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
CAS Number	12136-78-6 Y
ECHA InfoCard	100.032.016
PubChem CID	6336985
CompTox Dashboard (EPA)	DTXSID601014284
Properties
Chemical formula	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
Crystal structure	Tetragonal[1]
Space group	I4/mmm (No. 139), tI6
Lattice constant	a = 0.32112 nm, c = 0.7845 nm
Formula units (Z)	2
Hazards
Flash point	Non-flammable
Related compounds
Other cations	Chromium disilicide Tungsten disilicide
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.^[5]

Other ceramic materials used for heating elements include 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. Bibcode:1993JCrGr.129..266N. doi:10.1016/0022-0248(93)90456-7.
2. Soo-Jin Park; Min-Kang Seo (2011). Interface Science and Composites. Academic Press. pp. 563–. ISBN 978-0-12-375049-5.
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): 5976–5980. Bibcode:1980JAP....51.5976D. doi:10.1063/1.327517.{{cite journal}}: CS1 maint: multiple names: authors list (link)
5. Park, S.J.; Seo, M.K. (2011). Interface Science and Composites. Interface Science and Technology. Elsevier Science. p. 563. ISBN 978-0-12-375049-5. Retrieved 2023-09-09.