Aluminum carbide, chemical formula Al₄ C₃, is a

carbide In chemistry, a carbide usually describes a compound composed of carbon and a metal. In metallurgy, carbiding or carburizing is the process for producing carbide coatings on a metal piece. Interstitial / Metallic carbides The carbides of th ...

aluminum Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It ha ...

. 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

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 arrangement. 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. Other carbides (

IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations working for the advancement of the chemical sciences, especially by developing nomenclature and terminology. It is ...

nomenclature:

methide In chemistry, a carbide usually describes a compound composed of carbon and a metal. In metallurgy, carbiding or carburizing is the process for producing carbide coatings on a metal piece. Interstitial / Metallic carbides The carbides of th ...

s) also exhibit complex structures.

Reactions

Aluminum carbide hydrolyses with evolution of

methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Ea ...

. The reaction proceeds at room temperature but is rapidly accelerated by heating. : Al₄C₃ + 12 H₂O → 4 Al(OH)₃ + 3 CH₄ Similar reactions occur with other protic reagents: : Al₄C₃ + 12 HCl → 4 AlCl₃ + 3 CH₄ Reactive hot isostatic pressing (hipping) at ≈40 MPa of the appropriate mixtures of Ti, Al₄C₃ graphite, for 15 hours at 1300 °C yields predominantly single-phase samples of Ti₂AlC_0.5N_0.5, 30 hours at 1300 °C yields predominantly single-phase samples of Ti₂AlC ( Titanium Aluminium Carbide).

Preparation

Aluminum carbide is prepared by direct reaction of aluminum and carbon in an

electric arc furnace An electric arc furnace (EAF) is a furnace that heats material by means of an electric arc. Industrial arc furnaces range in size from small units of approximately one-tonne capacity (used in foundries for producing cast iron products) up to ...

. : 4 Al + 3 C → Al₄C₃ An alternative reaction begins with alumina, but it is less favorable because of generation of

carbon monoxide Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simple ...

. : 2 Al₂O₃ + 9 C → Al₄C₃ + 6 CO

Silicon carbide Silicon carbide (SiC), also known as carborundum (), is a hard chemical compound containing silicon and carbon. A semiconductor, it occurs in nature as the extremely rare mineral moissanite, but has been mass-produced as a powder and crystal s ...

also reacts with aluminum to yield Al₄C₃. This conversion limits the mechanical applications of SiC, because Al₄C₃ is more brittle than SiC. : 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. 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 Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is ...

coating, or using a layer of

sacrificial metal A sacrificial metal is a metal used as a sacrificial anode in cathodic protection that corrodes to prevent a primary metal from corrosion or rusting. It may also be used for galvanization. Equation When two metals touch each other and water is pr ...

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

graphite Graphite () is a crystalline form of the element carbon. It consists of stacked layers of graphene. Graphite occurs naturally and is the most stable form of carbon under standard conditions. Synthetic and natural graphite are consumed on lar ...

particles.

Occurrence

Small amounts of aluminum carbide are a common impurity of technical

calcium carbide Calcium carbide, also known as calcium acetylide, is a chemical compound with the chemical formula of Ca C2. Its main use industrially is in the production of acetylene and calcium cyanamide. The pure material is colorless, while pieces of te ...

. In electrolytic manufacturing of aluminum, aluminum carbide forms as a corrosion product of the graphite electrodes. In

metal matrix composite In materials science, a metal matrix composite (MMC) is a composite material with fibers or particles dispersed in a metallic matrix, such as copper, aluminum, or steel. The secondary phase is typically a ceramic (such as alumina or silicon carb ...

s based on aluminum matrix reinforced with non-metal carbides (

silicon carbide Silicon carbide (SiC), also known as carborundum (), is a hard chemical compound containing silicon and carbon. A semiconductor, it occurs in nature as the extremely rare mineral moissanite, but has been mass-produced as a powder and crystal s ...

, boron carbide, etc.) or

carbon fibre Carbon fiber-reinforced polymers (American English), carbon-fibre-reinforced polymers (Commonwealth English), carbon-fiber-reinforced plastics, carbon-fiber reinforced-thermoplastic (CFRP, CRP, CFRTP), also known as carbon fiber, carbon compo ...

s, 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 Titanium diboride (TiB2) is an extremely hard ceramic which has excellent heat conductivity, oxidation stability and wear resistance. TiB2 is also a reasonable electrical conductor,J. Schmidt et al. "Preparation of titanium diboride TiB2 by spark ...

Applications

Aluminum carbide particles finely dispersed in aluminum matrix lower the tendency of the material to creep, especially in combination with

particles. Aluminum carbide can be used as an

abrasive An abrasive is a material, often a mineral, that is used to shape or finish a workpiece through rubbing which leads to part of the workpiece being worn away by friction. While finishing a material often means polishing it to gain a smooth, reflec ...

in high-speed

cutting tool In the context of machining, a cutting tool or cutter is typically a hardened metal tool that is used to cut, shape, and remove material from a workpiece by means of machining tools as well as abrasive tools by way of shear deformation. The major ...

s. It has approximately the same hardness as topaz.E. Pietsch, ed.: "Gmelins Hanbuch der anorganischen Chemie: Aluminium, Teil A", Verlag Chemie, Berlin, 1934–1935.

References