Cerium hexaboride

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Cerium hexaboride
CaHexaboride.jpg
Identifiers
CAS number 12008-02-5 YesY
EC number 234-526-9
Properties
Molecular formula CeB6
Molar mass 204.986 g/mol
Density 4.80 g/cm3
Melting point 2,552 °C; 4,625 °F; 2,825 K
Solubility in water insoluble
Structure
Crystal structure Cubic
Space group Pm3m ; Oh
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 YesY (verify) (what is: YesY/N?)
Infobox references
A cerium hexaboride top hat cathode. Image courtesy of Applied Physics Technologies

Cerium hexaboride (CeB6, also called cerium boride, CeBix, CEBIX, and (incorrectly) CeB) is an inorganic chemical, a boride of cerium. It is a refractory ceramic material. It has low work function and one of the highest electron emissivity known, and is stable in vacuum. The principal use of cerium hexaboride is a coating of hot cathodes, or hot cathodes made of cerium hexaboride crystals. It usually operates at temperature of 1450 °C.

Lanthanum hexaboride (LaB6) and cerium hexaboride (CeB6) are used as coating of some high-current hot cathodes. Hexaborides show low work function, around 2.5 eV. They are also somewhat resistant to cathode poisoning. Cerium boride cathodes show lower evaporation rate at 1700 K than lanthanum boride, but it becomes equal at 1850 K and higher above that. Cerium boride cathodes have one and half the lifetime of lanthanum boride, due to its higher resistance to carbon contamination. Boride cathodes are about ten times as "bright" than the tungsten ones and have 10–15 times longer lifetime. In some laboratory tests, CeB6 has proven to be more resistant to the negative impact of carbon contamination than LaB6. They are used e.g. in electron microscopes, microwave tubes, electron lithography, electron beam welding, X-Ray tubes, and free electron lasers.

Cerium hexaboride, like lanthanum hexaboride, slowly evaporates during the cathode operation. In conditions where CeB6 cathodes are operated under 1850 K, CeB6 should maintain its optimum shape longer and therefore last longer. While the process is about 30% slower than with lanthanum boride, the cerium boride deposits are reported to be more difficult to remove.[1]

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