The CO2 Snow Cleaning process removes micron and submicron particulates and hydrocarbon-based contamination. Carbon dioxide snow cleaning is nondestructive, nonabrasive, residue-free, and environmentally friendly - there is no chemical waste. This expansion leads to the nucleation of tiny dry ice particles and a high velocity gas carrier stream.
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Thermodynamically, we showed that the passage of either liquid or gaseous CO2 through an orifice leads to formation of dry ice or snow. With proper nozzle geometry the snow stream can obtain high velocities and effectively remove both particulate and organic contamination. The removal of organic and particulate residues from surfaces during CO2 snow cleaning can be explained by two different mechanisms - one for particulate removal, the other for organic contamination removal.The mechanism for particle removal involves a combination of aerodynamic forces -- forces related to a moving high velocity gas, and momentum transfer between the dry ice and surface contamination.
Many cleaning methods exist and each has their own advantages and disadvantages. We will discuss water and solvent-based methods, ultrasonics, wiping, high speed air blowing, vacuum methods, lasers, replica tape, and argon-nitrogen cryogenic aerosol. Manual wiping with solvents is usually quick, and common in the optics industry.
Example 2 - Cleaning a Si Wafer Demo - Video on left - We contaminated a Si wafer with facial grease at a trade show. Cleaning was quick and easy as seen in the video below. The sample is held by a vacuum chuck that was on a hot plate at about 40 C. Video on right - Another Si wafer on a stainless steel plate heated to about 50 C.
By far, the most users of CO2 snow cleaning are in the optical fields and applications. CO2 snow cleaning has successfully cleaned individual optical pieces, systems, substrates of all kinds, mirrors, gratings, and other kinds of optics. Cleaning applications include types of glasses, both coated and uncoated, IR and UV optics, Si and Ge based optics, 3-5 and 2-6 optics, diamond turned optics, mirrors, gratings, telescope mirrors, and more. After some examples below, we discuss proper cleaning methods.
CO2 Snow Cleaning can be used to clean items after soot deposits from fires. There are several factors to consider, the major two are: 1 - How hot did the item get, and 2 - Can the item withstand cleaning process. Soot has been removed from items after exposure to fires. We found by testing that if the item got "hot enough, " the soot can react with some substrates.
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