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Electrostatic dust distribution

  1. Mar 24, 2009 #1
    Hi,

    I am more familiar with the world of biology and chemistry, however I am trying to come up with a method to evenly distribute dust over a surface area which may require a bit of Physics help.

    I was wondering is there any way of say, positively charging an aluminium foil surface and negatively charging the dust that I am interested in and then releasing this dust in an enclosed chamber whereby this would fall and stick onto the aluminum foil surface (and nothing else, say I use a non conducting material to contruct my chamber) in an even manner so that I can get relatively constant amounts of dust per square cm?

    Thanks.
     
  2. jcsd
  3. Mar 24, 2009 #2
    Put the dust on the charged surface, tap it, it should distribute itself evenly.
     
  4. Mar 25, 2009 #3
    Thank you.

    So after removing the charge from the surface dust should remain evenly distributed?
     
  5. Mar 25, 2009 #4

    berkeman

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    Staff: Mentor

    Welcome to the PF. Maybe some of the technology behind photocopiers can help you:

    http://home.howstuffworks.com/photocopier.htm

    The toner adheres to the drum via electrostatic force. You may be able to use a similar technique on your flat surface, and turn it upside-down in a dust pile and take it out.
     
  6. Mar 25, 2009 #5
    Thanks.

    Yes another issue I face is I have a known quantities of dust (0.08g and 18g) which I want to distribute over individual surfaces evenly so I have to somehow ensure all of this dust gets transferred onto the surface.
     
  7. Mar 25, 2009 #6

    berkeman

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    Staff: Mentor

    Can you say a bit more about what you are going to do with this dusty surface? Can the surface be coated with an adhesive to hold the dust in place once it is applied? Or does the surface need to give up the dust when touched, or whatever?

    Also, how uniformly does the dust need to be distributed? How is the dust stored prior to application to the surface? In a bag, or airborne, or some other source?

    It would probably be practical to just release the dust some distance above the surface, with a rectangular tube (conducting so that very little of the dust sticks) to guide the dust down to the surface where it lands and stays. You just need to figure out a practical way to launch/agitate the dust into the air in the column, so that it has a fairly mixed distribution as it falls. As long as the dust particles are irregularly shaped, they should randomize their paths fairly well as they fall some distance down the tube to the surface, I would think.
     
    Last edited: Mar 25, 2009
  8. Mar 25, 2009 #7
    Yes sorry for not being more specific earlier.

    The dust is dust from soil (contaminated with metals). After distributing it evenly over a surface (I am thinking alfoil) a hand press would be done so that this dust then adheres to the hand so I can eventually calculate the transfer rate of the dust from the surface to the hand.

    The dust needs to be distributed fairly evenly over the surface say micrograms per square cm with slight errors permissible of course. I am still playing around with the size of the surface which may be either 600 square cm or 300 square cm.

    Thanks.
     
  9. Mar 25, 2009 #8

    berkeman

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    Very cool. CSI visits PF online for investigative help. Neon lights in the background, safety glasses, fume hoods, handcuffs. I'm in.

    So the surface needs to be non-adherent for the hand-press test, but have the soil dust fairly evenly distributed. I'd just use a conducting (metal, grounded) plenum about 3 meters tall, and shake the soil out into the plenum slowly with wide distribution. You should get good enough distribution for your CSI work.
     
  10. Mar 25, 2009 #9
    Thanks. Sorry but this is not even close to CSI work.

    I will try out what you have said and see if that works.
     
  11. Mar 26, 2009 #10
    I have a feeling that if you tried this, the dust particles would migrate towards the edges, much like the electrons do inside a conductor.

    I agree with berkeman--you'll get a pretty even distribution if you agitate the dust some considerable distance above your collection surface and simply let it fall. Assuming that the dust is composed of very small, lightweight particles, these will be easily carried by microcurrents in the air. Hopefully this will cause enough agitation to produce a homogeneous cloud of dust. Make sure that the room or container in which you drop the dust is very large compared to the size of the collection plate. Also use a much larger mass of dust than the 0.18 g (or whatever amount) needed, as most of it is not going to land on the plate.

    I am not sure about the idea of guiding the dust down with a tube. I would worry that the tube would influence the paths of the falling dust particles adjacent to it in some way--say, by electrostatic attraction or eddy currents. Safer just to launch a giant cloud of dust in a large room/container with a relatively small plate placed in the middle of the floor. When the required mass of dust has coated the plate, cover it over.
     
  12. Mar 26, 2009 #11
    Thanks for the reply.

    Yes I agree using a tube may influence the path of the falling dust. I could try allowing a larger distance for the dust particles to fall from. However unfortunately I only need to get a very small amount of dust on the surface. And I have only a limited supply of this contaminated dust so I cannot experiment with letting a larger quantity fall and collecting only a small amount over my surface..

    Perhaps I could place the surface as the base of an enclosed pyramidal structure which has a height of say 1m. I could then release the dust from the apex of this pyramidal structure and allow it to fall onto the surface.

    Would you think even this structure would influence the dust fall out pattern significantly? I am able to work with some error with the surface distribution.
     
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