乾冰vs普通冰

Dry ice is the genericized trademark 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. Its sublimation and deposition point is -78.5 °C (-109.3 °F). Its enthalpy of sublimation (ΔHsub) @ -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.

Dry ice is readily manufactured:[citation needed]


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.[citation needed]



Ice is the name given to any one of the 14 known solid phases of water. However in non-scientific contexts, it usually describes ice Ih, which is the most abundant of these phases. It is a crystalline solid, which can appear transparent or an opaque bluish-white color depending on the presence of impurities such as air. The addition of other materials such as soil may further alter appearance. The most common phase transition to ice Ih occurs when liquid water is cooled below 0 °C (273.15 K, 32 °F) at standard atmospheric pressure. However, it can also deposit from a vapor with no intervening liquid phase such as in the formation of frost. Ice appears in varied forms such as hail, ice cubes, and glaciers. It plays an important role with many meteorological phenomena. The ice caps of the polar regions are of significance for the global climate and particularly the water cycle.