stoichiometric_steve
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Gallium-Aluminium alloy preparation
Is it as easy as mixing the two at the mp of Gallium or will i need to melt the Aluminium as well?
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Fleaker
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The aluminum need not be liquid for this to work. I do not think it will alloy well even if the aluminum is very finely granulated if this is done at
gallium's low mp--it will form a paste. At 400C with the gallium under argon it is a different story. You can mix the two at ~30C put under inert
atmosphere and then heat. The gallium is sticky stuff, so do it in a sacrificial melting container.
Someone looking for a more environmentally friendly replacement to Hg-amalgam reduction? 
Neither flask nor beaker.
"Kid, you don't even know just what you don't know. "
--The Dark Lord Sauron
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stoichiometric_steve
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| Quote: | Originally posted by Fleaker
Someone looking for a more environmentally friendly replacement to Hg-amalgam reduction? |
Quite so. But this time i just want to generate a shitload of H2 without the hassle of drying and washing it of impurities.
Does it really have to be 400degC or can it be less, since my hotplates dont go much higher than 360degC.
Did anyone check if H2 is also released from this alloy and an alcohol?
[Edited on 12-1-2009 by stoichiometric_steve]
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JohnWW
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No, if you wanted to make a Ga-Al alloy, simply gently heat the Ga (m. pt. 29.7646ºC) until it is liquid, and it will start to readily form an alloy
by dissolving the Al. (This is why Ga is not allowed to be carried on board civilian aircraft). However, the resulting amalgam will have a higher
melting point than the liquid Ga, so you would have to keep heating the mixture until all the Al is dissolved.
The Al-Ga phase diagram is given at http://www.greencarcongress.com/images/2007/08/27/woodall.pn... or http://www.greencarcongress.com/2007/08/purdue-research.html .
Al alloys containing Ga are brittle (like some Hg amalgams e.g. that with Zn), due to the rapid penetration by Ga of the grain boundaries in the Al.
Gallium, which expands by about 3% on solidification, forms an eutectic liquid phase with aluminium at 26.5ºC, containing about 0.8% Al, and itself
has a high solubility in aluminium; see e.g. http://www.msm.cam.ac.uk/phase-trans/2003/FSW/a.pdf . It can also disrupt the Al2O3 oxide film, similarly with Hg-Al amalgams, leading to the
potential for liquid Ga-Al amalgams to be used as an alternative to Hg-Al ones as a reducing agent in organic chemistry ; and, see http://ceramicartdaily.net/postmeeting/Production/Production... and http://www.icc2008.ru/SS/GP23.htm , for H2 generation from water. See also http://en.wikipedia.org/wiki/Gallium .
Because Ga is a rare and expensive metal, you should think of how to recover it after using it. The chemical similarity to Al would probably best call
for an ion-exchange separation of some sort, on a lab scale. However, industrially, most gallium is obtained by extraction from the crude aluminium
hydroxide solution (derived from bauxite, in which it occurs at about 50 ppm by weight) of the Bayer process for producing alumina and aluminum; see
http://www.nationmaster.com/encyclopedia/Gallium . It is used chiefly for making gallium arsenide (GaAs) and gallium nitride (GaN), used as
semiconductors in electronic components, this representing about 98% of the gallium consumption in the USA. World-wide GaAs makes up 95% of the annual
global gallium consumption. It is also used in small quantities as a dopant in Si and Ge p-type semiconductors.
[Edited on 13-1-09 by JohnWW]
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stoichiometric_steve
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| Quote: | Originally posted by JohnWW
Because Ga is a rare and expensive metal, you should think of how to recover it after using it. |
Thanks for that exhaustively informative post!
My opinion was that the Ga, after the reaction of the alloy with water is over, is left in the elemental state - am i correct? Hence, it should not be
a problem at all to recover it.
Shit, i should have looked at that powerpoint thing a bit earlier, the Galinstan alloy would probably have been quite a bit cheaper than pure Ga
itself - and its alloy properties are even better...
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JohnWW
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The Ga in an Al-Ga amalgam may be left largely unchanged as the metal after the reaction with water (or with alcohols or carboxylic acids) liberating
hydrogen. However, because Ga is above hydrogen in the electrochemical series, although not as much as Al, some of it is likely to dissolve, so there
would be a steady loss of Ga as Ga+++ or as the hydroxide if the cycle is repeated by re-alloying with Al. The metal is slowly attacked by aqueous
acids; Ga is just above Fe and Cd in the electrochemical series, just below Zn and Cr, and quite some way below Al and Ti. According to the CRC
Handbook of Tables for Applied Engineering Science, the potential for Al+++ + 3e- -> Al is -1.706 v, while for Ga+++ + 3e- -> Ga it is only
-0.360 v. (zero for H+ to H2).
Other uses of Ga include in solders, in certain anti-cancer and antibacterial drugs, in high-temperature thermometers, in liquid-metal switches
(especially when alloyed with In and Sn), and to make mirrors (as it sticks to porcelain and glass), including telescope mirrors as an easier
alternative to coating with Al spray or vapor.
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Fleaker
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John, thanks for the phase diagram!
The issue is not whether it dissolves or not, undoubtedly it does, but whether it dissolves quickly. I tried this once before with folded up thick
aluminum foil and I only got it to all dissolve with heat. At ~30C the gallium just stuck up on the foil.
After the hydrogen evolution ceases, gallium will remain but it will be very dirty with a bunch of hydrous aluminum oxide. You can separate most of
the crud off of it by density difference but I'm sure a lot of Al(OH)3 remains. Pity that gallium is so soluble in base like aluminum. It doesn't
dissolve that well in acid though (like indium).
Gallium is what, 60 cents a gram for 4N?
Steve, it'll be good to see this-- would you be so inclined as to make a detailed post on this when you do it?
[Edited on 12-1-2009 by Fleaker]
Neither flask nor beaker.
"Kid, you don't even know just what you don't know. "
--The Dark Lord Sauron
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chemoleo
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Seems Al foil dissolves quite easily!!!
Check these utube links:
http://www.youtube.com/watch?v=xYk_nr4p_r4
http://www.youtube.com/watch?v=4tvR1khXKnI
Never Stop to Begin, and Never Begin to Stop...
Tolerance is good. But not with the intolerant! (Wilhelm Busch)
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UnintentionalChaos
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Fleaker, it would be nice if it were even that cheap, but maybe Im looking in the wrong places. ebay usually runs quite a bit over $1/gram, usually
around $2/gram. I am currently unaware of any other easily accessible sources.
Department of Redundancy Department - Now with paperwork!
'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
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stoichiometric_steve
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I bought 50 grams of 99.99% Ga from ebay for 39 EUR.
Fleaker, what exactly do you want me to make a detailed post of, the alloying, the other chemistry?
The purpose of this project was to find a source of hydrogen that doesnt require the purchase of a H2 cylinder (which is also an option, but i'd
rather not) for catalytic hydrogenation.
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IrC
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"My opinion was that the Ga, after the reaction of the alloy with water is over, is left in the elemental state - am i correct? Hence, it should not
be a problem at all to recover it"
I have done many experiments along these lines, and even added other metals such as Indium, Magnesium, Bismuth, and dozens of other metals. The Mg is
really difficult, I had to green scrubby pad the Mg ribbon forever until it would dissolve in the molten alloy. It appeared that Mg dissolved better
in an Al Ga melt upon adding Indium to the mix first.
After my ingot cooled, I noticed the metal getting firecracker hot when I tried cleaning it with water. Putting a small piece in water generated a
large volume of gas and heat. I noticed that after this action in water the Ga ALWAYS sweated out as pure as it can be as a liquid metal which should
be easy to recover. This was true in all my experiments with many varied proportions of various other metals. While I had no accurate way to measure
the MP temperature at the time, one batch seemed to sweat out a silver liquid metal with a lower MP than pure Ga. This was with a few percent Silver,
Tin and Hg added.
[Edited on 1-15-2009 by IrC]
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chief
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By the way: What is a good online-source for phase-diagrams ?
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JohnWW
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The ASM Metals Handbook is online somewhere, and Smithells Light Metals Handbook, as rapidshare and torrent downloads; try this search string on
Google:
"Handbook Of Metals" OR "Metals Handbook" PDF OR ZIP OR RAR OR ISO "rapidshare.com" OR megaupload OR ifile OR mihd OR mediafire OR badongo OR torrent
.
They would have a comprehensive range of phase diagrams of alloys.
Try also this search string on Google:
"phase diagram" alloy PDF OR ZIP OR RAR OR DJVU "rapidshare.com" OR megaupload OR ifile OR mihd OR mediafire OR badongo OR torrent
BTW Because natural bauxite, Al2O3, contains about 50 ppm of Ga2O3, before any attempt is made to separate the Ga by selective pH-controlled
precipitation of the hydroxide (which is the process used to remove the Fe2O3 and SiO2 impurities), technical-grade Al made without removal of the Ga
would be slightly softer and with a slightly lower melting-point than pure Al.
[Edited on 17-1-09 by JohnWW]
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IrC
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If someone knows a lot about the chemistry (or physics) involved in the addition of Ga to Al causing the Al to react with H2O as if it had no oxide
barrier I would appreciate if you could expound on the subject. I found this property by accident a decade ago and did not realize it's use in energy
production until I read the article recently posted here. I need to dig up the notebooks and sample results and play with this idea more. I find this
interesting and worthwhile to investigate. Are there any good articles anyone is aware of that I could search for? Also, what would be the best way to
collect the Ga after reacting with water? So far the best way I found was to add the leftover material to a new mix and simply skimming the slag out.
All of the Ga ends up going back into the new batch as I can find little Ga left in the slag created by the new batch. Is this an alloy, amalgam, or a
eutectic? One experiment I tried was using this material as a plate in an experimental battery. Of all the mixtures of metals I have experimented with
so far this is the most interesting and in light of the hydrogen production article posted previously possibly this is a good area to start doing some
research.
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Nitrous
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Can Al/Ga almagam be used in the Meerwein-Ponndorf-Verley reduction to reduce aldehydes and ketones to alcohols? Can the Al/Ga itseif be enough to
reduce aldehydes and ketones to alcohols when water is added? Gallium is such an interesting metal.
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