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walruslover69
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Just from skimming through the wiki articles on aluminum acetates, It states that the triacetate hydrolyzes in solution to the mono and di acetate.
You could prevent this by using really concentrated acetic acid solution or acetic anhydride, but then you are just producing the triacetate directly
without the need for any of the method.
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AJKOER
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Thanks for all the comments to date.
I am working on a new related experiment, easier to read and comprehend, to be released soon which provides more insight into the kinetics!
My alcohol enriched final mix is losing some volume, but it may still take a while to view any crystals.
Interestingly, I was cleaning up a vessel that I left with some residual solution which included the graphite electrode (as part of the decanting to
remove the 'mess') and was hit by a strong smell from apparently an electron/radical induced reaction involving acetate and ammonia (strong over
powering and a bit sweet smell). I suspect this accidental composition is best avoided.
[Edited on 27-11-2018 by AJKOER]
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woelen
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Quote: Originally posted by AJKOER  | | [...]Interestingly, I was cleaning up a vessel that I left with some residual solution which included the graphite electrode (as part of the decanting
to remove the 'mess') and was hit by a strong smell from apparently an electron/radical induced reaction involving acetate and ammonia (strong over
powering and a bit sweet smell). I suspect this accidental composition is best avoided. |
Sure that the smell comes from an electron/radical induced reaction? Isn't it simply an impurity in the vinegar used, or in the ammonia, or in the
alcohol? What grade chemicals did you use?
Impurities in household chemicals can be anything and they can produce all kinds of smells when allowed to interact with other chemicals for a longer
time. No useful data can be derived from such experiments, especially more subtle side effects usually tell nothing about the original reaction, they
just come from the impurities.
I have an example of this from my own experience.
One day, I made nickel nitrate by dissolving a few dutch coins (dubbeltje, 10 cents, appr. 99.5% Ni, 0.5% Sn according to info from some numismatic
website).
I precipitated the nickel(II) with sodium hydroxide and obtained a green precipitate of Ni(OH)2. Next, I filtered this and added a solution of
Na2S2O8. This leads to formation of a black precipitate of some higher oxidation state of nickel (oxidation state +3, maybe even a little +4). Next, I
added the black precipitate to an acid solution (dilute H2SO4). And what happens? I get formation of O2, the precipitate dissolves and I get a
pink/purple solution. Not a pure pink color, but a somewhat dull/dirty looking pink. I was really stunned about this. How could nickel produce pink
solutions?
I soon found out, however, that the pink color was due to manganese impurity and with the strongly oxidizing Na2S2O8 a tiny amount of permanganate ion
was formed. Apparently those dubbeltjes contained a tiny amount of manganese, not mentioned in the numismatic websites. They only list what is added
in the alloy, but the used metals may contain tiny amounts of impurities. Even 0.01% of manganese will lead to visible pink color when converted to
permanganate.
My lesson from this experience is to be very cautious when observing secondary effects, which are totally unexpected. Nearly always these effects are
due to impurities, albeit not always. It has become a second nature for me to investigate the occurrence of such secondary effects and only very few
times there really is an interesting thing and something new is observed.
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MrHomeScientist
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woelen, how did you find out that manganese was the culprit? Did you do an experiment, or find a more detailed analysis report for
the metal?
In either case, this should be a good lesson for Joker. When you see something interesting, you shouldn't immediately jump to some arcane "radical" or
"HOCl"-related conclusion just because that's your favorite pet theory. "Huh that smells funny. It must be radicals!"
There's no reason to invoke a million obscure research papers and overly complicated mechanisms when "impurities in your household materials" explains
things just as well.
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Tsjerk
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As far as I could figure out AJOEKER uses kitchen vinegar as source of vinegar, which in combination with bleach would give a wide variety of
chlorinated organic substances which are known to have a very perceivable smell.
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DraconicAcid
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| Quote: |
Given the theory presented above, the observed pale blue coloration developed in the synthesis following the introduction of pure aqueous NH3 in
distilled water, may be due to HCN or a harmless bluish tinge created from the addition of aqueous ammonia to an aluminum salt (see https://mysite.du.edu/~jcalvert/phys/alumin.htm and search on 'bluish').
In any event, perform the experiment in a well vented area.
I believe the reduction in color upon boiling with added vinegar, suggests a successful preparation with a minor threat of HCN |
Your only indication that you produced cyanide was that it was blue, and the blue colour went away when you acidified it?
You do realize that cyanide ion isn't blue, right?
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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Deathunter88
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| Quote: Originally posted by MrHomeScientist |
In either case, this should be a good lesson for Joker. When you see something interesting, you shouldn't immediately jump to some arcane "radical" or
"HOCl"-related conclusion just because that's your favorite pet theory. "Huh that smells funny. It must be radicals!"
There's no reason to invoke a million obscure research papers and overly complicated mechanisms when "impurities in your household materials" explains
things just as well. |
A million times this. Someone needs to teach AJKOER the concept of Occam's razor. On a side note, why has he not been banned yet?
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j_sum1
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Level heads prevail.
Even this thread has provoked some good discussion related to sound practice and how to draw appropriate conclusions. I think such discussions are
valuable and of particular benefit to newbies. I like it that we can have a civil thread where we call out crap for what it is, and discuss what is
reasonable. This kind of thing is rare on the internets.
How much of this AKOJER takes on board is really up to him. I don't see that he has done anything banworthy.
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MrHomeScientist
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I think a clever title for him would be appropriate. Something like deltaH's "Dangerous source of unreferenced speculation".
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AJKOER
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| Quote: | Per Draconic Acid:
[rquote]
Given the theory presented above, the observed pale blue coloration developed in the synthesis following the introduction of pure aqueous NH3 in
distilled water, may be due to HCN or a harmless bluish tinge created from the addition of aqueous ammonia to an aluminum salt (see https://mysite.du.edu/~jcalvert/phys/alumin.htm and search on 'bluish').
In any event, perform the experiment in a well vented area.
I believe the reduction in color upon boiling with added vinegar, suggests a successful preparation with a minor threat of HCN
Your only indication that you produced cyanide was that it was blue, and the blue colour went away when you acidified it?
You do realize that cyanide ion isn't blue, right?
|
No, DraconicAcid, you miss a significant part of my thread which I personally felt was needed to address a potential safety issue with the experiment.
Here it is:
| Quote: Originally posted by AJKOER | .....
........
I did notice this article (see 'Excision of CN− and OCN− from acetamide and some amide derivatives triggered by low energy electrons' by Constanze
Koenig-Lehmann, et al, abstract at https://pubs.rsc.org/en/Content/ArticleLanding/2008/CP/b8121... ). To quote in part:
"Low energy electron attachment to acetamide and some of its derivatives shows unique features in that the unimolecular reactions of the transient
anions are remarkably complex, involving multiple bond cleavages and the formation of new molecules. Each of the three compounds acetamide
(CH3C(O)NH2), glycolamide (CH2OHC(O)NH2) and cyanoacetamide (CH2CNC(O)NH2) shows a pronounced resonance located near 2 eV and decomposing into CN−
along a concerted reaction forming a neutral H2O molecule and the corresponding radical (methyl and methoxy). "
Per the above, I would express the basis of a possible reaction as:
Al --> Al(lll) + 3 e-
3 x [ CH3C(O)NH2 + e- --> •CH3 + CN- + H2O ]
Net: Al + 3 CH3C(O)NH2 --> 3 •CH3 + Al(lll) + 3 CN- + 3 H2O
......
[Edited on 10-11-2018 by AJKOER][/rquote]
where the corresponding net reaction in the current case could be:
Net: Al + 3 CH2CONH2 --?--> 3 •CH2 + Al(lll) + 3 CN- + 3 H2O
indicating a possible, but small, cyanide presence.
In the current experiment, the action of the hydroxyl radical on elemental carbon is a path to CO:
•OH + C = •H + CO (EDIT see comments and references at http://www.sciencemadness.org/talk/viewthread.php?tid=97845#... )
Also, given the possible presence of CO, from the same referenced SM thread above:
[Edited on 4-10-2014 by AJKOER][/rquote]
--------------------------------------------------------------------
A bit harder, try this path (see https://chemiday.com/en/reaction/3-1-0-261):
CO + NH3 --500 C, Al2O3--> HCN + H2O
"Carbon monoxide react with ammonia to produce hydrogen cyanide and water. The technical method production hydrogen cyanide. This reaction takes place
at a temperature of 500-800°C, an overpressure. In this reaction, the catalyst is can be V2O5, CeO2 Al2O3, ThO2."
Text sounds like a translation.
At such high temperatures, I would expect:
NH3 + Heat ---> •H + •NH2
based on the action of hv on ammonia (see R1 at https://journals.ametsoc.org/doi/pdf/10.1175/1520-0469%28197... )
Then, subsequent reactions with CO forming HCN and H2O.
------------------------------------------------------------------
The above speculated radical mechanism is interesting, if correct, as the hydrogen atom radical can be formed at RT by the action of NaOH (or HCl) on
Aluminum metal where some .H radical could be imbued on the surface of the Aluminum........
.......
Some possible paths to a cyanide presence. Assuming the presence of CO, I would suggest also the simple path:
CO + •NH2 = •CONH2 (or •CN + H2O)
•H2N + CO = •H2NCO (or •NC + H2O)
•H2NCO + •CONH2 = H2NC(O)C(O)NH2 (oxamide)
(Or: •NC + •CN = NCCN )
Per Wiki on Cyanogen (https://en.wikipedia.org/wiki/Cyanogen ) to quote:
“Cyanogen is the anhydride of oxamide:
H2NC(O)C(O)NH2 → NCCN + 2 H2O
…….
Like other cyanides, cyanogen is very toxic, as it readily undergoes reduction to cyanide, …”
Given the theory presented above, the observed pale blue coloration developed in the synthesis following the introduction of pure aqueous NH3 in
distilled water, may be due to HCN or a harmless bluish tinge created from the addition of aqueous ammonia to an aluminum salt (see https://mysite.du.edu/~jcalvert/phys/alumin.htm and search on 'bluish').
In any event, perform the experiment in a well vented area.
I believe the reduction in color upon boiling with added vinegar, suggests a successful preparation with a minor threat of HCN.
....
[Edited on 4-10-2014 by AJKOER] |
Apparently my having opine on possible paths to cyanide (some even recently) and my not connecting dots leading to someone personal injury was not a
risk I was willing to dismiss entirely whether it be an immediate or delayed hazard.
And, guess what, the presence of electrons did eventual create some unknown breakdown product! What I failed to mention is how I felt after seeming
minor exposure to the fumes, I just decided to issue a warning.
----------------------------------------
By the way this is not the first time working with electrochemical cells and organics produced an unexpected breakdown product (like CHCl3), see http://www.sciencemadness.org/talk/viewthread.php?tid=27530 , partial extract below:
| Quote: Originally posted by AJKOER | I would like to interject a point on perhaps an overlooked aspect of my bleach battery cell experiment from a new perspective of totally informed
hindsight.
Electrosynthesis can occur not only via standard electrolysis, but apparent also via an in situ formed electrochemical cell as well, per my
recollection (see as examples http://edepot.wur.nl/385426 and http://pubs.rsc.org/en/content/articlelanding/2010/gc/c0gc00... ).
In my experiment, I did in fact produced a battery cell, and given the added sea salt which may have promoted some solvated electron activity, one
could describe the process as an attempted electrosynthesis path to assist in the cleavage formation of chloroform from citric acid/citrate. Possible
reactions of interest would be:
HOCl -> HCl + 1/2 O2 (minor decomposition pathway)
O2 + e-(aq) = .O2- (see Table l, p. 14 at http://iopscience.iop.org/article/10.1088/0022-3727/48/42/42... )
Cl2 + .O2- = .Cl2- + O2 (see Reaction 36 at SUPPLEMENTAL SECTION PARTICIPATION OF THE HALIDES IN PHOTOCHEMICAL REACTIONS IN NATURAL WATERS AND
TREATED WATERS by Yi Yang and Joseph J. Pignatello)
HOCl + e-(aq) -> OH- + .Cl
.Cl + Cl- = .Cl2- (see https://books.google.com/books?id=mRoJUB5fxRwC&pg=PA321&... )
To test this hypothesis for those interested, if one repeats my experiment WITHOUT the presence of aluminum metal (which I usually source from
aluminum foil heated to red hot forming a more reactive gamma aluminum oxide coating rich in surface defects), one may observe lower or no yield of
CHCl3 (as there was no added cupric salt) if any electrosynthesis was likely involved.
-----------------------------------------------------------------
Another......
[Edited on 21-5-2018 by AJKOER] |
A word of advice, if working in a setting (high temperature combustion, electrolysis, photolysis, electrosynthesis,...) and you have mixtures of
elements like carbon, hydrogen and chlorine, expect possible creation of CHCl3, CxCly,...., as potential breakdown products.
Similarly, mix of carbon, hydrogen and nitrogen, HCN is a frequent product (example, combustion of certain plastics) .
Mix of carbon, hydrogen, nitrogen and oxygen, HCN, as detailed in my thread, is still a possibility.
Mix of carbon, chlorine and oxygen, watch out for COCl2.
Mix of H, P, and O, deadly PH3 may still appear as a breakdown product.
.........
[Edited on 28-11-2018 by AJKOER]
[Edited on 28-11-2018 by AJKOER]
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AJKOER
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| Quote: Originally posted by Tsjerk | | As far as I could figure out AJOEKER uses kitchen vinegar as source of vinegar, which in combination with bleach would give a wide variety of
chlorinated organic substances which are known to have a very perceivable smell. |
Sorry, but this thread is really about a path to 'Al Acetate via Al Foil/ Graphite/ 5% Vinegar/ 3% H2O2/ Sea Salt and Delayed NH3 (aq) Addition'.
No use of NaOCl or HOCl. However, the 3% H2O2 may have a bit of H3PO4 as a pH stablizer.
As what is in the Distilled White Vinegar (USA), see https://supremevinegar.com/2016/08/22/white-distilled-vinega... .
In China, to quote(see https://www.quora.com/What-does-vinegar-have-in-it ):
"The main components of Vinegar are Acetic Acid (3%--5%),and it also contains various Amino Acids, Organic, Acids, Sugars, Vitamins, Nutritional
Ingredients such as Alcohol and Ester."
[Edited on 28-11-2018 by AJKOER]
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AJKOER
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Woelen your impurity point is valid given I am working with household vinegar. This by preference based on cost and availability produced from
chemically pure alcohol, as I understand the history of recent preparations of white vinegar, acted upon by bacteria (as mandated in US) which implies
assorted organics.
Let me describe the composition of the residual mix from decanting, which led to the unknown compound, as sourced from unreacted Al foil, vinegar,
Al3+, NH4+, NaCl, O2/H2O2 and a graphite rod. If I happen to use Reynolds Aluminum Foil (see http://www.sciencemadness.org/talk/viewthread.php?tid=16337 ) add iron to feed a fenton reaction adding hydroxyl radicals. To the extent that the
electrochemical cell is likely still functioning, add some solvated electrons and therefrom associated reactive oxygen species (like superoxide,
H2O2,...).
A interesting aspect of a system with Fe ions and any O2 in the presence of Al3+, is the ability of the latter to form an intermediate complex with
superoxide (or perhydroxyl) to keeping cycling iron between complexes of Fe3+ and Fe2+, feeding a slow fenton (due to low iron concentration and
unfavorable pH), forming associated radicals (see http://www.sciencemadness.org/talk/viewthread.php?tid=96347#... ).
I see the potential for assorted radicals decomposing organics, and further interaction of those radicals, forming in time some stable breakdown
products.
[Edited on 28-11-2018 by AJKOER]
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AJKOER
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Just came across this in my readings, to quote:
"In addition, while other oxide nanocrystals were ineffective to promote hydrogen generation in tap water, TiO2 nanocrystals (P90, w14 nm in diameter)
were found to be highly effective in facilitating the production of hydrogen from the reaction of Al with tap water, comparable to the well-known
g-Al2O3."
Article: 'Generation of hydrogen from aluminum and water - Effect of metal oxide nanocrystals and water quality' by Hong-Wen Wang, et al, in
International Journal of Hydrogen Energy, Volume 36, Issue 23, November 2011, Pages 15136-15144, Link: https://depts.washington.edu/solgel/documents/pub_docs/journ... .
Well, apparently, comparable to the well-known gamma-Al2O3 in some circles.
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Texium
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That's all well and good, but you never proved that YOU made gamma aluminum oxide to begin with!
Everything you've been doing is just cargo cult science. You do "experiments" and cite copious references, but upon looking for any sort of scientific rigor among your many lengthy
posts, it all falls apart.
If your posts were academic journal articles, they'd be all Conclusion with almost no Experimental and absolutely no Analysis, and frankly, that
doesn't work.
Edit- Relevant bit from the Wikipedia page I linked:
| Quote: | | An example of cargo cult science is an experiment that uses another researcher's results in lieu of an experimental control. Since the other
researcher's conditions might differ from those of the present experiment in unknown ways, differences in the outcome might have no relation to the
independent variable under consideration. |
[Edited on 11-30-2018 by Texium (zts16)]
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AJKOER
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True, I do not have the means to directly inspect the treated Aluminum and state there exists some gamma aluminum oxide.
However, there is some indirect evidence present, I would suggest, due to the property of the gamma aluminum oxide layer given its weaken structure
allowing reaction with tap water, to form hydrogen disrupting the protective layer (here tap water implies to me H2O with transition metal and/or
bicarbonate presence, like ferrous bicarbonate).
Bottom line, significant dissolving (or, at least, partial) of the treated Al is possibly suggestive/consistent with a weaken gamma aluminum oxide
presence, but not conclusive.
Going forward, I will qualify my reference to an attempt of employing high temperature to induce a gamma aluminum oxide presence as being suggestive
(or possible) to a limited extent.
-------------------------------------------------------------------
As to the history as I came to become acquainted with the heat treating process, it starts with much experimental frustration on how apparently inert
Al foil was behaving (which is not surprising as the Aluminum wrap product industry survives on a perpetuation of the belief that annealed/acrylic
coated Al is relatively inert/safe). The mention of plastic coatings in a thread led to a fire test of a strip of foil. The residue was tested in a
Bleach battery cell and was evidently more active in reacting in the system HOCl/Cu/NaCl. Then came a document search to understand possibly why (and
also to check the box on plausible explanations), which led to a very little known white paper that was not even precisely on topic, mechanical and
high temperature induced layer of gamma alumina on fine Aluminum powders. Research on gamma alumina mentions temperature ranges that are apparently
consistent with heating Al to red hot.
No cargo cult science here, as all related experimenting was performed by myself. Even my cited white paper can't be borrowed science as it is in a
different specialized field working with powders. I am only suggesting, by itself, a temperature treatment path, which per one posited explanation,
ascribes an induced gamma alumina layer on larger pieces of Aluminum. In any account, the process appears to assist in the attack of Al in repeated
runs and varying experimental settings (some of which are posted on SM).
[EDIT] Those assuming as an explanation enhanced reactivity due to an increased Al2O3 presence (from heating) should review my cited half cell
reactions for the Bleach battery detailed previously on the first page of this thread.
[Edited on 30-11-2018 by AJKOER]
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AJKOER
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Pictures of alcohol assisted evaporation displaying mainly amorphous salt(s). Shiny crystals from sunlight reflection likely potassium impurity from
sea salt.
[Edited on 1-12-2018 by AJKOER]
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AJKOER
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| Quote: Originally posted by AJKOER |
True, I do not have the means to directly inspect the treated Aluminum and state there exists some gamma aluminum oxide.
......
[Edited on 30-11-2018 by AJKOER] |
Actually, there may be some direct evidence that gamma aluminum oxide has been created!
In pictures I have presented relating to the electrosynthesis based attack of heat treated aluminum on SM, I have observed and described in words the
creation a white fluffy powder. For example, from http://www.sciencemadness.org/talk/viewthread.php?tid=94166#... :
| Quote: Originally posted by AJKOER | Now, at 48 hours, a fluffy white precipitate visible. The aluminum foil displays only minor degradation.
.........
[Edited on 26-9-2018 by AJKOER] |
Interestingly, I just came across this reference (link: https://www.researchgate.net/post/What_is_Aluminium_oxide_so... ) to quote Wolfgang H. Muss at Paracelsus Medical University Salzburg:
"gamma-Al2O3 is a hygroscopic powder (white and fluffy) insoluble in water, but in strong acids and bases."
So with the dissolution of the underlying Aluminum metal, any created gamma-Al2O3 may be perhaps visible as a 'white and fluffy' precipitate.
If accurate, this means the technique of heat treating Aluminum metal of equal surface areas/volumes, targeting gamma-Al2O3 formation, may have a
visible barometer of success.
--------------------------------------------------------------
More research suggests many possible alumina formation per the experiment from which I referenced the picture, so heat induced gamma alumina formation
may not be discernible (see p.39 at https://www.osti.gov/servlets/purl/4037173 ), to quote from this extensive 1960 work:
"Bergmann studied the electrolytic oxidation of aluminum in dilute aqueous hydrogen peroxide and carbon dioxide solutions in order to obtain
high-purity aluminas. Using high-purity aluminum as cathode and platinum as anode, he observed the formation of predominantly amorphous products of
the composition Al2O3. 2.94H2O to Al2O3. 3.O2H2O containing varying amounts of beta alumina trihydrate (hydrogen peroxide series) and alpha alumina
monohydrate-beta alumina trihydrate mixtures (carbon dioxide series), respectively."
What I also find interesting is how Bergman selected an experimental design to create alumina using dilute hydrogen peroxide or aqueous carbon dioxide
with a highly noble electrode of platinum (versus my choice of carbon). My selections were derived from my understanding of radical chemistry, which
was not significantly advanced at the time Bergman did his experiments.
My understanding is that alpha alumina is similar in appearance to gamma, and that gamma alumina in water in time converts into alpha.
An interesting point on ammonia created clear Al(OH)3 gels (noted on page 69) was that the immediate form of the clear gel is more reactive (like
easily reacts with NaOH or HCl), at least for a few hours!
[Edited on 2-12-2018 by AJKOER]
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AJKOER
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| Quote: Originally posted by AJKOER |
......I am only suggesting, by itself, a temperature treatment path, which per one posited explanation, ascribes an induced gamma alumina layer on
larger pieces of Aluminum......
[Edited on 30-11-2018 by AJKOER] |
A curious find on the web to quote from Sciencemadness Wiki at http://www.sciencemadness.org/smwiki/index.php/Aluminium_sul...
“Preparation
Aluminium sulfate can be made by reacting sulfuric acid with aluminium oxide, hydroxide, halide or with hot aluminium metal.
2 Al(OH)3 + 3 H2SO4 → Al2(SO4)3 + 6 H2O
2 Al + 3 H2SO4 → Al2(SO4)3 + 3 H2 “
So a possible implication that somehow a hot piece of Aluminum can be attacked by H2SO4 perhaps due to disruption of its protective layer?
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Tsjerk
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https://en.wikipedia.org/wiki/Grimms%27_Fairy_Tales
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AJKOER
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Perhaps but still don't known, as more research suggests (to me) perhaps the role of solvated electrons in the case of Aluminum alloys, resulting in
the hydrogen atom radical (from H+, and some water), which could lead to hydrogen gas disruption of the protective layer (paralleling the gamma
alumina and tap water scheme for pure Al), and/or perhaps even a direct sulfate radical attack!
My evidence, the property of Aluminum ALLOYS to apparently rapidly attack Al if H2SO4 concentration is between 40% to 95% with a peak at 80%, but not
so for pure Al, as that requires heating the aluminum metal.
In the case of Iron and H2SO4, the process is one of 'dissolution and diffusion' of any formed sulfate layer away from the surface.
Source: See https://books.google.com/books?id=KXwgAZJBWb0C&pg=RA1-PT... .
[Edited on 4-12-2018 by AJKOER]
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j_sum1
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| Quote: Originally posted by AJKOER | | My evidence, the property of Aluminum ALLOYS to apparently rapidly attack Al if H2SO4 concentration is between 40% to 95% with a peak at 80%, but not
so for pure Al, as that requires heating the aluminum metal. |
I would love to see a write-up of the experiment you did on this. My (limited) experience is that Al is pretty much impervious to acids unles there
are halides around or something like Hg or Ga to weaken the structure at the grain boundaries.
Specifically, what kind of alloy are we talking about here that is attacked by H2SO4? And how much different is it from the behaviour of pure Al?
It would be nice to establish some basic observations before speculating on complex mechanisms.
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AJKOER
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| Quote: Originally posted by j_sum1 | | Quote: Originally posted by AJKOER | | My evidence, the property of Aluminum ALLOYS to apparently rapidly attack Al if H2SO4 concentration is between 40% to 95% with a peak at 80%, but not
so for pure Al, as that requires heating the aluminum metal. |
I would love to see a write-up of the experiment you did on this. My (limited) experience is that Al is pretty much impervious to acids unles there
are halides around or something like Hg or Ga to weaken the structure at the grain boundaries.
Specifically, what kind of alloy are we talking about here that is attacked by H2SO4? And how much different is it from the behaviour of pure Al?
It would be nice to establish some basic observations before speculating on complex mechanisms. |
I usual quote from my source, but not doable in the 2 pages presented commentary in the 'Handbook of Corrosion Data' which refers to what it calls
'Material Summaries' from 'a survey of the available literature'. In the 'Aluminum.' section its basically generally states what I say with respect to
Al alloys used industrially. Also, there is some detail with respect to certain Aluminum alloy numbers, etc.
As to what literature, what precise alloys, date of various works,..., someone can spend $618.72 for details, if included, as I suspect this expert
book is likely for people making decisions involved in designing or buying containers to hold/transport various acids and such and avoiding
significant corrosion issues (hence the value added book price).
This reference focuses on industrial use of Al (and other metals) expressed in the form of available numbered alloys (one of which may be the pure
metal).
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Some background points on the Kinetics of Corrosion:
1> Alloys with a highly electropositive metal like Aluminum may create a galvanic corrosion scenario starting with the flow of electrons.
2> Next, to quote a source, ‘Kinetics of Corrosion Inhibition of Aluminum in Acidic Media by Water-Soluble Natural Polymeric Pectates as Anionic
Polyelectrolyte Inhibitors’ by Refat M. Hassan and Ishaq A. Zaafarany, in Materials (Basel). 2013 Jun; 6(6): 2436–2451, doi: 10.3390/ma6062436,
link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5458939/ :
“The corrosion rate was found to be a function of the concentration of the acid. This result indicates that at least one of the corrosion paths of
dissolution of Al metal in HCl solution should involve the presence of hydrogen ions in the rate-determining step…
3.1. Corrosion Mechanism
We propose a suitable mechanism of corrosion, in accordance with the above experimental observations. The corrosion of metal involves an
electrochemical process [47,48,49] resulting from dissolution of Al metal in the acid. This process can be expressed by the anodic and cathodic
processes, which are defined by Equations (4) and (5), respectively,
Al(s) <--Ox--> Al3+ + 3 e- (4)
2 H+ + 2 e- <--Red--> H2 (5)
The overall electrochemical process can be written as follows:
(6) 2 Al(s) + 6 H+ <-->2 Al3+ + 3 H2(g) (6)
The cathodic reaction produces Hchemisorbed by picking up an electron that released in the anodic reaction (H+ + e = Hchemisorbed ) in Al corrosion in
HCl. In such acidic solutions, the Hchemisorbed on the metal surface reacts by combining with other adsorbed Hchemisorbed to form H2 gas molecule,
which bubbles from the metal surface. A very small amount of the uncombined Hchemisorbed will remain; however, this amount does not affect the whole
process. “
3> Also from a source: ‘The mechanism of hydrogen embrittlement: the stress interaction between a crack, a hydrogen cluster, and moving
dislocations’ by A.T. Yokobori Jr. , In International Journal of Fracture, July 2004, Volume 128, Issue 1–4, pp 121–131, link: https://link.springer.com/article/10.1023/B:FRAC.0000040974.... , to quote:
“In this paper, the stress corrosion cracking model on the basis of hydrogen diffusion and concentration toward the elastic-plastic stress field
around a crack and the interaction of dislocations and hydrogen around a crack tip are proposed to clarify the mechanism of stress corrosion cracking
for ductile and brittle materials.”
Taking into account the above, my summary on the removal of the protective layer begins with electrons reacting with H+ to form the hydrogen atoms
radical. There is then a the diffusion of hydrogen atoms radicals which have been chemisorbed. With increasing concentration of the hydrogen atom
radical, some combining creating hydrogen gas bubbles. This can lead to cracking and dislodging of the aluminum oxide layer.
[Edited on 5-12-2018 by AJKOER]
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j_sum1
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I ask because you said, "my evidence". I assumed you had done some kind of experiment.
It should not be too difficult to cite some literature if you have a good source. It does not need to be pages and pages. In fact, one good
quotation and maybe a cut and paste of a supporting diagram is probably better.
You seem to be claiming a number of unfamiliar properties of aluminium. I confess to not being able to follow all that you have written. Before a
deep discussion of mechanisms and radicals I think establishment of some fundamental properties is important. I am not aware of any significant
reaction between alloys of Al and sulfuric acid. I may well be wrong. I am asking you to fill in that blank before taking us deep down the rabbit
hole.
[edit]
You have added some material that was not present when I composed my post.
Among your references I see some standard electrolysis oxidation and reduction.
I also see something about stress corrosion cracking.
Neither of these seem pertinent to the discussion (which originally was acetates and cyanides). I am now challenging you to back up what you have
claimed with respect to sulfuric acid.
It seems to me pointless to make such a large number of tangential claims and not connect them to an overall objective.
Likewise it seems pointless to write in such a convoluted fashion that others on the board (smarter people than me) cannot follow.
And it seems strange that you do not respond to specific challenges to the data you present and the claims you make.
[Edited on 5-12-2018 by j_sum1]
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AJKOER
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A more readable reference with graphs, see https://books.google.com/books?id=iEeiQEeLOmYC&pg=PA33&a... which does confirm generally that pure Al is more corrosion resistant than an
Aluminum alloy. Interestingly, in Figure 7 the author notes that aluminum oxide containing iron is actually a semiconductor, capable of allowing the
passage of electrons, and likely fostering the formation of local galvanic cells (leading to corrosion).
Also discussion at https://books.google.com/books?id=iEeiQEeLOmYC&pg=PA39&a... . In particular, read paragraphs relating to "Effect of Purity: Trace Elements"
and "Effect of Hydrogen" on that page.
Of note, once corrosion is present, apparently in some cases, the rate of corrosion can proceed proportional to the concentration of NaCl (an
accelerant).
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With respect to H2SO4 specifically, see Figure 3, p. 689, at https://www.nrc.gov/docs/ML0633/ML063390144.pdf that clearly shows at around 80%, a contour displaying the highest corrosion in inches per year of
1.2 . To quote a general comment from the text:
"Dilute sulfuric acid solutions, up to ~ 10% in concentration, causes some attack on aluminum base alloys, but the action is not sufficiently rapid at
room temperature to prevent their use in special applications. In the concentration range of ~40 to 95%, rather rapid attack occurs. In extremely
concentrated or fuming acid, the rate of attack drops again to a very low value."
Also:
"As evident in Table 8, aluminum (and its alloys) becomes the anode in galvanic cells with most metals, protecting them by corroding sacrificially.
Only magnesium and zinc are more anodic and corrode to protect aluminum. This type of corrosion can be found in strong acidic or strong basic
solutions, as illustrated in Figure 6 [4,1O]. The rate of corrosion can vary from several microns per year to several microns per hour."
Also with respect to a temporarily more reactive Al(OH)3 gel created by ammonia precipitation subject to time aging, the comment:
"The aluminum hydroxide gel is not stable, but crystallizes with time to give, first, the rhombohedral monohydrate (Al2O3-H2O or boehmite), then the
monoclinic trihydrate (A12O3.3H2O or bayerite), and finally another monoclinic trihydrate (hydrargilite). This development of aluminum hydroxide is
known as "aging" [4]."
Here is a guide with another source as to explaining what could be occurring with regard to varying acid concentrations acting on Aluminum, to quote
(see http://www.conways.co.za/pdf/afsa_corrosion_pocket_guide.pdf ):
“In the case of aluminium and other non ferrous metals, this sulphuric acid is absorbed in the corrosion process. It gives rise to the formation of
metallic sulphates. However, in iron and steel the sulphuric acid is regenerated as a result of hydrolysis and the corrosion reaction continues.”
So lower than 100% H2SO4 concentrations could be engaging with water in a recycling action on the attack of the protective layer for select Aluminum
aollys (with Fe,...). A peak concentration of 80% could be reflective of the significance of the recycling action in the presence of water. I would
think that water presence for creating solvated electrons could also be a part of the process.
Also, with respect to precise behavior of H2SO4 at varying concentrations, note this commentary in the case of its action on steel (not aluminum):
“Depending on acid concentration and the metal involved, sulfuric acid can behave as either a reducing acid or an oxidizing acid. In lower
concentrations (up to about 70%) and temperatures on steel or stainless steel, it is reducing. At concentrations over 70%, and into the oleum range,
the acid is oxidizing to steel and stainless steel.”
where, with respect to Aluminum metal, I would expect a shift to the oxidizing concentrations of H2SO4 would be less corrosive, so 80% appears
reasonable with high H+, 20% water for possible recycling path to H+ and solvating electrons, and not deep into the oxidizing range commencing at 70%.
[Edited on 5-12-2018 by AJKOER]
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