Molybdenum disilicide

Molybdenum disilicide (MoSi2, or molybdenum silicide), an intermetallic compound, a silicide of molybdenum, is a refractory ceramic with primary use in heating elements. 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. The thermal stability of MoSi2 alongside its high emissivity make this material, alongside WSi2 attractive for applications as a high emissivity coatings in heat shields for atmospheric entry.[3] MoSi2 is a gray metallic-looking material with tetragonal crystal structure (alpha-modification); its beta-modification is hexagonal and unstable.[4] It is insoluble in most acids but soluble in nitric acid and hydrofluoric acid.

Molybdenum disilicide
Names
IUPAC name
Molybdenum disilicide
Other names
Molybdenum(VIII) silicide
Identifiers
ECHA InfoCard 100.032.016
Properties
MoSi2
Molar mass 152.11 g/mol
Appearance gray metallic solid
Density 6.26 g/cm3[1][2]
Melting point 2,030 °C (3,690 °F; 2,300 K)[2]
Structure
Tetragonal[1]
I4/mmm (No. 139), tI6
a = 0.32112 nm, c = 0.7845 nm
Hazards
Flash point Non-flammable
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
Infobox references

While MoSi2 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 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 MoSi2-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-MoSi2 due to its rapid cooling.

Molybdenum disilicide heating elements can be used for temperatures up to 1800 °C, in electric furnaces used in laboratory and production environment in production of glass, steel, electronics, ceramics, 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.

Other ceramic materials used for heating elements are e.g. silicon carbide, barium titanate, and lead titanate composite materials.

Molybdenum disilicide is used in microelectronics as a contact material. It is often used as a shunt over polysilicon lines to increase their conductivity and increase signal speed.

References
  1. A. Nørlund Christensen (1993). "Crystal growth and characterization of the transition metal silicides MoSi2 and WSi2". Journal of Crystal Growth. 129 (1–2): 266–268. doi:10.1016/0022-0248(93)90456-7.
  2. Soo-Jin Park; Min-Kang Seo (18 July 2011). Interface Science and Composites. Academic Press. pp. 563–. ISBN 978-0-12-375049-5. Retrieved 30 December 2011.
  3. High emissivity coatings on fibrous ceramics for reusable space systems Corrosion Science 2019
  4. F. M. d’Heurle, C. S. Petersson, and M. Y. Tsai (1980). "Observations on the hexagonal form of MoSi2 and WSi2 films produced by ion implantation and on related snowplow effects". J. Appl. Phys. 51 (11): 5976. doi:10.1063/1.327517.CS1 maint: multiple names: authors list (link)
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