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Near Perfect Vacuum?

  1. Apr 11, 2004 #1
    I remember thinking when I was much younger what might happen if I took a pencil, dipped it in rubber, let it dry, then snapped the pencil in half and pulled the ends apart.
    My thoughts were that a vacuum is created at the point(s) of break when pulled, with the rubber surrounding that immediate area pressing inwards due to atmospheric pressure.
    But a lot of debris at the snap point within the "partial vacuum"
    Thinking later on, I wondered what would happen if some other suitable material besides a pencil might be useful. Such as a crystal rod or such that would fracture relatively cleanly. Good thought, but still debris.
    Then I thought about a metallic conductive rod, similarly coated in a rubber-type compound, bent enough to fracture. Pulled apart, a partial vacuum as before is created. But I then apply an electrical field, such to where one of the rod halves is positive, the other negative.
    Could it be, under those circumstances, that any microscopic metallic dust created during fracture is now charged and "sticks" to the positive side, creating a near perfect vacuum?
  2. jcsd
  3. Apr 11, 2004 #2
    A very strange thought indeed. Can you expand on it? I don't know
    what you are talking about.
  4. Apr 11, 2004 #3
    Rubber does not do well at ultra high vacuum. Most UHV chambers use copper seals instead of viton rubber for this reason.
  5. Apr 11, 2004 #4
    There is a method called "getting" that decreases the gas in a "vacuum" tube by vaporizing a metal filament therein, thereby creating and deposting a metal-gas compound on the tube walls.
  6. Apr 13, 2004 #5
    Thanks guys. Good info.
    Eyesaw, sorry if I confused you. This can happen when I ramble on!

    So, let me clarify with an example that works, but does not work perfectly. Through this, you will see what I am getting at:
    Let's take a quartz rod, say 1-foot long and 1-inch diameter.
    This rod is dipped in a liquid "rubber" compound such that the rubber completely surrounds the quartz rod with a rubberized coating of, say, 1/4th inch.
    The rubberized coating is allowed to cure.
    So, now we have a quartz rod completely coated by a 1/4th inch layer of cured rubberized compound.
    Carefully holding the coated rod through whatever means, we "tap" the center of the rod(which is 6-inches from either end) with a suitable implement.
    The rod fractures at that mid-point, though not perfectly.
    Is the picture clear? We now have a 1-foot quartz rod coated in rubber that has been fractured(only the quartz) in the middle of the rod.
    I clamp each end of the rod in a pulling device, and slowly pull the two halves apart.
    Remember, the rod, though now split in half, was entirely surrounded by rubber.
    So, when the 2 halves are pulled apart, a vacuum is created between the fracture points of the rod inside the rubberized coating and increases the more the rod ends are pulled apart.
    I hope this is a clearer picture, Eyesaw.

    Anyway, now that you have the basic concept, I ran into several conceptual design problems. First, because a vacum is created at the point of rod separation, the "rubber" compound surrounding the outside area at that point will be pushed in towards the created vacuum. This is, of course, simply due to the fact that the outside atmospheric pressure is greater than the pressure of the vacuum created, so it will tend to "suck" the rubber in.
    That aspect can be dealt with to some degree by simple coating thickness modifications at the area of intended fracture, or by "reinforcing" that rubberized area.
    Another problem is whether or not a crystal rod can be coated with a suitable rubberized material without trapping external gasses against the rod during the coating process. Advanced manufacturing techniques I am aware of leads me to believe that that problem is able to be reasonably handled.
    But my biggest conceptual problem occurs during rod fracture. That is, I believe that during fracture, microscopic crystal particles are sheared from the fracture line and introduced into the created vacuum. So the event creates one hell-of-a good vacuum, in my opinion, but not perfect due to the microscopic crystal dust floating around in the vacuum space between the fractured rod halves coated in a rubberized compund.
    Fine. I hope this is also clear.
    So, then my thoughts developed to somehow dealing with that microscopic dust.
    What is needed, is to get that microscopic "dust" to settle down and adhere to some part of the inside, creating a near perfect vacuum.

    Anyway, there's a whole lot more to this, Eyesaw, but perhaps you have a better picture of the general idea.
    Last edited: Apr 13, 2004
  7. Apr 13, 2004 #6
    Even if you executed your plan perfectly and started pulling vacuum in the void you would have gas desorbing from the rubber walls contaminating your vacuum.

    Rubber is not a good seal for UHV because it leaks and degasses. If you want a vacuum better than 1x10-10 torr you need metal seals, ultra clean surfaces and high pumping speeds.
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