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Evaporative cooling in a vacuum

  1. Nov 21, 2003 #1
    I am having a problem at work and I'm hoping some of the brains on this board can help.

    I'm using a Focused Ion beam to induce insulator deposition using a siloxane liquid. The liquid is stored in a small container with a valve to let the gas escape the container. This small container is located inside a vacuum chamber.

    The vacuum chamber has a pressure of 1.5e-6 millibar when the siloxane valve is closed.

    When the valve is opened I see the pressure rise to 8.0e-6 which is where I want to perform deposition.

    As I watch the pressure I notice a slow linear drop with time. This effect causes the deposition process to fail.

    As far as I know the chamber pressure is determined by the vapor pressure of the liquid and the size of the valve(which also has a limiting aperture in it)

    My questions are:
    1. Is this pressure drop due to the temperature of the liquid dropping due to evaporative cooling? This drop in temperature would also drop the vapor pressure right?

    2. Is there a formula to calculate the vapor pressure vs temperature, or to calculate how fast the liquid will cool in the presence of a vacuum? or some other formula to help me characterize this effect.

    3. Could the gauge used to measure the pressure level become inaccurate in the presence of an insulator like siloxane? It's a hot cathode Ionization gauge.

    4. Is there something else that could be going on that I haven't mentioned.

    Thanks for any help
     
  2. jcsd
  3. Nov 21, 2003 #2
    Would Boyle's law's be of any help?
     
  4. Nov 21, 2003 #3
    I dont know, where do I find information on this law?

    Thanks
     
  5. Nov 21, 2003 #4
    I had found several citations when I ran a google search.
     
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