| Pressure Ranges Used in Vacuum Technology and their Characteristic Features |
| Rough Vacuum | Medium Vacuum | High Vacuum | UHV | |
| Pressure range in mbar | 1,013...1 | 1...103 | 10-7...10-7 | <10-7 |
| Particle number density in cm-3 | 1023..1020 | 1016...1013 | 1013...109 | <109 |
| Mean Free path in cm | <10-2 | 10-2...10 | 10...105 | >105 |
| Impingement rate in cm-2 s-1 | 1019...1016 | 1020...1017 | 1017...1013 | <1013 |
| Monolayer time in seconds | <10-5 | 10-5...10-2 | 10-2...100 | >100 |
| Type of gas flow | Viscous flow | Knudsen flow | Molecular flow | Molecular Flow |
| Other features | Convection dependant on pressure | Marked change of the thermal pressure | Marked reduction of the volumx10-related collision rate | Surface effects dominate |
Please Note all figures are approximate and relate to air 20°C.
| Outgassing Rates of Materials |
| as a Function of Time |
| Outgassing Rate in mbar L /S /cm² | ||||
| Material | after half hour | after 1 hour | after 3 hours | after 5 hours |
| Ag | 1.5x10-08 | 1.1x10-08 | 2x10-09 | - |
| Al | 2x10-08 | 6x10-09 | - | - |
| Cu | 4x10-08 | 2x10-08 | 6x10-09 | 3.5x10-09 |
| Stainless Steel | - | 9x10-08 | 3.5x10-08 | 2.5x10-08 |
| Silicone | 1.5x10-05 | 8x10-06 | 3.5x10-06 | 1.5x10-06 |
| Perbunan | 4x10-06 | 3x10-06 | 1.5x10-06 | 1x10-06 |
| Acrylic Glass | 1.5x10-06 | 1.2x10-06 | 8x10-07 | 5x10-07 |
| Viton | 7x10-07 | 4x10-07 | 2x10-07 | 1.5x10-07 |
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