Calcium Carbide

Abstract

Chemically pure calcium carbide, Ca 2 C, is a colorless solid; however, the pure material can be prepared only by very special techniques. Commercial calcium carbide is composed of calcium carbide, calcium oxide, CaO, and other impurities present in the raw materials. Industrial‐grade calcium carbide contains about 80% as CaC 2 , 15% CaO, and 5% other impurities. In the United States calcium carbide‐based acetylene is mainly used in the oxyacetylene welding market, although some continues to be used for production of such chemicals as vinyl ethers and acetylenic alcohols. Calcium carbide is used extensively as a desulfurizing reagent in steel and ductile iron production, allowing steel mills to use high sulfur coke. The exothermic reaction of calcium carbide and water‐yielding acetylene forms the basis of the most important industrial use of calcium carbide. An important use of calcium carbide has developed in the iron and steel industries, where the carbide has been found to be an effective desulfurizing agent for blast‐furnace iron. Calcium carbide is produced commercially by reaction of high purity quicklime and a reducing agent such as coke in an electric furnace at 2000–2200°C. Commercial calcium carbide, containing about 80% CaC 2 , is formed in the liquid state. The liquid calcium carbide is tapped from the furnace into cooling molds. Calcium carbide is classed as a hazardous chemical under U.S. Department of Transportation regulations. Domestic shipments are mainly in steel tote bins. Containers must be marked “Flammable solid, dangerous when wet” and have the United Nations designation UN 1402. Although acetylene is considered to be a material having a very low toxicity, a threshold limit value (TLV) of 2500 ppm has been established by NIOSH. In the presence of a small amount of water carbide may become incandescent and ignition of the evolved air–acetylene mixture may occur. Nonsparking tools should be used when working in the area of acetylene‐generating equipment.