All cryogens can present the hazard of unwanted condensation of substances that boil at higher temperatures. Table 6.1 shows the estimated vapor pressures of some of the substances that, if present, can be condensed, usually to a solid, at cryogenic temperatures.1 From the magnitude of these vapor pressures it can be seen that, in some cases, even undetectable amounts of substances can be condensed, although probably only negligible quantities of solids could accumulate at such low concentrations. Table 6.1 indicates that any cryogen can almost totally condense water vapor and carbon dioxide. Air can be condensed to a liquid at liquid-nitrogen temperatures (possibly resulting in a condensate enriched in oxygen; see Section 6.1.2.). Argon, nitrogen, and oxygen are condensed to solids at the temperatures of liquid neon, liquid hydrogen, or liquid helium. Finally, all substances, other than helium, are solids at the temperature of liquid helium.
KeywordsLiquid Helium Cryogenic Temperature Liquid Hydrogen Valve Seat Cryogenic System
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