What is dry ice?

What is dry ice?
Highlights

What Is Dry Ice? Liquid carbon dioxide vaporises causing a rapid lowering of temperature of the remaining liquid.

Dry ice is the solid form of carbon dioxide. It is used primarily as a cooling agent. Its advantages include lower temperature than that of water ice and not leaving any residue (other than incidental frost from moisture in the atmosphere).

It is useful for preserving frozen foods, ice cream, etc., where mechanical cooling is unavailable.

Dry ice is easily manufactured. First, gases with a high concentration of carbon dioxide are produced. Such gases can be a byproduct of another process, such as producing ammonia from nitrogen and natural gas, or large-scale fermentation. Second, the carbon dioxide-rich gas is pressurised and refrigerated until it liquifies.
Next, the pressure is reduced. When this occurs some liquid carbon dioxide vaporises causing a rapid lowering of temperature of the remaining liquid.
As a result, the extreme cold causes the liquid to solidify into a snow-like consistency. Finally, 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 forms: blocks and cylindrical pellets. These are commonly used in shipping because they sublimate relatively slowly due to a low ratio of surface area to volume.
Pellets are around 1 cm (0.4 in) in diameter and can be bagged easily. This form is suited to small scale use, for example at grocery stores and laboratories.
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