An alloy is a combination of metals and of a metal or another element. Alloys are defined by a metallic bonding character. An alloy may be a mixture of metallic phases. Intermetallic compounds are alloys with a defined crystal structure. Zintl phases are sometimes considered alloys depending on bond types. Alloys are used in a wide variety of applications. In some cases, a combination of metals may reduce the overall cost of the material while preserving important properties. In other cases, the combination of metals imparts synergistic properties to the constituent metal elements such as corrosion resistance or mechanical strength. Examples of alloys are steel, brass, duralumin and amalgams; the alloy constituents are measured by mass percentage for practical applications, in atomic fraction for basic science studies. Alloys are classified as substitutional or interstitial alloys, depending on the atomic arrangement that forms the alloy, they can be heterogeneous or intermetallic. An alloy is a mixture of chemical elements, which forms an impure substance that retains the characteristics of a metal.
An alloy is distinct from an impure metal in that, with an alloy, the added elements are well controlled to produce desirable properties, while impure metals such as wrought iron are less controlled, but are considered useful. Alloys are made by mixing two or more elements, at least one of, a metal; this is called the primary metal or the base metal, the name of this metal may be the name of the alloy. The other constituents may or may not be metals but, when mixed with the molten base, they will be soluble and dissolve into the mixture; the mechanical properties of alloys will be quite different from those of its individual constituents. A metal, very soft, such as aluminium, can be altered by alloying it with another soft metal, such as copper. Although both metals are soft and ductile, the resulting aluminium alloy will have much greater strength. Adding a small amount of non-metallic carbon to iron trades its great ductility for the greater strength of an alloy called steel. Due to its very-high strength, but still substantial toughness, its ability to be altered by heat treatment, steel is one of the most useful and common alloys in modern use.
By adding chromium to steel, its resistance to corrosion can be enhanced, creating stainless steel, while adding silicon will alter its electrical characteristics, producing silicon steel. Like oil and water, a molten metal may not always mix with another element. For example, pure iron is completely insoluble with copper; when the constituents are soluble, each will have a saturation point, beyond which no more of the constituent can be added. Iron, for example, can hold a maximum of 6.67% carbon. Although the elements of an alloy must be soluble in the liquid state, they may not always be soluble in the solid state. If the metals remain soluble when solid, the alloy forms a solid solution, becoming a homogeneous structure consisting of identical crystals, called a phase. If as the mixture cools the constituents become insoluble, they may separate to form two or more different types of crystals, creating a heterogeneous microstructure of different phases, some with more of one constituent than the other phase has.
However, in other alloys, the insoluble elements may not separate until after crystallization occurs. If cooled quickly, they first crystallize as a homogeneous phase, but they are supersaturated with the secondary constituents; as time passes, the atoms of these supersaturated alloys can separate from the crystal lattice, becoming more stable, form a second phase that serve to reinforce the crystals internally. Some alloys, such as electrum, an alloy consisting of silver and gold, occur naturally. Meteorites are sometimes made of occurring alloys of iron and nickel, but are not native to the Earth. One of the first alloys made by humans was bronze, a mixture of the metals tin and copper. Bronze was an useful alloy to the ancients, because it is much stronger and harder than either of its components. Steel was another common alloy. However, in ancient times, it could only be created as an accidental byproduct from the heating of iron ore in fires during the manufacture of iron. Other ancient alloys include pewter and pig iron.
In the modern age, steel can be created in many forms. Carbon steel can be made by varying only the carbon content, producing soft alloys like mild steel or hard alloys like spring steel. Alloy steels can be made by adding other elements, such as chromium, vanadium or nickel, resulting in alloys such as high-speed steel or tool steel. Small amounts of manganese are alloyed with most modern steels because of its ability to remove unwanted impurities, like phosphorus and oxygen, which can have detrimental effects on the alloy. However, most alloys were not created until the 1900s, such as various aluminium, titanium and magnesium alloys; some modern superalloys, such as incoloy and hastelloy, may consist of a multitude of different elements. As a noun, the term alloy is used to describe a mixture of atoms in which the primary constituent is a metal; when used as a verb, the term refers to the act of mixing a metal with other elements. The primary metal is called the matrix, or the solvent; the secondary constituents are called s
Pyrolusite is a mineral consisting of manganese dioxide and is important as an ore of manganese. It is a black, amorphous appearing mineral with a granular, fibrous or columnar structure, sometimes forming reniform crusts, it has a metallic luster, a black or bluish-black streak, soils the fingers. The specific gravity is about 4.8. Its name is from the Greek for fire and to wash, in reference to its use as a way to remove tints from glass. Pyrolusite and romanechite are among the most common manganese minerals. Pyrolusite occurs associated with manganite, hausmannite, chalcophanite and hematite under oxidizing conditions in hydrothermal deposits, it occurs in bogs and results from alteration of manganite. The metal is obtained by reduction of the oxide with sodium, aluminium, or by electrolysis. Pyrolusite is extensively used for the manufacture of spiegeleisen and ferromanganese and of various alloys such as manganese-bronze; as an oxidizing agent it is used in the preparation of chlorine. Natural pyrolusite has been used in batteries, but high-quality batteries require synthetic products.
Pyrolusite is used to prepare disinfectants and for decolorizing glass. When mixed with molten glass it oxidizes the ferrous iron to ferric iron, so discharges the green and brown tints; as a coloring material, it is used in calico dyeing. Black, manganese oxides with a dendritic crystal habit found on fracture or rock surfaces are assumed to be pyrolusite although careful analyses of numerous examples of these dendrites has shown that none of them are in fact pyrolusite. Instead, they are other forms of manganese oxide; some of the most famous early cave paintings in Europe were executed by means of manganese dioxide. Blocks of pyrolusite are found at Neanderthal sites, it may have been kept as a pigment for cave paintings, but it has been suggested that it was powdered and mixed with tinder fungus for lighting fires. Manganese dioxide, in the form of umber, was one of the earliest natural substances used by human ancestors, it was used as a pigment at least from the middle paleolithic. It may have been used by the Neanderthals in fire-making.
The ancient Greeks had a term μάγνης or Μάγνης λίθος meaning stone of the area called Μαγνησία, referring to Magnesia in Thessaly or to areas in Asia Minor with that name. Two minerals are called namely lodestone and pyrolusite; the term μαγνησία was used for manganese dioxide. In the 16th century it was called "manganesum", it was called Alabandicus and Braunstein. The name of the element manganese was derived from "manganesum", whereas "magnesia" came to mean the oxide of a different element, magnesium. Other manganese oxides: Birnessite Psilomelane This article incorporates text from a publication now in the public domain: Chisholm, Hugh, ed.. "Pyrolusite". Encyclopædia Britannica. 22. Cambridge University Press. P. 693
Specular reflection known as regular reflection, is the mirror-like reflection of waves, such as light, from a surface. In this process, each incident ray is reflected at the same angle to the surface normal as the incident ray, but on the opposing side of the surface normal in the plane formed by incident and reflected rays; the result is. The law of reflection states that for each incident ray the angle of incidence equals the angle of reflection, the incident and reflected directions are coplanar; this behavior was first described by Hero of Alexandria. It may be contrasted with diffuse reflection, in which light is scattered away from the surface in a range of directions rather than just one; when light hits a surface, there are three possible outcomes. Light may be absorbed by the material, light may be transmitted through the surface, or light may be reflected. Materials show some mix of these behaviors, with the proportion of light that goes to each depending on the properties of the material, the wavelength of the light, the angle of incidence.
For most interfaces between materials, the fraction of the light, reflected increases with increasing angle of incidence θ i. Reflected light can be divided into specular reflection and diffuse reflection. Specular reflection reflects all light which arrives from a given direction at the same angle, whereas diffuse reflection reflects that light in a broad range of directions. An example of the distinction between specular and diffuse reflection would be glossy and matte paints. Matte paints have exclusively diffuse reflection, while glossy paints have both specular and diffuse reflection. A surface built from a non-absorbing powder, such as plaster, can be a nearly perfect diffuser, whereas polished metallic objects can specularly reflect light efficiently; the reflecting material of mirrors is aluminum or silver. The law of reflection describes the angle of reflected light: the angle of incident light is the same as the angle of the reflected light; the law of reflection arises from diffraction of a plane wave with small wavelength on a flat boundary: when the boundary size is much larger than the wavelength electrons of the boundary are seen oscillating in phase only from one direction – the specular direction.
If a mirror becomes small compared to the wavelength, the law of reflection no longer holds, the behavior of light is more complicated. The law of reflection can be equivalently expressed using linear algebra; the direction of a reflected ray is determined by the vector of incidence and the surface normal vector. Given an incident direction d ^ i from the surface to the light source and the surface normal direction d ^ n, the specularly reflected direction d ^ s is: d ^ s = 2 d ^ n − d ^ i, where d ^ n ⋅ d ^ i is a scalar obtained with the dot product. Different authors may define the reflection directions with different signs. Assuming these Euclidean vectors are represented in column form, the equation can be equivalently expressed as a matrix-vector multiplication: d ^ s = R d ^ i, where R is the so-called Householder transformation matrix, defined as: R = I − 2 d ^ n d ^ n T. Reflectivity is the ratio of the power of the reflected wave to that of the incident wave, it is a function of the wavelength of radiation, is related to the refractive index of the material as expressed by Fresnel's equations.
In regions of the electromagnetic spectrum in which absorption by the material is significant, it is related to the electronic absorption spectrum through the imaginary component of the complex refractive index. The electronic absorption spectrum of an opaque material, difficult or impossible to measure directly, may therefore be indirectly determined from the reflection spectrum by a Kramers-Kronig transform; the polarization of the r
Manganite is a mineral composed of manganese oxide-hydroxide, MnO, crystallizing in the monoclinic system. Crystals of manganite are prismatic and striated parallel to their length; the color is dark steel-grey to iron-black, the luster brilliant and submetallic. The streak is dark reddish brown; the hardness is 4, the specific gravity is 4.3. There is a perfect cleavage parallel to the brachypinacoid, less-perfect cleavage parallel to the prism faces. Twinned crystals are not infrequent; the mineral contains 89.7% manganese sesquioxide. Manganite occurs with other manganese oxides in deposits formed by circulating meteoric water in the weathering environment in clay deposits and laterites, it forms by low temperature hydrothermal action in veins in association with calcite and siderite. Associated with pyrolusite, braunite and goethite. Manganite occurs in specimens exhibiting good crystal form at Ilfeld in the Harz Mountains of Germany, where the mineral occurs with calcite and barite in veins traversing porphyry.
Crystals have been found at Ilmenau in Thuringia, Neukirch near Sélestat in Alsace, Granam near Towie in Aberdeenshire, in Upton Pyne near Exeter, UK and Negaunee, United States, in the Pilbara of Western Australia. Good crystals have been found at Atikokan and Nova Scotia, Canada; as an ore of manganese it is much less abundant than psilomelane. Although described with various other names as early as 1772, the name manganite was first applied in a publication by W. Haidinger in 1827; the mineral was used in prehistoric times as a pigment, by humans, as a fire starter by Neanderthalers. Manganite is believed to have been used in prehistoric times to start a wood fire. Manganite lowers the combustion temperature of wood from 350 degrees Celsius to 250 degrees Celsius. Manganite powder has been a common find in Neanderthal archaeological sites; the thermolysis of manganite was researched by J. LAURENCE KULP and JOSE N. PERFETTI Department of Geology, Columbia University, New York City, N. Y. in their article in Mineral Society, 1950, Thermal study of some manganese oxide minerals.
In this article Manganese oxide This article incorporates text from a publication now in the public domain: Chisholm, Hugh, ed.. "Manganite". Encyclopædia Britannica. 17. Cambridge University Press. P. 571
Siderite is the name of a type of iron meteorite. Siderite is a mineral composed of iron carbonate, it takes its name from the Greek word σίδηρος sideros, “iron”. It is a valuable iron mineral, since it contains no sulfur or phosphorus. Zinc and manganese substitute for the iron resulting in the siderite-smithsonite, siderite-magnesite and siderite-rhodochrosite solid solution series. Siderite has Mohs hardness of 3.75-4.25, a specific gravity of 3.96, a white streak and a vitreous lustre or pearly luster. It crystallizes in the trigonal crystal system, are rhombohedral in shape with curved and striated faces, it occurs in masses. Color ranges from black, the latter being due to the presence of manganese. Siderite is found in hydrothermal veins, is associated with barite, fluorite and others, it is a common diagenetic mineral in shales and sandstones, where it sometimes forms concretions, which can encase three-dimensionally preserved fossils. In sedimentary rocks, siderite forms at shallow burial depths and its elemental composition is related to the depositional environment of the enclosing sediments.
In addition, a number of recent studies have used the oxygen isotopic composition of sphaerosiderite as a proxy for the isotopic composition of meteoric water shortly after deposition. Although spathic iron ores, such as siderite, have been economically important for steel production, they are far from ideal as an ore, their hydrothermal mineralisation tends to form them as small ore lenses following steeply dipping bedding planes. This makes them not amenable to opencast working, increases the cost of working them by mining with horizontal stopes; as the individual ore bodies are small, it may be necessary to duplicate or relocate the pit head machinery, winding engine and pumping engine, between these bodies as each is worked out. This makes mining the ore an expensive proposition compared to typical ironstone or haematite opencasts; the recovered ore has drawbacks. The carbonate ore is more difficult to smelt than other oxide ore. Driving off the carbonate as carbon dioxide requires more energy and so the ore'kills' the blast furnace if added directly.
Instead the ore must be given a preliminary roasting step. Developments of specific techniques to deal with these ores began in the early 19th century with the work of Sir Thomas Lethbridge in Somerset. His'Iron Mill' of 1838 used a three-chambered concentric roasting furnace, before passing the ore to a separate reducing furnace for smelting. Details of this Mill were the invention of Charles Sanderson, a steel maker of Sheffield, who held the patent for it; these differences between spathic ore and haematite have led to the failure of a number of mining concerns, notably the Brendon Hills Iron Ore Company. Spathic iron ores have negligible phosphorus; this led to their one major benefit. Although the first demonstrations by Bessemer in 1856 had been successful attempts to reproduce this were infamously failures. Work by the metallurgist Robert Forester Mushet discovered that the reason for this was the nature of the Swedish ores that Bessemer had innocently used, being low in phosphorus. Using a typical European high-phosphorus ore in Bessemer's converter gave a poor quality steel.
To produce high quality steel from a high-phosphorus ore, Mushet realised that he could operate the Bessemer converter for longer, burning off all the steel's impurities including the unwanted phosphorus and the essential carbon, but re-adding carbon, with manganese, in the form of a obscure ferromanganese ore with no phosphorus, spiegeleisen. This created a sudden demand for spiegeleisen. Although it was not available in sufficient quantity as a mineral, steelworks such as that at Ebbw Vale in South Wales soon learned to make it from the spathic siderite ores. For a few decades, spathic ores were now in demand and this encouraged their mining. In time though, the original'acidic' liner, made from siliceous sandstone or ganister, of the Bessemer converter was replaced by a'basic' liner in the developed Gilchrist Thomas process; this removed the phosphorus impurities as slag, produced by chemical reaction with the liner, no longer required spiegeleisen. From the 1880s demand for the ores fell once again and many of their mines, including those of the Brendon Hills, closed soon after
Carbon is a chemical element with symbol C and atomic number 6. It is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds, it belongs to group 14 of the periodic table. Three isotopes occur 12C and 13C being stable, while 14C is a radionuclide, decaying with a half-life of about 5,730 years. Carbon is one of the few elements known since antiquity. Carbon is the 15th most abundant element in the Earth's crust, the fourth most abundant element in the universe by mass after hydrogen and oxygen. Carbon's abundance, its unique diversity of organic compounds, its unusual ability to form polymers at the temperatures encountered on Earth enables this element to serve as a common element of all known life, it is the second most abundant element in the human body by mass after oxygen. The atoms of carbon can bond together in different ways, termed allotropes of carbon; the best known are graphite and amorphous carbon. The physical properties of carbon vary with the allotropic form.
For example, graphite is opaque and black while diamond is transparent. Graphite is soft enough to form a streak on paper, while diamond is the hardest occurring material known. Graphite is a good electrical conductor. Under normal conditions, carbon nanotubes, graphene have the highest thermal conductivities of all known materials. All carbon allotropes are solids under normal conditions, with graphite being the most thermodynamically stable form at standard temperature and pressure, they are chemically resistant and require high temperature to react with oxygen. The most common oxidation state of carbon in inorganic compounds is +4, while +2 is found in carbon monoxide and transition metal carbonyl complexes; the largest sources of inorganic carbon are limestones and carbon dioxide, but significant quantities occur in organic deposits of coal, peat and methane clathrates. Carbon forms a vast number of compounds, more than any other element, with ten million compounds described to date, yet that number is but a fraction of the number of theoretically possible compounds under standard conditions.
For this reason, carbon has been referred to as the "king of the elements". The allotropes of carbon include graphite, one of the softest known substances, diamond, the hardest occurring substance, it bonds with other small atoms, including other carbon atoms, is capable of forming multiple stable covalent bonds with suitable multivalent atoms. Carbon is known to form ten million different compounds, a large majority of all chemical compounds. Carbon has the highest sublimation point of all elements. At atmospheric pressure it has no melting point, as its triple point is at 10.8±0.2 MPa and 4,600 ± 300 K, so it sublimes at about 3,900 K. Graphite is much more reactive than diamond at standard conditions, despite being more thermodynamically stable, as its delocalised pi system is much more vulnerable to attack. For example, graphite can be oxidised by hot concentrated nitric acid at standard conditions to mellitic acid, C66, which preserves the hexagonal units of graphite while breaking up the larger structure.
Carbon sublimes in a carbon arc, which has a temperature of about 5800 K. Thus, irrespective of its allotropic form, carbon remains solid at higher temperatures than the highest-melting-point metals such as tungsten or rhenium. Although thermodynamically prone to oxidation, carbon resists oxidation more than elements such as iron and copper, which are weaker reducing agents at room temperature. Carbon is the sixth element, with a ground-state electron configuration of 1s22s22p2, of which the four outer electrons are valence electrons, its first four ionisation energies, 1086.5, 2352.6, 4620.5 and 6222.7 kJ/mol, are much higher than those of the heavier group-14 elements. The electronegativity of carbon is 2.5 higher than the heavier group-14 elements, but close to most of the nearby nonmetals, as well as some of the second- and third-row transition metals. Carbon's covalent radii are taken as 77.2 pm, 66.7 pm and 60.3 pm, although these may vary depending on coordination number and what the carbon is bonded to.
In general, covalent radius decreases with higher bond order. Carbon compounds form the basis of all known life on Earth, the carbon–nitrogen cycle provides some of the energy produced by the Sun and other stars. Although it forms an extraordinary variety of compounds, most forms of carbon are comparatively unreactive under normal conditions. At standard temperature and pressure, it resists all but the strongest oxidizers, it does not react with hydrochloric acid, chlorine or any alkalis. At elevated temperatures, carbon reacts with oxygen to form carbon oxides and will rob oxygen from metal oxides to leave the elemental metal; this exothermic reaction is used in the iron and steel industry to smelt iron and to control the carbon content of steel: Fe3O4 + 4 C → 3 Fe + 4 COCarbon monoxide can be recycled to smelt more iron: Fe3O4 + 4 CO → 3 Fe + 4 CO2with sulfur to form carbon disulfide and with steam in the coal-gas reaction: C + H2O → CO + H2. Carbon combines with some metals at high temperatures to form metallic carbides, such as the iron carbide cementite in steel and tungsten carbide used as an abrasive and for making hard tips for cutting tools.
The system of carbon allotropes spans a range of extremes: Atomic carbon is a ver