Ferrites are a class of chemical compounds with the formula AB2O4, where A and B represent various metal cations, usually including iron. A chemical compound is a substance consisting of two or more different elements chemically bonded together in a fixed proportion by Mass. A chemical formula is a way of expressing information about the Atoms that constitute a particular Chemical compound, and how the relationship between those atoms changes An ion is an Atom or Molecule which has lost or gained one or more Valence electrons giving it a positive or negative electrical charge These ceramic materials are used in applications ranging from magnetic components in microelectronics. The word ceramic is derived from the Greek word κεραμικός ( keramikos)
Ferrites are a class of spinels, materials that adopt a crystal motif consisting of cubic close-packed (FCC) oxides (O2-) with A cations occupying one eighth of the octahedral holes and B cations occupying half of the octahedral holes. The spinels are any of a class of Minerals of general formulation XY2 O 4 which Crystallize in the cubic (isometric The magnetic material known as "ZnFe" has the deceptively simple formula ZnFe2O4, with Fe3+ occupying the octahedral sites and half of the tetrahedral sites. The remaining tetrahedral sites in this spinel are occupied by Zn2+. [1]
Contents |
Properties
Ferrites are usually non-conductive ferrimagnetic ceramic compounds derived from iron oxides such as hematite (Fe2O3) or magnetite (Fe3O4) as well as oxides of other metals. In Physics, a ferrimagnetic material is one in which the Magnetic moment of the atoms on different sublattices are opposed as in Antiferromagnetism; however Altogether there are sixteen known Iron Oxides and oxyhydroxides Hematite, also spelt hæmatite, is the Mineral form of Iron(III oxide (Fe2O3 one of several Iron oxides Magnetite is not to be confused with Magnesite or Maghemite. Magnetite is a ferrimagnetic Mineral with chemical An oxide is a Chemical compound containing at least one Oxygen atom as well as at least one other element Ferrites are, like most other ceramics, hard and brittle. In terms of the magnetic properties, ferrites are often classified as "soft" and "hard" which refers to their low or high coercivity of their magnetism, respectively. In Materials science, the coercivity, also called the coercive field, of a ferromagnetic material is the intensity of the applied Magnetic
Soft ferrites
Ferrites that are used in transformer or electromagnetic cores contain nickel, zinc, or manganese compounds. A transformer is a device that transfers Electrical energy from one circuit to another through inductively coupled Electrical conductors Electromagnetism is the Physics of the Electromagnetic field: a field which exerts a Force on particles that possess the property of The magnetic core is a key component in electrical and electromechanical devices such as Electromagnets Transformers and Inductors A magnetic core is a Nickel (ˈnɪkəl is a metallic Chemical element with the symbol Ni and Atomic number 28 Zinc (ˈzɪŋk from Zink is a Metallic Chemical element with the symbol Zn and Atomic number 30 Manganese (ˈmæŋgəniːz is a Chemical element, designated by the symbol Mn. They have a low coercivity and are called soft ferrites. In Materials science, the coercivity, also called the coercive field, of a ferromagnetic material is the intensity of the applied Magnetic Because of their comparatively low losses at high frequencies, they are extensively used in the cores of Switched-Mode Power Supply (SMPS) and RF transformers and inductors. A switched-mode power supply, switching-mode power supply or SMPS, is an electronic Power supply unit (PSU that incorporates a switching regulator Radio frequency ( RF) is a Frequency or rate of Oscillation within the range of about 3 Hz to 300 GHz An inductor is a passive electrical component designed to provide Inductance in a circuit A common ferrite, abbreviated "MnZn," is composed of the oxides of manganese and zinc.
Hard ferrites
In contrast, permanent ferrite magnets (or "hard ferrites"), which have a high remanence after magnetization, are composed of iron and barium or strontium oxides. Remanence is the magnetization left behind in a medium after an external Magnetic field is removed Barium (ˈbɛəriəm is a Chemical element. It has the symbol Ba, and Atomic number 56 Strontium (ˈstrɒntiəm /ˈstrɒnʃiəm/) is a Chemical element with the symbol Sr and the Atomic number 38 In a magnetically saturated state they conduct magnetic flux well and have a high magnetic permeability. Seen in some Magnetic materials saturation is the state reached when an increase in applied external Magnetizing field H cannot increase the Magnetic flux, represented by the Greek letter Φ ( Phi) is a measure of quantity of Magnetism, taking into account the strength and the extent of a Magnetic In Electromagnetism, permeability is the degree of Magnetization of a material that responds linearly to an applied Magnetic field. This enables these so-called ceramic magnets to store stronger magnetic fields than iron itself. In Physics, a magnetic field is a Vector field that permeates space and which can exert a magnetic force on moving Electric charges They are the most commonly used magnets in radios. The maximum magnetic field B is about 0. 35 tesla and the magnetic field strength H is about 30 to 160 kiloampere turns per meter (400 to 2000 oersteds). The tesla (symbol T) is the SI derived unit of Magnetic field B (which is also known as "magnetic flux density" and "magnetic Oersted (abbreviated as Oe) is the unit of magnetizing field (also known as magnetic field strength or intensity in the CGS system of units (Hill 2006)
Production
Ferrites are produced by heating an intimate mixture of powdered precursors are heated and pressed in a mold. During the heating process, calcination of carbonates occurs:
- MCO3 → MO + CO2
The oxides of barium and strontium are typically supplied as their carbonates, BaCO3 or SrCO3. In Chemistry, a carbonate is a salt or Ester of Carbonic acid. Barium carbonate ( Ba[[Carbonate CO]]3 also known as witherite, is a Chemical compound used in Rat poison, Bricks Strontium carbonate (SrCO3 is the carbonate salt of strontium that has the appearance of a white or grey powder The resulting mixture of oxides undergoes sintering. Sintering is a method for making objects from powder, by heating the material (below its Melting point - solid state sintering until its particles adhere Afterwards the cooled product is milled to particles smaller than 2 μm in order to produce Weiss domains in the size of one particle. Weiss domains are small areas in a Crystal structure of a ferromagnetic material with uniformly oriented magnetic momenta Next the powder is pressed into a shape, dried, and re-sintered. The shaping may be performed in an external magnetic field, in order to achieve a preferred orientation of the particles (anisotropy). Anisotropy (pronounced with stress on the third syllable ˌænaɪˈsɒtrəpi is the property of being directionally dependent as opposed to Isotropy, which means homogeneity
Small and geometrically easy shapes may be produced with dry pressing. However, in such a process small particles may agglomerate and lead to poorer magnetic properties compared to the wet pressing process. Direct calcination and sintering without re-milling is possible as well but leads to poor magnetic properties.
Electromagnets are pre-sintered as well (pre-reaction), milled and pressed. However, the sintering takes place in a specific atmosphere, for instance one with an oxygen shortage). Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the The chemical composition and especially the structure vary strongly between the precursor and the sintered product.
Uses
Ferrite cores are used in electronic inductors, transformers, and electromagnets where the high electrical resistance of the ferrite leads to very low eddy current losses. A ferrite bead is a passive electric component used to suppress high frequency noise in electronic circuits An inductor is a passive electrical component designed to provide Inductance in a circuit A transformer is a device that transfers Electrical energy from one circuit to another through inductively coupled Electrical conductors An electromagnet is a type of Magnet in which the Magnetic field is produced by the flow of an electric current. Electrical resistance is a ratio of the degree to which an object opposes an Electric current through it measured in Ohms Its reciprocal quantity is An eddy current (also known as Foucault current) is an electrical phenomenon discovered by French physicist Léon Foucault in They are commonly seen as a lump in a computer cable, called a ferrite bead, which helps to prevent high frequency electrical noise (radio frequency interference) from exiting or entering the equipment. A ferrite bead is a passive electric component used to suppress high frequency noise in electronic circuits
Early computer memories stored data in the residual magnetic fields of hard ferrite cores, which were assembled into arrays of core memory. Magnetic core memory, or ferrite-core memory, is an early form of Random access Computer memory. Ferrite powders are used in the coatings of magnetic recording tapes. Magnetic tape is a medium for Magnetic recording generally consisting of a thin magnetizable coating on a long and narrow strip of Plastic. One such type of material is iron (III) oxide. Iron(III oxide —also known as ferric oxide, Hematite, red iron oxide, synthetic maghemite, colcothar, or simply Rust —is
Ferrite particles are also used as a component of radar-absorbing materials or coatings used in stealth aircraft and in the expensive absorption tiles lining the rooms used for electromagnetic compatibility measurements. Stealth technology also known as LOT (Low Observability Technology is a sub-discipline of military Electronic countermeasures which covers a range of techniques used with Electromagnetic compatibility (EMC is the branch of electrical sciences which studies the unintentional generation propagation and reception of electromagnetic energy with reference to
Most common radio magnets, including those used in loudspeakers, are ferrite magnets. Ferrite magnets have largely displaced Alnico magnets in these applications. Alnico is an acronym referring to alloys which are composed primarily of Aluminium (symbol Al) Nickel (symbol Ni) and Cobalt (symbol
It is a common magnetic material for electromagnetic instrument pickups, because of price and relatively high output. A pickup device acts as a Transducer that captures mechanical vibrations (usually from suitably equipped Stringed instruments such as the Electric guitar However, such pickups lack certain sonic qualities found in other pickups, such as those that use Alnico alloys or more sophisticated magnets.
References
- ^ Shriver, D. F. ; Atkins, P. W. ; Overton, T. L. ; Rourke, J. P. ; Weller, M. T. ; Armstrong, F. A. “Inorganic Chemistry” W. H. Freeman, New York, 2006. ISBN: 0-7167-4878-9.
External links
Manufacturers
Sources
- Meeldijk, Victor Electronic Components: Selection and Application Guidelines, 1997 Wiley [ISBN 0-471-18972-3]
- Ott, Henry Noise Reduction Techniques in Electronic Systems 1988 Wiley [ISBN 0-471-85068-3]
- Luecke, Gerald and others General Radiotelephone Operator License Plus Radar Endorsement 2004, Master Pub. [ISBN 0-945053-14-2]
- Bartlett, Bruce and others Practical Recording Techniques 2005 Focal Press [ISBN 0-240-80685-9]
- Hill Technical Sales [1]
- Schaller, George E. Ferrite Processing & Effects on Material Performance [2]
Dapyx Software network: MP3 Explorer | Ebook Manager | Zenithic