Exposure of a True Metal Surface?

Discussion in 'Chemistry' started by Facial, Oct 10, 2010.

  1. Facial Valued Senior Member

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    It is commonly known that most metals, e.g. iron, do not have the free metal exposed to the open atmosphere. It has a thin layer of oxide, even when it appears to be shiny. The same reason causes an iron surface to be very resistant to soldering unless a flux, which removes the oxide surface, is applied.

    Recently I have been wondering whether dipping, say, a nail into oil or some other inert liquid, then abrading it with some sandpaper, can expose an active surface for a little longer. Is it possible, or does oxide layers still form? I feel that for oil, oxides will still form because of a small portion of free radicals. What do you think?
     
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  3. Communist Hamster Cricetulus griseus leninus Valued Senior Member

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    You can use surface cleaning techniques such as plasma in a vacuum to expose a metal surface, yeah. It's not hard. The plasma reacts with the oxides and organic grime on the surface to give volatile products which evaporate, leaving a metal surface exposed.

    Sandpaper, really?

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  5. spidergoat Valued Senior Member

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    You can use a weak acid like vinegar. This has been used with copper powder to get it to weld for powdered metallurgy. Some oxides like aluminum are more difficult to deal with.
     
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  7. Facial Valued Senior Member

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    I've heard of weak acids before. Organic ones such as vinegar and oxalic acid can facilitate the bonding of organic molecules to the surface, although I personally think this has something to do with the affinity to the amorphous oxide layer, not really the aluminum metal. For copper it would definitely expose the true metal surface in solution, but once the acid is removed then the oxides form again instantly. For the purposes of welding, a thinly just-formed oxide layer is enough to overcome in mechanical compaction such that the metal is able to expose itself again under plastic deformation.

    I've soldered many times using aluminum foil to catch drips. According to experience, there are some conditions in a normal atmosphere that does allow solder to join with aluminum, but it's EXTREMELY rare. Only witnessed it several times in high school, where I did something like 100+ solder jobs for a Rube Goldberg type competition. You have to have a scratch, and a consistent pool of solder and flux on aluminum foil to get it, but even then encountering a join is rare.

    Aluminum can be abraded readily using fine sandpaper - there is no question that, for about a picosecond (according to Wiki), a true metal surface is exposed.
     
  8. spidergoat Valued Senior Member

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    You could do it in a vacuum, or in a vessel filled with a neutral gas.
     
  9. Chipz Banned Banned

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    I would presume that unless the 'preservative' being used has some pretty special characteristics, the initial interaction with a solder gun is going to oxidize it pretty quickly.
     
  10. Emil Valued Senior Member

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    I hope you kidding.

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    Have you heard about the red oxide of iron?Or about rust?

    You know why it is used argon welding machine for aluminum welding?



     
  11. ElectricFetus Sanity going, going, gone Valued Senior Member

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    yes, organic and silicone oils should do, they repel oxygen nicely, only way to safely store some of the alkaline metals in fact.
     
  12. Facial Valued Senior Member

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    The worry I have with organic oils is that the small amounts of oxygen that are inevitably dissolved will instantly react, or that the creation of a metal surface will catalyze the formation of radicals which attach themselves to the metal.
     
  13. Emil Valued Senior Member

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    sodium in water

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    potassium in water

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  14. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    If one is using a torch with both gas fuel and oxygen then typically the fuel come from torch more centrally. If you place flame near copper so there is a small circle of fuel only on the hot copper, you will see what appears to be pure copper spot that the fuel has reduced to only Cu. I don't remember exactly how I have done this - perhaps in a O2 starved flame.
     
  15. Nasor Valued Senior Member

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    Oxygen is usually much more soluble in oils than it is in water. Oxygen is non-polar, after all. People store alkaline metals in oils to keep them away from water, not oxygen.
     
  16. Facial Valued Senior Member

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    Ah yes, I think it's called a reducing flame. Maybe an inert atmosphere is the only way to go.
     
  17. Facial Valued Senior Member

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    Makes sense. However, it's elusive to find data on this. Where have you found yours?
     
  18. Nasor Valued Senior Member

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    Just google "oxygen solubility coefficients in oil" or something similar. I don't know of any sources off the top of my head, it was just something that I remembered.
     
  19. Facial Valued Senior Member

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    Aho and Wahlroos 1966 pops up, that paper seems to imply 4X greater solubility in oils than in water. Interesting.
     
  20. Emil Valued Senior Member

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    I was convinced, until now, as the oil protects the iron from rust, oxidation.

     
  21. Facial Valued Senior Member

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    Most oils are still much better than nothing for protecting against rust, because hydroxyl radicals (OH-) and iron cations (Fe 2+, 3+), which are critical to the formation of rust, are polar and much lower solubility in oil.

    It's more accurate to say that metal surfaces passivate in oil, forming an oxide layer (and at elevated temperatures, organic groups) to prevent further corrosion.
     
  22. Emil Valued Senior Member

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    I have no idea what you're talking.

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  23. Odin'Izm Procrastinator Registered Senior Member

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    Normally acids are used for stripping the oxide layer from steels and copper base alloys, and oils saturated with inert gases for storage. In the case of aluminium normally alloying or surface treatment is needed to stop the oxide from forming for galvanic protection scenarios.
     

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