Aluminium carbide

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Aluminium carbide
Unit cell ball and stick model of aluminium carbide
Identifiers
CAS number 1299-86-1 YesY, 12656-43-8
PubChem 16685054
ChemSpider 21241412 YesY
EC number 215-076-2
UN number UN 1394
MeSH Aluminum+carbide
Jmol-3D images Image 1
Properties
Molecular formula 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]
Solubility in water decomposes
Structure
Crystal 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
Specific
heat capacity
C
116.8 J/mol K
Std molar
entropy
So298
88.95 J/mol K
Std enthalpy of
formation
ΔfHo298
-209 kJ/mol
Gibbs free energy ΔG -196 kJ/mol
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

Aluminium carbide, chemical formula Al4C3, is a carbide of aluminium. 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]

Aluminium carbide has an unusual crystal structure that consists of two types of layers. It is based on AlC4 tetrahedra of two types and thus two types of carbon atoms. One is surrounded by a deformed octahedron of 6 Al atoms at a distance of 217 pm. The other is surrounded by 4 Al atoms at 190–194 pm and a fifth Al atom at 221 pm.[3] Other carbides (IUPAC nomenclature: methides) also exhibit complex structures.

Reactions[edit]

Aluminium carbide hydrolyses with evolution of methane. The reaction proceeds at room temperature but is rapidly accelerated by heating.[4]

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]

Aluminium carbide is prepared by direct reaction of aluminium 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 aluminium to yield Al4C3. This conversion limits the mechanical applications of SiC, because Al4C3 is more brittle than SiC.[5]

4 Al + 3 SiC → Al4C3 + 3 Si

In aluminium-matrix composites reinforced with silicon carbide, the chemical reactions between silicon carbide and molten aluminium 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.[6] 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.[7]

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

Occurrence[edit]

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

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

Applications[edit]

Aluminium carbide particles finely dispersed in aluminium matrix lower the tendency of the material to creep, especially in combination with silicon carbide particles.[8]

Aluminium carbide can be used as an abrasive in high-speed cutting tools.[9] It has approximately the same hardness as topaz.[10]

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. pp. 196–200. 
  3. ^ a b Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 297. ISBN 0080379419. 
  4. ^ qualitative inorganic analysis. CUP Archive. p. 102. 
  5. ^ Deborah D. L. Chung (2010). Composite Materials: Functional Materials for Modern Technologies. Springer. p. 315. ISBN 1-84882-830-6. 
  6. ^ 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. 
  7. ^ Guillermo Requena. "A359/SiC/xxp: A359 Al alloy reinforced with irregularly shaped SiC particles". MMC-ASSESS Metal Matrix Composites. Retrieved 2007-10-07. 
  8. ^ S.J. Zhu, L.M. Peng, Q. Zhou, Z.Y. Ma, K. Kucharova, J. Cadek (1998). "Creep behaviour of aluminium strengthened by fine aluminium carbide particles and reinforced by silicon carbide particulates DS Al-SiC/Al4C3composites" (abstract). Acta Technica CSAV (5): 435–455. 
  9. ^ Jonathan James Saveker et al. "High speed cutting tool" U.S. Patent 6,033,789, Issue date: Mar 7, 2000
  10. ^ E. Pietsch, ed.: "Gmelins Hanbuch der anorganischen Chemie: Aluminium, Teil A", Verlag Chemie, Berlin, 1934–1935.