Calcium carbide
[CAS# 75-20-7]

Identification

• Classification: Inorganic chemical industry >> Inorganic salt >> Carbides and carbonates
• Name: Calcium carbide
• Molecular Formula: CaC₂
• Molecular Weight: 64.10
• CAS Registry Number: 75-20-7
• EC Number: 200-848-3

Properties

• Density: 2.22 g/mL
• Melting point: 447 ºC
• Boiling point: 2300 ºC
• Water solubility: hydrolyses

Safety Data

• Hazard Symbols: GHS02 Danger
• Hazard Statements: H260
• Precautionary Statements: P223-P231+P232-P280-P302+P335+P334-P370+P378-P402+P404-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Substances or mixtures which in contact with water emit flammable gases	Water-react.	1	H260
Skin irritation	Skin Irrit.	2	H315
Serious eye damage	Eye Dam.	1	H318
Specific target organ toxicity - single exposure	STOT SE	3	H335

• Transport Information: UN 1402

Discovory and Applicatios

Calcium carbide is an inorganic chemical compound with the formula CaC₂, first synthesized in the late 19th century through the reaction of lime (CaO) with carbon at high temperatures in an electric arc furnace. Its discovery revolutionized chemical manufacturing by providing a convenient method to produce acetylene gas, which became a critical feedstock for various chemical and industrial processes. Calcium carbide is a grayish-black solid with a high melting point and reacts vigorously with water to release acetylene (C₂H₂) and calcium hydroxide, a reaction that underpins most of its practical applications.

The primary application of calcium carbide is the production of acetylene gas. Acetylene generated from calcium carbide is widely used in welding and cutting operations due to its high flame temperature when combusted with oxygen. This made calcium carbide essential in metalworking industries before the widespread availability of liquefied petroleum gases. Additionally, acetylene serves as a key intermediate in organic synthesis, enabling the production of chemicals such as vinyl chloride, acrylonitrile, and synthetic rubber precursors.

Calcium carbide is also used in the manufacture of calcium cyanamide, a nitrogen fertilizer. When reacted with nitrogen gas at high temperatures, calcium carbide forms calcium cyanamide, which releases nitrogen slowly in soil, promoting plant growth. This application contributed to agricultural productivity in the early to mid-20th century, particularly in regions where traditional fertilizers were scarce or expensive.

In modern agriculture, calcium carbide has been employed to induce ripening of fruits, although its use for this purpose is now restricted in many countries due to safety concerns. The acetylene released from calcium carbide acts as a plant hormone analog, promoting fruit maturation. However, impurities in technical-grade calcium carbide, including traces of arsenic and phosphorous compounds, pose health risks, leading to regulatory limitations.

Industrial and chemical research applications also rely on calcium carbide. It is utilized as a reducing agent in metallurgical processes, particularly in the production of metals from their oxides, and as a precursor for various organo-silicon and acetylene-derived compounds. Its reactivity and availability as a solid source of acetylene make it a convenient reagent in laboratory and pilot-scale syntheses.

Safety and environmental considerations are crucial when handling calcium carbide. It reacts violently with water and moisture, producing flammable acetylene gas, which can form explosive mixtures with air. Protective measures, dry storage, and proper handling are essential to prevent accidents. The compound is also corrosive and can cause burns upon contact with skin or eyes.

The discovery and industrial development of calcium carbide highlight its significance as both a chemical reagent and a source of acetylene. Its applications in welding, organic synthesis, fertilizer production, and chemical research underscore its enduring relevance in multiple sectors, even as alternative technologies have reduced reliance on carbide in some areas. The compound remains a foundational material in chemical and industrial processes due to its versatility, reactivity, and historical importance.

References

2025. A comparison of calcium sources for ion-trap loading via laser ablation. Applied physics. B, Lasers and optics.
DOI: 10.1007/s00340-025-08521-z

2025. Hepatorenal toxicity and antioxidant response to calcium carbide-supplemented diet in male Wistar rats. Nutrire.
DOI: 10.1186/s41110-025-00362-2

2025. A Hybrid Fuzzy AHP-TOPSIS Analysis for Selecting the Optimal Catalyst To Maximize Bio-Oil Yield from Waste Plastics Pyrolysis. Waste and Biomass Valorization.
DOI: 10.1007/s12649-025-03209-z