What is "ferrite"

"compound of ferric oxide and another metallic oxide," 1851, from Latin ferrum "iron" (see ferro-) + -ite (2).

n. The interstitial solid solution of carbon in body-centered cubic iron.

n. a solid solution in which alpha iron is the solvent

Ferrite may refer to:

• Ferrite (iron), iron or iron alloys with a body centred cubic crystal structure.
• Ferrite (magnet) (e.g. FeO or BaFeO), ferrimagnetic ceramic materials used in magnetic applications.
• Ferrite bead, a component placed on the end of a data cable to reduce interference.
• Ferrite core, a structure on which the windings of electric transformers and other wound components are formed.
• Calcium aluminoferrite, Ca(Al,Fe)O, a mineral found in cements

A ferrite is a type of ceramic compound composed of iron oxide (FeO) combined chemically with one or more additional metallic elements. They are both electrically nonconductive and ferrimagnetic, meaning they can be magnetized or attracted to a magnet. Ferrites can be divided into two families based on their magnetic coercivity, their resistance to being demagnetized. Hard ferrites have high coercivity, hence they are difficult to demagnetize. They are used to make magnets, for devices such as refrigerator magnets, loudspeakers and small electric motors. Soft ferrites have low coercivity. They are used in the electronics industry to make ferrite cores for inductors and transformers, and in various microwave components. Yogoro Kato and Takeshi Takei of the Tokyo Institute of Technology synthesized the first ferrite compounds in 1930.

Ferrite, also known as α-ferrite (α-Fe) or alpha iron, is a solid solution of limited amounts of carbon in iron with a body-centered cubic (B.C.C) crystal structure. It is this crystalline structure which gives steel and cast iron their magnetic properties, and is the classic example of a ferromagnetic material.

It has a strength of 280 N/mm and a hardness of approximately 80 Brinell.

Mild steel (carbon steel with up to about 0.2 wt% C) consist mostly of ferrite, with increasing amounts of pearlite (a fine lamellar structure of ferrite and cementite) as the carbon content is increased. Since bainite (shown as ledeburite on the diagram at the bottom of this page) and pearlite each have ferrite as a component, any iron-carbon alloy will contain some amount of ferrite if it is allowed to reach equilibrium at room temperature. The exact amount of ferrite will depend on the cooling processes the iron-carbon alloy undergoes as it cools from liquid state.

In pure iron, ferrite is stable below . Above this temperature the face-centred cubic form of iron, austenite (gamma-iron) is stable. Above , up to the melting point at , the body-centred cubic crystal structure is again the more stable form, as delta-ferrite (δ-Fe). Ferrite above the critical temperature A ( Curie temperature) of , where it is paramagnetic rather than ferromagnetic. The term is beta ferrite or beta iron (β-Fe). The term beta iron is not any longer used because it is crystallographically identical to, and its phase field contiguous with, α-Fe.

Only a very small amount of carbon can be dissolved in ferrite; the maximum solubility is about 0.02 wt% at and 0.005% carbon at . This is because carbon dissolves in iron interstitially, with the carbon atoms being about twice the diameter of the interstitial "holes", so that each carbon atom is surrounded by a strong local strain field. Hence the enthalpy of mixing is positive (unfavourable), but the contribution of entropy to the free energy of solution stabilises the structure for low carbon content. also is the minimum temperature at which iron-carbon austenite (0.8 wt% C) is stable; at this temperature there is a eutectoid reaction between ferrite, austenite and cementite.

Because of its significance for planetary cores, the physical properties of iron at high pressures and temperatures have also been studied extensively. α-ferrite, which is the form of iron that is stable under standard conditions, can be subjected to pressures up to ca. 15 GPa before transforming into a high-pressure form termed ε-iron, which crystallizes in a hexagonal close-packed (hcp) structure.