Aluminium carbide, Al₄C₃

Aluminium carbide, Al₄C₃, is prepared by heating fragments of aluminium with sugar carbon in a carbon crucible in the electric furnace and rapidly cooling the product. It may also be prepared by heating a mixture of aluminium powder and carbon for twenty minutes in a Perrot furnace or over the blowpipe; or the reaction may be started by inflaming a mixture of aluminium powder and barium peroxide on the surface. Aluminium carbide is also produced by heating aluminium with hexachlor-benzene at 225°. According to Pring, the production of the carbide in the electric furnace is apparently due to the reaction: -

6Al + 3CO ⇔ Al₄C₃ + Al₂O₃,

but the elements aluminium and carbon can unite directly, the combination in vacuo becoming perceptible at 650° and rapid at 1400°.

Aluminium carbide, purified by washing with a cold, concentrated solution of potassium hydroxide, and then with alcohol and ether, forms yellow, rhombohedral crystals of density at 2.36. At temperatures between 400° and 1400° aluminium carbide is stable in vacuo; but above 1400° it dissociates at an appreciable rate, and at 1800° the change is rapid. Accordingly, at high temperatures alumina is reduced by carbon with the formation of much free aluminium, while at lower temperatures aluminium carbide only is produced. At temperatures below 1400° aluminium carbide acts as a reducing agent on metallic oxides, e.g.: -

Al₄C₃ + 12CuO = 12Cu + 3CO₂ + 2Al₂O₃,

but at higher temperatures alloys are produced, the carbon only being oxidised. With metallic chlorides it yields organometallic compounds.

Aluminium carbide is slowly but completely decomposed by water, aluminium hydroxide and methane being produced: -

Al₄C₃ + 12H₂O = 4Al(OH)₃ + 3CH₄.