Sciencemadness Discussion Board
Not logged in [Login ]
Go To Bottom

Printable Version  
Author: Subject: aluminium amalgam
Jor
International Hazard
*****




Posts: 950
Registered: 21-11-2007
Member Is Offline

Mood: No Mood

[*] posted on 5-1-2009 at 07:10
aluminium amalgam


2 days ago I wanted to see what happens to aluminium foil to wich some HgCl2-solution is added. I took a fairly large piece of aluminium foil (about 10x10cm), and put it in a beaker, like you put a filterpaper in funnel. I prepared a HgCl2-solution by dissolving a very small spatula (10-20mg) HgO in 0,3mL 2M HCl.

I dropped this solution spread over the foil. After a small induction period there was a violently reaction producing fumes and fizzing noise. I assume this is the water and HCl reaction with the amalgated aluminium. Now after 2 days, I expected all aluminium to be oxidised by oxygen, because I thought the Hg 'moves' through the entire foil.
But what I have is normal foil, wich 6 dark grey lines (where I put the drops of HgCl2-solution).

I have heard from someone that an aluminium amalgam will turn into a white mass of Al2O3 in days.

Is this story bullshit?
Is the temperature too low (0 C) ?
Is the amount of used mercury too small?

Or what else could it be? Any ideas?

I tried this experiment for the fun of it, and I expected only Al2O3 to be left after a few days, so I could just dissolve mercury in nitric, and dispose of it in my heavy metal waste bottle. But doing that now doesn't sound like great idea, the remainders aluminium will give a good lot of NO2 with nitric.
I can dissolve the aluminium in NaOH, but that sounds like a lot of hydrogen and heat. Not really fun, concerning explosion hazard. Or is there not enough heat to ignite the H2?

[Edited on 5-1-2009 by Jor]
View user's profile View All Posts By User
Filemon
Hazard to Others
***




Posts: 126
Registered: 26-4-2006
Member Is Offline

Mood: No Mood

[*] posted on 5-1-2009 at 07:43


==> http://www.cientificosaficionados.com/experimentos/peste%20d...
View user's profile View All Posts By User
querjek
Hazard to Self
**




Posts: 76
Registered: 26-8-2008
Member Is Offline

Mood: No Mood

[*] posted on 5-1-2009 at 08:41


Did you try refluxing it?



it's all about chemistry.
View user's profile View All Posts By User
smuv
International Hazard
*****




Posts: 842
Registered: 2-5-2007
Member Is Offline

Mood: Jingoistic

[*] posted on 5-1-2009 at 10:45


Quote:
Now after 2 days, I expected all aluminium to be oxidised by oxygen


Water is the oxidizing agent in these reactions, not oxygen. The reaction stopped because it ran out of water. In the future do this in solution. I recommend checking a practical organic chemistry book to see the basics of this reaction.




"Titanium tetrachloride…You sly temptress." --Walter Bishop
View user's profile View All Posts By User
Jor
International Hazard
*****




Posts: 950
Registered: 21-11-2007
Member Is Offline

Mood: No Mood

[*] posted on 5-1-2009 at 11:36


???

The because of the mercury, the aluminium metal is no more protected by an isolating layer Al2O3. This means Al-metal is exposed to air, and this should react with oxygen immediatly. I though that was the function of mercury, disordering the nicely isolating thin layer of oxide and exposing the metal.

So oxygen should freely react with it? Am I missing something?
View user's profile View All Posts By User
smuv
International Hazard
*****




Posts: 842
Registered: 2-5-2007
Member Is Offline

Mood: Jingoistic

[*] posted on 5-1-2009 at 15:47


Ok, you are trying to do this while I was thinking more along the lines of oxidation of aluminum by R-OH in bulk R-OH solvent.

I think the popsci article above is exaggerated, while I am sure the rate of corrosion would be much faster, I do not think it would could 'rust a plane to pieces before it had a chance to land'. If you want to see a truly quick way of 'rusting' aluminum, cover the aluminum completely with a 2% mercuric chloride solution.




"Titanium tetrachloride…You sly temptress." --Walter Bishop
View user's profile View All Posts By User
not_important
International Hazard
*****




Posts: 3873
Registered: 21-7-2006
Member Is Offline

Mood: No Mood

[*] posted on 5-1-2009 at 18:39


I did this sort of thing was I was a kid, at first by sandpapering a chunk of aluminium and rubbing mercury on that spot, and later using mercury salts.

You can see the oxide 'hair' grow sometimes, if you get a good coating. But you need to cut through the existing oxide film for that to happen, and over a moderately large area.

Try putting a drop or two of 5% hydrochloric acid on the aluminium first, and spreading that about, then add the solution of Hg salt. What may have happened is that there was too little HCL to dissolve much of the oxide layer, it cut through some thin spots - scratches, all the small amount of mercury reacted at that area, and the narrowness of the gap restricted access to oxygen.
View user's profile View All Posts By User

  Go To Top