Aluminium carbide

Aluminium carbide is a chemical compound with the chemical formula Al₄C₃. It is a carbide of aluminium. It has the appearance of pale yellow to brown crystals. It is stable up to 1,400 °C (2,550 °F). It decomposes in water with the production of methane.

Aluminium carbide

Unit cell ball and stick model of aluminium carbide
Names
Preferred IUPAC name Aluminium carbide
Other names Tetraaluminium tricarbide Aluminium methanide
Identifiers
CAS Number	1299-86-1 Y 12656-43-8 N
3D model (JSmol)	Interactive image
ChemSpider	21241412 Y
ECHA InfoCard	100.013.706
EC Number	215-076-2
MeSH	Aluminum+carbide
PubChem CID	16685054
UN number	1394
CompTox Dashboard (EPA)	DTXSID10107594
InChI InChI=1S/3C.4Al/q3*-4;4*+3 Y Key: TWHBEKGYWPPYQL-UHFFFAOYSA-N Y InChI=1/3C.4Al/q3*-4;4*+3 Key: TWHBEKGYWPPYQL-UHFFFAOYAR
SMILES [Al+3].[Al+3].[Al+3].[Al+3].[C-4].[C-4].[C-4]
Properties
Chemical 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	2,100 °C (3,810 °F; 2,370 K)[2]
Boiling point	decomposes at 1400 °C[3]
Solubility in water	Evolves methane (CH4), Al(OH)3, and heat.
Structure
Crystal structure	Rhombohedral, hR21, space group[3]
Space group	R3m（No. 166）
Lattice constant	a = 0.3335 nm, b = 0.3335 nm, c = 0.85422 nm α = 78.743°, β = 78.743°, γ = 60°
Thermochemistry
Heat capacity (C)	116.8 J/(mol·K)
Std molar entropy (S⦵298)	88.95 J/(mol·K)
Std enthalpy of formation (ΔfH⦵298)	−209 kJ/mol
Gibbs free energy (ΔfG⦵)	−196 kJ/mol
Hazards[2]
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H228, H261, H315, H319, H335
Precautionary statements	P223, P231+P232, P261, P264, P271, P280, P302+P352, P304+P340+P312, P305+P351+P338, P332+P313, P335+P334, P337+P313, P362, P370+P378, P402+P404, P403+P233, P405, P501
NFPA 704 (fire diamond)	[4] 2 2 2 W
Safety data sheet (SDS)	Fisher Science SDS[4]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

Preparation

Aluminium carbide is prepared by direct reaction of aluminium and carbon in an electric arc furnace.^[5]

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.^[6]

4 Al + 3 SiC → Al₄C₃ + 3 Si

Reactions

Aluminium carbide hydrolyses with evolution of methane^[7] and considerable amounts of heat.^[8]

Al₄C₃ + 12 H₂O → 4 Al(OH)₃ + 3 CH₄

The addition of 10g of Al₄C₃ to 10g of water was found to reach a maximum temperature of 387 °F (197 °C) at a time of 11 minutes in one study, while in another the addition of 20g of Al₄C₃ to 10g of water reached a maximum temperature of 280 °F (138 °C). Reversing the order and adding 10g of water to 20g of Al₄C₃ reached a maximum temperature of 349 °F (176 °C).^[8]

Similar reactions occur with other protic reagents:^[1]

Al₄C₃ + 12 HCl → 4 AlCl₃ + 3 CH₄

Composites

Reactive hot isostatic pressing (hipping) at ≈40 megapascals (390 atm) of the appropriate mixtures of Ti, Al₄C₃-graphite, for 15 hours at 1,300 °C (2,370 °F) yields predominantly single-phase samples of Ti₂AlC_0.5N_0.5, 30 hours at 1,300 °C (2,370 °F) yields predominantly single-phase samples of Ti₂AlC (Titanium aluminium carbide).^[9]

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.^[10] 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.^[11]

An aluminium-aluminium carbide composite material can be made by mechanical alloying, by mixing aluminium powder with graphite particles.^{[citation needed]}

Structure

Aluminium carbide has an unusual crystal structure that consists of alternating layers of Al₂C and Al₂C₂. Each aluminium 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.^[5][12]

Occurrence

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.^[13]

In metal matrix composites based on aluminium matrix reinforced with non-metal carbides (silicon carbide, boron carbide, etc.) or carbon fibres, aluminium carbide often forms as an unwanted product. In case of carbon fibre, it reacts with the aluminium matrix at temperatures above 500 °C (932 °F); better wetting of the fibre and inhibition of chemical reaction can be achieved by coating it with e.g. titanium boride.^{[citation needed]}

Applications

Aluminium carbide particles finely dispersed in aluminium matrix lower the tendency of the material to creep, especially in combination with silicon carbide particles.^[14]

Aluminium carbide can be used as an abrasive in high-speed cutting tools.^{[citation needed]} It has approximately the same hardness as topaz.^{[citation needed]}

See also

• List of compounds with carbon number 1