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McGraw Hill Financial, Inc. is an American publicly traded corporation headquartered in Rockefeller Center in New York City. Its primary areas of business are financial, publishing, and business services.
A metallic chemical element, Nd, atomic number 60, atomic weight 144.24. Neodymium belongs to the rare-earth group of elements. The naturally occurring element includes six isotopes. The oxide, Nd<sub>2</sub>O<sub>3</sub>, is a light-blue powder. It dissolves in mineral acids to give reddish-violet solutions. For properties of the metal
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A metallic chemical element, symbol Al, atomic number 13, atomic weight 26.98154, in group 13 of the periodic system. Pure aluminum is soft and lacks strength, but it can be alloyed with other elements to increase strength and impart a number of useful properties. Alloys of aluminum are light, strong, and readily formable by many metalworking processes; they can be easily joined, cast, or machined, and accept a wide variety of finishes. Because of its many desirable physical, chemical, and metallurgical properties, aluminum has become the most widely used nonferrous metal.
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A metallic element, Mn, atomic number 25, and atomic weight 54.9380 g/mole. Manganese is one of the transition elements of the first long period of the periodic table, falling between chromium and iron. The principal properties of manganese are given in the table. It is the twelfth most abundant element in the Earth's crust (approximately 0.1%) and occurs naturally in several forms, primarily as the silicate (MnSiO<sub>3</sub>) but also as the carbonate (MnCO<sub>3</sub>) and a variety of oxides, including pyrolusite (MnO<sub>2</sub>) and hausmannite (Mn<sub>3</sub>O<sub>4</sub>). Weathering of land deposits has led to large amounts of the oxide being washed out to sea, where they have aggregated into the so-called manganese nodules containing 15–30% Mn. Vast deposits, estimated at over 10<sup>12</sup> metric tons, have been detected on the seabed, and a further 10<sup>7</sup> metric tons is deposited every year. The nodules also contain smaller amounts of the oxides of other metals such as iron (Fe), cobalt (Co), nickel (Ni), and copper (Cu). The economic importance of the nodules as a source of these important metals is enormous.
Industry:Science
A metallic element, symbol Hf, atomic number 72, and atomic weight 178.49. There are five naturally occurring isotopes. It is one of the less abundant elements in the Earth's crust.
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A metallic rare-earth element, Dy, atomic number 66 and atomic weight 162.50. The naturally occurring element is composed of seven stable isotopes. Dysprosium forms a white oxide, Dy<sub>2</sub>O<sub>3</sub>, which dissolves in acid to give a yellowish-green solution.
Industry:Science
A metal-semiconductor diode (two terminal electrical device) that exhibits a very nonlinear relation between voltage across it and current through it; formally known as a metallic disk rectifier. Original metallic disk rectifiers used selenium of copper oxide as the semiconductor coated on a metal disk. Today, the semiconductor is usually single-crystal silicon with two separate thin metal layers deposited on it to form electrical contacts. One of the two layers is made of a metal which forms a Schottky barrier to the silicon. The other forms a very low resistance, so-called ohmic, contact. The Schottky barrier is an electron or hole barrier caused by an electric dipole charge distribution associated with the contact potential difference which forms between a metal and a semiconductor under equilibrium conditions. The barrier is very abrupt at the surface of the metal because the charge is primarily on the surface. However, in the semiconductor, the charge is distributed over a small distance, and the potential gradually varies across this distance (see <b>illus.</b>).
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A metalworking process used to fabricate parts of simple or complex shape from a wide variety of metals and alloys in the form of powders. The process involves shaping of the powder and subsequent bonding of its individual particles by heating or mechanical working. Powder metallurgy is a highly flexible and automated process that is environmentally friendly, with a low relative energy consumption and a high level of materials utilization. Thus it is possible to fabricate high-quality parts to close tolerance at low cost. Powder metallurgy processing encompasses an extensive range of ferrous and nonferrous alloy powders, ceramic powders, and mixes of metallic and ceramic powders (composite powders).
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A metamorphic rock consisting largely or entirely of quartz. Most quartzites are formed by metamorphism of sandstone; but some have developed by metasomatic introduction of quartz, SiO<sub>2</sub>, often accompanied by other chemical elements, for example, metals and sulfur (ore quartzites). The geological relations and the shape of quartzite bodies serve to distinguish between them (see <b>illus.</b>). The metasomatic quartzites are often found as contact products of intrusive bodies.
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A metamorphic rock that has been subjected to heating during contact metamorphism around intrusive igneous rocks. Hornfels is typically fine-grained, although where it is subjected to high temperatures, large crystals called porphyroblasts can form. In outcrop, hornfels is notoriously tough and can be difficult to sample. Mineral grains in hornfels are randomly oriented, with no preferred alignment of crystals to form foliation or cleavage planes. This texture indicates that the hornfels was not subjected to significant stresses during contact metamorphism.
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A metamorphic silicate mineral related chemically and structurally to the epidote group of minerals. Its composition is Ca(H<sub>2</sub>O)Al<sub>2</sub>(OH)<sub>2</sub>(Si<sub>2</sub>O<sub>7</sub>), and it is a sorosilicate based on the dimeric (Si<sub>2</sub>O<sub>7</sub>)<sup>6<sup>−</sup></sup> radical, where two (SiO<sub>4</sub>) tetrahedra link at a common vertex to form a bow-tie arrangement. The water molecule is bonded directly to the calcium ion and is tightly held. Although the calcium (Ca<sup>2+</sup>) and the aluminum (Al<sup>3+</sup>) cations are octahedrally coordinated by anions (and the water molecule), and the silicon cation (Si<sup>4+</sup>) is tetrahedrally coordinated by the anions, the structure is not limitingly closest-packed.
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