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Calcium carbide, universally identified in industrial chemistry, metallurgy, chemical engineering, and mineralogy by Calcium carbide (CaC2) stoichiometry CaC2, is an inorganic compound and one of the most critical synthetic electrothermal solid-state chemical precursors in heavy industry.
Calcium carbide in Calcium carbide (CaC2) pure form is a colorless and transparent crystalline material, whereas commercial or technical-grade calcium carbide presents as a dense, hard, grey, dark brown, bluish-grey, or blackish crystalline solid with a coarse crystalline fracture pattern.
Technical-grade Calcium carbide possesses a distinct, pungent, garlic-like odor upon exposure to ambient air, caused by trace gaseous impurities—primarily phosphine (PH3), hydrogen sulfide (H2S), and arsine (AsH3)—liberated through immediate reaction with atmospheric humidity.
E-Number: Not applicable (strictly non-food additive; prohibited for human consumption).
CAS Registry Number: 75-20-7.
Chemical Name: Calcium dicarbide (IUPAC name: calcium acetylide).
Common Synonyms: Calcium carbide, Karpit, Acetylenogen, Calcium dicarbide, Dicalcium carbide, Acetylenyl calcium.
EC / EINECS Number: 200-848-3.
PubChem CID: 6332.
ChemSpider ID: 6092.
RTECS Number: EV9400000.
UNII Code: 2362Y7R49C.
Synonyms: Calcium carbide, Calcium dicarbide, Calcium acetylide, Carbide of calcium, Carbide, Calcium ethynediide, Acetylide calcium, Calcium acetylene compound, Acetylene generator compound, Acetylene precursor, Calcium carbide technical grade, Calcium carbide industrial grade, Carbide lime precursor, Carpit, Acetylenogen, Calcium dicarbide (CaC2), Calcium carbide reagent grade, Calcium carbide commercial grade
As an extremely reactive dicarbide/acetylide salt composed of a calcium divalent cation (Ca2+) and a triply-bonded dicarbon acetylide dianion (C2 2-), Calcium carbide functions primarily as an indispensable industrial feedstock for the thermal generation of acetylene gas (ethyne, C2H2).
Calcium carbide operates through an intensely exothermic, spontaneous hydrolysis reaction upon contact with liquid water or moisture, yielding highly flammable acetylene gas and leaving a thick, strongly basic suspension of calcium hydroxide (slaked lime slurry, Ca(OH)2).
Calcium carbide high chemical energy, thermodynamic stability at extreme temperatures, potent reducing capacity, high desulfurizing affinity, and role as an acetylene generator make Calcium carbide a pivotal substance across steelmaking, organic chemical synthesis, metal fabrication, pyrotechnics, and historical illumination systems.
Key Properties, Crystallography, and Identifiers
UN Dangerous Goods Number: UN 1402 (Hazard Class 4.3: Substances which, in contact with water, emit flammable gases).
HS Code (Harmonized System): 2849.10.00 (Carbides of calcium).
Molecular Formula: CaC2.
Molecular Mass: 64.099 g/mol.
Physical Appearance: Grey to dark brown/black dense crystalline solid, lumps, or granules depending on purity and crushed particle sizing.
Crystal Structure: Tetragonal crystal system at room temperature (isostructural with thorium dicarbide, ThC2, space group I4/mmm); transitions to a cubic phase (NaCl-type structure) at temperatures above 450 C.
Odor: Pure material is odorless; commercial material exhibits a strong, garlic-like, sulfurous odor due to trace phosphine (PH3) and hydrogen sulfide (H2S) impurities.
Flavor Profile: Not applicable (highly corrosive, toxic, and dangerously reactive; non-consumable).
Density: 2.22 g/cm3 at 20 C.
Melting Point: 2160 C (3920 F).
Boiling Point: 2300 C (4170 F) under inert argon atmosphere; decomposes at elevated thermal thresholds under oxygen.
Flash Point: Calcium carbide is a non-flammable solid Calcium carbide (CaC2); however, liberated acetylene gas (C2H2) generated upon moisture contact has a flash point of -18 C (-0.4 F) and an extremely broad explosion limit in air (2.5% to 82% by volume).
Solubility in Water: Reacts violently, rapidly, and exothermically with water (hydrolysis reaction); Calcium carbide (CaC2) cannot be dissolved without chemical decomposition.
Solubility in Organic Solvents: Insoluble in diethyl ether, ethanol, benzene, toluene, and hydrocarbons; decomposes in protic organic solvents (such as alcohols and carboxylic acids) releasing acetylene or acetylenic derivatives.
Optimal Chemical Reactivity Range: Highly reactive with liquid water, steam, atmospheric moisture, alcohols, organic acids, mineral acids, halogens, and oxidizing agents; reacts with dry molecular nitrogen (N2) at elevated thermal conditions (1000 C to 1200 C) to form calcium cyanamide.
Enthalpy of Formation (std): -59.8 kJ/mol.
Enthalpy of Hydrolysis Reaction: Approx. -130 kJ/mol of CaC2 consumed.
Mechanism of Action: Calcium carbide undergoes instantaneous nucleophilic substitution/hydrolysis upon exposure to water (CaC2 + 2 H2O -)
