Barium
ferrite, abbreviated BaFe, BaM, is the
chemical compound
A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...
with the
formula BaFe
12O
19.
This and related
ferrite materials are components in
magnetic stripe card
The term digital card can refer to a physical item, such as a memory card on a camera, or, increasingly since 2017, to the digital content hosted
as a virtual card or cloud card, as a digital virtual representation of a physical card. They share ...
s and
loudspeaker
A loudspeaker (commonly referred to as a speaker or speaker driver) is an electroacoustic transducer that converts an electrical audio signal into a corresponding sound. A ''speaker system'', also often simply referred to as a "speaker" or ...
magnets.
BaFe is described as Ba
2+(Fe
3+)
12(O
2−)
19. The Fe
3+ centers are
ferrimagnetically coupled, and one unit cell of BaM has a net magnetic moment of 40''μ''
B.
This area of technology is usually considered to be an application of the related fields of
materials science and
solid state chemistry Solid-state chemistry, also sometimes referred as materials chemistry, is the study of the synthesis, structure, and properties of solid phase materials, particularly, but not necessarily exclusively of, non-molecular solids. It therefore has a str ...
.
Barium ferrite is a highly
magnetic material
A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, steel, nickel ...
, has a high packing density, and is a metal
oxide. Studies of this material date at least as far back as 1931, and it has found applications in magnetic card strips, speakers, and
magnetic tapes.
One area in particular it has found success in is long-term data storage; the material is magnetic, resistant to temperature change, corrosion and oxidization.
Chemical structure
The Fe
3+ centers, with a
high-spin d
5 configuration, are
ferrimagnetically coupled.
This area of technology is usually considered to be an application of the related fields of
materials science and
solid state chemistry Solid-state chemistry, also sometimes referred as materials chemistry, is the study of the synthesis, structure, and properties of solid phase materials, particularly, but not necessarily exclusively of, non-molecular solids. It therefore has a str ...
.
A related family of industrially useful "hexagonal ferrites" are known, also containing
barium.
In contrast to the usual
spinel structure, these materials feature
hexagonal close-packed
In geometry, close-packing of equal spheres is a dense arrangement of congruent spheres in an infinite, regular arrangement (or lattice). Carl Friedrich Gauss proved that the highest average density – that is, the greatest fraction of space occu ...
framework of oxides. Furthermore, some of the oxygen centers are replaced by Ba
2+ ions. Formulas for these species include BaFe
12O
19, BaFe
15O
23, and BaFe
18O
27.
A one-step hydrothermal process can be used to form crystals of barium ferrite, by mixing
barium chloride
Barium chloride is an inorganic compound with the formula Ba Cl2. It is one of the most common water-soluble salts of barium. Like most other water-soluble barium salts, it is white, highly toxic, and imparts a yellow-green coloration to a flame. ...
,
ferrous chloride
Iron(II) chloride, also known as ferrous chloride, is the chemical compound of formula FeCl2. It is a paramagnetic solid with a high melting point. The compound is white, but typical samples are often off-white. FeCl2 crystallizes from water as ...
,
potassium nitrate
Potassium nitrate is a chemical compound with the chemical formula . This alkali metal nitrate salt is also known as Indian saltpetre (large deposits of which were historically mined in India). It is an ionic salt of potassium ions K+ and nitr ...
, and
sodium hydroxide with a hydroxide to chloride concentration ratio of 2:1. Nano-particles are prepared from
ferric nitrate, barium chloride,
sodium citrate Sodium citrate may refer to any of the sodium salts of citric acid (though most commonly the third):
* Monosodium citrate
* Disodium citrate
* Trisodium citrate
The three forms of salt are collectively known by the E number E331.
Applications ...
, and sodium hydroxide. The typical preparation, however, is by
calcining
Calcination refers to thermal treatment of a solid chemical compound (e.g. mixed carbonate ores) whereby the compound is raised to high temperature without melting under restricted supply of ambient oxygen (i.e. gaseous O2 fraction of air), gener ...
barium carbonate
Barium carbonate is the inorganic compound with the formula BaCO3. Like most alkaline earth metal carbonates, it is a white salt that is poorly soluble in water. It occurs as the mineral known as witherite. In a commercial sense, it is one of ...
with
iron(III) oxide:
:
BaCO3 + 6
Fe2O3 ->text
Text may refer to:
Written word
* Text (literary theory), any object that can be read, including:
**Religious text, a writing that a religious tradition considers to be sacred
**Text, a verse or passage from scripture used in expository preachin ...
/chem> BaFe12O19 + CO2
Properties
Barium ferrite has been considered for long term data storage. The material has proven to be resistant to a number of different environmental stresses, including humidity and corrosion. Because ferrites are already oxidized it can not be oxidized any further. This is one reason ferrites are so resistant to corrosion. Barium ferrite also proved to be resistant to thermal demagnetization, another issue common with long-term storage. The Curie temperature
In physics and materials science, the Curie temperature (''T''C), or Curie point, is the temperature above which certain materials lose their permanent magnetic properties, which can (in most cases) be replaced by induced magnetism. The Cur ...
is typically around 450 C (723 K).
When barium ferrite magnets increase in temperature, their high intrinsic coercivity improves, this is what makes it more resistant to thermal demagnetization. Ferrite magnets are the only type of magnets that become substantially more resistant to demagnetization as temperature increases. This characteristic of barium ferrite makes it a popular choice in motor and generator designs and also in loudspeaker applications. Ferrite magnets can be used in temperatures up to 300 °C, which makes it a perfect to be used in the applications mentioned above. Ferrite magnets are extremely good insulators and don't allow any electrical current to flow through them and they are brittle which shows their ceramic characteristics. Ferrite magnets also have good machining properties, which allows for the material to be cut in many shapes and sizes.
Chemical properties
Barium ferrites are robust ceramic
A ceramic is any of the various hard, brittle, heat-resistant and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcelain ...
s that are generally stable to moisture and corrosion-resistant.
BaFe is also an oxide so it does not break down due to oxidation as much as a metal alloy might; giving BaFe a much greater life expectancy.
Mechanical properties
Metal particles (MP) have been used to store data on tapes and magnetic strips but they have reached their limit for high capacity data storage. In order to increase their capacity by (25x) on data tape the MP had to increase the tape length by (45%) and track density by over (500%) which made it necessary to reduce the size of the individual particles. As the particles were reduced in size, the passivizing coating needed to prevent the oxidation and deterioration of the MP had to become thicker. This presented a problem for as the passivation coating got thicker it became harder to achieve an acceptable signal to noise ratio.
Barium ferrite completely out classes MP, mostly because BaFe is already in its oxidized state and so is not restricted in its size by a protective coating. Also due to its hexagonal pattern it is easier to organize compared to the unorganized rod like MP. Another factor is the difference in the size of the particles, in MP the size ranges from 40 to 100 nm while the BaFe is only 20 nm. So the smallest MP particle is still double the size of the BaFe particles.
Applications
Barium ferrite is used in applications such as recording media, permanent magnets, and magnetic stripe cards (credit cards, hotel keys, ID cards). Due to the stability of the material, it is able to be greatly reduced in size, making the packing density much greater. Earlier media devices utilized doped acicular oxide materials to yield the coercivity values necessary to record. In recent decades, barium ferrite has replaced acicular oxides; without any dopants, the acicular oxides produce very low coercivity values, making the material very magnetically soft, while barium ferrite's higher coercivity levels make the material magnetically hard and thus a superior choice for recording material applications.
Magnetic Stripes
ID cards using barium ferrite are made with a magnetic fingerprint that identifies them, allowing readers to self-calibrate.
Speaker magnets
Barium ferrite is a common material for speaker magnets. The materials can be formed into almost any shape and size using a process called sintering
Clinker nodules produced by sintering
Sintering or frittage is the process of compacting and forming a solid mass of material by pressure or heat without melting it to the point of liquefaction.
Sintering happens as part of a manufacturing ...
, whereby powdered barium ferrite is pressed into a mold, and then heated until it fuses together. The barium ferrite turns into a solid block while still retaining its magnetic properties. The magnets have an excellent resistance to demagnetization, allowing them to still be useful in speaker units over a long period of time.
Tape Data Storage Media
Barium ferrite is used for enterprise level[https://www.fujifilm.com/us/en/business/data-storage/fujifilm-technologies/barium-ferrite] and commodity Linear Tape-Open (LTO) tape storage media. Because of its high density, barium ferrite has led to data capacity improvements in both enterprise and LTO tapes over prior metal particle (MP) media technology.
Developments in the field have also resulted in the reduction of the size of BaFe particles to about 20 nm. This contrasts with MP technology, which has problems shrinking the particles past 100 nm.
The shape is another factor. Metal particles are often cylindrical shapes that do not pack or stack well. Barium ferrite has better packing properties. BaFe can be reduced to a smaller size and higher packing density because of its hexagonal structure and can be stacked more effectively. This leads to better control over magnetic orientation and improved signal-to-noise characteristics.
Natural occurrence
The compound occurs in the nature, although is exceedingly rare. It is called barioferrite and is related to pyrometamorphism.
References
{{Barium compounds
Barium compounds
Ferrites