Supercritical Fluids Overview Above a certain temperature, a gas will not change to liquid phase with increased pressure. Instead, it changes to supercritical phase, which is neither gas nor liquid, but has properties of each. Carbon dioxide (CO2) is the most commonly used supercritical fluid (SCF) in cleaning applications. In this state it is an excellent solvent and can penetrate into very small cracks. This makes it very good for cleaning complex parts with tight tolerances. The process works well on liquid contaminants, including silicone oils, hydrocarbon oils, and machining fluids. Efforts are under way to improve the removal of particles and salts, which currently are not removed well by SCFs. Some particle removal is being seen in liquid-phase CO2. Nonmetallic materials such as gaskets and o-rings need to be tested for compatibility with the process. Systems are commercially available. Capital costs probably will exceed $100,000. Ongoing operating costs can be very low. The process can be designed as a closed-loop system in which the contaminant is collected and the CO2 is reused. The only waste is the removed material. State Information | Glossary | Conversion Checklist | Comments Home | Process Advisor | Alternatives | Links | Search All SAGE material, Copyright© 1992, Research Triangle Institute Last Update: 18 March 1995 sage@rti.org http://clean.rti.org/alt.cfm?id=sc&cat=ov