|CAS number||, 12656-43-8|
|UN number||UN 1394|
|Jmol-3D images||Image 1|
|Molar mass||143.95853 g/mol|
|Appearance||colorless (when pure) hexagonal crystals|
decomposes at 1400 °C
|Solubility in water||decomposes|
|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 °|
| (what is: / ?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
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.
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. Other carbides (IUPAC nomenclature: methides) also exhibit complex structures.
- Al4C3 + 12 H2O → 4 Al(OH)3 + 3 CH4
Similar reactions occur with other protic reagents:
- Al4C3 + 12 HCl → 4 AlCl3 + 3 CH4
- 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
- 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. 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.
An aluminium-aluminium carbide composite material can be made by mechanical alloying, by milling aluminium powder with graphite particles.
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.
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