Aluminum carbide is a chemical compound with the formula Al4C3. It is hard, brittle, and sparks when struck. It is used as an abrasive and is an important component of high-speed cutting tools. It decomposes in contact with water to produce methane gas. It is also known as wustite or topaz. The production of aluminum carbide is usually accomplished through mechanical alloying, whereby the aluminum metal is mixed with graphite flakes. This is usually done by ball milling. However, the resulting composite material suffers from brittleness. This is caused by the formation of aluminum carbide at the interface between the aluminium particles. This weakens the composite material and reduces its strength and durability. This problem can be remedied by using a surface surfactant. Li et al. (2022) used hexadecyl trimethyl ammonium bromide to modify the surface of the aluminium and prevent the formation of aluminum carbide during grinding. This resulted in a better quality aluminium carbide.
Whether a compound is considered ionic or covalent depends on the difference between the electronegativity of the metal and the electronegativity of the non-metal. When the differences are large enough, ionic bonding can occur. This is because the transfer of electrons results in the filling of orbitals on both the metal and the non-metal ions. This is the basis for the octet rule.
Carbides are compounds formed by the reaction of carbon with less electronegative elements. These reactions give rise to three general classes of carbides: ionic, interstitial and covalent. Ionic carbides contain discrete metal cations and carbon anions. They are formed when carbon reacts at high temperatures with electropositive metals such as those of groups 1 and 2. Covalent carbides, meanwhile, form from small carbon atoms with larger transition metals such as beryllium or aluminum.