Dry ice at normal pressures does not melt into liquid carbon dioxide, but rather “sublimates” (matter changing from a solid to gaseous form) directly into carbon dioxide gas. Hence it is called “dry ice” as opposed to normal “wet” ice (frozen water). Dry ice is produced by compressing carbon dioxide gas to a liquid form, removing excess heat, and then letting the liquid carbon dioxide expand quickly. This expansion causes a drop temperature so that some of the CO2 freezes into “snow” which is then compressed.
Different types of dry ice machines produce dry ice in various forms, most commonly: “blocks” (10-15 kg), “nuggets” (3-5 cm x 10-14 mm), and “pellets” (.5-1.5 cm x 3 mm). The smaller forms are more expensive, but generally more functional. As an industrial product, dry ice has been around for approximately 80 years and is mainly a consumable in the food production and transport industries. Since its invention many other applications have been found. A more recent one is Dry Ice Blasting.
Dry ice has a temperature of – 78.5 Celsius ( -173o F). It has a specific weight is approximately 1450kg/m3, and is free of water (pure CO2 = 100% dry) meaning it is not conductive. Dry ice converts to CO2 vapor on surface impact, is free of oxygen (anti bacterial) and non-toxic (food grade CO2). Solid Co2 constantly sublimates after formation, even when stored in a proper insulated container. However, there is no danger since the container’s lid releases excess gas/pressure at 1-2bar (15-30psi) through the seals. Using high quality insulated containers with cellophane wrapped tightly around the lid/seals, dry ice may be a usable blasting media for up to two weeks.