CO2 ice pellets (or carbon dioxide snow)
Gaseous or liquid CO2 is drawn from a room-temperature gas cylinder or high-pressure dewar and expanded through a nozzle, whereby it partly undergoes a phase change to the solid state to produce dry ice snowflakes, i.e. crystalline CO2 propelled by the gas stream. The dry ice, with a temperature of -79°C, can also be extruded through a die resulting in dry ice pellets the size of a rice grain. The blasting media is propelled onto the surface to be cleaned through a special nozzle. Cleaning action is performed when the snow particles impact a contaminated surface, dislodge adherent contaminant particles, and carry them away in the gas stream.
The process is effective in removing very small (micron or submicron) particles, where fluid drag normally restricts the performance of liquid phase cleaning. The CO2 snow cleaning process also is believed to attack hydrocarbon film by dissolving hydrocarbon molecules in a temporal liquid CO2 phase which is then carried away by subsequent flow of snow and gas. CO2 snow performs ultrapure cleaning of light oils down to submicron size on the most delicate, sensitive materials ranging from bonding wires to precision mirrors in telescopes. The CO2 snow crystals generated by the snow gun are extremely gentle and adjustable to a wide range of size and intensity. It is used to remove light oils and fingerprints from mirrors, lenses, and other delicate surfaces, and from precision assemblies, without scratching the surface. The process is used to remove paste fluxes in soldering. CO2 snow can clean hybrid circuitry and integrated circuits without disturbing the bonding wires. This unique ability cannot be duplicated by any other cleaning mechanism.
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