AVS 59th Annual International Symposium and Exhibition
    Vacuum Technology Tuesday Sessions
       Session VT-TuP

Paper VT-TuP3
Investigation of a Method for Measurement of Water Vapor Coverage on Technical Surfaces

Tuesday, October 30, 2012, 6:00 pm, Room Central Hall

Session: Vacuum Technology Poster Session and Student-built Vacuum System Poster Competition
Presenter: M. Sefa, Laboratory Lotric d.o.o., Slovenia
Authors: M. Sefa, Laboratory Lotric d.o.o., Slovenia
J. Šetina, Institute of Metals and Technology, Slovenia
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Coverage of a surface by a gas can be determined by desorption method where amount of gas is calculated by integrating the released flux. This can be measured fairly straight forward in a case when desorbed gas don’t re-adsorb on surfaces of measurement chamber. Then mass conservation laws are applicable and flux can be determined by measurement of a pressure drop across the orifice of known conductance. In the case of adsorbing gas, like water vapor, the flux through the orifice is not equal to the flux coming from the sample, because significant amount can be re-adsorbed by the surfaces of measurement chamber.To determine surface coverage of water vapor on technical surfaces we have developed a special procedure where adsorption and desorption on the surfaces of measurement chamber can be taken into account. The sample is exposed to water vapor at known pressure (in the range from 0.1 kPa to 2.5 kPa) in a preparation chamber. After equilibration of surface coverage with the gas phase, the preparation chamber is opened to a measurement chamber which is continuously pumped through a known conductance. In the case of water vapor the shape of pressure burst is significantly influenced in the beginning by adsorption and later by desorption in the measurement chamber. However, the time integral of pressure burst over sufficiently long period represents the amount of water vapor coming from preparation chamber. This amount is sum of gas phase, desorbed amount from surfaces of preparation chamber and desorbed amount from the sample surface.In the presentation the measurement system will be described and examples of water coverage measurements on surfaces of Cu, Ni, Al and stainless steel will be given.