holes.
The transfer occurs until equilibrium is reached by a process called recombination, a product of this process is charged ions, which result in an electric field. Excited Electrons A difference in electric potential on a material would cause it to leave thermal equilibrium. This introduces electrons and holes to the system, which interact via a process called ambipolar diffusion, whenever thermal equilibrium is disturbed in a semiconducting material, the amount of holes and electrons changes
Brass is a metal alloy made of copper and zinc, the proportions of zinc and copper can be varied to create a range of brasses with varying properties. It is an alloy, atoms of the two constituents may replace each other within the same crystal structure. By comparison, bronze is principally an alloy of copper and tin, however and brass may include small proportions of a range of other elements including arsenic, aluminium and silicon. The term is applied to a variety of brasses. Modern practice in museums and archaeology increasingly avoids both terms for objects in favour of the all-embracing copper alloy. It is used in zippers, Brass is often used in situations in which it is important that sparks not be struck, such as in fittings and tools used near flammable or explosive materials. Brass has higher malleability than bronze or zinc, the relatively low melting point of brass and its flow characteristics make it a relatively easy material to cast. By varying the proportions of copper and zinc, the properties of the brass can be changed, allowing hard, the density of brass is 8.4 to 8.73 grams per cubic centimetre.
Today, almost 90% of all alloys are recycled. Because brass is not ferromagnetic, it can be separated from ferrous scrap by passing the scrap near a powerful magnet, Brass scrap is collected and transported to the foundry where it is melted and recast into billets. Billets are heated and extruded into the form and size. The general softness of brass means that it can often be machined without the use of cutting fluid, aluminium makes brass stronger and more corrosion-resistant. Aluminium causes a highly beneficial hard layer of oxide to be formed on the surface that is thin, transparent. Tin has an effect and finds its use especially in seawater applications. Combinations of iron, aluminium and manganese make brass wear and tear resistant, to enhance the machinability of brass, lead is often added in concentrations of around 2%. Since lead has a melting point than the other constituents of the brass. The pattern the globules form on the surface of the brass increases the available surface area which in turn affects the degree of leaching.
In addition, cutting operations can smear the lead globules over the surface and these effects can lead to significant lead leaching from brasses of comparatively low lead content
Mu-metal is a nickel–iron soft magnetic alloy with very high permeability, which is used for shielding sensitive electronic equipment against static or low-frequency magnetic fields. One such composition is approximately 77% nickel, 16% iron, 5% copper, the name came from the Greek letter mu which represents permeability in physics and engineering formulae. A number of different proprietary formulations of the alloy are sold under names such as MuMETAL, Mumetall. Mu-metal typically has relative permeability values of 80, 000–100,000 compared to several thousand for ordinary steel and it is a soft magnetic material, it has low magnetic anisotropy and magnetostriction, giving it a low coercivity so that it saturates at low magnetic fields. This gives it low hysteresis losses when used in AC magnetic circuits, mu-metal objects require heat treatment after they are in final form—annealing in a magnetic field in hydrogen atmosphere, which increases the magnetic permeability about 40 times. The annealing alters the materials crystal structure, aligning the grains and removing impurities, especially carbon.
The high permeability of mu-metal provides a low reluctance path for magnetic flux, magnetic shielding made with high-permeability alloys like mu-metal works not by blocking magnetic fields but by providing a path for the magnetic field lines around the shielded area. Thus, the best shape for shields is a closed container surrounding the shielded space, the effectiveness of mu-metal shielding decreases with the alloys permeability, which drops off at both low field strengths and, due to saturation, at high field strengths. Thus, mu-metal shields are made of several enclosures one inside the other. Because mu-metal saturates at low fields, sometimes the outer layer in such multilayer shields is made of ordinary steel. Its higher saturation value allows it to handle stronger magnetic fields, RF magnetic fields above about 100 kHz can be shielded by Faraday shields, ordinary conductive metal sheets or screens which are used to shield against electric fields. Superconducting materials can expel magnetic fields by the Meissner effect.
The bandwidth could be increased by adding inductance to compensate and this was first done by wrapping the conductors with a helical wrapping of metal tape or wire of high magnetic permeability, which confined the magnetic field. Telcon invented mu-metal to compete with permalloy, the first high-permeability alloy used for cable compensation, mu-metal was developed by adding copper to permalloy to improve ductility. 50 miles of fine wire were needed for each mile of cable. The first year of production Telcon was making 30 tons per week, in the 1930s this use for mu-metal declined, but by World War II many other uses were found in the electronics industry, as well as the fuzes inside magnetic mines. Mu-metal is used to shield equipment from magnetic fields, for example, Electric power transformers, which are built with mu-metal shells to prevent them from affecting nearby circuitry. Hard disks, which have mu-metal backings to the found in the drive to keep the magnetic field away from the disk
In materials science, quenching is the rapid cooling of a workpiece to obtain certain material properties. A type of heat treating, quenching prevents undesired low-temperature processes, such as phase transformations, in steel alloyed with metals such as nickel and manganese, the eutectoid temperature becomes much lower, but the kinetic barriers to phase transformation remain the same. This allows quenching to start at a temperature, making the process much easier. High speed steel has added tungsten, which serves to raise kinetic barriers, even cooling such alloys slowly in air has most of the desired effects of quenching. Extremely rapid cooling can prevent the formation of all crystal structure, if the percentage of carbon is less than 0.4 percent, quenching is not possible. Quench hardening is a process in which steel and cast iron alloys are strengthened and hardened. These metals consist of metals and alloys. This is done by heating the material to a certain temperature and this produces a harder material by either surface hardening or through-hardening varying on the rate at which the material is cooled.
The material is often tempered to reduce the brittleness that may increase from the quench hardening process. Items that may be quenched include gears and wear blocks, pearlite is not an ideal material for many common applications of steel alloys, as it is quite soft. Steels with this Martensitic structure are used in applications when the workpiece must be highly resistant to deformation. The process of quenching is a progression, beginning with heating the sample, most materials are heated to between 815 and 900 °C, with careful attention paid to keeping temperatures throughout the workpiece uniform. Minimizing uneven heating and overheating is key to imparting desired material properties, the second step in the quenching process is soaking. Workpieces can be soaked in air, a bath, or a vacuum. The recommended time allocation in salt or lead baths is up to 6 minutes, soaking times can range a little higher within a vacuum. As in the step, it is important that the temperature throughout the sample remains as uniform as possible during soaking.
Once the workpiece has finished soaking, it moves on to the cooling step, during this step, the part is submerged into some kind of quenching fluid, different quenching fluids can have a significant effect on the final characteristics of a quenched part. Water is one of the most efficient quenching media where maximum hardness is desired, when hardness can be sacrificed, mineral oils are often used
Heat treating is a group of industrial and metalworking processes used to alter the physical, and sometimes chemical, properties of a material. The most common application is metallurgical, Heat treatments are used in the manufacture of many other materials, such as glass. Heat treatment involves the use of heating or chilling, normally to extreme temperatures, Heat treatment techniques include annealing, case hardening, precipitation strengthening, tempering and quenching. Metallic materials consist of a microstructure of small crystals called grains or crystallites, the nature of the grains is one of the most effective factors that can determine the overall mechanical behavior of the metal. Heat treatment provides an efficient way to manipulate the properties of the metal by controlling the rate of diffusion, Heat treating is often used to alter the mechanical properties of a metallic alloy, manipulating properties such as the hardness, toughness and elasticity. The crystal structure consists of atoms that are grouped in a specific arrangement.
In most elements, this order will rearrange itself, depending on conditions like temperature and pressure and this rearrangement, called allotropy or polymorphism, may occur several times, at many different temperatures for a particular metal. When in the state, the process of diffusion causes the atoms of the dissolved element to spread out. If the alloy is cooled to a state, the atoms of the dissolved constituents may migrate out of the solution. This type of diffusion, called precipitation, leads to nucleation and this forms a microstructure generally consisting of two or more distinct phases. Steel that has been cooled slowly, for instance, forms a structure composed of alternating layers of ferrite and cementite. After heating the steel to the phase and quenching it in water. This is due to the fact that the steel will change from the phase to the martensite phase after quenching. It should be noted that some pearlite or ferrite may be present if the quench did not rapidly cool off all the steel, unlike iron-based alloys, most heat treatable alloys do not experience a ferrite transformation.
In these alloys, the nucleation at the grain-boundaries often reinforces the structure of the crystal matrix, typically a slow process, depending on temperature, this is often referred to as age hardening. Many metals and non-metals exhibit a transformation when cooled quickly. When a metal is cooled quickly, the insoluble atoms may not be able to migrate out of the solution in time. This is called a diffusionless transformation, when the crystal matrix changes to its low temperature arrangement, the atoms of the solute become trapped within the lattice
Grain growth is the increase in size of grains in a material at high temperature. This occurs when recovery and recrystallisation are complete and further reduction in the energy can only be achieved by reducing the total area of grain boundary. The term is used in metallurgy but is used in reference to ceramics. Most materials exhibit the Hall–Petch effect at room-temperature and so display a higher yield stress when the size is reduced. At high temperatures the opposite is true since the open, disordered nature of grain boundaries means that vacancies can diffuse more rapidly down boundaries leading to more rapid Coble creep, depending on the second phase in question this may have positive or negative effects. Grain growth has long been studied primarily by the examination of sectioned and etched samples under the optical microscope, the boundary between one grain and its neighbour is a defect in the crystal structure and so it is associated with a certain amount of energy. As a result, there is a driving force for the total area of boundary to be reduced.
If the grain increases, accompanied by a reduction in the actual number of grains per volume. For example, shrinkage velocity of a spherical grain embedded inside another grain is v = M σ2 R and this driving pressure is very similar in nature to the Laplace pressure that occurs in foams. Ideal grain growth is a case of normal grain growth where boundary motion is driven only by local curvature of the grain boundary. It results in the reduction of the amount of grain boundary surface area i. e. total energy of the system. Additional contributions to the force by e. g. elastic strains or temperature gradients are neglected. Theoretically, the energy for boundary mobility should equal that for self-diffusion. In general these equations are found to hold for ultra-high purity materials, in common with recovery and recrystallisation, growth phenomena can be separated into continuous and discontinuous mechanisms. In the former the microstructure evolves from state A to B in a uniform manner, in the latter, the changes occur heterogeneously and specific transformed and untransformed regions may be identified.
If there are additional factors preventing boundary movement, such as Zener pinning by particles and this is an important industrial mechanism in preventing the softening of materials at high temperature. Certain materials especially refractories which are processed at high temperatures end up with large grain size. To mitigate this problem in a common sintering procedure, a variety of dopants are often used to inhibit grain growth, F. J. Humphreys and M. Hatherly, Recrystallization and related annealing phenomena, Elsevier
The interdisciplinary field of materials science, commonly termed materials science and engineering, involves the discovery and design of new materials, with an emphasis on solids. Materials science still incorporates elements of physics and engineering, as such, the field was long considered by academic institutions as a sub-field of these related fields. Materials science is a syncretic discipline hybridizing metallurgy, solid-state physics and it is the first example of a new academic discipline emerging by fusion rather than fission. Many of the most pressing scientific problems humans currently face are due to the limits of the materials that are available, breakthroughs in materials science are likely to affect the future of technology significantly. Materials scientists emphasize understanding how the history of a material influences its structure, the understanding of processing-structure-properties relationships is called the § materials paradigm. This paradigm is used to advance understanding in a variety of areas, including nanotechnology, biomaterials.
Such investigations are key to understanding, for example, the causes of various accidents and incidents. The material of choice of a given era is often a defining point, phrases such as Stone Age, Bronze Age, Iron Age, and Steel Age are great examples. Originally deriving from the manufacture of ceramics and its putative derivative metallurgy, materials science is one of the oldest forms of engineering, modern materials science evolved directly from metallurgy, which itself evolved from mining and ceramics and the use of fire. Materials science has driven, and been driven by, the development of technologies such as rubbers, semiconductors. Before the 1960s, many materials science departments were named metallurgy departments, reflecting the 19th, a material is defined as a substance that is intended to be used for certain applications. There are a myriad of materials around us—they can be found in anything from buildings to spacecraft, Materials can generally be divided into two classes and non-crystalline.
The traditional examples of materials are metals, ceramics and advanced materials that are being developed include nanomaterials and biomaterials, etc. The basis of science involves studying the structure of materials. Once a materials scientist knows about this structure-property correlation, they can go on to study the relative performance of a material in a given application. The major determinants of the structure of a material and thus of its properties are its constituent chemical elements and these characteristics, taken together and related through the laws of thermodynamics and kinetics, govern a materials microstructure, and thus its properties. As mentioned above, structure is one of the most important components of the field of materials science, Materials science examines the structure of materials from the atomic scale, all the way up to the macro scale. Characterization is the way materials scientists examine the structure of a material, structure is studied at various levels, as detailed below
For the use of this term in mathematics and physics, see phase space. Common components of a phase diagram are lines of equilibrium or phase boundaries, phase transitions occur along lines of equilibrium. Triple points are points on phase diagrams where lines of equilibrium intersect, triple points mark conditions at which three different phases can coexist. For example, the phase diagram has a triple point corresponding to the single temperature and pressure at which solid, liquid. The solidus is the temperature below which the substance is stable in the solid state, the liquidus is the temperature above which the substance is stable in a liquid state. There may be a gap between the solidus and liquidus, within the gap, the substance consists of a mixture of crystals, the simplest phase diagrams are pressure–temperature diagrams of a single simple substance, such as water. The axes correspond to the pressure and temperature, the phase diagram shows, in pressure–temperature space, the lines of equilibrium or phase boundaries between the three phases of solid and gas.
The fusion curves for water and Antimony are with negative slopes, the curves on the phase diagram show the points where the free energy becomes non-analytic, their derivatives with respect to the coordinates change discontinuously. For example, the capacity of a container filled with ice will change abruptly as the container is heated past the melting point. The open spaces, where the energy is analytic, correspond to single phase regions. Single phase regions are separated by lines of non-analytical behavior, where phase transitions occur, in the diagram on the left, the phase boundary between liquid and gas does not continue indefinitely. Instead, it terminates at a point on the diagram called the critical point. This reflects the fact that, at high temperatures and pressures. In water, the critical point occurs at around Tc =647.096 K, pc =22.064 MPa, the existence of the liquid–gas critical point reveals a slight ambiguity in labelling the single phase regions. Thus, the liquid and gaseous phases can blend continuously into each other, the solid–liquid phase boundary can only end in a critical point if the solid and liquid phases have the same symmetry group.
Thus, the substance requires a temperature for its molecules to have enough energy to break out of the fixed pattern of the solid phase. A similar concept applies to liquid–gas phase changes, because of its particular properties, is one of the several exceptions to the rule. In addition to temperature and pressure, other properties may be graphed in phase diagrams