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Filter that can filter out all but the smallest particles

  1. Jun 8, 2005 #1


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    Hey guys i was wondering something. When some product claims it has a filter that can filter out all but the smallest particles (like oxygen or H2O)... how can it do that? I mean i just imagine a huge grid of super duper tiny pins making holes only an atom or 2 wide.... obviously that cant be how they do it so how do they do it?
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  3. Jun 8, 2005 #2
    In what context you are speaking? What is the medium that you want to filter? Anyhow, you shouldn't mean it in literal sense. Some filters filter something by absorption, some by coalescing and some by actually trapping etc. For example, carbon molecular seives absorb oxygen and other gases. Hydrophopic filters made up of borosilicate micro glass fibres coalesce water particles and filter them out.

    Reverse osmosys system filters have a pore size of 0.001 microns and trap ions.
  4. Jun 8, 2005 #3

    You mean 1 nanometer? I wonder how they create such things.
  5. Jun 8, 2005 #4


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    Well ive seen stuff on say, modern marvels and the CG they use shows like, a grid system and then you see the molecules come by and some cant get throug the holes and others can.

    Are they just not being literally serious?
  6. Jul 1, 2005 #5


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    A really high-quality filter is actually tailored to the thing that it's supposed to keep out. If you want to exclude bowling balls, page-wire is great. Fuel filters in a car are made to let gasoline (or deisel) pass with the least resistance possible while keeping out any particulate matter. This of course lets water pass as well, so other methods are used to keep that out. Chemical filters use absorbtion, adsorbtion, or neutralization of the offending substance. The trick is to make the porousity just right so that it doesn't clog up with things smaller than the target. The best natural filter is the part of the water cycle where rocks take out the big stuff, gravel the medium stuff, and sand the small stuff. By the time the water gets back into a stream or river, it's pure.
  7. Jul 2, 2005 #6


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    Just to clarify this; it's dependent upon the materials chosen to make the filter and what properties you wish to use for the filtration (size, charge, etc.).

    Here's a site with a fairly simple explanation of nanomaterials used for making filters and other types of porous membranes.
  8. Jul 2, 2005 #7
    Other factors help explain the ability to create micro-sized 'spaces' or holes. for instance, many filter designs use fibres which can be quite long or large, but closely packed so that the spaces between are very small. You don't actually have to 'drill' holes that small, and the sizes can be achieved by manipulation of much larger objects to make the spaces.

    Also, nets can be made by a combination of physical holes and electromagnetic forces, or electrostatic behaviour of polar molecules and orientations. Surface catalysts work on similar principles.

    The size of the holes you make is only really limited by your cleverness in design.
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