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  • Study of water vapor pressure equilibration time in vacuum system
    Sefa, Makfir ; Šetina, Janez ; Erjavec, Bojan
    Water vapor adsorption and desorption on surfaces of vacuum chamber can play important role on distribution of water vapor partial pressure inside the chamber. It is well known that adsorption energy ... of water molecules at room temperature on technical surfaces is within unfavorable range which means very long time to remove adsorbed layers. This has a consequence that vacuum systems have to be baked at temperatures over 100 [compositum]C to reduce water vapor outgassing in reasonable time and achieve ultrahigh vacuum. When water vapor is admitted locally in the vacuum system, the distribution of water partial pressure within the system can deviate significantly from distribution of another non adsorbing gas that would be admitted at the same location. We have made a study of time delay to reach uniform pressure distribution inside vacuum chamber after introduction of water vapor. Measurements were done in a static mode. This means that the system was isolated from pumps and then different quantities of water vapor were introduced. We have observed adsorption of considerable amount of water molecules on the surfaces of the chamber. After fast decrease of water partial pressure in first few minutes, the adsorption continued at significantly reduced rate, but for very long time. Even after more than 24 hours the water pressure was still decreasing. Three SRGs were connected to the chamber through connection tubes of different lengths. Relative difference of SRG readings became smaller than 0.3% within less than 1 h, which means that nearly uniform distribution of water vapor was achieved much faster than equilibrium surface coverage. Results are important for estimation of necessary waiting time for comparison calibration of vacuum gauges with water vapor.
    Vir: Programme and book of abstracts (Str. 146)
    Vrsta gradiva - prispevek na konferenci
    Leto - 2012
    Jezik - angleški
    COBISS.SI-ID - 919466

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