vacuum technology

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vacuum technology

all processes and physical measurements carried out under conditions of below-normal atmospheric pressure. A process or physical measurement is generally performed in a vacuum for one of the following reasons: (1) to remove the constituents of the atmosphere that could cause a physical or chemical reaction during the process (e.g., vacuum melting of reactive metals such as titanium); (2) to disturb an equilibrium condition that exists at normal room conditions, such as the removal of occluded or dissolved gas or volatile liquid from the bulk of material (e.g., degassing of oils, freeze-drying) or desorption of gas from surfaces (e.g., the cleanup of microwave tubes and linear accelerators during manufacture); (3) to extend the distance that a particle must travel before it collides with another, thereby helping the particles in a process to move without collision between source and target (examples of uses are in vacuum coating, particle accelerators, television picture tubes); (4) to reduce the number of molecular impacts per second, thus reducing chances of contamination of surfaces prepared in vacuum (useful in clean-surface studies)

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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