Aluminium carbide

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Aluminium carbide
Unit cell ball and stick model of aluminium carbide
Names
Preferred IUPAC name
Aluminum carbide
Other names
Aluminium carbide
Identifiers
3D model (Jmol)
ChemSpider
ECHA InfoCard 100.013.706
EC Number 215-076-2
MeSH Aluminum+carbide
UN number UN 1394
Properties
Al4C3
Molar mass 143.95853 g/mol
Appearance colorless (when pure) hexagonal crystals[1]
Odor odorless
Density 2.36 g/cm3[1]
Melting point 2,200 °C (3,990 °F; 2,470 K)
Boiling point decomposes at 1400 °C[2]
decomposes
Structure
Rhombohedral, hR21, space group R3m, No. 166. a = 0.3335 nm, b = 0.3335 nm, c = 0.85422 nm, α = 78.743 °, β = 78.743 °, γ = 60 °[2]
Thermochemistry
116.8 J/mol K
88.95 J/mol K
-209 kJ/mol
-196 kJ/mol
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Aluminum carbide, chemical formula Al4C3, is a carbide of aluminum. It has the appearance of pale yellow to brown crystals. It is stable up to 1400 °C. It decomposes in water with the production of methane.

Structure[edit]

Aluminum carbide has an unusual crystal structure that consists of alternating layers of Al2C and Al2C2. Each aluminum atom is coordinated to 4 carbon atoms to give a tetrahedral arraignment. Carbon atoms exist in 2 different binding environments; one is a deformed octahedron of 6 Al atoms at a distance of 217 pm. The other is a distorted trigonal bipyramidal structure of 4 Al atoms at 190–194 pm and a fifth Al atom at 221 pm.[3][4] Other carbides (IUPAC nomenclature: methides) also exhibit complex structures.

Reactions[edit]

Aluminum carbide hydrolyses with evolution of methane. The reaction proceeds at room temperature but is rapidly accelerated by heating.[5]

Al4C3 + 12 H2O → 4 Al(OH)3 + 3 CH4

Similar reactions occur with other protic reagents:[1]

Al4C3 + 12 HCl → 4 AlCl3 + 3 CH4

Preparation[edit]

Aluminum carbide is prepared by direct reaction of aluminum and carbon in an electric arc furnace.[3]

4 Al + 3 C → Al4C3

An alternative reaction begins with alumina, but it is less favorable because of generation of carbon monoxide.

2 Al2O3 + 9 C → Al4C3 + 6 CO

Silicon carbide also reacts with aluminum to yield Al4C3. This conversion limits the mechanical applications of SiC, because Al4C3 is more brittle than SiC.[6]

4 Al + 3 SiC → Al4C3 + 3 Si

In aluminum-matrix composites reinforced with silicon carbide, the chemical reactions between silicon carbide and molten aluminum generate a layer of aluminium carbide on the silicon carbide particles, which decreases the strength of the material, although it increases the wettability of the SiC particles.[7] This tendency can be decreased by coating the silicon carbide particles with a suitable oxide or nitride, preoxidation of the particles to form a silica coating, or using a layer of sacrificial metal.[8]

An aluminum-aluminum carbide composite material can be made by mechanical alloying, by mixing aluminum powder with graphite particles.

Occurrence[edit]

Small amounts of aluminum carbide are a common impurity of technical calcium carbide. In electrolytic manufacturing of aluminum, aluminum carbide forms as a corrosion product of the graphite electrodes.[9]

In metal matrix composites based on aluminum matrix reinforced with non-metal carbides (silicon carbide, boron carbide, etc.) or carbon fibres, aluminum carbide often forms as an unwanted product. In case of carbon fibre, it reacts with the aluminum matrix at temperatures above 500 °C; better wetting of the fibre and inhibition of chemical reaction can be achieved by coating it with e.g. titanium boride.[citation needed]

Applications[edit]

Aluminum carbide particles finely dispersed in aluminum matrix lower the tendency of the material to creep, especially in combination with silicon carbide particles.[10]

Aluminum carbide can be used as an abrasive in high-speed cutting tools.[11] It has approximately the same hardness as topaz.[12]

See also[edit]

References[edit]

  1. ^ a b c Mary Eagleson (1994). Concise encyclopedia chemistry. Walter de Gruyter. p. 52. ISBN 3-11-011451-8. 
  2. ^ a b Gesing, T. M.; Jeitschko, W. (1995). "The Crystal Structure and Chemical Properties of U2Al3C4 and Structure Refinement of Al4C3". 50. Zeitschrift für Naturforschung B, A journal of chemical sciences: 196–200. 
  3. ^ a b Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 297. ISBN 0-08-037941-9. 
  4. ^ Solozhenko, Vladimir L.; Kurakevych, Oleksandr O. (2005). "Equation of state of aluminum carbide Al4C3". Solid State Communications. 133 (6): 385–388. doi:10.1016/j.ssc.2004.11.030. ISSN 0038-1098. 
  5. ^ qualitative inorganic analysis. CUP Archive. p. 102. 
  6. ^ Deborah D. L. Chung (2010). Composite Materials: Functional Materials for Modern Technologies. Springer. p. 315. ISBN 1-84882-830-6. 
  7. ^ Urena, S. Gomez De, Gil, Escalera and Baldonedo (1999). "Scanning and transmission electron microscopy study of the microstructural changes occurring in aluminium matrix composites reinforced with SiC particles during casting and welding: interface reactions". Journal of Microscopy. 196 (2): 124–136. doi:10.1046/j.1365-2818.1999.00610.x. PMID 10540265. 
  8. ^ Guillermo Requena. "A359/SiC/xxp: A359 Al alloy reinforced with irregularly shaped SiC particles". MMC-ASSESS Metal Matrix Composites. Retrieved 2007-10-07. 
  9. ^ Jomar Thonstad; et al. (2001). Aluminum Electrolysis : Fundamentals of the Hall-Héroult Process 3rd ed. Aluminum-Verlag. p. 314. ISBN 3-87017-270-3. 
  10. ^ S.J. Zhu; L.M. Peng; Q. Zhou; Z.Y. Ma; K. Kucharova; J. Cadek (1998). "Creep behaviour of aluminum strengthened by fine aluminum carbide particles and reinforced by silicon carbide particulates DS Al-SiC/Al4C3composites" (abstract). Acta Technica CSAV (5): 435–455. 
  11. ^ Jonathan James Saveker et al. "High speed cutting tool" U.S. Patent 6,033,789, Issue date: Mar 7, 2000
  12. ^ E. Pietsch, ed.: "Gmelins Hanbuch der anorganischen Chemie: Aluminium, Teil A", Verlag Chemie, Berlin, 1934–1935.