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This article does not cite any references or sources. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (January 2010) This article is about transformer cores. For the computer memory technology, see Ferrite core memory. Several ferrite cores A ferrite core is a structure on which the windings of electric transformers and other wound components are formed. It is used for its properties of high magnetic permeability coupled with low electrical conductivity (which helps prevent eddy currents). There are two broad applications for ferrite cores which differ in size and frequency of operation: signal transformers are of small size and higher frequencies, power transformers are of large size and lower frequencies. Cores can also be classified by shape: there are toroidal cores, shell cores, cylindrical cores, and so on. The ferrite cores used for power transformers are working in the range of low frequencies (1 to 50 kHz usually) and are quite big in size, can be toroidal, or shell or C shape and are useful in all kinds of switching electronic devices (especially power supplies from 1 watt to 100 watts maximum, since powerful applications are usually out of range of ferritic single core and required grain oriented laminations cores). The ferrite cores used for signals have a range of applications from 1 kHz to many MHz, perhaps as much as 300 MHz, and have found their main application in electronics. Ferrite is a class of ceramic material with useful electromagnetic properties and an interesting history. Ferrite is rigid and brittle. Like other ceramics, ferrite can chip and break if handled roughly. Luckily it is not as fragile as porcelain and often such chips and cracks will be merely cosmetic. Ferrite varies from silver gray to black in color. The electromagnetic properties of ferrite materials can be affected by operating conditions such as temperature, pressure, field strength, frequency and time. There are basically two varieties of ferrite: soft and hard. This is not a tactile quality but rather a magnetic characteristic. 'Soft ferrite' does not retain significant magnetization whereas 'hard ferrite' magnetization is considered permanent. Ferrite has a cubic crystalline structure with the chemical formula MO⋅Fe2O3 where Fe2O3 is iron oxide and MO refers to a combination of two or more divalent metal oxides (e.g. ZnO, NiO, MnO and CuO). The addition of such metal oxides in various amounts allows the creation of many different materials whose properties can be tailored for a variety of uses. Ferrite components are pressed from a powdered precursor and then sintered (fired) in a kiln. The mechanical and electromagnetic properties of the ferrite are heavily affected by the sintering process which is time-temperature-atmosphere dependent. Ferrite shrinks when sintered. Depending on the specific ferrite, this shrinkage can range from 10% to 17% in each dimension. Thus the unfired component's volume may be as much as 60% larger than the sintered value. Maintaining correct dimensional tolerances as well as the prevention of cracking and warpage related to this shrinkage are fundamental concerns of the manufacturing process. See also Zinc ferrite