DRY ICE

'Dry ice' is the genericized trademark^[1] for solid carbon dioxide. It is commonly used as a versatile cooling agent.
Unlike water, which passes its solid point and becomes molten, dry ice sublimes, changing directly to a gas at atmospheric pressure. Its sublimation and deposition point is -78.5 °C (-109.3 °F). Its enthalpy of sublimation (ΔH_sub) @ -78.5 °C (-109.3 °F) is 199.0 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.^[2]

Contents

History

Manufacture

Applications

Use in blast cleaning

References

History

Dry ice was first observed in 1825 by the French chemist Charles Thilorier.^[3][4]
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. Throughout the next 60 years, dry ice was observed and tested by many scientists.

Manufacture

Dry ice is readily manufactured:
# Carbon dioxide 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.
Dry ice is typically produced in two standard sizes: solid blocks and cylindrical pellets. A standard block is most common and will normally be about 30 kg. These are largely used in the shipping industry because they sublime slowly due to a relatively small surface area. The pellets are around 1 cm in diameter and can be bagged easily. This form of dry ice is more suited to small scale use, for example at grocery stores and laboratories. Dry ice is also inexpensive; it costs about US$2 per kilogram.

Applications

The main applications of dry ice are related to its low temperature. It is commonly used in to package items that need to remain cold or frozen, such as ice cream, without needing any mechanical cooling source. In doctor's surgeries, it is used to freeze warts to make removal easier^[5]. 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 organic solvent is a useful freezing mixture for cold chemical reactions.
Dry ice can also be used to provide cooling for making ice cream^[6]
Dry ice is also used as a convenient source of carbon dioxide. It is used to carbonate water and other liquids such as beer. It is also used as bait, in order to trap mosquitoes and other insects^[7]
When dry ice is put in water, sublimation is accelerated and low-sinking dense clouds of fog are created. This is often used in theaters and nightclubs for dramatic effects.

Use in blast cleaning

One of the largest alternative uses of dry ice around the world is dry ice blast cleaning. Dry ice pellets are shot out of a jet nozzle with compressed air. This can remove residues from industrial equipment; examples of materials being removed: ink, glue, oil, paint, mold and rubber. Further, dry ice blasting can replace: sandblasting, steam blasting, water blasting or other (potentially environmentally damaging) solvent blasting.
Dry ice blasting involves three factors:
# kinetic energy
# thermal shock
# thermal kinetic energy
The kinetic energy of the dry ice pellets is transferred when it hits the surface, directly dislodging residues, as in other blasting methods. The thermal shock effect occurs when the cold dry ice hits a much warmer surface and rapid sublimation occurs. The thermal kinetic effect is the result of the rapid sublimation of the dry ice hitting the surface. These factors combined cause small "micro-explosions" of gaseous carbon dioxide where each pellet of dry ice impacts, dislodging the residue.

References

1. dry ice
2. Solar Navigator on Carbon Dioxide, retrieved 05 July 2007
3. Thilyorier and the First Solidification of a "Permanent" Gas (1835), Duane H. D. Roller; M. Thilorier, , , Isis, 1952
4. Solidification de l'Acide carbonique, Charles Thilorier, , , Comptes rendus, 1835
5. Management of warts., Lyell A., , , British medical journal, 1966
6. How to make the best treacle tart and ice cream in the world Heston Blumenthal
7. Comparative effectiveness of three adult mosquito sampling methods in habitats representative of four different biomes of California., Reisen WK, Boyce K, Cummings RC, Delgado O, Gutierrez A, Meyer RP, Scott TW., , , J Am Mosq Control Assoc., 1999