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www.pfeiffer-vacuum.net<br />
Solid<br />
Liquid<br />
Gaseous<br />
Figure 1.10: Saturation vapor pressure of water<br />
Source: Jousten (publisher) Wutz, Handbuch Vakuumtechnik, Vieweg Verlag<br />
Water vapor pressure<br />
mbar<br />
SOLID LIQUID<br />
Melts<br />
Sublimate<br />
GASEOUS<br />
Vaporization<br />
Triple Point<br />
Temperature<br />
Diffusion with desorption<br />
At operation below 10 - 6 mbar, desorption of plastic surfaces, particularly the seals, assumes<br />
greater significance. Plastics mainly give off the gases that are dissolved in these plastics,<br />
which first must diffuse on the surface.<br />
Following extended pump downtimes, desorption from plastics can therefore dominate the<br />
metal surfaces. Although the surface areas of the seals are relatively small; the decrease<br />
in the desorption rate over time occurs more slowly in the case of metal surfaces. As an<br />
approximation it can be assumed that the reduction over time will occur at the square root<br />
of the time.<br />
°C<br />
Page 23<br />
<strong>Vacuum</strong><br />
<strong>Technology</strong>
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