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Powder puzzle

  1. Apr 24, 2007 #1

    DaveC426913

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    I found a powder in my driveway earlier today. I have no idea where it could have come from but I'm curious because it seems so out of place.

    It's very dark brown, almost, but not quite black (see attached) and utterly uniform in colour.

    It's extremely fine, finer than icing sugar. So fine that I can't even feel it between my fingers. Its granularity is perfectly uniform.

    It covers very well. Rubbing it between my fingers gives me very black fingers.

    It was in a little pile (about a teaspoon), near my car, very well-defined, as if someone had accidentally-yet-carefully poured it there.

    I can't think of anything in or out of my car that would be like this. My neighbor is a mechanic, and has dead cars in our shared driveway.



    Can anyone think of any cool tests I can perform on it to find out what it is? Obviously a microscope would be extremely helpful. I only recovered a tiny amount, a fraction of a teaspoon.


    You know, it's got to be water-based powdered paint... It fits all the criteria. Except how it got there...
     

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    Last edited: Apr 24, 2007
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  3. Apr 25, 2007 #2

    chemisttree

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    Some basic home tests can go a long way to help you classify the powder but probably not identify it exactly.

    Water soluble? pH of solution? Is the powder wettable or not? Does it sink or float?
    Does it burn? What does the ash look like? Is the ash soluble? pH of ash solution? Flame smoky or burns cleanly? Does it melt before burning?
    These tests can be performed on just a couple of pinches of the material. Use an old spoon or screwdriver for the flame test.

    If the stuff dissolves in water, the pH will tell you something about the chemical nature of the stuff. The flame test will tell you if it is an organic substance or not or perhaps a mixture of inorganic/organic. The ash (if any) will tell you something about the metal content (calcium, sodium, potassium, zinc, etc...) If it melts it could be a micronized polymer.

    Was anyone doing concrete work in your area recently? Especially exposed aggregate work. Some water reducing admixtures and retarders are fine brown powders. Mortar colors can be any color of the rainbow and some are soluble that contain insoluble carrier powders.

    The attached pic doesn't show up on my computer. Maybe it is still being approved for posting...
     
  4. Apr 25, 2007 #3

    berkeman

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    The image isn't pending approval, it's just not there.

    Dave, could it be soot? Does it have a smell (careful)?
     
  5. Apr 25, 2007 #4

    berkeman

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    Hey, I just had a thought. Is the powder ferrous? If you run a magnet over it, is it attracted to the magnet? If so, it may just be rust from somewhere on the cars.
     
  6. Apr 28, 2007 #5

    DaveC426913

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    Ooh! Good one! It is indeed ferrous!

    It has no odor. (First test I did. Forgot to mention it.)

    Had no noticeable effect on pH, alkalinity, hardness (or total bromide for that matter :rolleyes: ).

    It still doesn't want to dissolve in water. Some of it forms a fine layer on the surface (as I would expect of any fine powder), some of it sort of breaks up, muddying the water a little. Much of it just sort of sits there.

    Flame causes little red hot grains to spit and drop off, but I have a feeling that would happen with any fine powder. The ash is - surprise - black powder.


    (P.S. I can see the pic, it's just VERY dark.)
     

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    Last edited: Apr 28, 2007
  7. Apr 29, 2007 #6

    mrjeffy321

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    So it wont dissolve in water.....but will it dissolve in acid? And if so, what type of acid and what is the color of the solution?
     
  8. Apr 29, 2007 #7

    DaveC426913

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    What acid would you have me try?
     
  9. Apr 29, 2007 #8
    If it was near your car, it could be ground up matter from brake pads or cack that's accumulated on them - that's black. I don't know what brake pads are made from, though.
     
  10. Apr 29, 2007 #9

    chemisttree

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    HCl (muratic) would be a good acid to try. You probably have a ferromagnetic metallic powder. Not many metals or metal oxides are ferromagnetic. It narrows down the choices.

    It could be brake dust as Sojurner suggests. The ferrometallic component would be powdered iron from your rotors. The dark black powder could be graphite (edit: or it could be amorphous carbon) plus some powdered metal(s) from the semimetallic pads mixed in with it. I don't think that the pads contain any ferrous metals but I don't know for sure.
     
    Last edited: Apr 30, 2007
  11. May 3, 2007 #10

    DaveC426913

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    Let's just reiterate here:
    - the powder is completely and utterly uniform in colour and granularity - like, manufacture-quality consistency. There aren't two colours or two components.

    I'd buy the brake dust thing (especially since I've been having wheel-bearing problems the last few weeks) except for a couple of contra-indicators:
    - the perfectly well-defined pile
    - the utter consistency of the particles

    Maybe I should ask my neighbor, whom I share the driveway with, if he's been using any powdered paints lately.

    Gotta get this stuff under a scope...
     
  12. May 4, 2007 #11

    chemisttree

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    AHA! Bearing problems! I had the same thing appear on the ground after replacing a CV joint. It seems that I buggered up the bearing somehow while chiseling off the nut holding the CV joint on. The bearing ground itself into a fine powder while I drove the car. The wheel was slightly wobbly, which caused the recently replaced brakes not to work very well, and each time I got in the car the wheel wobbled slightly and this powder came out. Very finely ground and it only spilled out when I got into the car. After I had a new bearing pressed in the problems and the powder went away.
     
  13. May 23, 2007 #12

    DaveC426913

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    OK, so I took it to a lab. Here're the results.

    Acetic acid: none to marginal solubility - merely muddies the solution
    Conc. hydrochloric acid - very soluble - turns solution bilious yellow-green
    Sodium hydrochloride - not soluble at all

    Definitely magnetic.
    Not radioactive.

    I had better pix using the microscope CCD but they didn't take.

    Pic 1 - 10x mag smeared out on a piece of paper
    Pic 2 - 1000x mag fixed on slide
    Pic 3 - solution of HCL
     

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    Last edited: May 23, 2007
  14. May 24, 2007 #13

    chemisttree

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    Sounds like an iron (II or III) oxide or hydroxide with finely divided iron/steel particles and possibly a little copper oxide. Pic #3 indicates that the powder is not completely soluble in HCl? Kind of greenish yellow. I would dilute the solution with about 2 - 3 tsp of distilled water (not tap water) and test with iron and copper water quality strips. Accurate to 0.02 to 5 ppm for iron and 0.5 to 10 ppm for copper.

    http://www.omega.com/pptst/WTS_Series.html

    What is 'sodium hydrochloride'? Sodium hypochlorite? Sodium chloride? Sodium hydroxide? Probably sodium hydroxide...

    Try to isolate the HCl solution by dilution with a couple of tsp of water and settling out and removing the insolubles. A bit of coffee filter jammed loosely (but not too loose) into a pipette or an eyedropper is a good small scale plug filter for this task. Use the bulb of the eyedropper to help push the solution through the plug filter. The solution should be faintly yellow green. Add some clear ammonia solution (not sudsy) dropwise until the pH is >10. Solids should form and form a floc. Try to get this to settle or filter using the plug filter. This will be the brown iron hydroxide (if present). The copper should remain in solution which will be deep blue.
     
  15. May 24, 2007 #14

    DaveC426913

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    Brain f*rt. Yeah. NaOH.
     
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