Molybdenum disilicide 3307890 224791768 2008-07-10T12:54:58Z Wiki felix 123 7448507 {{Chembox new | ImageFile = | ImageSize = | IUPACName = | OtherNames = | Section1 = {{Chembox Identifiers | CASNo = 12136-78-6 | PubChem = | SMILES = }} | Section2 = {{Chembox Properties | Formula = MoSi<sub>2</sub> | MolarMass = 152.111 | Appearance = grey metallic | Density = | MeltingPt = 2030 °C | BoilingPt = | Solubility = }} | Section3 = {{Chembox Hazards | MainHazards = | FlashPt = | Autoignition = }} }} '''Molybdenum disilicide''' ('''{{Molybdenum}}{{Silicon}}<sub>2</sub>''', '''molybdenum silicide''', or '''MOSI2'''), an [[intermetallic compound]], a [[silicide]] of [[molybdenum]], is a [[refractory material|refractory]] [[ceramic]] with primary use in [[heating element]]s. It has moderate density, melting point 2030 °C, and is electrically conductive. At high temperatures it forms a [[passivation layer]] of [[silicon dioxide]], protecting it from further oxidation. Its [[CAS number]] is {{CASREF|CAS=12136-78-6}}. It is a gray metallic-looking material with [[tetragonal]] [[crystal structure]] (alpha-modification); its beta-modification is [[hexagonal (crystal system)|hexagonal]] and unstable. It is insoluble in acids and soluble in [[nitric acid]] and [[hydrofluoric acid]]. [[Image:Kanthal-super.jpg|thumb|left|Heating elements of MoSi<sub>2</sub>]] While MoSi<sub>2</sub> has excellent resistance to oxidation and high [[Young's modulus]] at temperatures above 1000 °C, it is [[brittle]] in lower temperatures. Also, at above 1200 °C it loses [[creep (deformation)|creep]] resistance. These properties limits its use as a structural material, but may be offset by using it together with another material as a [[composite material]]. Molybdenum disilicide and MoSi<sub>2</sub>-based materials are usually made by [[sintering]]. [[Plasma spraying]] can be used for producing its dense monolithic and composite forms; material produced this way may contain a proportion of β-MoSi<sub>2</sub> due to its rapid cooling. Molybdenum disilicide heating elements can be used for temperatures up to 1800 °C, in electric [[furnace]]s used in laboratory and production environment in production of [[glass]], [[steel]], [[electronics]], [[ceramic]]s, and in [[heat treatment]] of materials. While the elements are brittle, they can operate at high power without aging, and their electrical resistivity does not increase with operation time. Their maximum operating temperature has to be lowered in atmospheres with low oxygen content due to breakdown of the passivation layer. Molybdenum disilicide heating elements are mainly sold by [[Kanthal]] (under the name [http://www.kanthal.com/sandvik/0971/internet/s003237.nsf/html/Startpage?opendocument ''Kanthal Super'']) and [http://www.mhi-inc.com/PG3/high-temperature-heating-elements.html ''MHI Inc.''] (under the trade name MP1800, MP1850 and above). [http://www.mhi-inc.com ''MHI Inc.''] is based out of Cincinnati, Ohio, USA. Other ceramic materials used for heating elements are eg. [[silicon carbide]], [[barium titanate]], and [[lead titanate]] [[composite material]]s. [[Category:Ceramic materials]] [[Category:Silicides]] [[Category:Molybdenum compounds]] [[Category:Semiconductor materials]] [[Category:Refractory materials]]