1.
Steel
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Steel is an alloy of iron and other elements, primarily carbon, that is widely used in construction and other applications because of its high tensile strength and low cost. Steels base metal is iron, which is able to take on two forms, body centered cubic and face centered cubic, depending on its temperature. It is the interaction of those allotropes with the elements, primarily carbon. In the body-centred cubic arrangement, there is an atom in the centre of each cube. Carbon, other elements, and inclusions within iron act as hardening agents that prevent the movement of dislocations that otherwise occur in the lattices of iron atoms. The carbon in steel alloys may contribute up to 2. 1% of its weight. Steels strength compared to pure iron is possible at the expense of irons ductility. With the invention of the Bessemer process in the mid-19th century and this was followed by Siemens-Martin process and then Gilchrist-Thomas process that refined the quality of steel. With their introductions, mild steel replaced wrought iron, further refinements in the process, such as basic oxygen steelmaking, largely replaced earlier methods by further lowering the cost of production and increasing the quality of the product. Today, steel is one of the most common materials in the world and it is a major component in buildings, infrastructure, tools, ships, automobiles, machines, appliances, and weapons. Modern steel is generally identified by various grades defined by assorted standards organizations, the noun steel originates from the Proto-Germanic adjective stakhlijan, which is related to stakhla. The carbon content of steel is between 0. 002% and 2. 1% by weight for plain iron–carbon alloys and these values vary depending on alloying elements such as manganese, chromium, nickel, iron, tungsten, carbon and so on. Basically, steel is an alloy that does not undergo eutectic reaction. In contrast, cast iron does undergo eutectic reaction, too little carbon content leaves iron quite soft, ductile, and weak. Carbon contents higher than those of steel make an alloy, commonly called pig iron, while iron alloyed with carbon is called carbon steel, alloy steel is steel to which other alloying elements have been intentionally added to modify the characteristics of steel. Common alloying elements include, manganese, nickel, chromium, molybdenum, boron, titanium, vanadium, tungsten, cobalt, and niobium. Additional elements are important in steel, phosphorus, sulfur, silicon, and traces of oxygen, nitrogen, and copper. Alloys with a higher than 2. 1% carbon content, depending on other element content, cast iron is not malleable even when hot, but it can be formed by casting as it has a lower melting point than steel and good castability properties
2.
Allotropes of iron
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Iron represents perhaps the best-known example for allotropy in a metal. At atmospheric pressure, there are three forms of iron, alpha iron a. k. a. ferrite, gamma iron a. k. a. austenite. At very high pressure, a form exists, called epsilon iron hexaferrum. Some controversial experimental evidence exists for another form that is stable at very high pressures and temperatures. The phases of iron at atmospheric pressure are important because of the differences in solubility of carbon, the high-pressure phases of iron are important as models for the solid parts of planetary cores. The inner core of the Earth is generally assumed to consist essentially of a crystalline iron-nickel alloy with ε structure, the outer core surrounding the solid inner core is believed to be composed of liquid iron mixed with nickel and trace amounts of lighter elements. As molten iron cools down, it solidifies at 1,538 °C into its δ allotrope, δ-iron can dissolve as much as 0. 09% of carbon by mass at 1,493 °C. As the iron cools further to 1,394 °C its crystal structure changes to a face centered cubic crystalline structure, in this form it is called gamma iron or Austenite. γ-iron can dissolve considerably more carbon and this γ form of carbon saturation is exhibited in stainless steel. Beta ferrite and beta iron are obsolete terms for the form of ferrite. The primary phase of low-carbon or mild steel and most cast irons at room temperature is ferromagnetic ferrite, the A2 forms the low-temperature boundary of the beta iron field in the phase diagram in Figure 1. For this reason, the phase is not usually considered a distinct phase. At 912 °C the crystal structure again becomes BCC as α-iron is formed, the substance assumes a paramagnetic property. α-iron can dissolve only a small concentration of carbon, at 770 °C, the Curie point, the iron is a fairly soft metal and becomes ferromagnetic. As the iron passes through the Curie temperature there is no change in crystalline structure and this is the stable form of iron at room temperature. Antiferromagnetism in alloys of epsilon-Fe with Mn, Os and Ru has been observed. An alternate stable form, if it exists, may appear at pressures of at least 50 GPa and temperatures of at least 1,500 K, as of December 2011, recent and ongoing experiments are being conducted on high-pressure and Superdense carbon allotropes. Superdense carbon allotropes Allotropy Austenite Curie point Eutectic system Ferrite Tempering
3.
Austenite
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Austenite, also known as gamma-phase iron, is a metallic, non-magnetic allotrope of iron or a solid solution of iron, with an alloying element. In plain-carbon steel, austenite exists above the eutectoid temperature of 1000 K. The austenite allotrope exists at room temperature in stainless steel and it is named after Sir William Chandler Roberts-Austen. From 912 to 1,394 °C alpha iron undergoes a transition from body-centred cubic to the face-centred cubic configuration of gamma iron. This is similarly soft and ductile but can dissolve considerably more carbon and this gamma form of iron is exhibited by the most commonly used type of stainless steel for making hospital and food-service equipment. Austenitization means to heat the iron, iron-based metal, or steel to a temperature at which it changes crystal structure from ferrite to austenite, the more open structure of the austenite is then able to absorb carbon from the iron-carbides in carbon steel. An incomplete initial austenitization can leave undissolved carbides in the matrix, for some irons, iron-based metals, and steels, the presence of carbides may occur during the austenitization step. The term commonly used for this is two-phase austenitization, austempering is a hardening process that is used on iron-based metals to promote better mechanical properties. The metal is heated into the region of the iron-cementite phase diagram. The metal is annealed in this temperature range until the austenite turns to bainite or ausferrite, by changing the temperature for austenitization, the austempering process can yield different and desired microstructures. A higher austenitization temperature can produce a carbon content in austenite. The carbon content in austenite as a function of austempering time has been established, as austenite cools, the carbon diffuses out of the austenite and forms carbon rich iron-carbide and leaves behind carbon poor ferrite. Depending on alloy composition, a layering of ferrite and cementite, called pearlite and this is a very important case, as the carbon does not have time to diffuse due to the high cooling rate, which results in carbon being trapped and as a result forms hard martensite. Too high a rate of thick sections may cause the outer layers of the heat treated part to transform from austenite while the inner portion is still in its less dense austenite form. The difference in rates of the inner and outer portion of the part may cause cracks to develop in the outer portion. By alloying the steel with tungsten, the diffusion is slowed. Such a material is said to have its hardenability increased, tempering following quenching will transform some of the brittle martensite into tempered martensite. Heating white cast iron above 727 °C causes the formation of austenite in crystals of primary cementite and this austenisation of white iron occurs in primary cementite at the interphase boundary with ferrite
4.
Cementite
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Cementite, also known as iron carbide, is an intermetallic compound of iron and carbon, more precisely an intermediate transition metal carbide with the formula Fe3C. By weight, it is 6. 67% carbon and 93. 3% iron and it has an orthorhombic crystal structure. It is a hard, brittle material, normally classified as a ceramic in its pure form, therefore, in carbon steels and cast irons that are slowly cooled, a portion of the carbon is in the form of cementite. Cementite forms directly from the melt in the case of white cast iron, in carbon steel, cementite precipitates from austenite as austenite transforms to ferrite on slow cooling, or from martensite during tempering. An intimate mixture with ferrite, the product of austenite. Cementite changes from ferromagnetic to paramagnetic at its Curie temperature of approximately 480 K, a natural iron carbide occurs in iron meteorites and is called cohenite after the German mineralogist Emil Cohen, who first described it. The figure shows the behaviour at room temperature. There are other forms of iron carbides that have been identified in tempered steel. These include Epsilon carbide, hexagonal close-packed Fe2-3C, precipitates in plain-carbon steels of carbon content >0. 2%, non-stoichiometric ε-carbide dissolves above ~200 °C, where Hägg carbides and cementite begin to form. Hägg carbide, monoclinic Fe5C2, precipitates in hardened tool steels tempered at 200-300 °C, characterization of different iron carbides is not at all a trivial task, and often X-ray diffraction is complemented by Mössbauer spectroscopy. Foundations of Materials Science and Engineering, microstructure of Steels and Cast Irons. Ester Esna du Plessis The Crystal Structures of Iron Carbides, Ph. D, formation of Fe7C3 and Fe5C2 type metastable carbides during the crystallization of an amorphous Fe75C25 alloy
5.
Graphite
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Graphite, archaically referred to as plumbago, is a crystalline form of carbon, a semimetal, a native element mineral, and one of the allotropes of carbon. Graphite is the most stable form of carbon under standard conditions, therefore, it is used in thermochemistry as the standard state for defining the heat of formation of carbon compounds. Highly ordered pyrolytic graphite or more correctly highly oriented pyrolytic graphite refers to graphite with a spread between the graphite sheets of less than 1°. The name graphite fiber is sometimes used to refer to carbon fibers or carbon fiber-reinforced polymer. Graphite occurs in rocks as a result of the reduction of sedimentary carbon compounds during metamorphism. It also occurs in rocks and in meteorites. Minerals associated with graphite include quartz, calcite, micas and tourmaline, in meteorites it occurs with troilite and silicate minerals. Small graphitic crystals in meteoritic iron are called cliftonite, Graphite is not mined in the United States, but U. S. production of synthetic graphite in 2010 was 134 kt valued at $1.07 billion. Graphite has a layered, planar structure, the individual layers are called graphene. In each layer, the atoms are arranged in a honeycomb lattice with separation of 0.142 nm. Atoms in the plane are bonded covalently, with three of the four potential bonding sites satisfied. The fourth electron is free to migrate in the plane, making graphite electrically conductive, however, it does not conduct in a direction at right angles to the plane. Bonding between layers is via weak van der Waals bonds, which allows layers of graphite to be easily separated, the two known forms of graphite, alpha and beta, have very similar physical properties, except for that the graphene layers stack slightly differently. The alpha graphite may be flat or buckled. The alpha form can be converted to the form through mechanical treatment. The acoustic and thermal properties of graphite are highly anisotropic, since phonons propagate quickly along the tightly-bound planes, graphites high thermal stability and electrical and thermal conductivity facilitate its widespread use as electrodes and refractories in high temperature material processing applications. However, in oxygen containing atmospheres graphite readily oxidizes to form CO2 at temperatures of 700 °C, Graphite is an electric conductor, consequently, useful in such applications as arc lamp electrodes. It can conduct electricity due to the vast electron delocalization within the carbon layers and these valence electrons are free to move, so are able to conduct electricity
6.
Martensite
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It includes a class of hard minerals occurring as lath- or plate-shaped crystal grains. When viewed in section, the lenticular crystal grains may be incorrectly described as acicular. Austenite is γ-Fe, a solution of iron and alloying elements. As a result of the quenching, the cubic austenite transforms to a highly strained body-centered tetragonal form called martensite that is supersaturated with carbon. The shear deformations that result produce a number of dislocations. The highest hardness of a steel is 400 Brinell whereas martensite can achieve 700 Brinell. The martensitic reaction begins during cooling when the austenite reaches the start temperature. For a eutectoid steel, between 6 and 10% of austenite, called retained austenite, will remain. The percentage of retained austenite increases from insignificant for less than 0. 6% C steel, to 13% retained austenite at 0. 95% C, a very rapid quench is essential to create martensite. For steel 0-0. 6% carbon the martensite has the appearance of lath, for steel greater than 1% carbon it will form a plate like structure called plate martensite. Between those two percentages, the appearance of the grains is a mix of the two. The strength of the martensite is reduced as the amount of retained austenite grows, the process produces dislocation densities up to 1013/cm2. The great number of dislocations, combined with precipitates that originate and pin the dislocations in place, thus, martensite can be thermally induced or stress induced. One of the differences between the two phases is that martensite has a tetragonal crystal structure, whereas austenite has a face-centered cubic structure. Martensite has a lower density than austenite, so that the martensitic transformation results in a change of volume. Of considerably greater importance than the change is the shear strain which has a magnitude of about 0.26. Martensite is not shown in the phase diagram of the iron-carbon system because it is not an equilibrium phase. Equilibrium phases form by slow cooling rates that allow sufficient time for diffusion, since chemical processes accelerate at higher temperature, martensite is easily destroyed by the application of heat
7.
Microstructure
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Microstructure is the small scale structure of a material, defined as the structure of a prepared surface of material as revealed by a microscope above 25× magnification. The microstructure of a material can strongly influence physical properties such as strength, toughness, ductility, hardness, corrosion resistance and these properties in turn govern the application of these materials in industrial practice. Microstructure at scales smaller than can be viewed with optical microscopes is often called nanostructure, the nanostructure of biological specimens is referred to as ultrastructure. A microstructure’s influence on the mechanical and physical properties of a material is governed by the different defects present or absent of the structure. These defects can take many forms but the ones are the pores. Even if those pores play an important role in the definition of the characteristics of a material. In fact, for materials, different phases can exist at the same time. These phases have different properties and if managed correctly, can prevent the fracture of the material, the concept of microstructure is observable in macrostructural features in commonplace objects. Galvanized steel, such as the casing of a lamp post or road divider, each polygon is a single crystal of zinc adhering to the surface of the steel beneath. Zinc and lead are two metals which form large crystals visible to the naked eye. The atoms in each grain are organized one of seven 3d stacking arrangements or crystal lattices. The direction of alignment of the matrices differ between adjacent crystals, leading to variance in the reflectivity of each presented face of the grains on the galvanized surface. The average grain size can be controlled by processing conditions and composition and this is to increase the strength of the material. To quantify microstructural features, both morphological and material property must be characterized, image processing is a robust technique for determination of morphological features such as volume fraction, inclusion morphology, void and crystal orientations. To acquire micrographs, optical as well as electron microscopy are commonly used, to determine material property, Nanoindentation is a robust technique for determination of properties in micron and submicron level for which conventional testing are not feasible. Conventional mechanical testing such as tensile testing or dynamic analysis can only return macroscopic properties without any indication of microstructural properties. However, nanoindentation can be used for determination of local properties of homogeneous as well as heterogeneous materials. When a polished flat sample reveals traces of its microstructure, it is normal to capture the image using macrophotography
8.
Carbon steel
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The term carbon steel may also be used in reference to steel which is not stainless steel, in this use carbon steel may include alloy steels. As the carbon percentage content rises, steel has the ability to become harder and stronger through heat treating, however, regardless of the heat treatment, a higher carbon content reduces weldability. In carbon steels, the carbon content lowers the melting point. Mild steel, also known as steel and Low carbon steel. It is now the most common form of steel because its price is relatively low while it provides material properties that are acceptable for many applications, mild steel contains approximately 0. 05–0. 25% carbon making it malleable and ductile. Mild steel has a low tensile strength, but it is cheap and easy to form. It is often used large quantities of steel are needed. The density of steel is approximately 7.85 g/cm3. Low-carbon steels suffer from yield-point runout where the material has two yield points, the first yield point is higher than the second and the yield drops dramatically after the upper yield point. If a low-carbon steel is only stressed to some point between the upper and lower yield point then the surface develop Lüder bands, low-carbon steels contain less carbon than other steels and are easier to cold-form, making them easier to handle. Carbon steels which can successfully undergo heat-treatment have a content in the range of 0. 30–1. 70% by weight. Trace impurities of other elements can have a significant effect on the quality of the resulting steel. Trace amounts of sulfur in particular make the steel red-short, that is, brittle, low-alloy carbon steel, such as A36 grade, contains about 0. 05% sulfur and melts around 1, 426–1,538 °C. Manganese is often added to improve the hardenability of low-carbon steels and these additions turn the material into a low-alloy steel by some definitions, but AISIs definition of carbon steel allows up to 1. 65% manganese by weight. Carbon steel is broken down into four classes based on content,0.05 to 0. 25% carbon content. Balances ductility and strength and has good resistance, used for large parts, forging. Very strong, used for springs, swords, and high-strength wires, steels that can be tempered to great hardness. Used for special purposes like knives, axles or punches, most steels with more than 2. 5% carbon content are made using powder metallurgy
9.
Pearlite
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Pearlite is a two-phased, lamellar structure composed of alternating layers of ferrite and cementite that occurs in some steels and cast irons. During slow cooling of an alloy, pearlite forms by a eutectoid reaction as austenite cools below 727 °C. Pearlite is a microstructure occurring in many grades of steels. The eutectoid composition of austenite is approximately 0, likewise steels with higher carbon content will form cementite before reaching the eutectoid point. The proportion of ferrite and cementite forming above the point can be calculated from the iron/iron—carbide equilibrium phase diagram using the lever rule. Steels with pearlitic or near-pearlitic microstructure can be drawn into thin wires, such wires, often bundled into ropes, are commercially used as piano wires, ropes for suspension bridges, and as steel cord for tire reinforcement. High degrees of wire drawing leads to pearlitic wires with yield strengths of several gigapascals and it makes pearlite one of the strongest structural bulk materials on earth. Some hypereutectoid pearlitic steel wires, when cold wire drawn to true strains above 5, although pearlite is used in many engineering applications, the origin of its extreme strength is not well understood. Bainite is a structure with lamellae much smaller than the wavelength of visible light. It is prepared by rapid cooling. Unlike pearlite, whose formation involves the diffusion of all atoms, eutectoid steel can in principle be transformed completely into pearlite, hypoeutectoid steels can also be completely pearlitic if transformed at a temperature below the normal eutectoid. Pearlite can be hard and strong but is not particularly tough and it can be wear resistant because of a strong lamellar network of ferrite and cementite. Examples of applications include cutting tools, high strength wires, knives, chisels, comprehensive information on pearlite Introduction to Physical metallurgy by Sidney H. Avner, second edition, McGraw hill publications. Steels, Processing, Structure, and Performance, Chapter 15 High-Carbon Steels, Fully Pearlitic Microstructures and Applications by George Krauss,2005 Edition, ASM International
10.
Bainite
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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, Bain and Davenport also 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
11.
Ledeburite
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In iron and steel metallurgy, ledeburite is a mixture of 4. 3% carbon in iron and is a eutectic mixture of austenite and cementite. It is named after the metallurgist Karl Heinrich Adolf Ledebur and he was the first professor of metallurgy at the Bergakademie Freiberg. Ledeburite arises when the content is between 2. 06% and 6. 67%. The eutectic mixture of austenite and cementite is 4. 3% carbon, Fe3C, 2Fe, ledeburite-II is composed of cementite-I with recrystallized secondary cementite and of pearlite. The pearlite results from the decay of the austenite that comes from the ledeburite-I at 723 °C. During more rapid cooling, bainite can develop instead of pearlite, and with very rapid cooling martensite can develop
12.
Tempering (metallurgy)
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Tempering is a process of heat treating, which is used to increase the toughness of iron-based alloys. The exact temperature determines the amount of hardness removed, and depends on both the composition of the alloy and on the desired properties in the finished product. For instance, very hard tools are often tempered at low temperatures, tempering is a heat treatment technique applied to ferrous alloys, such as steel or cast iron, to achieve greater toughness by decreasing the hardness of the alloy. The reduction in hardness is usually accompanied by an increase in ductility, tempering is usually performed after quenching, which is rapid cooling of the metal to put it in its hardest state. Tempering is accomplished by controlled heating of the quenched work-piece to a temperature below its critical temperature. Heating above this temperature is avoided, so as not to destroy the very-hard, quenched microstructure, precise control of time and temperature during the tempering process is crucial to achieve the desired balance of physical properties. Low tempering temperatures may only relieve the stresses, decreasing brittleness while maintaining a majority of the hardness. Higher tempering temperatures tend to produce a reduction in the hardness, sacrificing some yield strength. In carbon steels, tempering alters the size and distribution of carbides in the martensite, tempering is also performed on normalized steels and cast irons, to increase ductility, machinability, and impact strength. Tempering is an ancient heat-treating technique, the oldest known example of tempered martensite is a pick axe which was found in Galilee, dating from around 1200 to 1100 BC. The process was used throughout the ancient world, from Asia to Europe, tempering was often confused with quenching and, often, the term was used to describe both techniques. I shall employ the word tempering in the sense as softening. In metallurgy, one may encounter many terms that have specific meanings within the field. Terms such as hardness, impact resistance, toughness, and strength can carry many different connotations, some of the terms encountered, and their specific definitions are, Strength, also called rigidity, this is resistance to permanent deformation and tearing. Strength, in metallurgy, is still a vague term, so is usually divided into yield strength, tensile strength, shear strength. Toughness, Resistance to fracture, as measured by the Charpy test, toughness often increases as strength decreases, because a material that bends is less likely to break. Hardness, Hardness is often used to strength or rigidity but, in metallurgy. In conventional metal alloys, there is a relation between indentation hardness and tensile strength, which eases the measurement of the latter
13.
Crucible steel
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Crucible steel is a term that applies to steel made by two different methods in the modern era, although it has been produced in varying locales throughout history. It is made by melting iron and other materials in a crucible, Crucible steel was produced in South and Central Asia during the medieval era. The homogeneous crystal structure of this cast steel improved its strength, only recently it has become apparent that places in Central Asia like Merv in Turkmenistan and Akhsiket in Uzbekistan were important centres of production of crucible steel. The Central Asian finds are all from excavations and date from the 8th to 12th centuries AD, while crucible steel is more attributed to the Middle East in early times, there have been swords discovered in Europe, particularly in Scandinavia. The swords in question have the ambiguous name inlaid into it and these swords actually date to a 200-year period from the 9th century to the early 11th century. It is speculated by many that the process of making the blades originated in the Middle East, in the first centuries of the Islamic period, there appear some scientific studies on swords and steel. The best known of these are by Jabir ibn Hayyan 8th century, al-Kindi 9th century, Al-Biruni in the early 11th century, al-Tarsusi in the late 12th century, and Fakhr-i-Mudabbir 13th century. Any of these far more information about Indian and damascene steels than appears in the entire surviving literature of classical Greece. Indian/Sri Lankan crucible steel is commonly referred to as wootz, which is agreed to be an English corruption of the word ukko or hookoo. As yet the scale of excavations and surface surveys is too limited to link the literary accounts to archaeometallurgical evidence. The known sites of crucible steel production in south India, i. e. at Konasamudram and Gatihosahalli, date from at least the medieval period. One of the earliest known sites, which shows some promising evidence that may be linked to ferrous crucible processes in Kodumanal. The site is dated between the third century BC and the third century AD, by the seventeenth century the main centre of crucible steel production seems to have been in Hyderabad. The process was quite different from that recorded elsewhere. Wootz from Hyderabad or the Decanni process for making watered blades involved a co-fusion of two different kinds of iron, one was low in carbon and the other was a steel or cast iron. Wootz steel was exported and traded throughout ancient Europe, China, the Arab world, and became particularly famous in the Middle East. Recent archaeological investigations have suggested that Sri Lanka also supported innovative technologies for iron, the Sri Lankan system of crucible steel making was partially independent of the various Indian and Middle Eastern systems. Their method was something similar to the method of carburization of wrought iron, the earliest confirmed crucible steel site is located in the knuckles range in the northern area of the Central Highlands of Sri Lanka dated to 6th −10th centuries AD
14.
Spring steel
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Spring steel is a name given to a wide range of steels used widely in the manufacture of springs, prominently in automotive and industrial suspension applications. These steels are generally low-alloy, medium-carbon steel or high-carbon steel with a high yield strength. This allows objects made of spring steel to return to their original shape despite significant deflection or twisting, many grades of steel can be hardened and tempered to suit application as a spring, however, some steels exhibit more desirable characteristics for spring applications. Applications include piano wire such as ASTM A228, spring clamps, antennas, springs, and vehicle coil springs, leaf springs, and s-tines. Spring steel is commonly used in the manufacture of metal swords both historically and for stage combat due to its resistance to bending, snapping or shattering. Spring steel is one of the most popular used in the fabrication of lockpicks due to its pliability. Tubular spring steel is used in the gear of some small aircraft due to its ability to absorb the impact of landing. It is also used in the making of knives, especially for the Nepalese kukri. It is used in binder clips, martensite Bibliography Oberg, Erik, Franklin D. Jones, Holbrook L. Horton, Henry H. Ryffel. Christopher J. McCauley, Riccardo Heald, Muhammed Iqbal Hussain, eds
15.
Alloy steel
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Alloy steel is steel that is alloyed with a variety of elements in total amounts between 1. 0% and 50% by weight to improve its mechanical properties. Alloy steels are broken down into two groups, low-alloy steels and high-alloy steels, the difference between the two is somewhat arbitrary, Smith and Hashemi define the difference at 4. 0%, while Degarmo, et al. define it at 8. 0%. Most commonly, the alloy steel refers to low-alloy steels. Strictly speaking, every steel is an alloy, but not all steels are called alloy steels, the simplest steels are iron alloyed with carbon. However, the alloy steel is the standard term referring to steels with other alloying elements added deliberately in addition to the carbon. Common alloyants include manganese, nickel, chromium, molybdenum, vanadium, silicon, less common alloyants include aluminum, cobalt, copper, cerium, niobium, titanium, tungsten, tin, zinc, lead, and zirconium. The following is a range of improved properties in alloy steels, strength, hardness, toughness, wear resistance, corrosion resistance, hardenability, to achieve some of these improved properties the metal may require heat treating. Some of these uses in exotic and highly-demanding applications, such as in the turbine blades of jet engines, in spacecraft. Because of the properties of iron, some steel alloys find important applications where their responses to magnetism are very important, including in electric motors. A few common low alloy steels are, D6AC 300M 256A Alloying elements are added to certain properties in the material. Manganese, silicon, or aluminum are added during the process to remove dissolved oxygen, sulfur. Manganese, silicon, nickel, and copper are added to increase strength by forming solid solutions in ferrite, chromium, vanadium, molybdenum, and tungsten increase strength by forming second-phase carbides. Nickel and copper improve corrosion resistance in small quantities, zirconium, cerium, and calcium increase toughness by controlling the shape of inclusions. Sulfur lead, bismuth, selenium, and tellurium increase machinability, the alloying elements tend to form either solid solutions or compounds or carbides. Nickel is very soluble in ferrite, therefore, it forms compounds, aluminium dissolves in the ferrite and forms the compounds Al2O3 and AlN. Silicon is also very soluble and usually forms the compound SiO2•MxOy, manganese mostly dissolves in ferrite forming the compounds MnS, MnO•SiO2, but will also form carbides in the form of 3C. Chromium forms partitions between the ferrite and carbide phases in steel, forming C, Cr7C3, and Cr23C6, the type of carbide that chromium forms depends on the amount of carbon and other types of alloying elements present. Tungsten and molybdenum form carbides if there is enough carbon and an absence of stronger carbide forming elements, they form the carbides W2C and Mo2C, vanadium, titanium, and niobium are strong carbide forming elements, forming vanadium carbide, titanium carbide, and niobium carbide, respectively
16.
Maraging steel
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Maraging steels are steels that are known for possessing superior strength and toughness without losing malleability, although they cannot hold a good cutting edge. Aging refers to the extended heat-treatment process and these steels are a special class of low-carbon ultra-high-strength steels that derive their strength not from carbon, but from precipitation of intermetallic compounds. The principal alloying element is 15 to 25 wt. % nickel, secondary alloying elements, which include cobalt, molybdenum, and titanium, are added to produce intermetallic precipitates. Original development was carried out on 20 and 25 wt. % nickel, 8–12 wt. % cobalt, 3–5 wt. % molybdenum, addition of chromium produces stainless grades resistant to corrosion. Alternative variants of Ni-reduced maraging steels are based on alloys of Fe and Mn plus minor additions of Al, Ni, the Mn has a similar effect as Ni, i. e. it stabilizes the austenite phase. Hence, depending on their Mn content, Fe-Mn maraging steels can be fully martensitic after quenching them from the high temperature austenite phase or they can contain retained austenite, the latter effect enables the design of maraging-TRIP steels where TRIP stands for Transformation-Induced-Plasticity. Due to the low carbon content maraging steels have good machinability, prior to aging, they may also be cold rolled to as much as 90% without cracking. Maraging steels offer good weldability, but must be aged afterward to restore the properties to the heat affected zone. When heat-treated the alloy has very little change, so it is often machined to its final dimensions. Due to the alloy content maraging steels have a high hardenability. Since ductile FeNi martensites are formed upon cooling, cracks are non-existent or negligible, the steels can be nitrided to increase case hardness, and polished to a fine surface finish. Non-stainless varieties of maraging steel are moderately corrosion-resistant, and resist stress corrosion, corrosion-resistance can be increased by cadmium plating or phosphating. There is also a family of cobalt-free maraging steels which are cheaper but not quite as strong, there has been Russian and Japanese research in Fe-Ni-Mn maraging alloys. The steel is first annealed at approximately 820 °C for 15–30 minutes for thin sections and for 1 hour per 25 mm thickness for heavy sections and this is followed by air cooling to room temperature to form a soft, heavily-dislocated iron-nickel lath martensite. Overaging leads to a reduction in stability of the primary, metastable, coherent precipitates, leading to their dissolution, further excessive heat-treatment brings about the decomposition of the martensite and reversion to austenite. Maraging steels strength and malleability in the stage allows it to be formed into thinner rocket and missile skins than other steels. Maraging steels have very stable properties, and, even after overaging due to excessive temperature and these alloys retain their properties at mildly elevated operating temperatures and have maximum service temperatures of over 400 °C. They are suitable for engine components, such as crankshafts and gears, and their uniform expansion and easy machinability before aging make maraging steel useful in high-wear components of assembly lines and dies
17.
Stainless steel
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In metallurgy, stainless steel, also known as inox steel or inox from French inoxydable, is a steel alloy with a minimum of 10. 5% chromium content by mass. Stainless steel is notable for its resistance, and it is widely used for food handling. Stainless steel does not readily corrode, rust or stain with water as ordinary steel does, however, it is not fully stain-proof in low-oxygen, high-salinity, or poor air-circulation environments. There are various grades and surface finishes of stainless steel to suit the environment the alloy must endure, Stainless steel is used where both the properties of steel and corrosion resistance are required. Stainless steel differs from carbon steel by the amount of chromium present, unprotected carbon steel rusts readily when exposed to air and moisture. This iron oxide film is active and accelerates corrosion by making it easier for more iron oxide to form, since iron oxide has lower density than steel, the film expands and tends to flake and fall away. In comparison, stainless steels contain sufficient chromium to undergo passivation and this layer prevents further corrosion by blocking oxygen diffusion to the steel surface and stops corrosion from spreading into the bulk of the metal. Passivation occurs only if the proportion of chromium is high enough, Stainless steel’s resistance to corrosion and staining, low maintenance, and familiar lustre make it an ideal material for many applications. Storage tanks and tankers used to transport orange juice and other food are made of stainless steel. This also influences its use in kitchens and food processing plants, as it can be steam-cleaned and sterilized. High oxidation resistance in air at ambient temperature is achieved with addition of a minimum of 13% chromium. The chromium forms a layer of chromium oxide when exposed to oxygen. The layer is too thin to be visible, and the metal remains lustrous, the layer is impervious to water and air, protecting the metal beneath, and this layer quickly reforms when the surface is scratched. This phenomenon is called passivation and is seen in other metals, corrosion resistance can be adversely affected if the component is used in a non-oxygenated environment, a typical example being underwater keel bolts buried in timber. When stainless steel parts such as nuts and bolts are forced together, when forcibly disassembled, the welded material may be torn and pitted, a destructive effect known as galling. Galling can be avoided by the use of materials for the parts forced together, for example bronze and stainless steel. However, two different alloys electrically connected in a humid, even mildly acidic environment may act as a voltaic pile, nitronic alloys, made by selective alloying with manganese and nitrogen, may have a reduced tendency to gall. Additionally, threaded joints may be lubricated to provide a film between the two parts and prevent galling, low-temperature carburizing is another option that virtually eliminates galling and allows the use of similar materials without the risk of corrosion and the need for lubrication
18.
Weathering steel
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U. S. Steel holds the registered trademark on the name COR-TEN. Although USS sold its discrete plate business to International Steel Group in 2003, it still sells COR-TEN branded material in strip-mill plate, the original COR-TEN received the standard designation A242 from the ASTM International standards group. Newer ASTM grades are A588 and A606 for thin sheet, all alloys are in common production and use. Weathering refers to the composition of these steels, allowing them to exhibit increased resistance to atmospheric corrosion compared to other steels. This is because the forms a protective layer on its surface under the influence of the weather. The corrosion-retarding effect of the layer is produced by the particular distribution and concentration of alloying elements in it. The layer protecting the surface develops and regenerates continuously when subjected to the influence of the weather, in other words, the steel is allowed to rust in order to form the protective coating. The mechanical properties of weathering steels depend on which alloy and how thick the material is. The original A242 alloy has a strength of 50 kilopounds per square inch. It has yield strength of 46 ksi and ultimate strength of 67 ksi for medium weight rolled shapes and plates from 0. 75–1 inch thick. The thickest rolled sections and plates – from 1. 5–4 in thick have yield strength of 42 ksi, a 588 has a yield strength of at least 50 ksi, and ultimate tensile strength of 70 ksi for all rolled shapes and plate thicknesses up to 4 in thick. It is very used in marine transportation, in the construction of intermodal containers as well as visible sheet piling along recently widened sections of Londons M25 motorway. The first use of weathering steel for architectural applications was the John Deere World Headquarters in Moline, the building was designed by architect Eero Saarinen, and completed in 1964. The main buildings of Odense University, designed by Knud Holscher and Jørgen Vesterholt and built 1971–1976, are clad in weathering steel, earning them the nickname Rustenborg. In 1977, Robert Indiana created a Hebrew version of the Love sculpture made from weathering steel using the four-letter word ahava for the Israel Museum Art Garden in Jerusalem, in Denmark, all masts for supporting the catenary on electrified railways are made of weathering steel for aesthetic reasons. Weathering steel was used in 1971 for the Highliner electric cars built by the St. Louis Car Company for Illinois Central Railroad, the use of weathering steel was seen as a cost-cutting move in comparison with the contemporary railcar standard of stainless steel. A subsequent order in 1979 was built to similar specs, including weathering steel bodies, the cars were painted, a standard practice for weathering steel railcars. The durability of weathering steel did not live up to expectations and these cars have been retired by 2016
19.
Tool steel
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Tool steel refers to a variety of carbon and alloy steels that are particularly well-suited to be made into tools. Their suitability comes from their distinctive hardness, resistance to abrasion and deformation, as a result, tool steels are suited for their use in the shaping of other materials. With a carbon content between 0. 5% and 1. 5%, tool steels are manufactured under controlled conditions to produce the required quality. The presence of carbides in their plays the dominant role in the qualities of tool steel. The four major alloying elements in tool steel that form carbides are, tungsten, the rate of dissolution of the different carbides into the austenite form of the iron determines the high temperature performance of steel. Proper heat treatment of these steels is important for adequate performance, the manganese content is often kept low to minimize the possibility of cracking during water quenching. There are six groups of tool steels, water-hardening, cold-work, shock-resistant, high-speed, hot-work, the choice of group to select depends on cost, working temperature, required surface hardness, strength, shock resistance, and toughness requirements. The more severe the service condition, the higher the content and consequent amount of carbides required for the tool steel. Tool steels are used for cutting, pressing, extruding, and coining of metals, the AISI-SAE grades of tool steel is the most common scale used to identify various grades of tool steel. Individual alloys within a grade are given a number, for example, A2, O1, W-group tool steel gets its name from its defining property of having to be water quenched. W-grade steel is essentially high carbon plain-carbon steel and this group of tool steel is the most commonly used tool steel because of its low cost compared to others. They work well for parts and applications where high temperatures are not encountered. Its hardenability is low, so W-group tool steels must be subjected to a rapid quenching, requiring the use of water and these steels can attain high hardness and are rather brittle compared to other tool steels. W-steels are still sold, especially for springs, but are less widely used than they were in the 19th. This is partly because W-steels warp and crack much more during quench than oil-quenched or air hardening steels, the toughness of W-group tool steels are increased by alloying with manganese, silicon and molybdenum. Up to 0. 20% of vanadium is used to fine grain sizes during heat treating. 0. 76–0. 90% carbon, forging dies, hammers,0. 91–1. 10% carbon, general purpose tooling applications that require a good balance of wear resistance and toughness, such as rasps, drills, cutters, and shear blades. 1. 11–1. 30% carbon, files, small drills, lathe tools, razor blades, and other light-duty applications where more wear resistance is required without great toughness
20.
Cast iron
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Cast iron is a group of iron-carbon alloys with a carbon content greater than 2%. Its usefulness derives from its low melting temperature. Carbon ranging from 1. 8–4 wt%, and silicon 1–3 wt% are the main alloying elements of cast iron, Iron alloys with less carbon content are known as steel. While this technically makes the Fe–C–Si system ternary, the principle of cast iron solidification can be understood from the simpler binary iron–carbon phase diagram, cast iron tends to be brittle, except for malleable cast irons. It is resistant to destruction and weakening by oxidation, the earliest cast iron artefacts date to the 5th century BC, and were discovered by archaeologists in what is now Jiangsu in China. Cast iron was used in ancient China for warfare, agriculture, during the 15th century, cast iron became utilized for artillery in Burgundy, France, and in England during the Reformation. The first cast iron bridge was built during the 1770s by Abraham Darby III, cast iron is also used in the construction of buildings. Cast iron is made by re-melting pig iron, often along with quantities of iron, steel, limestone, carbon. Phosphorus and sulfur may be burnt out of the iron, but this also burns out the carbon. Depending on the application, carbon and silicon content are adjusted to the desired levels, other elements are then added to the melt before the final form is produced by casting. Cast iron is melted in a special type of blast furnace known as a cupola. After melting is complete, the molten cast iron is poured into a furnace or ladle. Cast irons properties are changed by adding various alloying elements, or alloyants, next to carbon, silicon is the most important alloyant because it forces carbon out of solution. A low percentage of silicon allows carbon to remain in solution forming iron carbide, a high percentage of silicon forces carbon out of solution forming graphite and the production of grey cast iron. Other alloying agents, manganese, chromium, molybdenum, titanium and vanadium counteracts silicon, promotes the retention of carbon, nickel and copper increase strength, and machinability, but do not change the amount of graphite formed. The carbon in the form of graphite results in an iron, reduces shrinkage, lowers strength. Sulfur, largely a contaminant when present, forms iron sulfide, the problem with sulfur is that it makes molten cast iron viscous, which causes defects. To counter the effects of sulfur, manganese is added because the two form into manganese sulfide instead of iron sulfide, the manganese sulfide is lighter than the melt so it tends to float out of the melt and into the slag
21.
Ductile iron
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While most varieties of cast iron are brittle, ductile iron has much more impact and fatigue resistance, due to its nodular graphite inclusions. On October 25,1949, Keith Dwight Millis, Albert Paul Gagnebin, Ductile iron is not a single material but part of a group of materials which can be produced with a wide range of properties through control of their microstructure. The common defining characteristic of this group of materials is the shape of the graphite, in ductile irons, graphite is in the form of nodules rather than flakes as in grey iron. Nodule formation is achieved by adding nodulizing elements, most commonly magnesium and, less often now, yttrium, often a component of mischmetal, has also been studied as a possible nodulizer. Austempered Ductile Iron was discovered in the 1950s but was commercialized and achieved only some years later. In ADI, the structure is manipulated through a sophisticated heat treating process. The aus portion of the name refers to austenite, improved corrosion resistance can be achieved by replacing 15% to 30% of the iron in the alloy with varying amounts of nickel, copper, or chromium. Much of the production of ductile iron is in the form of ductile iron pipe. Ductile iron is specifically useful in automotive components, where strength needs surpass that of aluminum. Other major industrial applications include off-highway diesel trucks, Class 8 trucks, agricultural tractors, in wind power industry nodular cast iron is used for hubs and structural parts like machine frames. Nodular cast iron is suitable for large and complex shapes and high loads, SG iron is used in many grand piano harps. Malleable iron Smith, William F. Hashemi, Javad, Foundations of Materials Science and Engineering, McGraw-Hill, media related to Ductile iron at Wikimedia Commons Ductile Iron Society Ductile Iron Pipe Research Association
22.
Malleable iron
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Malleable iron is cast as white iron, the structure being a metastable carbide in a pearlitic matrix. Through an annealing heat treatment, the structure as first cast is transformed into the malleable form. Carbon agglomerates into small roughly spherical aggregates of graphite leaving a matrix of ferrite or pearlite according to the heat treatment used. Three basic types of iron are recognized within the casting industry, blackheart malleable iron, whiteheart malleable iron. Malleable iron was used as early as the 4th century BCE, by the Tang Dynasty, the use of malleable iron in China waned, although there are malleable iron artifacts dating to the 9th century. Malleable iron is mentioned in England in a patent dating to the 1670s, réaumur conducted extensive research on malleable iron in 1720. He discovered that iron castings which were too hard to be worked could be softened by packing them into iron ore or hammer slag, creating malleable iron began in the United States in 1826 when Seth Boyden started a foundry for the production of harness hardware and other small castings. Like similar irons with the carbon formed into spherical or nodular shapes, incorrectly considered by some to be an old or dead material, malleable iron still has a legitimate place in the design engineers toolbox. Malleable iron is a choice for small castings or castings with thin cross sections. Other nodular irons produced with graphite in the shape can be difficult to produce in these applications. Malleable iron also exhibits better fracture toughness properties in low temperature environments than other nodular irons, the ductile to brittle behavior transformation temperature is lower than many other ductile iron alloys. Thicker sections of a casting will cool slowly, allowing some primary graphite to form and this graphite forms random flake-like structures and will not transform to carbide during heat treatment. When stress is applied to such a casting in application, the strength will be lower than expected for white iron. Such iron is said to have a mottled appearance, some countermeasures can be applied to enhance the formation of the all white structure, but malleable iron foundries often avoid producing heavy sections. After the casting and heat treatment processes, malleable iron can be shaped through cold working and this is possible due to malleable irons desirable property of being less strain rate sensitive than other materials. It is often used for small castings requiring good tensile strength, uses include electrical fittings, hand tools, pipe fittings, washers, brackets, fence fittings, power line hardware, farm equipment, mining hardware, and machine parts
23.
Wrought iron
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Wrought iron is an iron alloy with a very low carbon content in contrast to cast iron. It is a mass of iron with fibrous slag inclusions which gives it a grain resembling wood. Wrought iron is tough, malleable, ductile, corrosion-resistant and easily welded, before the development of effective methods of steelmaking and the availability of large quantities of steel, wrought iron was the most common form of malleable iron. A wrought product is one that has been worked by forging, extruding, rolling, hammering, etcetera, to change its form. Wrought iron is a worked iron product that is seldom produced today as other cheaper. Historically, a modest amount of iron was refined into steel. The demand for wrought iron reached its peak in the 1860s with the adaptation of ironclad warships, however, as properties such as brittleness of mild steel improved, it became less costly and more widely available than wrought iron, whose usage then declined. Wrought iron is no longer produced on a commercial scale, many products described as wrought iron, such as guard rails, garden furniture and gates, are actually made of mild steel. They retain that description because they are made to resemble objects which in the past were wrought by hand by a blacksmith, the word wrought is an archaic past participle of the verb to work, and so wrought iron literally means worked iron. Wrought iron is a term for the commodity, but is also used more specifically for finished iron goods. It was used in that sense in British Customs records. Cast iron, unlike wrought iron, is brittle and cannot be worked either hot or cold, Cast iron can break if struck with a hammer. In the 17th, 18th, and 19th centuries, wrought iron went by a variety of terms according to its form, origin. While the bloomery process produced wrought iron directly from ore, cast iron or pig iron were the materials used in the finery forge. Pig iron and cast iron have higher content than wrought iron. Cast and especially pig iron have excess slag which must be at least partially removed to produce quality wrought iron, at foundries it was common to blend scrap wrought iron with cast iron to improve the physical properties of castings. Fusion eventually became accepted as relatively more important than composition below a given low carbon concentration. Another difference is that steel can be hardened by heat treating, historically, wrought iron was known as commercially pure iron, however, it no longer qualifies because current standards for commercially pure iron require a carbon content of less than 0.008 wt%
24.
Iron oxide
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Iron oxides are chemical compounds composed of iron and oxygen. All together, there are sixteen known iron oxides and oxyhydroxides, common rust is a form of iron oxide. Iron oxides are used as inexpensive, durable pigments in paints, coatings. Colors commonly available are in the end of the yellow/orange/red/brown/black range. When used as a coloring, it has E number E172. Limonite Iron oxide nanoparticles List of inorganic pigments Information from Nano-Oxides, http, //chemed. chem. purdue. edu/demos/demosheets/12.3. html http, //minerals. usgs. gov/minerals/pubs/commodity/iron_oxide/ CDC - NIOSH Pocket Guide to Chemical Hazards de
25.
Oxide
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An oxide /ˈɒksaɪd/ is a chemical compound that contains at least one oxygen atom and one other element in its chemical formula. Oxide itself is the dianion of oxygen, an O2– atom, Metal oxides thus typically contain an anion of oxygen in the oxidation state of −2. Most of the Earths crust consists of oxides, the result of elements being oxidized by the oxygen in air or in water. Hydrocarbon combustion affords the two principal carbon oxides, carbon monoxide and carbon dioxide, even materials considered pure elements often develop an oxide coating. For example, aluminium foil develops a skin of Al2O3 that protects the foil from further corrosion. Individual elements can form multiple oxides, each containing different amounts of the element. Certain elements can form many different oxides, such those of nitrogen, due to its electronegativity, oxygen forms stable chemical bonds with almost all elements to give the corresponding oxides. Noble metals are prized because they resist direct chemical combination with oxygen, two independent pathways for corrosion of elements are hydrolysis and oxidation by oxygen. The combination of water and oxygen is even more corrosive, virtually all elements burn in an atmosphere of oxygen, or an oxygen rich environment. In the presence of water and oxygen, some elements— sodium—react rapidly, even dangerously, in part for this reason, alkali and alkaline earth metals are not found in nature in their metallic, i. e. native, form. Caesium is so reactive with oxygen that it is used as a getter in vacuum tubes, the surface of most metals consists of oxides and hydroxides in the presence of air. A well-known example is aluminium foil, which is coated with a film of aluminium oxide that passivates the metal. The aluminium oxide layer can be built to greater thickness by the process of electrolytic anodising, though solid magnesium and aluminium react slowly with oxygen at STP—they, like most metals, burn in air, generating very high temperatures. Finely grained powders of most metals can be explosive in air. Consequently, they are used in Solid-fuel rockets. In dry oxygen, iron forms iron oxide, but the formation of the hydrated ferric oxides, Fe2O3−x2x. Free oxygen production by photosynthetic bacteria some 3.5 billion years ago precipitated iron out of solution in the oceans as Fe2O3 in the important iron ore hematite. Oxides have a range of different structures, from molecules to polymeric
26.
Redox
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Redox is a chemical reaction in which the oxidation states of atoms are changed. Any such reaction involves both a process and a complementary oxidation process, two key concepts involved with electron transfer processes. Redox reactions include all chemical reactions in which atoms have their oxidation state changed, in general, the chemical species from which the electron is stripped is said to have been oxidized, while the chemical species to which the electron is added is said to have been reduced. It can be explained in terms, Oxidation is the loss of electrons or an increase in oxidation state by a molecule, atom. Reduction is the gain of electrons or a decrease in state by a molecule, atom. As an example, during the combustion of wood, oxygen from the air is reduced, the reaction can occur relatively slowly, as in the case of rust, or more quickly, as in the case of fire. Redox is a portmanteau of reduction and oxidation, the word oxidation originally implied reaction with oxygen to form an oxide, since dioxygen was historically the first recognized oxidizing agent. Later, the term was expanded to encompass oxygen-like substances that accomplished parallel chemical reactions, ultimately, the meaning was generalized to include all processes involving loss of electrons. The word reduction originally referred to the loss in weight upon heating a metallic ore such as an oxide to extract the metal. In other words, ore was reduced to metal, antoine Lavoisier showed that this loss of weight was due to the loss of oxygen as a gas. Later, scientists realized that the atom gains electrons in this process. The meaning of reduction then became generalized to all processes involving gain of electrons. Even though reduction seems counter-intuitive when speaking of the gain of electrons, it help to think of reduction as the loss of oxygen. Since electrons are charged, it is also helpful to think of this as reduction in electrical charge. The electrochemist John Bockris has used the words electronation and deelectronation to describe reduction and oxidation processes respectively when they occur at electrodes and these words are analogous to protonation and deprotonation, but they have not been widely adopted by chemists. The term hydrogenation could be used instead of reduction, since hydrogen is the agent in a large number of reactions. But, unlike oxidation, which has been generalized beyond its root element, the word redox was first used in 1928. The processes of oxidation and reduction occur simultaneously and cannot happen independently of one another, the oxidation alone and the reduction alone are each called a half-reaction, because two half-reactions always occur together to form a whole reaction
27.
Iron
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Iron is a chemical element with symbol Fe and atomic number 26. It is a metal in the first transition series and it is by mass the most common element on Earth, forming much of Earths outer and inner core. It is the fourth most common element in the Earths crust, like the other group 8 elements, ruthenium and osmium, iron exists in a wide range of oxidation states, −2 to +6, although +2 and +3 are the most common. Elemental iron occurs in meteoroids and other low oxygen environments, but is reactive to oxygen, fresh iron surfaces appear lustrous silvery-gray, but oxidize in normal air to give hydrated iron oxides, commonly known as rust. Unlike the metals that form passivating oxide layers, iron oxides occupy more volume than the metal and thus flake off, Iron metal has been used since ancient times, although copper alloys, which have lower melting temperatures, were used even earlier in human history. Pure iron is soft, but is unobtainable by smelting because it is significantly hardened and strengthened by impurities, in particular carbon. A certain proportion of carbon steel, which may be up to 1000 times harder than pure iron. Crude iron metal is produced in blast furnaces, where ore is reduced by coke to pig iron, further refinement with oxygen reduces the carbon content to the correct proportion to make steel. Steels and iron alloys formed with metals are by far the most common industrial metals because they have a great range of desirable properties. Iron chemical compounds have many uses, Iron oxide mixed with aluminium powder can be ignited to create a thermite reaction, used in welding and purifying ores. Iron forms binary compounds with the halogens and the chalcogens, among its organometallic compounds is ferrocene, the first sandwich compound discovered. Iron plays an important role in biology, forming complexes with oxygen in hemoglobin and myoglobin. Iron is also the metal at the site of many important redox enzymes dealing with cellular respiration and oxidation and reduction in plants. A human male of average height has about 4 grams of iron in his body and this iron is distributed throughout the body in hemoglobin, tissues, muscles, bone marrow, blood proteins, enzymes, ferritin, hemosiderin, and transport in plasma. The mechanical properties of iron and its alloys can be evaluated using a variety of tests, including the Brinell test, Rockwell test, the data on iron is so consistent that it is often used to calibrate measurements or to compare tests. An increase in the content will cause a significant increase in the hardness. Maximum hardness of 65 Rc is achieved with a 0. 6% carbon content, because of the softness of iron, it is much easier to work with than its heavier congeners ruthenium and osmium. Because of its significance for planetary cores, the properties of iron at high pressures and temperatures have also been studied extensively
28.
Oxygen
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Oxygen is a chemical element with symbol O and atomic number 8. It is a member of the group on the periodic table and is a highly reactive nonmetal. By mass, oxygen is the third-most abundant element in the universe, after hydrogen, at standard temperature and pressure, two atoms of the element bind to form dioxygen, a colorless and odorless diatomic gas with the formula O2. This is an important part of the atmosphere and diatomic oxygen gas constitutes 20. 8% of the Earths atmosphere, additionally, as oxides the element makes up almost half of the Earths crust. Most of the mass of living organisms is oxygen as a component of water, conversely, oxygen is continuously replenished by photosynthesis, which uses the energy of sunlight to produce oxygen from water and carbon dioxide. Oxygen is too reactive to remain a free element in air without being continuously replenished by the photosynthetic action of living organisms. Another form of oxygen, ozone, strongly absorbs ultraviolet UVB radiation, but ozone is a pollutant near the surface where it is a by-product of smog. At low earth orbit altitudes, sufficient atomic oxygen is present to cause corrosion of spacecraft, the name oxygen was coined in 1777 by Antoine Lavoisier, whose experiments with oxygen helped to discredit the then-popular phlogiston theory of combustion and corrosion. One of the first known experiments on the relationship between combustion and air was conducted by the 2nd century BCE Greek writer on mechanics, Philo of Byzantium. In his work Pneumatica, Philo observed that inverting a vessel over a burning candle, Philo incorrectly surmised that parts of the air in the vessel were converted into the classical element fire and thus were able to escape through pores in the glass. Many centuries later Leonardo da Vinci built on Philos work by observing that a portion of air is consumed during combustion and respiration, Oxygen was discovered by the Polish alchemist Sendivogius, who considered it the philosophers stone. In the late 17th century, Robert Boyle proved that air is necessary for combustion, English chemist John Mayow refined this work by showing that fire requires only a part of air that he called spiritus nitroaereus. From this he surmised that nitroaereus is consumed in both respiration and combustion, Mayow observed that antimony increased in weight when heated, and inferred that the nitroaereus must have combined with it. Accounts of these and other experiments and ideas were published in 1668 in his work Tractatus duo in the tract De respiratione. Robert Hooke, Ole Borch, Mikhail Lomonosov, and Pierre Bayen all produced oxygen in experiments in the 17th and the 18th century but none of them recognized it as a chemical element. This may have been in part due to the prevalence of the philosophy of combustion and corrosion called the phlogiston theory, which was then the favored explanation of those processes. Established in 1667 by the German alchemist J. J. Becher, one part, called phlogiston, was given off when the substance containing it was burned, while the dephlogisticated part was thought to be its true form, or calx. The fact that a substance like wood gains overall weight in burning was hidden by the buoyancy of the combustion products
29.
Water
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Water is a transparent and nearly colorless chemical substance that is the main constituent of Earths streams, lakes, and oceans, and the fluids of most living organisms. Its chemical formula is H2O, meaning that its molecule contains one oxygen, Water strictly refers to the liquid state of that substance, that prevails at standard ambient temperature and pressure, but it often refers also to its solid state or its gaseous state. It also occurs in nature as snow, glaciers, ice packs and icebergs, clouds, fog, dew, aquifers, Water covers 71% of the Earths surface. It is vital for all forms of life. Only 2. 5% of this water is freshwater, and 98. 8% of that water is in ice and groundwater. Less than 0. 3% of all freshwater is in rivers, lakes, and the atmosphere, a greater quantity of water is found in the earths interior. Water on Earth moves continually through the cycle of evaporation and transpiration, condensation, precipitation. Evaporation and transpiration contribute to the precipitation over land, large amounts of water are also chemically combined or adsorbed in hydrated minerals. Safe drinking water is essential to humans and other even though it provides no calories or organic nutrients. There is a correlation between access to safe water and gross domestic product per capita. However, some observers have estimated that by 2025 more than half of the population will be facing water-based vulnerability. A report, issued in November 2009, suggests that by 2030, in developing regions of the world. Water plays an important role in the world economy, approximately 70% of the freshwater used by humans goes to agriculture. Fishing in salt and fresh water bodies is a source of food for many parts of the world. Much of long-distance trade of commodities and manufactured products is transported by boats through seas, rivers, lakes, large quantities of water, ice, and steam are used for cooling and heating, in industry and homes. Water is an excellent solvent for a variety of chemical substances, as such it is widely used in industrial processes. Water is also central to many sports and other forms of entertainment, such as swimming, pleasure boating, boat racing, surfing, sport fishing, Water is a liquid at the temperatures and pressures that are most adequate for life. Specifically, at atmospheric pressure of 1 bar, water is a liquid between the temperatures of 273.15 K and 373.15 K
30.
Spectroscopy
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Spectroscopy /spɛkˈtrɒskəpi/ is the study of the interaction between matter and electromagnetic radiation. Historically, spectroscopy originated through the study of visible light dispersed according to its wavelength, later the concept was expanded greatly to include any interaction with radiative energy as a function of its wavelength or frequency. Spectroscopic data is represented by an emission spectrum, a plot of the response of interest as a function of wavelength or frequency. Spectroscopy and spectrography are terms used to refer to the measurement of radiation intensity as a function of wavelength and are used to describe experimental spectroscopic methods. Spectral measurement devices are referred to as spectrometers, spectrophotometers, spectrographs or spectral analyzers, daily observations of color can be related to spectroscopy. Neon lighting is an application of atomic spectroscopy. Neon and other noble gases have characteristic emission frequencies, neon lamps use collision of electrons with the gas to excite these emissions. Inks, dyes and paints include chemical compounds selected for their characteristics in order to generate specific colors. A commonly encountered molecular spectrum is that of nitrogen dioxide, gaseous nitrogen dioxide has a characteristic red absorption feature, and this gives air polluted with nitrogen dioxide a reddish-brown color. Rayleigh scattering is a spectroscopic scattering phenomenon that accounts for the color of the sky, Spectroscopy is used in physical and analytical chemistry because atoms and molecules have unique spectra. As a result, these spectra can be used to detect, identify and quantify information about the atoms, Spectroscopy is also used in astronomy and remote sensing on earth. The measured spectra are used to determine the composition and physical properties of astronomical objects. One of the concepts in spectroscopy is a resonance and its corresponding resonant frequency. Resonances were first characterized in mechanical systems such as pendulums, mechanical systems that vibrate or oscillate will experience large amplitude oscillations when they are driven at their resonant frequency. A plot of amplitude vs. excitation frequency will have a peak centered at the resonance frequency and this plot is one type of spectrum, with the peak often referred to as a spectral line, and most spectral lines have a similar appearance. In quantum mechanical systems, the resonance is a coupling of two quantum mechanical stationary states of one system, such as an atom, via an oscillatory source of energy such as a photon. The coupling of the two states is strongest when the energy of the matches the energy difference between the two states. The energy of a photon is related to its frequency by E = h ν where h is Plancks constant, spectra of atoms and molecules often consist of a series of spectral lines, each one representing a resonance between two different quantum states
31.
Iron(III) oxide
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Iron oxide or ferric oxide is the inorganic compound with the formula Fe2O3. It is one of the three main oxides of iron, the two being iron oxide, which is rare, and iron oxide, which also occurs naturally as the mineral magnetite. As the mineral known as hematite, Fe2O3 is the source of iron for the steel industry. Fe2O3 is ferromagnetic, dark red, and readily attacked by acids, Iron oxide is often called rust, and to some extent this label is useful, because rust shares several properties and has a similar composition. To a chemist, rust is considered a material, described as hydrated ferric oxide. Fe2O3 can be obtained in various polymorphs, in the main ones, α and γ, iron adopts octahedral coordination geometry. That is, each Fe center is bound to six oxygen ligands, α-Fe2O3 has the rhombohedral, corundum structure and is the most common form. It occurs naturally as the mineral hematite which is mined as the ore of iron. It is antiferromagnetic below ~260 K, and exhibits weak ferromagnetism between 260 K and the Néel temperature,950 K and it is easy to prepare using both thermal decomposition and precipitation in the liquid phase. Its magnetic properties are dependent on many factors, e. g. pressure, particle size and it is metastable and converted from the alpha phase at high temperatures. It occurs naturally as the mineral maghemite and it is ferromagnetic and finds application in recording tapes, although ultrafine particles smaller than 10 nanometers are superparamagnetic. It can be prepared by thermal dehydratation of gamma iron oxide-hydroxide, another method involves the careful oxidation of Fe3O4. The ultrafine particles can be prepared by decomposition of iron oxalate. Several other phases have been identified or claimed, the β-phase is cubic body centered, metastable, and at temperatures above 500 °C converts to alpha phase. It can be prepared by reduction of hematite by carbon, pyrolysis of iron chloride solution, the epsilon phase is rhombic, and shows properties intermediate between alpha and gamma, and may have useful magnetic properties. Preparation of the pure epsilon phase has proven challenging due to contamination with alpha. Material with a proportion of epsilon phase can be prepared by thermal transformation of the gamma phase. This phase is metastable, transforming to the alpha phase at between 500 and 750 °C
32.
Patina
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Patina is a thin layer that variously forms on the surface of stone, on copper, bronze and similar metals, on wooden furniture, or any such acquired change of a surface through age and exposure. Patinas can provide a covering to materials that would otherwise be damaged by corrosion or weathering. They may also be aesthetically appealing, Patina also refers to accumulated changes in surface texture and colour that result from normal use of an object such as a coin or a piece of furniture over time. Archaeologists also use the term patina to refer to a layer that develops over time that is due to a range of complex factors on flint tools. This has led stone tool analysts in recent times to generally prefer the term cortification as a term to describe the process than patination. It also refers to development as the result of weathering of a layer, called cortex by geologists. The word patina comes from the Latin for shallow dish, figuratively, patina can refer to any fading, darkening or other signs of age, which are felt to be natural or unavoidable. The chemical process by which a patina forms is called patination, in clean air rural environments, the patina is created by the slow chemical reaction of copper with carbon dioxide and water, producing a basic copper carbonate. In industrial and urban air environments containing sulfurous acid rain from coal-fired power plants or industrial processes, a patina layer takes many years to develop under natural weathering. Buildings in damp coastal/marine environments will develop patina layers faster than ones in dry inland areas, facade cladding with alloys of copper, e. g. brass or bronze, will weather differently from pure copper cladding. Even a lasting gold colour is possible with copper-alloy cladding, for example Colston Hall in Bristol, or the Novotel at Paddington Central, often, antique and well-used firearms will develop a patina on the steel after the bluing, parkerizing, or other finish has worn. Firearms in this state are considered more valuable than ones that have been re-blued or parkerized. The patina protects the firearm from the more damaging rust that would occur were the patina to be polished off, the process is often called distressing. A wide range of chemicals, both household and commercial, can give a variety of patinas and they are often used by artists as surface embellishments either for color, texture, or both. Patination composition varies with the elements and these will determine the color of the patina. For copper alloys, such as bronze, exposure to chlorides leads to green, the basic palette for patinas on copper alloys includes chemicals like ammonium sulfide, liver of sulfur, cupric nitrate and ferric nitrate. For artworks, patination is often accelerated by applying chemicals with heat. Colors range from matte sandstone yellow to deep blues, greens, whites, reds, some patina colors are achieved by the mixing of colors from the reaction with the metal surface with pigments added to the chemicals
33.
Corrosion
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Corrosion is a natural process, which converts a refined metal to a more chemically-stable form, such as its oxide, hydroxide, or sulfide. It is the destruction of materials by chemical and/or electrochemical reaction with their environment. Corrosion engineering is the dedicated to controlling and stopping corrosion. In the most common use of the word, this means electrochemical oxidation of metal in reaction with an oxidant such as oxygen or sulfur, rusting, the formation of iron oxides, is a well-known example of electrochemical corrosion. This type of damage typically produces oxide or salt of the original metal, corrosion can also occur in materials other than metals, such as ceramics or polymers, although in this context, the term degradation is more common. Corrosion degrades the useful properties of materials and structures including strength, appearance and permeability to liquids, many structural alloys corrode merely from exposure to moisture in air, but the process can be strongly affected by exposure to certain substances. Corrosion can be concentrated locally to form a pit or crack, because corrosion is a diffusion-controlled process, it occurs on exposed surfaces. As a result, methods to reduce the activity of the surface, such as passivation and chromate conversion. However, some corrosion mechanisms are less visible and less predictable, in a galvanic couple, the more active metal corrodes at an accelerated rate and the more noble metal corrodes at a slower rate. When immersed separately, each metal corrodes at its own rate, what type of metal to use is readily determined by following the galvanic series. For example, zinc is used as a sacrificial anode for steel structures. Galvanic corrosion is of major interest to the industry and also anywhere water contacts pipes or metal structures. Factors such as size of anode, types of metal. The surface area ratio of the anode and cathode directly affects the corrosion rates of the materials, galvanic corrosion is often prevented by the use of sacrificial anodes. In any given environment, one metal will be more noble or more active than others. Two metals in electrical contact share the same electrons, so that the tug-of-war at each surface is analogous to competition for free electrons between the two materials. Using the electrolyte as a host for the flow of ions in the same direction, the resulting mass flow or electric current can be measured to establish a hierarchy of materials in the medium of interest. This hierarchy is called a series and is useful in predicting and understanding corrosion
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Metal
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A metal is a material that is typically hard, opaque, shiny, and has good electrical and thermal conductivity. Metals are generally malleable—that is, they can be hammered or pressed permanently out of shape without breaking or cracking—as well as fusible and ductile, about 91 of the 118 elements in the periodic table are metals, the others are nonmetals or metalloids. Some elements appear in both metallic and non-metallic forms, astrophysicists use the term metal to collectively describe all elements other than hydrogen and helium, the simplest two, in a star. The star fuses smaller atoms, mostly hydrogen and helium, to larger ones over its lifetime. In that sense, the metallicity of an object is the proportion of its matter made up of all chemical elements. Many elements and compounds that are not normally classified as metals become metallic under high pressures, the atoms of metallic substances are typically arranged in one of three common crystal structures, namely body-centered cubic, face-centered cubic, and hexagonal close-packed. In bcc, each atom is positioned at the center of a cube of eight others, in fcc and hcp, each atom is surrounded by twelve others, but the stacking of the layers differs. Some metals adopt different structures depending on the temperature, atoms of metals readily lose their outer shell electrons, resulting in a free flowing cloud of electrons within their otherwise solid arrangement. This provides the ability of metallic substances to easily transmit heat, while this flow of electrons occurs, the solid characteristic of the metal is produced by electrostatic interactions between each atom and the electron cloud. This type of bond is called a metallic bond, Metals are usually inclined to form cations through electron loss, reacting with oxygen in the air to form oxides over various timescales. Examples,4 Na + O2 →2 Na2O2 Ca + O2 →2 CaO4 Al +3 O2 →2 Al2O3, the transition metals are slower to oxidize because they form a passivating layer of oxide that protects the interior. Others, like palladium, platinum and gold, do not react with the atmosphere at all, some metals form a barrier layer of oxide on their surface which cannot be penetrated by further oxygen molecules and thus retain their shiny appearance and good conductivity for many decades. The oxides of metals are generally basic, as opposed to those of nonmetals, exceptions are largely oxides with very high oxidation states such as CrO3, Mn2O7, and OsO4, which have strictly acidic reactions. Painting, anodizing or plating metals are good ways to prevent their corrosion, however, a more reactive metal in the electrochemical series must be chosen for coating, especially when chipping of the coating is expected. Water and the two form an electrochemical cell, and if the coating is less reactive than the coatee. Metals in general have high conductivity, high thermal conductivity. Typically they are malleable and ductile, deforming under stress without cleaving, in terms of optical properties, metals are shiny and lustrous. Sheets of metal beyond a few micrometres in thickness appear opaque, although most metals have higher densities than most nonmetals, there is wide variation in their densities, lithium being the least dense solid element and osmium the densest
35.
Chloride
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The chloride ion /ˈklɔəraɪd/ is the anion Cl−. It is formed when the element chlorine gains an electron or when a compound such as chloride is dissolved in water or other polar solvents. Chloride salts such as sodium chloride are often soluble in water. It is an essential electrolyte located in all body fluids responsible for maintaining acid/base balance, transmitting nerve impulses and regulating fluid in, less frequently, the word chloride may also form part of the common name of chemical compounds in which one or more chlorine atoms are covalently bonded. For example, methyl chloride, with the standard name chloromethane is a compound with a covalent C−Cl bond in which the chlorine is not an anion. A chloride ion is much larger than an atom,167 and 99 pm. The ion is colorless and diamagnetic, in aqueous solution, it is highly soluble in most cases, however, some chloride salts, such as silver chloride, lead chloride, and mercury chloride are slightly soluble in water. In aqueous solution, chloride is bound by the end of the water molecules. Some chloride-containing minerals include the chlorides of sodium, potassium, and magnesium, called serum chloride, the concentration of chloride in the blood is regulated by the kidneys. A chloride ion is a component of some proteins, e. g. it is present in the amylase enzyme. The chlor-alkali industry is a consumer of the worlds energy budget. This process converts sodium chloride into chlorine and sodium hydroxide, which are used to make many other materials and chemicals, in the petroleum industry, the chlorides are a closely monitored constituent of the mud system. An increase of the chlorides in the mud system may be an indication of drilling into a high-pressure saltwater formation and its increase can also indicate the poor quality of a target sand. Chloride is also a useful and reliable chemical indicator of river / groundwater fecal contamination, as chloride is a non-reactive solute, many water regulating companies around the world utilize chloride to check the contamination levels of the rivers and potable water sources. Chloride salts such as sodium chloride are used to preserve food, chloride is an essential electrolyte, trafficking in and out of cells through chloride channels and playing a key role in maintaining cell homeostasis and transmitting action potentials in neurons. Characteristic concentrations of chloride in model organisms are, in both E. coli and budding yeast are 10-200mM, in mammalian cell 5-100mM and in blood plasma 100mM, chloride can be oxidized but not reduced. The first oxidation, as employed in the process, is conversion to chlorine gas. Chlorine can be oxidized to other oxides and oxyanions including hypochlorite, chlorine dioxide, chlorate
36.
Rebar
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Rebars surface is often patterned to form a better bond with the concrete. Rebar has been used in construction since at least the 15th century, more recently, during the 18th century, rebar was used to form the carcass of the Leaning Tower of Nevyansk in Russia, built on the orders of the industrialist Akinfiy Demidov. The cast iron used for the rebar was of high quality, the carcass of the tower was connected to its cast iron tented roof, crowned with one of the first known lightning rods. More recently these techniques have been refined by embedding the steel bars in the concrete, concrete is a material that is very strong in compression, but relatively weak in tension. To compensate for this imbalance in concretes behavior, rebar is cast into it to carry the tensile loads, rebar is also employed to confer resistance to concentrated loads by providing enough localized resistance and stiffness for a load to spread through a wider area. Rebar may also be used to other steel bars in the correct position to accommodate their loads. External steel tie bars can constrain and reinforce masonry structures, as illustrated by the Nevyansk Tower or ancient structures in Rome, masonry structures and the mortar holding them together have similar properties to concrete and also have a limited ability to carry tensile loads. Some standard masonry units like blocks and bricks are made with voids to accommodate rebar and this combination is known as reinforced masonry. Steel has a thermal expansion coefficient nearly equal to that of modern concrete, if this were not so, it would cause problems through additional longitudinal and perpendicular stresses at temperatures different from the temperature of the setting. To prevent such a failure, rebar is either deeply embedded into adjacent structural members, or bent and hooked at the ends to lock it around the concrete and other rebar. This first approach increases the friction locking the bar into place, common rebar is made of unfinished tempered steel, making it susceptible to rusting. Normally the concrete cover is able to provide a pH value higher than 12 avoiding the corrosion reaction, too little concrete cover can compromise this guard through carbonation from the surface, and salt penetration. Too much concrete cover can cause bigger crack widths which also compromises the local guard and this phenomenon is known as oxide jacking. This is a problem where the concrete is exposed to salt water, as in bridges where salt is applied to roadways in winter. Even damaged bars have shown better performance than uncoated reinforcing bars, though issues from debonding of the coating from the bars. These bars are used in over 70,000 bridge decks in the USA, fiber-reinforced polymer rebar is also used in high-corrosion environments. It is available in forms, such as spirals for reinforcing columns, common rods. Most commercially available rebar is made from glass fibre reinforced thermoset resins
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Concrete
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Concrete is a composite material composed of coarse aggregate bonded together with a fluid cement that hardens over time. Most concretes used are lime-based concretes such as Portland cement concrete or concretes made with other hydraulic cements, when aggregate is mixed together with dry Portland cement and water, the mixture forms a fluid slurry that is easily poured and molded into shape. The cement reacts chemically with the water and other ingredients to form a matrix that binds the materials together into a durable stone-like material that has many uses. Often, additives are included in the mixture to improve the properties of the wet mix or the finished material. Most concrete is poured with reinforcing materials embedded to provide tensile strength, famous concrete structures include the Hoover Dam, the Panama Canal, and the Roman Pantheon. The earliest large-scale users of technology were the ancient Romans. The Colosseum in Rome was built largely of concrete, and the dome of the Pantheon is the worlds largest unreinforced concrete dome. Today, large concrete structures are made with reinforced concrete. After the Roman Empire collapsed, use of concrete became rare until the technology was redeveloped in the mid-18th century, today, concrete is the most widely used man-made material. The word concrete comes from the Latin word concretus, the passive participle of concrescere, from con-. Perhaps the earliest known occurrence of cement was twelve years ago. A deposit of cement was formed after an occurrence of oil shale located adjacent to a bed of limestone burned due to natural causes and these ancient deposits were investigated in the 1960s and 1970s. On a human timescale, small usages of concrete go back for thousands of years and they discovered the advantages of hydraulic lime, with some self-cementing properties, by 700 BC. They built kilns to supply mortar for the construction of houses, concrete floors. The cisterns were kept secret and were one of the reasons the Nabataea were able to thrive in the desert, some of these structures survive to this day. In the Ancient Egyptian and later Roman eras, it was re-discovered that adding volcanic ash to the mix allowed it to set underwater, similarly, the Romans knew that adding horse hair made concrete less liable to crack while it hardened, and adding blood made it more frost-resistant. Crystallization of strätlingite and the introduction of pyroclastic clays creates further fracture resistance, german archaeologist Heinrich Schliemann found concrete floors, which were made of lime and pebbles, in the royal palace of Tiryns, Greece, which dates roughly to 1400–1200 BC. Lime mortars were used in Greece, Crete, and Cyprus in 800 BC, the Assyrian Jerwan Aqueduct made use of waterproof concrete
38.
Column
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A column or pillar in architecture and structural engineering is a structural element that transmits, through compression, the weight of the structure above to other structural elements below. In other words, a column is a compression member, the term column applies especially to a large round support with a capital and a base or pedestal and made of stone, or appearing to be so. A small wooden or metal support is called a post. For the purpose of wind or earthquake engineering, columns may be designed to resist lateral forces, other compression members are often termed columns because of the similar stress conditions. Columns are frequently used to support beams or arches on which the parts of walls or ceilings rest. In architecture, column refers to such an element that also has certain proportional. A column might also be an element not needed for structural purposes, many columns are engaged. All significant Iron Age civilizations of the Near East and Mediterranean made some use of columns, egyptian columns are famously present in the Great Hypostyle Hall of Karnak, where 134 columns are lined up in 16 rows, with some columns reaching heights of 24 metres. Some of the most elaborate columns in the ancient world were those of the Persians and they included double-bull structures in their capitals. The Hall of Hundred Columns at Persepolis, measuring 70 ×70 metres, was built by the Achaemenid king Darius I, many of the ancient Persian columns are standing, some being more than 30 metres tall. The Minoans used whole tree-trunks, usually turned upside down in order to prevent re-growth, stood on a set in the stylobate. These were then painted as in the most famous Minoan palace of Knossos, the Minoans employed columns to create large open-plan spaces, light-wells and as a focal point for religious rituals. These traditions were continued by the later Mycenaean civilization, particularly in the megaron or hall at the heart of their palaces. Being made of wood these early columns have not survived, but their bases have and through these we may see their use. The Greeks developed the classical orders of architecture, which are most easily distinguished by the form of the column and their Doric, Ionic, and Corinthian orders were expanded by the Romans to include the Tuscan and Composite orders. Columns, or at least large structural exterior ones, became less significant in the architecture of the Middle Ages. Early columns were constructed of stone, some out of a piece of stone. Monolithic columns are among the heaviest stones used in architecture, other stone columns are created out of multiple sections of stone, mortared or dry-fit together
39.
Golden Gate Bridge
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The Golden Gate Bridge is a suspension bridge spanning the Golden Gate strait, the one-mile-wide, one-point-seven-mile-long channel between San Francisco Bay and the Pacific Ocean. The bridge is one of the most internationally recognized symbols of San Francisco, California, and it has been declared one of the Wonders of the Modern World by the American Society of Civil Engineers. The Frommers travel guide describes the Golden Gate Bridge as possibly the most beautiful, certainly the most photographed and it opened in 1937 and was, until 1964, the longest suspension bridge main span in the world, at 4,200 feet. Before the bridge was built, the only practical short route between San Francisco and what is now Marin County was by boat across a section of San Francisco Bay. A ferry service began as early as 1820, with a scheduled service beginning in the 1840s for the purpose of transporting water to San Francisco. Once for railroad passengers and customers only, Southern Pacifics automobile ferries became very profitable, the trip from the San Francisco Ferry Building took 27 minutes. Many wanted to build a bridge to connect San Francisco to Marin County, San Francisco was the largest American city still served primarily by ferry boats. Because it did not have a permanent link with communities around the bay, experts said that ferocious winds and blinding fogs would prevent construction and operation. San Franciscos City Engineer estimated the cost at $100 million, which would have been $2.12 billion in 2009 and he asked bridge engineers whether it could be built for less. One who responded, Joseph Strauss, was an engineer and poet who had, for his graduate thesis. At the time, Strauss had completed some 400 drawbridges—most of which were inland—and nothing on the scale of the new project. Strausss initial drawings were for a massive cantilever on each side of the strait, connected by a central suspension segment, Local authorities agreed to proceed only on the assurance that Strauss would alter the design and accept input from several consulting project experts. A suspension-bridge design was considered the most practical, because of recent advances in metallurgy, Strauss spent more than a decade drumming up support in Northern California. The bridge faced opposition, including litigation, from many sources, the Department of War was concerned that the bridge would interfere with ship traffic. The navy feared that a collision or sabotage to the bridge could block the entrance to one of its main harbors. Unions demanded guarantees that local workers would be favored for construction jobs, in May 1924, Colonel Herbert Deakyne held the second hearing on the Bridge on behalf of the Secretary of War in a request to use federal land for construction. Another ally was the automobile industry, which supported the development of roads. The bridges name was first used when the project was discussed in 1917 by M. M
40.
San Francisco
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San Francisco, officially the City and County of San Francisco, is the cultural, commercial, and financial center of Northern California. It is the birthplace of the United Nations, the California Gold Rush of 1849 brought rapid growth, making it the largest city on the West Coast at the time. San Francisco became a consolidated city-county in 1856, after three-quarters of the city was destroyed by the 1906 earthquake and fire, San Francisco was quickly rebuilt, hosting the Panama-Pacific International Exposition nine years later. In World War II, San Francisco was a port of embarkation for service members shipping out to the Pacific Theater. Politically, the city votes strongly along liberal Democratic Party lines, San Francisco is also the headquarters of five major banking institutions and various other companies such as Levi Strauss & Co. Dolby, Airbnb, Weebly, Pacific Gas and Electric Company, Yelp, Pinterest, Twitter, Uber, Lyft, Mozilla, Wikimedia Foundation, as of 2016, San Francisco is ranked high on world liveability rankings. The earliest archaeological evidence of habitation of the territory of the city of San Francisco dates to 3000 BC. Upon independence from Spain in 1821, the became part of Mexico. Under Mexican rule, the system gradually ended, and its lands became privatized. In 1835, Englishman William Richardson erected the first independent homestead, together with Alcalde Francisco de Haro, he laid out a street plan for the expanded settlement, and the town, named Yerba Buena, began to attract American settlers. Commodore John D. Sloat claimed California for the United States on July 7,1846, during the Mexican–American War, montgomery arrived to claim Yerba Buena two days later. Yerba Buena was renamed San Francisco on January 30 of the next year, despite its attractive location as a port and naval base, San Francisco was still a small settlement with inhospitable geography. The California Gold Rush brought a flood of treasure seekers, with their sourdough bread in tow, prospectors accumulated in San Francisco over rival Benicia, raising the population from 1,000 in 1848 to 25,000 by December 1849. The promise of fabulous riches was so strong that crews on arriving vessels deserted and rushed off to the gold fields, leaving behind a forest of masts in San Francisco harbor. Some of these approximately 500 abandoned ships were used at times as storeships, saloons and hotels, many were left to rot, by 1851 the harbor was extended out into the bay by wharves while buildings were erected on piles among the ships. By 1870 Yerba Buena Cove had been filled to create new land, buried ships are occasionally exposed when foundations are dug for new buildings. California was quickly granted statehood in 1850 and the U. S. military built Fort Point at the Golden Gate, silver discoveries, including the Comstock Lode in Nevada in 1859, further drove rapid population growth. With hordes of fortune seekers streaming through the city, lawlessness was common, and the Barbary Coast section of town gained notoriety as a haven for criminals, prostitution, entrepreneurs sought to capitalize on the wealth generated by the Gold Rush
41.
Salt spray
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Sea spray refers to aerosol particles that are formed directly from the ocean, mostly by ejection into the atmosphere by bursting bubbles at the air-sea interface. Sea salt aerosol contains both inorganic salts and organic matter from the ocean and it is thought that the amount of organic matter transferred to SSA depends on microbiological activity. The organic matter in sea spray can contain dissolved organic matter or even themselves, like bacteria. Salt spray is largely responsible for corrosion of metallic objects near the coastline, as the salts accelerate the process in the presence of abundant atmospheric oxygen. Salts do not dissolve in air directly, but are suspended as fine particulates, the salt spray test is the notable measure of material endurance, particularly if the material will be used outdoors and must perform in a mechanical load bearing or otherwise critical role. These results are often of great interest to the industries, whose products may suffer extreme acceleration of corrosion
42.
Exploratorium
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The Exploratorium is a public learning laboratory in San Francisco exploring the world through science, art, and human perception. Its mission is to create inquiry-based experiences that transform learning worldwide, the Exploratorium was founded by physicist and educator Frank Oppenheimer and opened in 1969 at the Palace of Fine Arts, its home until January 2,2013. On April 17,2013, the Exploratorium reopened at Piers 15 and 17 on San Franciscos Embarcadero, since the museums founding, over 1,000 participatory exhibits have been created, approximately 600 of which are on the floor at any given time. The exhibit-building workshop space is contained within the museum and is open to view, since Oppenheimers death in 1985, the Exploratorium has expanded into other domains, including its 50, 000-page website and two iPad apps on sound and color. It has also inspired an international network of participatory museums working to engage the public with general science education, the new Exploratorium building is also working to showcase environmental sustainability efforts as part of its goal to become the largest net-zero museum in the country. The Exploratorium offers visitors a variety of ways—including exhibits, webcasts, websites and events—to explore, in 2011, the Exploratorium received the National Science Board 2011 Public Service Science Award for its contributions to public understanding of science and engineering. The Exploratorium is the brainchild of Frank Oppenheimer, an experimental physicist, Oppenheimer, who worked on the Manhattan Project with his brother J. He was blacklisted from academic positions across the country, and withdrew with his family to run a Colorado cattle ranch for almost a decade. Oppenheimer also began lending a hand with science projects of high school students, eventually becoming the sole science teacher at the high school in Pagosa Springs. The field trips and experiments he did with his school students would become a blueprint for the hands-on methods of teaching and learning he would later bring to the Exploratorium. He received a grant from the National Science Foundation, which he used to build models of nearly a hundred science experiments, convinced of the need for public museums to supplement science curricula at all levels, he toured Europe and studied museums on a Guggenheim Fellowship in 1965. Back in the United States, Oppenheimer was invited to do the planning for a new branch of the Smithsonian. In 1967, the Oppenheimers came to San Francisco with a view towards opening an independent museum of their own. Many prominent scientists and cultural figures endorsed the project, and the offers of support in conjunction with a $50,000 grant from the San Francisco Foundation made the museum realizable, in late August 1969, the Exploratorium opened with little fanfare at the Palace of Fine Arts. An early proposal would have erected a wall between the workshop where exhibits were being developed and the visitor areas. Above the workshop was a sign, made by the wife of George Gamow, a physicist, educator, the inscription said Here Is Being Created the Exploratorium a Community Museum Dedicated to Awareness. Oppenheimer served as the director until his death in 1985. Dr. Robert L. White served as Director from 1987 to 1990, dr. Goéry Delacôte served as Executive Director from 1991 until 2005
43.
Pitting corrosion
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Pitting corrosion, or pitting, is a form of extremely localized corrosion that leads to the creation of small holes in the metal. The corrosion penetrates the mass of the metal, with a limited diffusion of ions, the mechanism of pitting corrosion is probably the same as crevice corrosion. The more conventional explanation for pitting corrosion is that it is an autocatalytic process, for example, when a metal is present in an oxygenated NaCl electrolyte, the pit acts as anode and the metal surface acts as cathode. The localised production of metal ions in the pit gives a local excess of positive charge which attracts the negative chlorine ions from the electrolyte to produce charge neutrality. The pit is anodic and the locus of rapid dissolution of the metal, the metal corrosion initiation is autocatalytic in nature however its propagation is not. This kind of corrosion is extremely insidious, as it causes loss of material with the small effect on its surface. The pits on the surface are often obscured by corrosion products, Pitting can be initiated by a small surface defect, being a scratch or a local change in composition, or a damage to the protective coating. Polished surfaces display higher resistance to pitting, Pitting Corrosion is defined by localised attack in an otherwise passive surface and only occurs for specific alloy / environment combinations. In contrast, alloy / environment combinations where the film is not very protective usually will not produce pitting corrosion. A good example of the importance of environment / alloy combinations is carbon steel, in environments where the pH is less than 10, carbon steel does not form a passivating oxide film and the addition of chloride results in uniform attack over the entire surface. However, at pH greater than 10 the oxide is very protecting, besides chlorides, other anions implicated in pitting include thiosulfates, fluorides and iodides. Thiosulfates are particularly aggressive species and are formed by oxidation of pyrite. Corrosion inhibitors, when present in sufficient amount, will provide protection against pitting, however, too low level of them can aggravate pitting by forming local anodes. A single pit in a point can cause a great deal of damage. One example is the explosion in Guadalajara, Mexico on April 22,1992, the vapours originated from a leak of gasoline through a single hole formed by corrosion between a steel gasoline pipe and a zinc-plated water pipe. Firearms can also suffer from pitting, most notably in the bore of the barrel when corrosive ammunition is used, deformities in the bore caused by pitting can greatly reduce the firearms accuracy. To prevent pitting in firearm bores, most modern firearms have a bore lined with chromium, Corrosion Crevice corrosion Micro pitting Panel edge staining Stress corrosion cracking Pitting Corrosion - Corrosion Doctors
44.
Salt
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Salt is present in vast quantities in seawater, where it is the main mineral constituent. The open ocean has about 35 grams of solids per litre, Salt is essential for life in general, and saltiness is one of the basic human tastes. The tissues of animals contain larger quantities of salt than do plant tissues, Salt is one of the oldest and most ubiquitous food seasonings, and salting is an important method of food preservation. Salt was also prized by the ancient Hebrews, the Greeks, the Romans, the Byzantines, the Hittites, Egyptians, and the Indians. Salt became an important article of trade and was transported by boat across the Mediterranean Sea, along specially built salt roads, the scarcity and universal need for salt has led nations to go to war over it and use it to raise tax revenues. Salt is used in ceremonies and has other cultural significance. Salt is processed from salt mines, or by the evaporation of seawater or mineral-rich spring water in shallow pools. Its major industrial products are caustic soda and chlorine, and is used in industrial processes including the manufacture of polyvinyl chloride, plastics, paper pulp. Of the annual production of around two hundred million tonnes of salt, only about 6% is used for human consumption. Other uses include water conditioning processes, de-icing highways, and agricultural use, edible salt is sold in forms such as sea salt and table salt which usually contains an anti-caking agent and may be iodised to prevent iodine deficiency. As well as its use in cooking and at the table, sodium is an essential nutrient for human health via its role as an electrolyte and osmotic solute. Excessive salt consumption can increase the risk of diseases, such as hypertension, in children. Such health effects of salt have long been studied, accordingly, numerous world health associations and experts in developed countries recommend reducing consumption of popular salty foods. The World Health Organization recommends that adults should consume less than 2,000 mg of sodium, humans have always tended to build communities either around sources of salt, or where they can trade for it. All through history the availability of salt has been pivotal to civilization, the word salary comes from the Latin word for salt because the Roman Legions were sometimes paid in salt. The Natron Valley was a key region that supported the Egyptian Empire to its north, because it supplied it with a kind of salt that came to be called by its name, natron. Even before this, what is now thought to have been the first city in Europe is Solnitsata, in Bulgaria, even the name Solnisata means salt works. A very ancient salt-works operation has been discovered at the Poiana Slatinei archaeological site next to a spring in Lunca, Neamț County
