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Calcium oxide
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Calcium oxide (CaO), commonly known as burnt lime, lime or quicklime, is a widely used chemical compound. It is a white, caustic and alkaline crystalline solid at room temperature. As a commercial product, lime often also contains magnesium oxide, silicon oxide and smaller amounts of aluminium oxide and iron oxide. The name lime (native lime) refers to a very rare mineral of the CaO composition.
Calcium oxide is usually made by the thermal decomposition of materials such as limestone, that contain calcium carbonate (CaCO3; mineral name: calcite) in a lime kiln.
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Encyclopedia
Calcium oxide (CaO), commonly known as burnt lime, lime or quicklime, is a widely used chemical compound. It is a white, caustic and alkaline crystalline solid at room temperature. As a commercial product, lime often also contains magnesium oxide, silicon oxide and smaller amounts of aluminium oxide and iron oxide. The name lime (native lime) refers to a very rare mineral of the CaO composition.
Calcium oxide is usually made by the thermal decomposition of materials such as limestone, that contain calcium carbonate (CaCO3; mineral name: calcite) in a lime kiln. This is accomplished by heating the material to above 825°C, a process called calcination or lime-burning, to liberate a molecule of carbon dioxide (CO2); leaving CaO. This process is reversible, since once the quicklime product has cooled, it immediately begins to absorb carbon dioxide from the air, until, after enough time, it is completely converted back to calcium carbonate.
Usage
As hydrated or slaked lime, Ca(OH)2 (mineral name: portlandite), it is used in mortar and plaster. Hydrated lime is very simple to make as lime is a basic anhydride and reacts vigorously with water. Lime is also used in glass production and its ability to react with silicates is also used in modern metal production industries (steel, magnesium, aluminium and others) to remove impurities as slag.
It is also used in water and sewage treatment to reduce acidity, to harden, as a flocculant, and to remove phosphates and other impurities; in paper making to dissolve lignin, as a coagulant, and in bleaching; in agriculture to improve acidic soils; and in pollution control, in gas scrubbers to desulfurize waste gases and to treat many liquid effluents. It has traditionally been used in the burial of bodies in open graves, to hide the smell of decomposition, as well as in forensic science, to reveal fingerprints. It is a refractory and a dehydrating agent and is used to purify citric acid, glucose, dyes and as a CO2 absorber. It is also used in pottery, paints and the food industry. Furthermore, quicklime is used in epidemics, plagues, and disasters to disintegrate bodies in order to help fight the spread of disease. CaO is a key ingredient in the nixtamalization process used to create corn hominy and masa or tortilla dough. In ancient India, before the discovery of soap, it was mixed with sand and used to clean ones body, while it was also used to build houses.
A relatively inexpensive substance, CaO produces heat energy by the formation of the hydrate, as in the following equation:
CaO + H2O ? Ca(OH)2 + 63.7kJ/mol of CaO
The hydrate can be reconverted to calcium oxide by removing the water in the reversible equation. If the hydrated lime is heated to redness, the CaO will be regenerated to reverse the reaction. As it hydrates, an exothermic reaction results. One litre of water combines with approximately 3.1 kg of calcium oxide to give calcium hydroxide plus 3.54MJ of energy. This process can be used to provide a convenient portable source of heat, as for on-the-spot food warming in a self-heating can.
In an experiment, when quicklime is heated to 4,300 degrees Fahrenheit, it emits an intense glow. This is caused by the rapidly heated atoms releasing light.
Annual worldwide production of calcium oxide is around 130 million metric tons. The United States and China are the largest producers, each producing around 20 million metric tons.
Use as a weapon
Historian and philosopher David Hume, in his history of England, recounts how during early in the reign of Henry III the English Navy destroyed an invading French fleet, by blinding the enemy fleet with "quicklime," the old name for calcium oxide: Also, quicklime was used as a component in Greek fire to make it ignite on contact with water.
D’Albiney employed a stratagem against them, which is said to have contributed to the victory: Having gained the wind of the French, he came down upon them with violence; and throwing in their faces a great quantity of quicklime, which he purposely carried on board, he so blinded them, that they were disabled from defending themselves.
David Hume, History of England, Volume II.
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