Mercury Diffusion Pump
Definition and meaning of Mercury Diffusion Pump in chemistry.
A mercury diffusion pump is a specialized type of vacuum pump that uses directed, high-speed vapor from continuously boiling mercury to capture gas molecules and evacuate a closed system to very low pressures.
In more detail
The pump operates by boiling liquid mercury to create a supersonic jet of heavy mercury vapor that shoots downwards through an internal nozzle assembly. Random gas molecules from the attached vacuum chamber diffuse into this dense vapor stream, collide heavily with the massive mercury atoms, and are swept downwards towards the bottom of the pump. The mercury vapor is then rapidly condensed by a water cooling jacket and returned to the boiler, while the accumulated gas is actively removed by a mechanical backing forepump. Although historically highly effective for achieving deep vacuums, mercury has largely been replaced by silicone oils due to its extreme toxicity.
Key facts
| Field | Physical Chemistry |
|---|---|
| Working Fluid | Boiling mercury vapor |
| Vacuum Range | High vacuum |
Mercury diffusion pumps were historically essential components in early mass spectrometers, electron microscopes, and particle accelerators to achieve the ultra-high vacuum necessary for their proper operation.
Frequently asked questions
Why are mercury diffusion pumps rarely used in modern laboratories today?
They have been almost entirely phased out due to the severe health and environmental hazards associated with mercury vapor toxicity, being safely replaced by modern oil diffusion or turbomolecular pumps.