Dry ice is solid carbon dioxide. It is commonly used as a versatile cooling agent. Dry ice sublimates, changing directly to a gas at atmospheric pressure. Its sublimation and deposition point is -78.5 °C (-109.3 °F). Its enthalpy of sublimation (ΔHsub) at -78.5 °C (-109.3 °F) is 571 kJ/kg (245.5 BTU/lb). The low temperature and direct sublimation to a gas makes dry ice a very effective coolant, since it is colder than ice and leaves no moisture as it changes state.(Although it can carbonate food that is near).

History

In 1835 the French chemist Charles Thilorier published the first account of dry ice. Upon opening the lid of a large cylinder containing liquid carbon dioxide he noted much of the carbon dioxide rapidly evaporated leaving solid dry ice in the container.

Manufacture

Dry ice is readily manufactured Carbon dioxide-rich gas is pressurized and refrigerated until it changes into its liquid form.

The pressure is reduced. When this occurs some liquid carbon dioxide vaporizes, and this causes a rapid lowering of temperature of the remaining liquid carbon dioxide. The extreme cold makes the liquid solidify into a snow-like consistency.

The snow-like solid carbon dioxide is compressed into either small pellets or larger blocks of dry ice.

Applications

Dry ice is commonly used to package items that need to remain cold or frozen, such as ice cream, without the use of mechanical cooling. In medicine it is used to freeze warts to make removal easier. In the construction industry it is used to loosen floor tiles by shrinking and cracking them, as well as to freeze water in valveless pipes to allow repair.

In laboratories, a slurry of dry ice in an organic solvent is a useful freezing mixture for cold chemical reactions.