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Author: Subject: aluminum resistant to nitric and sulfuric acid mixture
symboom
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shocked.gif posted on 7-6-2011 at 17:28
aluminum resistant to nitric and sulfuric acid mixture


Now i know hcl desolves aluminum and aqua regia also desolves.
is aluminum resistant to nitration of 98% sulfuric acid and fuming nitric acid mixture will it react with aluminum
aluminum is resistant to sulfuric acid and nitric acid separatly

aluminum forms a passavation layer with nitric acid
this is the only way its made

Aluminium nitrate is made by adding nitric acid to aluminium trichloride.
Aluminum nitrate can also be made by adding a lead nitrate solution to an aluminum sulfate solution. The insoluble lead sulfate is precipitated out of the solution, leaving a solution of aluminum nitrate.


aluminum sulfate formed by
Aluminium sulfate may be made by adding aluminium hydroxide, Al(OH)3, in sulfuric acid, H2SO4:
2 Al(OH)3 + 3 H2SO4 → Al2(SO4)3·6H2O

The compound decomposes to γ−alumina and sulfur trioxide when heated between 580 and 900°C. It combines with water forming hydrated salts of various compositions.

slowly hydrolyises forms a dilute sulfuric acid and aluminum oxide

[Edited on 8-6-2011 by symboom]
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AJKOER
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[*] posted on 8-6-2011 at 16:21


To be clear on an important point of chemistry, Aluminium is not resistant as it readily reacts with even H2O (liberating H2) and also oxygen to rapidly form Al2O3. It is the protective coating of Al2O3 on Al that is resistant!

It turns out that NH4OH readily reacts with Al2O3 (I have performed this reaction):

2 NH4OH + Al2O3 + H2O --> 2 Al(OH)3 + N2 + 3 H2

which is actually a two step reaction as the NH4OH directly reacts with Al2O3 liberating active Aluminium that rapidly reacts (like Sodium) in water!

Al2O3 + 2 NH4OH --> 2 Al + N2 + 5 H2O

2 Al + 6 H2O --> 2 Al(OH)3 + 3 H2

So even NH4OH, a weak base, dissolves Aluminium because it reacts with (removes) the Al2O3 and the WATER dissolves the aluminium!

In the case of excess NH4OH, the white clouds of Al(OH)3 eventually vanish with the formation of a clear NH3 complex (perhaps Al(OH)4- ).
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AndersHoveland
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[*] posted on 9-6-2011 at 14:31


The reaction between aluminum foil and ammonium hydoxide seems to be very slow.
I left the foil in the NH4OH for a whole hour and it did not dissolve. NaOH is much more rapid.

I have also noticed that aluminum foil does not seem to dissolve in dilute sulfuric acid, or in a solution of bisulfate, after 24 hours.

[Edited on 9-6-2011 by AndersHoveland]




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[*] posted on 10-6-2011 at 00:58


I also have tried Al + NH4OH (25% NH3)
Not anywhere near Al + NaOH
I did not noticed any reaction, even if I carefuly heated the test tube.
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[*] posted on 10-6-2011 at 03:03


Xenomorph, don't forget that NH4OH is a weak base, while NaOH is a strong base. Its like using 37% acetic acid instead of concentrated hydrochloric acid for a metal-acid reaction.



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[*] posted on 10-6-2011 at 04:04


Quote: Originally posted by AJKOER  
It turns out that NH4OH readily reacts with Al2O3 (I have performed this reaction):

2 NH4OH + Al2O3 + H2O --> 2 Al(OH)3 + N2 + 3 H2

which is actually a two step reaction as the NH4OH directly reacts with Al2O3 liberating active Aluminium that rapidly reacts (like Sodium) in water!

Al2O3 + 2 NH4OH --> 2 Al + N2 + 5 H2O

2 Al + 6 H2O --> 2 Al(OH)3 + 3 H2

So even NH4OH, a weak base, dissolves Aluminium because it reacts with (removes) the Al2O3 and the WATER dissolves the aluminium!

In the case of excess NH4OH, the white clouds of Al(OH)3 eventually vanish with the formation of a clear NH3 complex (perhaps Al(OH)4- ).


This is utter baloney on so many levels.

Alumina cannot split ammonia into its constituent elements in reasonable lab conditions. Perhaps leading ammonia gas over very hot alumina may cause some catalytic break down of the NH3 but I don’t recall ever hearing or reading about this either...

Ammonia solution is also generally recognised to be too weak to even dissolve freshly precipitated alumina, let alone a passivation layer! The pH of even a concentrated NH3 solution simply isn’t high enough to cause:

Al2O3 + 2 OH- + 7 H2O < === > 2 [Al(OH)4(H2O)2]-

… to push to the right.

Industrially, finely crushed Bauxite ore (alumina with ferric oxide contamination) is dissolved in very strong NaOH, often under pressure (to be able to heat above the BP of the alkali solution) and even then it takes appreciable time to accomplish complete dissolution of the aluminous part of the ore…

Also, Al3+ forms no known complexes with ammonia in aqueous medium.

Quote: Originally posted by AndersHoveland  
I have also noticed that aluminum foil does not seem to dissolve in dilute sulfuric acid, or in a solution of bisulfate, after 24 hours.

[Edited on 9-6-2011 by AndersHoveland]


Nope. Not true either, IMHO. Although it depends on what you call ‘dilute’, I guess. I regularly make significant amounts of alum (KAl(SO4)2.12H2O) by dissolving Al scrap in excess 50 w% H2SO4, then neutralising the excess acid with KOH. The dissolution of the aluminium is swift and generates quite a bit of heat.

By and large, aluminium is very reactive to ‘dilute’ strong acids and bases. It’s a very electropositive metal and its ions solvate (to [Al(H2O)6]3+) with great release of enthalpy.

Al scrap in concentrated HCl is so exothermic it can make the formed solution boil, something I found out to my detriment :mad: Whether it does or not largely depends on the amount of Al you've got reacting.


[Edited on 10-6-2011 by blogfast25]
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[*] posted on 10-6-2011 at 04:35


There are many videos of people blowing of Al + HCl bombs. It is a very exothermic reaction. I have done it uncontained.

Once, I tried dissolving aluminium in household ammonia. There was no reaction. I tried in a dilute solution of sodium hydroxide. I got a reaction. I also couldn't dissolve aluminium in household acetic acid, either, to make aluminium acetate. Aluminium is too metallic for its oxide to react with weak bases, and too high of an oxidation state to have it dissolving in weak acids.




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[*] posted on 10-6-2011 at 07:15


Quote: Originally posted by LanthanumK  
Aluminium is too metallic for its oxide to react with weak bases, and too high of an oxidation state to have it dissolving in weak acids.


Poorly formulated or inaccurate use of 'metallic'. The metals par excellence are the alkali metals and their oxides are strongly base forming. These oxides react with almost any acids, including the weak fatty acids if which acetic acid is a bit of a case in extremis.

Al is a bit of an 'inbetweener': forms a base forming oxide but it's also amphoteric. Freshly prepared alumina will dissolve in vinegar to form the acetate. And clean Al metal will probably dissolve in stronger (than vinegar, 4 - 5 V%) acetic acid, probably fairly vigorously at BP... Vinegar is only about 0.8 M in ethanoic acid: you wouldn't normally dissolve the metal in such weak HCl or H2SO4 either.

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[*] posted on 10-6-2011 at 10:30


@LanthanumK: I can't remember where, but Philou mentioned that ammonia reacts with the oxide layer to expose the aluminum which reacts with the water forming hydrogen.

Perhaps because of the low concentration of household ammonia the reaction is so slow as to not be vigorous enough to be visible making you think nothing was going on?
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[*] posted on 10-6-2011 at 11:39


Check Xenomorph's post above where no reaction was observed with 25% concentrated NH3.



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[*] posted on 10-6-2011 at 11:51


He didn't say how long he let it react though.
Anders said the reaction "seems to be very slow".
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[*] posted on 11-6-2011 at 13:59


AJKOER here yet again. My personal observation is that freshly burned Al foil is more reactive than the original foil with respect to action by NH4OH.

Also, only the edges of torn foil are producing bubbles with NH4OH and after time, not all the foil is dissolving (some foil strips remain resistance and are untouched).

But why? Per the link below, to quote:

"The oxide on top changes during annealing accompanied by a loss of water leading to a more compact oxide of generally higher resistance."

Also, to quote " Ethylene acrylic acid (EAA) films with 6% acrylic acid were melt coated onto this foil in a laboratory oven at 200°C by continuously laying a molten film on the foil as in slow motion extrusion coating."

However, despite all tempts to protect the foil, there is hope. To quote:

"Even at room temperature, acetic acid can easily pass through a coating infiltrating chemical bonds by advanced attack and leading to adhesion failure."

So by first soaking the Al foil in vinegar, you may prime the Al foil for dissolving, we hope.

Source Link:
http://pffc-online.com/the_place/paper_adhesion_coatings_alu...
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[*] posted on 14-6-2011 at 13:28


Talking about dissolving aluminium in stuff, I just dissolved 5.0 g of aluminium from can tabs in 250 ml of 1.4 M KOH (biodiesel grade). It dissolves pretty quick at around BP to potassium aluminate solution and hydrogen gas.

On filtering I found about a heaped tea spoon of brownish/black insoluble (but clearly hydrated) residue on the filter. I took a small sample and it dissolves effortlessly in 37 w% HCl, at RT. The solution is yellow, clear and tests strongly positive for Fe3+ with KSCN (blood red FeSCN2+ complex). So ‘can aluminium' contains small amounts of iron. Might test for manganese tomorrow…



[Edited on 14-6-2011 by blogfast25]
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[*] posted on 6-1-2013 at 15:05


Aluminum is actually resistant to nitric acid if the acid concentration is over 95%, but if the concentration is below 80%, or if the nitric acid is heated above 40 °C, the corrosion rate is much faster.
Handbook of corrosion data. Bruce D. Craig, David S. Anderson, ASM International






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[*] posted on 6-1-2013 at 15:32


NurdRage once made aluminium nitrate nonahydrate, and noted that Al could not be directly reacted with nitric acid due to passivation. Thus, IIRC he prepared aluminium chloride, which he then added to the HNO3 to form aluminium nitrate and nitrosyl chloride.



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[*] posted on 7-1-2013 at 01:57


Once upon a time, lacking a distillation apparatus, I placed sulfuric acid and ammonium nitrate in the bottom of a large glass jar, with an aluminum cylinder in the middle to support a very small jar, initially empty. The large jar was covered with polyethylene film, pushed down in the center to form a conical reservoir. Warmth was applied to the large jar, and ice water placed in the conical reservoir (a nitric acid "solar still"). I did note the aluminum pitted, but slowly, and probably just due to moisture. Incidentally, the receiver did contain acidic condensate, but I'd hardly call it distilled nitric.

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[*] posted on 10-1-2013 at 14:23


Aluminum reacts with copper sulfate to form copper and aluminium sulfate (should be done with excess aluminium to avoid getting copper sulfate impurities). The copper precipitates, and a crystallization of the filtered liquid will give aluminium sulfate. This will react with nitric acid.



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[*] posted on 12-1-2013 at 09:20


OK, in case anyone hasn't figured out why so much efforts goes into annealing and hardening aluminum foil against attack from food acids (like vinegar,..), my opinion is that otherwise any reported relatively rapid leaching into food (how long before you eat that sandwich or leftovers ) would result in a public relation nightmare and very bad for profits, but great for marketing of alternative plastic wraps.

Remember, there is an apparent health safety balloon already hanging over the industry. Chemists, acting in the capacity described in my earlier thread, are, in effect, guardians of public health and safety (by hardening the Aluminum foil).
------------------------------------------------

On the reaction between aqueous NH3 and Al2O3, one citation is a referenced wet air reaction with dilute aqueous ammonia with Ni and Al2O3 forming N2 (see https://docs.google.com/viewer?a=v&q=cache:K-SGbkpsoh8J:144.... ) under mild conditions. Per page 780, a 20% Ni/Al2O3 catalysis was superior to just NiO and Al2O3.

Now, those not accepting any reaction, just the dissolving of the Al2O3 in aqueous ammonia, must account for the slow formation, per my direct observation, of Al(OH)3 and a gas. Note, my observations are based on Al foil possibly having impurities such as Fe, Si and perhaps Ni.


[Edited on 13-1-2013 by AJKOER]
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[*] posted on 16-1-2013 at 05:52


NH4NO3 saturated water solution eats Al foil but the initiation of the reaction takes several days/weeks overpressure is observed and a white precipitate...
NH4NO3 is a mild acid owing to NH4(+).
I suppose the overal reaction is
Al +H2O --> Al(OH)3(s) + H2(g)

Cheese also eats through Al foil but it takes a few days...probably because of the NaCl and lactic acid plus proteins (amino acids and peptides).




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