Pages in category "Magnetic alloys"
The following 19 pages are in this category, out of 19 total. This list may not reflect recent changes (learn more).
The following 19 pages are in this category, out of 19 total. This list may not reflect recent changes (learn more).
1. Alloy – An alloy is a mixture of metals or a mixture of a metal and another element. Alloys are defined by a metallic bonding character, an alloy may be a solid solution of metal elements or a mixture of metallic phases. Intermetallic compounds are alloys with a stoichiometry and crystal structure. Zintl phases are sometimes considered alloys depending on bond types. Alloys are used in a 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, solder, brass, pewter, duralumin, bronze, the alloy constituents are usually measured by mass. Alloys are usually classified as substitutional or interstitial alloys, depending on the arrangement that forms the alloy. They can be classified as homogeneous, or heterogeneous or intermetallic. An alloy is a mixture of elements, which forms an impure substance that retains the characteristics of a metal. Alloys are made by mixing two or more elements, at least one of which is a metal and this is usually called the primary metal or the base metal, and the name of this metal may also be the name of the alloy. The other constituents may or may not be metals but, when mixed with the base, they will be soluble. The mechanical properties of alloys will often be different from those of its individual constituents. A metal that is very soft, such as aluminium, can be altered by alloying it with another soft metal. Although both metals are soft and ductile, the resulting aluminium alloy will have much greater strength. Adding a small amount of carbon to iron trades its great ductility for the greater strength of an alloy called steel. Due to its strength, but still substantial toughness, and its ability to be greatly altered by heat treatment, steel is one of the most useful. 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
2. Alnico – Alnico is an acronym referring to a family of iron alloys which in addition to iron are composed primarily of aluminium, nickel and cobalt, hence al-ni-co. They also include copper, and sometimes titanium, Alnico alloys are ferromagnetic, with a high coercivity and are used to make permanent magnets. Before the development of rare-earth magnets in the 1970s, they were the strongest type of permanent magnet, other trade names for alloys in this family are, Alni, Alcomax, Hycomax, Columax, and Ticonal. The composition of alnico alloys is typically 8–12% Al, 15–26% Ni, 5–24% Co, up to 6% Cu, up to 1% Ti, Alnico alloys can be magnetised to produce strong magnetic fields and have a high coercivity, thus making strong permanent magnets. Of the more commonly available magnets, only rare-earth magnets such as neodymium, Alnico magnets produce magnetic field strength at their poles as high as 1500 gausses, or about 3000 times the strength of Earths magnetic field. Some brands of alnico are isotropic and can be magnetized in any direction. Other types, such as alnico 5 and alnico 8, are anisotropic, with each having a direction of magnetization. Anisotropic alloys generally have greater capacity in a preferred orientation than isotropic types. Alnicos remanence may exceed 12,000 G, its coercivity can be up to 1000 oersteds and this means that alnico can produce a strong magnetic flux in closed magnetic circuits, but has relatively small resistance against demagnetization. The field strength at the poles of any permanent magnet depends very much on the shape and is well below the remanence strength of the material. Alnico alloys have some of the highest Curie temperatures of any material, around 800 °C. They are the only magnets that have useful magnetism even when heated red-hot and this property, as well as its brittleness and high melting point, is the result of the strong tendency toward order due to intermetallic bonding between aluminium and other constituents. They are also one of the most stable if they are handled properly. Alnico magnets are electrically conductive, unlike ceramic magnets, as of 2008, Alnico magnets cost about 44 USD/kg or 4.30 USD/BHmax. Alnico magnets are traditionally classified using numbers assigned by the Magnetic Materials Producers Association, for example and these classifications indicate chemical composition and magnetic properties. Alnico magnets are produced by casting or sintering processes, anisotropic alnico magnets are oriented by heating above a critical temperature and cooling in the presence of a magnetic field. After the heat treatment alnico becomes a material, named precipitation material—it consists of iron-. Without an external field there are local anisotropies of different orientations due to spontaneous magnetization, the precipitate structure is a barrier against magnetization changes, as it prefers few magnetization states requiring much energy to get the material into any intermediate state
3. Neodymium magnet – A neodymium magnet, the most widely used type of rare-earth magnet, is a permanent magnet made from an alloy of neodymium, iron and boron to form the Nd2Fe14B tetragonal crystalline structure. Developed in 1982 by General Motors and Sumitomo Special Metals, neodymium magnets are the strongest type of permanent magnet commercially available. They have replaced other types of magnets in the applications in modern products that require strong permanent magnets, such as motors in cordless tools, hard disk drives. However, compounds of neodymium with transition metals such as iron can have Curie temperatures well above room temperature, the strength of neodymium magnets is due to several factors. The tetragonal Nd2Fe14B crystal structure has exceptionally high uniaxial magnetocrystalline anisotropy and this means a crystal of the material preferentially magnetizes along a specific crystal axis, but is very difficult to magnetize in other directions. The resistance of the lattice to turning its direction of magnetization gives the compound a very high coercivity. The neodymium atom also can have a magnetic dipole moment because it has 7 unpaired electrons in its electron structure as opposed to 3 in iron. In a magnet it is the electrons, aligned so they spin in the same direction. This gives the Nd2Fe14B compound a high saturation magnetization and typically 1.3 teslas, therefore, as the maximum energy density is proportional to Js2, this magnetic phase has the potential for storing large amounts of magnetic energy. This magnetic energy value is about 18 times greater than ordinary magnets by volume and this property is higher in NdFeB alloys than in samarium cobalt magnets, which were the first type of rare-earth magnet to be commercialized. In practice, the properties of neodymium magnets depend on the alloy composition, microstructure. In 1982, General Motors and Sumitomo Special Metals discovered the Nd2Fe14B compound, the research was initially driven by the high raw materials cost of SmCo permanent magnets, which had been developed earlier. GM focused on the development of melt-spun nanocrystalline Nd2Fe14B magnets, while Sumitomo developed full-density sintered Nd2Fe14B magnets, GM commercialized its inventions of isotropic Neo powder, bonded Neo magnets, and the related production processes by founding Magnequench in 1986. The company supplied melt-spun Nd2Fe14B powder to bonded magnet manufacturers, the Sumitomo facility became part of the Hitachi Corporation, and currently manufactures and licenses other companies to produce sintered Nd2Fe14B magnets. Hitachi holds more than 600 patents covering neodymium magnets, chinese manufacturers have become a dominant force in neodymium magnet production, based on their control of much of the worlds sources of rare earth mines. The United States Department of Energy has identified a need to find substitutes for rare earth metals in permanent magnet technology, the Advanced Research Projects Agency-Energy has sponsored a Rare Earth Alternatives in Critical Technologies program, to develop alternative materials. In 2011, ARPA-E awarded 31.6 million dollars to fund Rare-Earth Substitute projects, the ingots are pulverized and milled, the powder is then sintered into dense blocks. The blocks are then heat-treated, cut to shape, surface treated and magnetized, in 2015, Nitto Denko Corporation of Japan announced their development of a new method of sintering neodymium magnet material
4. Magnetism – Magnetism is a class of physical phenomena that are mediated by magnetic fields. Electric currents and the moments of elementary particles give rise to a magnetic field. The most familiar effects occur in materials, which are strongly attracted by magnetic fields and can be magnetized to become permanent magnets. Only a few substances are ferromagnetic, the most common ones are iron, nickel and cobalt, the prefix ferro- refers to iron, because permanent magnetism was first observed in lodestone, a form of natural iron ore called magnetite, Fe3O4. The magnetic state of a material depends on temperature and other such as pressure. A material may exhibit more than one form of magnetism as these variables change, magnetism was first discovered in the ancient world, when people noticed that lodestones, naturally magnetized pieces of the mineral magnetite, could attract iron. The word magnet comes from the Greek term for lodestone, magnítis líthos, in ancient Greece, Aristotle attributed the first of what could be called a scientific discussion of magnetism to the philosopher Thales of Miletus, who lived from about 625 BC to about 545 BC. Around the same time, in ancient India, the Indian surgeon Sushruta was the first to use of the magnet for surgical purposes. In ancient China, the earliest literary reference to magnetism lies in a 4th-century BC book named after its author, the 2nd-century BC annals, Lüshi Chunqiu, also notes, The lodestone makes iron approach, or it attracts it. The earliest mention of the attraction of a needle is in a 1st-century work Lunheng, by the 12th century the Chinese were known to use the lodestone compass for navigation. They sculpted a directional spoon from lodestone in such a way that the handle of the spoon always pointed south, alexander Neckam, by 1187, was the first in Europe to describe the compass and its use for navigation. In 1269, Peter Peregrinus de Maricourt wrote the Epistola de magnete, in 1282, the properties of magnets and the dry compass were discussed by Al-Ashraf, a Yemeni physicist, astronomer, and geographer. In 1600, William Gilbert published his De Magnete, Magneticisque Corporibus, in this work he describes many of his experiments with his model earth called the terrella. From his experiments, he concluded that the Earth was itself magnetic and this landmark experiment is known as Ørsteds Experiment. James Clerk Maxwell synthesized and expanded these insights into Maxwells equations, unifying electricity, magnetism, in 1905, Einstein used these laws in motivating his theory of special relativity, requiring that the laws held true in all inertial reference frames. Magnetism, at its root, arises from two sources, Electric current, Spin magnetic moments of elementary particles. The magnetic moments of the nuclei of atoms are thousands of times smaller than the electrons magnetic moments. Nuclear magnetic moments are very important in other contexts, particularly in nuclear magnetic resonance
5. Mu-metal – Mu-metal is a nickel–iron soft magnetic alloy with very high permeability, which is used for shielding sensitive electronic equipment against static or low-frequency magnetic fields. One such composition is approximately 77% nickel, 16% iron, 5% copper, the name came from the Greek letter mu which represents permeability in physics and engineering formulae. A number of different proprietary formulations of the alloy are sold under names such as MuMETAL, Mumetall. Mu-metal typically has relative permeability values of 80, 000–100,000 compared to several thousand for ordinary steel and it is a soft magnetic material, it has low magnetic anisotropy and magnetostriction, giving it a low coercivity so that it saturates at low magnetic fields. This gives it low hysteresis losses when used in AC magnetic circuits, mu-metal objects require heat treatment after they are in final form—annealing in a magnetic field in hydrogen atmosphere, which increases the magnetic permeability about 40 times. The annealing alters the materials crystal structure, aligning the grains and removing impurities, especially carbon. The high permeability of mu-metal provides a low reluctance path for magnetic flux, magnetic shielding made with high-permeability alloys like mu-metal works not by blocking magnetic fields but by providing a path for the magnetic field lines around the shielded area. Thus, the best shape for shields is a closed container surrounding the shielded space, the effectiveness of mu-metal shielding decreases with the alloys permeability, which drops off at both low field strengths and, due to saturation, at high field strengths. Thus, mu-metal shields are made of several enclosures one inside the other. Because mu-metal saturates at low fields, sometimes the outer layer in such multilayer shields is made of ordinary steel. Its higher saturation value allows it to handle stronger magnetic fields, RF magnetic fields above about 100 kHz can be shielded by Faraday shields, ordinary conductive metal sheets or screens which are used to shield against electric fields. Superconducting materials can expel magnetic fields by the Meissner effect. The bandwidth could be increased by adding inductance to compensate and this was first done by wrapping the conductors with a helical wrapping of metal tape or wire of high magnetic permeability, which confined the magnetic field. Telcon invented mu-metal to compete with permalloy, the first high-permeability alloy used for cable compensation, mu-metal was developed by adding copper to permalloy to improve ductility. 50 miles of fine wire were needed for each mile of cable. The first year of production Telcon was making 30 tons per week, in the 1930s this use for mu-metal declined, but by World War II many other uses were found in the electronics industry, as well as the fuzes inside magnetic mines. Mu-metal is used to shield equipment from magnetic fields, for example, Electric power transformers, which are built with mu-metal shells to prevent them from affecting nearby circuitry. Hard disks, which have mu-metal backings to the found in the drive to keep the magnetic field away from the disk
6. Electrical steel – Electrical steel is a special steel tailored to produce specific magnetic properties, small hysteresis area resulting in low power loss per cycle, low core loss, and high permeability. Electrical steel is usually manufactured in cold-rolled strips less than 2 mm thick and these strips are cut to shape to make laminations which are stacked together to form the laminated cores of transformers, and the stator and rotor of electric motors. Laminations may be cut to their shape by a punch and die or, in smaller quantities, may be cut by a laser. Electrical steel is an alloy which may have from zero to 6. 5% silicon. Commercial alloys usually have silicon content up to 3. 2%, manganese and aluminum can be added up to 0. 5%. Silicon significantly increases the electrical resistivity of the steel, which decreases the induced currents and narrows the hysteresis loop of the material. However, the grain structure hardens and embrittles the metal, which affects the workability of the material. When alloying, the levels of carbon, sulfur, oxygen and nitrogen must be kept low. These compounds, even in particles as small as one micrometer in diameter, the presence of carbon has a more detrimental effect than sulfur or oxygen. Carbon also causes magnetic aging when it leaves the solid solution and precipitates as carbides. For these reasons, the level is kept to 0. 005% or lower. The carbon level can be reduced by annealing the steel in a decarburizing atmosphere, cold-rolled non-grain-oriented steel is often abbreviated to CRNGO. Grain-oriented electrical steel usually has a level of 3%. It is processed in such a way that the properties are developed in the rolling direction. The magnetic flux density is increased by 30% in the rolling direction. It is used for the cores of power and distribution transformers, CRGO is usually supplied by the producing mills in coil form and has to be cut into laminations, which are then used to form a transformer core, which is an integral part of any transformer. Grain-oriented steel is used in power and distribution transformers and in certain audio output transformers. CRNGO is less expensive than CRGO and it is used when cost is more important than efficiency and for applications where the direction of magnetic flux is not constant, as in electric motors and generators with moving parts
7. Heusler compound – A Heusler alloy is a ferromagnetic metal alloy based on a Heusler phase. Heusler phases are intermetallics with particular composition and face-centered cubic crystal structure and they are ferromagnetic as a result of the double-exchange mechanism between neighboring magnetic ions. The latter are usually manganese ions, which sit at the centers of the cubic structure. The term is named after a German mining engineer and chemist Friedrich Heusler and it contained two parts copper, one part manganese, and one part tin, that is Cu2MnSn, and has the following properties. Its magnetism varies considerably with heat treatment and composition and it has a room-temperature saturation induction of around 8,000 gauss, which exceeds that of the element nickel but is smaller than that of iron. In 1934, Bradley and Rogers showed that the room-temperature ferromagnetic phase was a fully ordered structure of the L21 type and this has a primitive cubic lattice of copper atoms with alternate cells body-centered by manganese and aluminium. The lattice parameter is 5.95 Ångströms, the molten alloy has a solidus temperature of about 910 °C. As it is cooled below this temperature, it transforms into disordered, solid, below 750 °C, a B2 ordered lattice forms with a primitive cubic copper lattice, which is body-centered by a disordered manganese-aluminium sublattice. Cooling below 610 °C causes further ordering of the manganese and aluminium sub-lattice to the L21 form, oxley found a value of 357 °C for the Curie temperature, below which the alloy becomes ferromagnetic. Neutron diffraction and other techniques have shown that a moment of around 3.7 Bohr magnetons resides almost solely on the manganese atoms. As these atoms are 4.2 Angstroms apart, the exchange interaction, the anti-phase domains grow as the alloy is annealed. There are two types of APBs corresponding to the B2 and L21 types of ordering, APBs also form between dislocations if the alloy is deformed. At the APB the manganese atoms will be closer than in the bulk of the alloy and, for non-stoichiometric alloys with an excess of copper and these antiferromagnetic layers completely supersede the normal magnetic domain structure and stay with the APBs if they are grown by annealing the alloy. This significantly modifies the properties of the non-stoichiometric alloy relative to the stoichiometric alloy which has a normal domain structure. Presumably this phenomenon is related to the fact that pure manganese is an antiferromagnet although it is not clear why the effect is not observed in the stoichiometric alloy, similar effects occur at APBs in the ferromagnetic alloy MnAl at its stoichiometric composition. Another useful Heusler alloy is the class of known as ferromagnetic shape memory alloys. These are generally composed of nickel, manganese and gallium and can change their length by up to 10% in a magnetic field, T. Block, M. J. Carey, B. A. Gurney, O. Jepsen. Band-structure calculations of the half-metallic ferromagnetism and structural stability of full-, national Pollutant Inventory – Copper and compounds fact sheet
8. Permalloy – Permalloy is a nickel–iron magnetic alloy, with about 80% nickel and 20% iron content. Commercial permalloy alloys typically have relative permeability of around 100,000, in addition to high permeability, its other magnetic properties are low coercivity, near zero magnetostriction, and significant anisotropic magnetoresistance. Permalloys electrical resistivity can vary as much as 5% depending on the strength, permalloys typically have the face centered cubic crystal structure with a lattice constant of approximately 0.355 nm in the vicinity of a nickel concentration of 80%. Permalloy is used in transformer laminations and magnetic recording heads, Permalloy was initially developed in the early 20th century for inductive compensation of telegraph cables. The right conditions for transmitting signals through cables without distortion were first worked out mathematically in 1885 by Oliver Heaviside. It was proposed by Carl Emil Krarup in 1902 in Denmark that the cable could be compensated by wrapping it with wire, increasing the inductance. However, iron did not have high permeability to compensate a transatlantic-length cable. After a prolonged search, permalloy was discovered in 1914 by Gustav Elmen of Bell Laboratories, later, in 1923, he found its permeability could be greatly enhanced by heat treatment. A wrapping of permalloy tape could reportedly increase the speed of a telegraph cable fourfold. This method of cable compensation declined in the 1930s, but by World War 2 many other uses for Permalloy were found in the electronics industry, molybdenum permalloy is an alloy of 81% nickel, 17% iron and 2% molybdenum. The latter was invented at Bell Labs in 1940, at the time, when used in long distance copper telegraph lines, it allowed a tenfold increase in maximum line working speed. Supermalloy, at 79% Ni, 16% Fe, and 5% Mo, is well known for its high performance as a soft magnetic material, characterized by high permeability. Loading coil Mu-metal Sendust Supermalloy Richard M. Bozorth, Ferromagnetism, Wiley-IEEE Press, P. Ciureanu and S. Middelhoek, eds. Thin Film Resistive Sensors, Institute of Physics Publishing, ISBN 0-7503-0173-2