Supercritical Fluids General Information Supercritical fluids are gases in a supercritical state, that is, at elevated temperature and pressure. The majority of commercially available supercritical fluid cleaning units use carbon dioxide (CO2). Supercritical fluids have both liquid and gas-like properties. This allows the fluid to penetrate very small gaps and complex assemblies. Supercritical CO2 has excellent solvent properties. One source compares it to hexane in solvency power. Supercritical CO2 removes: Silicone oils Flux residues Petroleum oils Machining oils Dielectric oils Lubricants Adhesive residues Plasticizers Fats and waxes. Candidates for supercritical CO2 cleaning include: Missile gyroscopes Accelerometers Thermal switches Nuclear valve seals Electromechanical assemblies Polymeric containers Special camera lenses Laser optics components Porous ceramics. A cosolvent can be added to supercritical CO2 to enhance its effectiveness. Parts are placed into a pressure vessel into which CO2 gas is introduced. The temperature and pressure are then raised until the supercritical state is reached. A basic system consists of: Compressor Heat exchanger (heating) Extraction vessel (pressure vessel) Pressure control valve (expansion) Heat exchanger (cooling) Separation vessel. Process temperatures may range from 35 to 65 °C. Pressures vary from about 2,000 psig (one reference says 1,070) to 4,000 psig. The process works well for complex shapes and assemblies. Nonmetallic materials must be tested for compatibility. The process works well for removing trace fluids. Some suppliers also claim effective removal of particle contamination. It may be possible to fine tune the operating pressure and temperature to match the soil being removed. Parts that cannot be subjected to elevated atmospheric pressures cannot be cleaned with supercritical fluids. This process has been developed for the precision cleaning industry. With further development it may become more broadly applicable. 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=gi