All About Dry Ice

Dry ice is solid CO₂ with a low temperature of -78° C (-109° F). At atmospheric pressure, solid CO₂ sublimates directly to vapor without a liquid phase. This unique property means that the dry ice simply "disappears" when it heats up, leaving no residue or waste to be cleaned. The CO₂ used to make dry ice is a natural by-product of several industrial manufacturing processes such as fermentation and petrochemical refining. The CO₂ given off by the above production processes is captured and stored without losses until needed. When dry ice is used no new CO₂ is produced. Instead, only the original CO₂ by-product is released which is why using dry ice is considered to be "carbon-neutral" and environmentally responsible.

CO₂ Properties

Carbon dioxide (Chemical Symbol = CO₂) is a natural byproduct of respiration, fermentation, and other industrial processes, existing as a colorless, odorless, and non-flammable gas. Its density at 25°C is 1.98 kg/m³ (0.123 lbs/ft³ at 32°F), about 1.65 times that of air, which means that CO₂ gas displaces oxygen in the environment (CO₂ sinks below oxygen).

Dry ice is the solid form of CO₂ and is white opaque in appearance. It is important to handle or store CO₂, whether solid or gas, in well-ventilated areas to reduce the danger of asphyxiation.

The detailed table below shows the chemical and physical properties of CO₂.

Dry ice sublimates or changes directly from solid to gas, without a liquid phase. The rate of sublimation must be taken into account when packing a container system since it gets smaller in size. Dry ice sublimates at a rate of 3% to 8% per day, depending on the thermal properties of the container and external temperature profile. One pound of dry ice will sublimate into 8.3 cu. ft. of carbon dioxide gas.

Slabs of dry ice last longer than pelletized dry ice, which sublimates faster.

* Scale in image below is for illustrative purposes only

Dry Ice Types

	Snow	Pellet	Nugget	Slab	Block
Description	Dry ice snow looks like water snow and has a very high sublimation rate compared to pellets, nuggets, slabs, and blocks. Dry ice snow requires less complex equipment to produce; however, it has a very short shelf life.	Dry ice pellets look like rice (3mm or 1/8") and are mainly used for dry ice blasting. Due to the pellets' lower sublimation rate and smaller size than dry ice snow, the use of pellets to freeze food for food processors has recently become more common.	With sizes ranging from 6 mm (1⁄4") to 19 mm (3⁄4") in diameter, dry ice nuggets are typically used for packaging and shipping food and product materials.	Dry ice slices or slabs are predominantly used by the airline catering industry because the typical slice size of 19 mm (3/4") fits nicely in catering carts. Some companies use slices for shipping.	Dry ice blocks have historically been made to keep packaged and shipped items cold for a long period of time. Today, dry ice blocks can also be utilized for dry ice blasting (Cold Jet patented block-shaver technology). Standard block sizes vary from country to continent.
Size	n/a	1 to 3 mm	6-19 mm	Standard size = 210 x 125 x 18 mm	Standard size = 250 x 250 x 125 mm
Sublimation Rate	Fastest sublimation rate Rapid refrigeration Shortest shelf-life	Quick sublimation rate Rapid refrigeration Short shelf-life	Average sublimation rate Average shelf-life	Slow sublimation rate Long shelf-life	Slowest sublimation rate Longest shelf-life
Applications	Flash-freezing	DI blasting Shipping small packages over short distances	Food processing Shipping large packages over long distances	Airline catering Shipping Cadaver cooling	DI blasting (shaved ice) Shipping Cadaver cooling
Primary Users	Meat processing plants	DI blasting companies Food processors	Meat processing plants Biological service companies (labs) Baking industry	Airline caterers Distributors	Grocery store warehouses Ice cream distributors

Deposition, Sublimation & Rate of Refrigeration

Dry ice undergoes the process of deposition or sublimation at the critical temperature of −78°C (-109.3°F). As CO₂ reaches temperatures below −78°C, it transitions directly from a gaseous to a solid state (i.e. dry ice forms) in a process called deposition. In contrast, as CO₂ reaches temperatures above −78°C, it transitions directly from a solid to gaseous state (i.e. dry ice disappears into CO₂ gas) in a process called sublimation. During the processes of deposition and sublimation, dry ice never reaches a liquid phase; thus, there is no residue or water waste associated with dry ice.

Note About High-Density Pellets