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Melgar
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I've done this preparation myself recently. The best way to do it is to melt pure aluminum, then add the galinstan while it's still molten. It's
VERY important that the aluminum be at least 99% pure or so. I used to use scrap electric fence wire, but now that I live in a city, I've found that
really cheap dollar-store aluminum pans are usually pure aluminum. Once you have experience working with pure aluminum, it's pretty easy to tell if
that's what you have or not. When you melt it, it sort of flows around inside its oxide shell, leaving a paper-thin bit of oxide crust behind, which
your torch will immediately heat to glowing. Alloys don't really flow when they melt, and they melt at much higher temperatures. It's sort of like
metallic concrete, as opposed to the much more readily melted pure aluminum. Pure aluminum is really lightweight and easy to bend. I ripped up a
dollar-store aluminum pot with my hands and a very small pair of pliers. I don't think I could have done that with an alloy. Pure aluminum is also
lighter-colored. As far as what contains pure aluminum, it's usually used in applications where electrical or thermal conductivity is more important
than mechanical strength. So cookware and wire, mostly. Probably the rotors of AC induction motors too, if you don't mind tearing them apart. As
far as tests you can do, the main alloying elements of aluminum are iron and silicon. If you dissolve a sample in dilute hydrochloric acid, you
should have a totally transparent solution at the end. A yellow tint indicates iron, and a brownish precipitate indicates an aluminum-silicon complex
that you don't want.
Once you have your pure aluminum, melt it down into a blob. It doesn't really matter the shape, but it has to be one contiguous piece. Then, while
it's molten, add the galinstan. You can probably use as little as 100:1 aluminum to galinstan. Your metal will immediately change physical
properties. It will get black and will break into chunks instead of flowing when you prod it. Once you've confirmed that the whole blob is like
this, cover it to protect it from air, and let it cool off. If you want, you can break it into chunks that are convenient sizes for use first. Store
the chunks of aluminum in a small glass jar. You can even handle them with your hands once they've cooled off.
When you want to use one for a reaction, just pluck it out, toss it in the reaction vessel, and turn on stirring. The aluminum will break up within a
few minutes, eventually into pieces about the size of sand, and give off hydrogen at a slow but steady rate. If you use a ratio of galinstan to
aluminum that's 1:10 or more, the reaction will be much more vigorous. Also, there's a temperature (thirty-something degrees C or so? possibly
gallium's melting point.) that if your vessel reaches it, the reaction will go much faster. You may or may not want that to happen, so control vessel
temperature appropriately.
Also, for a solvent, water works well, and methanol works well. I'd expect ethanol to work well too, but if you use isopropanol, just be aware that
this will result in the formation of aluminum isopropoxide, which has the tendency of converting ketones to alcohols. It can also do the reverse in
the presence of excess acetone, via Oppenhaur oxidation, if that's something you need to do.
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CRUSTY
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Quote: Originally posted by Melgar  | | I'd expect ethanol to work well too, but if you use isopropanol, just be aware that this will result in the formation of aluminum isopropoxide, which
has the tendency of converting ketones to alcohols. It can also do the reverse in the presence of excess acetone, via Oppenhaur oxidation, if that's
something you need to do. |
Ooh, thanks for pointing that out. I actually wasn't familiar with the Oppenhaur oxidation until now, I'll have to try that one.
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careysub
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I think the thin rolled aluminums (foil, and foil ware) are probably 1000 series alloys that are almost pure aluminum (e.g. 1145, 1235, etc.) - ~0.65%
silicon and rest being aluminum, so >99% aluminum.
Reynolds foil is apparently 8111 alloy now, which 98.5% aluminum, the rest iron and silicon (roughly half and half).
http://www.reynoldskitchens.com/media/10246730/reynolds_wrap...
Any reason for using galinstan instead of the much cheaper pure gallium?
[Edited on 23-7-2016 by careysub]
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Melgar
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Gallium was the most expensive metal in the alloy when I made the alloy myself. Indium is slightly more expensive per gram, but you don't need nearly
as much of it as you do gallium. And the tin was essentially free, since I just used lead-free solder, which is 95% tin.
Also, by using galinstan, you can have a MUCH higher aluminum content and still have it work. So it actually ends up being considerably cheaper. And
finally, galinstan can be purchased cheaply in the form of mercury-free thermometers that clearly have some sort of metal in their bulbs. They're
like $5 at drugstores, and maybe half that on Amazon.
[Edited on 7/23/16 by Melgar]
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careysub
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| Quote: Originally posted by Melgar |
Gallium was the most expensive metal in the alloy when I made the alloy myself. Indium is slightly more expensive per gram, but you don't need nearly
as much of it as you do gallium. And the tin was essentially free, since I just used lead-free solder, which is 95% tin.
Also, by using galinstan, you can have a MUCH higher aluminum content and still have it work. So it actually ends up being considerably cheaper. And
finally, galinstan can be purchased cheaply in the form of mercury-free thermometers that clearly have some sort of metal in their bulbs. They're
like $5 at drugstores, and maybe half that on Amazon.
[Edited on 7/23/16 by Melgar] |
Ah so, the indium and tin are actually contributing to the amalgam performance? I had supposed you were just using galinstan as an OTC gallium source.
The eutectic aspect did not seem important since gallium is so easily melted.
From Rotometals you can get gallium for 60 cents per gram, indium for a dollar a gram, and tin for 4 cents per gram, so the price for galinstan
ingredients is about the same as gallium alone, 60 cents per gram. I am sure that a $5 thermometer does not contain anything like 8 grams of
galinstan, so that is not really a cheap source by weight, though with a 100:1 ratio you obviously don't need much.
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Melgar
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| Quote: Originally posted by careysub | | Ah so, the indium and tin are actually contributing to the amalgam performance? I had supposed you were just using galinstan as an OTC gallium source.
The eutectic aspect did not seem important since gallium is so easily melted. |
Yes, but there are a lot more factors at play than just gallium's melting point. I'm not sure what they all are exactly, but I do know that
experimentally, the indium and tin really do make the reaction run a lot better. It's also a pretty simple matter to collect the unreacted galinstan
and reuse it once the reaction is done, whereas I was never able to do that with gallium for whatever reason.
Also, if you can find a better source of aluminum than foil, I'd recommend using it. Aluminum foil has the highest surface area to volume ratio of
any source of aluminum, and you need to melt it down into a blob with a relatively low surface area in order to properly alloy the metals.
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careysub
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I just checked eBay and discovered that you can get galinstan in bottles for $1 to $1.75/gram depending on size. 15 g for $26 with shipping.
I'll probably make galinstan from scratch though, just for fun.
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careysub
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This reduction agent preparation should have a write-up in pre-publication.
If it can replace the use of mercuric chloride in aluminum amalgam preparation that is a major improvement. Mercuric chloride is a very hazardous
substance.
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