Titanium boride
1100595
223270518
2008-07-03T10:04:40Z
Fivemack
230572
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| CASNo = 12045-63-5
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| Formula = TiB<sub>2</sub>
| MolarMass = 69.5 g/mol
| Appearance = metallic grey
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| Section3 = {{Chembox Structure
| CrystalStruct = Hexagonal, Space group P6/mmm. Lattice parameters at room temperature: ''a''=302.36 [[picometer|pm]], ''C''=322.04 pm
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'''Titanium Diboride''' (chemical formula TiB<sub>2</sub>) is an extremely hard [[ceramic]] compound (33 GPa) composed of [[titanium]] and [[boron]] that has very good [[wear resistance]]. It is resistant to oxidation in air at temperatures up to 1000C, and to [[hydrochloric acid|hydrochloric]] and [[hydrofluoric acid|hydrofluoric]] acids, but reacts with [[alkali]]s, [[nitric acid]] and [[sulphuric acid]]. Unusually for a ceramic, it is a reasonable electrical conductor (about 10<sup>5</sup> Siemens per centimetre), so can be used as an anode material in [[aluminium smelting]]; this also means it can be shaped by [[electrical discharge machining]].
It does not occur naturally in the earth; syntheses include heating a mixture of [[titanium dioxide]] and [[boron carbide]] to high temperature, followed by mechanical grinding, or reduction by the [[thermite reaction]] of a mixture of [[titanium dioxide]], [[boron oxide]] and [[magnesium]] powders followed by dissolving magnesium oxide from the reaction mix [http://gtresearchnews.gatech.edu/newsrelease/TIB2.html] which produces a finer powder.
Many TiB<sub>2</sub> applications are inhibited by economic factors, particularly the costs of densifying a high melting point material - the melting point is about 2970C, and, thanks to a layer of titanium dioxide that forms on the surface of the particles of a powder, it is very resistant to [[sintering]], though an admixture of about 10% [[silicon nitride]] helps with this [http://www.patentgenius.com/patent/6420294.html]. Current use of this material appears to be limited to specialized applications in such areas as impact resistant [[armor]], [[cutting tool]]s, [[crucible]]s and wear resistant coatings. It is also used as an [[inoculation (crystals)|inoculant]] to refine the grain size when [[casting]] [[aluminium alloy]]s.
[[Thin film]]s of TiB<sub>2</sub> have a wide range of potential industrial applications due to the wear and [[corrosion]] resistance properties that TiB<sub>2</sub> can provide to a cheap and/or tough substrate. The [[electroplating]] of TiB<sub>2</sub> layers possess two main advantages compared with plasma ([[physical vapor deposition|PVD]], [[chemical vapor deposition|CVD]]) methods: the growing rate of the layer is 200 times higher (up to 5 μm·s<sup>−1</sup>) and the inconveniences of covering complex shaped products are dramatically reduced.
==External links==
[[Category:Borides]]
[[Category:Titanium compounds]]
[[Category:Ceramic materials]]