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Author: Subject: how to tell the difference between Al, Mg, or Zinc
Sedit
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[*] posted on 19-12-2010 at 19:31
how to tell the difference between Al, Mg, or Zinc




Anode for water heaters are one of these three metals.

How do I determine which is which. I seen a test for Mg on the interenet that suggested dilute Acetic acid would bubble on Mg which it indeed is the case with this anode.

A pure chunk of Al reacts much more with HCl then the anode material. This to me excludes Al and Zn yet when I attempt to shave the material and burn it it just melts instead.

Can anyone come up with a better test then the crap ones im performing.

Can Mg melt without igniting?





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[*] posted on 19-12-2010 at 19:39


Density would be the easiest way to test it in my opinion, maybe try to bend it I think Al will bend while Mg would snap not sure thought.



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[*] posted on 19-12-2010 at 19:41


like a diamond hardness tester.

every element has a set hardness.

this will only work with pure compounds though.

still if something is softer than Al its not Al or is an aloy
that has a softer metal in it.



[Edited on 20-12-2010 by Ephoton]




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[*] posted on 19-12-2010 at 19:50


The bend test is kind of out of the question because no matter the element is wrapped around a stainless steel rod so that would screw all that up.

Its been slightly consumed so its not 100%pure although I did a good job with a wire bench grinder and some HCl which pretty much took it to its element but I still need something quick to tell me the difference.


Ill keep looking. Im pretty sure its not Al but Zn is a possibility however it does not go hey wire in HCl like Zn or Al do making me thing its Mg but it dont burn it just melts. Would a low temperature since my tourch is loosing fuel mean that it dont get up to the temperature needed to ignite it and just melts it instead? I doubt it , just tossing out ides.





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[*] posted on 19-12-2010 at 19:53


if its shinny and is not an alloy then I would use a hardness tester.

an after note ive attached a hardness table for you :)


[Edited on 20-12-2010 by Ephoton]

Attachment: hardness_table.pdf (20kB)
This file has been downloaded 511 times





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[*] posted on 19-12-2010 at 20:01


Quick test for zinc!

Melt/burn with a small gas torch to get the oxide - yellow when hot and white when cold indicates zinc.
If you add a drop of cobalt nitrate solution to this oxide and heat again you should get a green encrustation (Rinmann's Green).

Aluminium oxide when moistened with cobalt nitrate solution and heated on charcoal, apparently gives a bright blue infusible mass!

The above from Mellor!

[Edited on 20-12-2010 by Xenoid]
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[*] posted on 19-12-2010 at 21:23


I have no Cobalt nitrate so thats out of the questions but there is a test I just performed indicating that it is indeed Mg

This youtube link
http://www.youtube.com/watch?v=M0QxQvHH6ck

Suggest in order to test to see of your pencil sharpener, some of which are made of Mg can be tested with a drop of dilute acetic acid and check form the presence of bubbles. If its Aluminum then there should be no reaction yet if its Mg then bubbles appear.

Simple enough I thought so I performed a small test. I placed Al foil. Fresh Al shavings, mystery metal assumed to be Mg, some galvinized Steel which is zinc coated, and some pure Zn washers along with zinc shavings aquired from melted pennys...

All of this was tossed into a flask with some 5%AcOH and obvserved. The one bit of Al that can from a pencil sharpener which I thought may be Mg at first produced trace bubbles over time but this was neglectagle. However, none of the zinc samples did anything at all nor did the Al aquired from aluminum tubing.

In the midst of all this the supposed Mg produced a good amount of super fine bubbles from the surface of the metal so Im almost 100% sure at this point I have a sacfricial Mg anode even though it was pretty corroded at the time I aquired it I managed to clean it well enough for some test.


==========================================


This is what bothers me though, if it is Mg why can I not get it to light? It will just melt under the influence of heat.

Can Mg melt without igniting is not my #1 question. My propane torch is running out of fule and its cold as hell so I can't get that high temperature flame common with these only a slow steady almost candle like flame with surely lower temperatures then a full canister.

If I heat it faster do yall think it will burn?

I want a burn as proof positive that I have pure enough Mg to work will and I fear that the anode is some form of an alloy possible with Zn or Al.


[edit]

PS:@Ephoton

Look at Al and Mg hardness..... Not much chance of me telling the difference that way because there hardness is almost the same exact thing and I wouldnt be able to know if the Mg or Al im using for the test was some form of an alloy to that just tosses that test out the window for good.:(

[Edited on 20-12-2010 by Sedit]





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[*] posted on 19-12-2010 at 23:33


Ok folks I figured it out, it is indeed a Mg sacrafical anode.

I cleaned the crude off as stated above since it was semi used. A little dilute HCl then a wire wheel bench grinder followed with another dilute HCl was. Subsequent washes took place to ensure no acid remained.


I broke the Anode into managable pieces and then melted them in a Stainless steel crucible. Alot of slag came out(this is very important and I will explain in the recent potassium thread) I pured the molten Mg into a couple bullion molds and some was poured into flat thin sheats of what appeats pretty good quality. They are about 1mm thick or so and very soft.

Reaction with AcOH was very vigorus when heated yet Al and Zn reacted almost nil.


Once I got some clean samples from the smelting process I dropped it into water and Hydrogen bubbled pretty well from it especially when heated slightly. Now I will explain further about a oddity in the Potassium from Mg thread because it may have something to do with why some fail where as others have great success.


Thanks for the suggestions guys I think this threads a wrap for now.





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[*] posted on 20-12-2010 at 01:45


damb :( ye I noticed that a little after I posted it sorry.



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[*] posted on 20-12-2010 at 12:34


For future reference:

First, dissolve the metal using HCl, so you have a solution of either Mg2+, Al3+ or Zn2+.

Secondly, dilute NaOH solution is added dropwise.

In case of Mg2+, a precipitate will form which will persist upon further addition of NaOH. To this solution ammonium chloride is added, which will dissolve the precipitate. Finally, Na2HPO4 is added, which will form a precipitate of MgNH4PO4. (Na2HPO4 solution can be conveniently produced by adjusting the pH of H3PO4 solution).

In case of Al3+, upon addition of NaOH a precipitate will form which redissolves upon further addition of NaOH. Addition of NH4Cl will cause the precipitate to reappear (note that this behaviour is contrary to Mg).

In case of Zn2+, upon addition of NaOH a precipitate will form which also redissolves upon further addition of NaOH. However upon addition of NH4Cl, the solution remains clear and no precipate is formed. Addition of Na2S to this solution will cause precipitation of ZnS.

These methods can be conveniently performed on a test tube scale using simple reagents. The procedures are based on the European pharmacopoeia.




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[*] posted on 20-12-2010 at 13:17


Thats perfect Vulture thank you. I have roughly 30 grams or so of Mg so I think I will spare some if I get the chance to run a couple test on it to check the purity. I fear for the purity of sacrficial anodes but today I went to check the cooled block and there where pyramid shaped crystals pertruding out of the surface telling me the purity isn't to shabby.

And the best part is I only serious cut two different fingers why cleaning it last night so if my typing is a bit hackish please forgive:P


PS: I still must again ask..... Why am I having a hard time igniting it? Only the slag that forms manages to ignite yet the molten metal does not light, WHY?

[Edited on 20-12-2010 by Sedit]





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[*] posted on 20-12-2010 at 14:00


Quote: Originally posted by Sedit  
PS: I still must again ask..... Why am I having a hard time igniting it? Only the slag that forms manages to ignite yet the molten metal does not light, WHY?
Surface area. Molten metal has minimal surface area for atmospheric oxygen to get to it for a combustion reaction.
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[*] posted on 20-12-2010 at 15:09


Even seawater can cause noticeable corrosion/reaction to Mg and high Mg alloys, so that's another go/nogo test. Vulture's tests are better, but it's easy to carry around a bottle of salt water when visiting junk yards and the like.

Centuries ago several friends and I acquired some chunks of Mg castings. They were a flaming #$%^&*( to get to ignite, but rather fun once they got going - a thin stream of water directed at the combusting Mg gave satisfying pops, bangs, and flares.

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[*] posted on 20-12-2010 at 22:16


I believe I have some high Mg content alloy,


I remember when I was a kid we,,,,, borrowed:P some Mg ribbon from school.

We ignited it with nothing more then a lighter and a long amount of time but once it got going it stayed burning till the end.

With this stuff it mostly just melts with the occasional flare here or there which goes out if heat from the acetalyne torch is removed. Im just going to start looking into these anodes because I feel they contain other materials along side of Mg.





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