2572 °C (2845 K)
2850 °C (3123 K)
Calcium oxide (CaO), commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic and alkaline crystalline solid at room temperature.
The broadly used term lime connotes calcium-containing inorganic materials, in which carbonates, oxides and hydroxides of calcium, silicon, magnesium, aluminum, & iron predominate, such as limestone. By contrast, quicklime specifically applies to a single chemical compound.
Calcium oxide is usually made by the thermal decomposition of materials such as limestone, that contain calcium carbonate (CaCO3; mineral 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 quicklime. The quicklime is not stable and, when cooled, will spontaneously react with CO2 from the air until, after enough time, it is completely converted back to calcium carbonate.
See article on slaked lime, Ca(OH)2 (chemical name calcium hydroxide) (mineral portlandite) for a list of uses as slaked lime.
A relatively inexpensive substance, quicklime produces heat energy by the formation of the hydrate, calcium hydroxide, as in the following equation:
The hydrate can be reconverted to quicklime by removing the water in the reversible equation. If the hydrated lime is heated to redness, the quicklime will be regenerated to reverse the reaction. As it hydrates, an exothermic reaction results. One liter of water combines with approximately 3.1 kg of quicklime to give calcium hydroxide plus 3.54 MJ 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.
When quicklime is heated to 2400 °C (4300 °F), it emits an intense glow. This form of illumination is known as a limelight, and was used broadly in theatrical productions prior to the invention of electric lighting.
Annual worldwide production of quicklime is around 283 million metric tons. China is by far the world's largest producer, with a total of around 170 million metric tons per year. The United States is the next largest with around 20 million metric tons per year.
Full article ▸