MrHomeScientist
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Liquid metal alloy: A mercury substitute
Hey all,
I'm new to this forum, but from everything I've read I can tell that people in this community know what they are talking about! It's been great fun
reading different threads here, and I'm hoping someone might have some ideas for my little project.
I've always wanted to play with mercury, but it's toxicity makes me wary (I know it's not really that bad, but still). So, in my home lab I've been
looking into making low melting point alloys. My goal is to make a metal alloy that is liquid at room temperature and can act as a nontoxic mercury
substitute! Admittedly this won't have much practical purpose, but it's an interesting project for me and I think it would definitely be something
cool to play with.
To effectively act as a mercury substitute, it must be made from nontoxic elements (i.e. cadmium is out) and have similar properties as metallic
mercury (i.e. surface tension and beading behavior). I've made Galinstan (an liquid alloy of gallium, indium, and tin), but its gallium content makes
it quite messy. It also degrades over time, and if you're interested I posted a video that shows how I made it on my youtube page (click the www link
below). I did a little research, and I've concluded that gallium is likely the problem. It oxidizes in air when liquid, and it is this gallium oxide
that gives it its wetting behavior. Indium has similar wetting properties. I wonder if there's some way to protect it from oxidizing by adding another
component to the alloy? Or perhaps something that would bind the molecules of the alloy tighter together, to increase surface tension but still
keeping it liquid? I know galinstan thermometers use coated glass to prevent wetting, but I'd like to be able to take this material and roll it around
on any surface without it sticking to it (like mercury does, with a few exceptions).
This might not qualify as a true chemistry topic, but I'm hoping some people might have some ideas to share  Thanks for any thoughts!
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not_important
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Can't help with the non-stick issue. save noting that for electrochemical purposes, mercury can be difficult to replace as its overpotential is
unusual and the closest matches include lead and cadmium. For simple conductive liquid metal galinstan is fine, in some applications its density is
too low or requires recalibration of equipment.
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zed
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It would be nice if there were more liquid-metal options.
I would like to construct a "Brown Type" automatic valve for hydrogen generation.
In Brown's original valve, an external column of NaBH4 in water, in a burette, is supported by a hypodermic needle....The "needle" is inserted
through a septum into a hydrogen pressurized flask, and into a small reservoir of Mercury.
NaBH4 in water, flows down from the burrette, passes through the needle, floats to the surface of the small mercury reservoir, and overflows into a
waiting acid solution below.
When the overflowed NaBH4 reacts with the acid, H2 gas is generated, internal pressure rises, and flow through the needle stops, until such time as
enough H2 gas has been absorbed by the hydrogenation process, to cause a pressure drop.......Which then reactivates the valve.
Neat trick, but you gotta use Mercury. Don't know if Gallinstan is dense enough, and that business about "wetting" glass....and nearly everything
else? Makes me think it might not stay where it is supposed to.
So, the options are: toxic Mercury.....Or, Metallic "Flubber"....An alloy that won't stay where you want it to, because it's too sticky.
There is an illustration of the referred to apparatus, on pages 91, 92, in Vogel's Practical Organic Chemistry, 5th Edition.
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watson.fawkes
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Quote: Originally posted by zed  | | NaBH4 in water, flows down from the burrette, passes through the needle, floats to the surface of the small mercury reservoir, and overflows into a
waiting acid solution below. |
You need a liquid that immiscible with water/NaBH4, doesn't react with it, and
is more* dense than it. Those are the properties required to make the device work. Your liquid doesn't have to be a metal.
Alternately, your metal doesn't have to be at room temperature. Use a heater and thermostat (a simple one will suffice) and a low melting alloy. For
example, Rotometals has wide selection of them.
*Edit: sign error.
[Edited on 7-11-2010 by watson.fawkes]
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zed
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The liquid must be more dense than water. Also, heating the alloy, and controlling the temperature via heater and thermostat, would add another
level of complexity to the machine.
The beauty of Dr. Brown's automatic hydrogen generator, is its simplicity.
None-the-less, the Rotometals link is helpful. Might be useful for something else. Thank you.
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