Harristotle
Hazard to Others
Posts: 138
Registered: 30-10-2011
Location: Tinkerville
Member Is Offline
Mood: I tink therefore I am
|
|
Galinstan games
Hi to all!
I have been playing with galinstan recently, in the hope of designing a "soft robot". In this scheme, one might make a humanoid shape and mill it into
perspex, or cast it in PDMS silicone. By placing electrodes at various positions, I can imagine that you can make a "blob" of galinstan change shape,
move, and, well be a robot. There has to be a way for some of us Chemists to cash in on the STEM movement in schools 
Inspired by https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3948272/ , I set to work.
Galistan was made in the ratio of 68.5% Ga, 21.5% In, and 10% Sn.
13.7g Gallium (ebay)
4.3g Indium (ebay)
2.0g Tin (99% from pewter)
These were added to a graphite crucible, and placed on a refractory "mat" made from 1.5 cup of perlite, 500g refractory cement and 150ml water, that
had been previously set in an icecream container.
The metals were then torched with a MAP gas torch until thoroughly melted and mixed.
When cooled, they were washed and stored in an inverted plastic pasteur pipette.
Galistan alters its wetting characteristics depending on its degree of surface oxidation. If you make an anode out of it, its surface will oxidise,
and this lowers its surface tension. This means that it will wet surfaces. In contrast, when the surface is reduced and metallic, it beads up, and
won't wet.
By altering the surface oxidation, you can make a bead of galistan move in a controlled and regular manner.
To demonstrate this, the following cell was constructed.
The results of all of this can be seen here:
https://youtu.be/4gudJbKXGHM
While not completed, this project has reached a stage where it is fit to share. In doing so, I hope that it stimulates and interests someone.
I am very interested in any feedback or suggestions.
Cheers, H.
|
|
|
MrHomeScientist
International Hazard
Posts: 1806
Registered: 24-10-2010
Location: Flerovium
Member Is Offline
Mood: No Mood
|
|
Very cool idea! I played with galinstan a little a while back, and found it to wet everything it touches. I read somewhere that galinstan thermometers
use glass coated in gallium oxide to eliminate that effect. Did you coat your apparatus at all, or was it purely the applied current that stopped
wetting?
|
|
|
Melgar
Anti-Spam Agent
Posts: 2004
Registered: 23-2-2010
Location: Connecticut
Member Is Offline
Mood: Estrified
|
|
As soon as it melts, gallium or galinstan will fall in blobs to the floor or ground, and splatter everywhere. Not good if you have carpeting. Your
feet will be black for months, from gallium particles.
I've been playing with gallium and galinstan a lot recently. Try a eutectic mixture of gallium and indium, it melts at 15C and is exactly 75% gallium
and 25% indium by mass. That's kind of fun, because you'll feel it stay noticeably cold as it melts. Galinstan melts around the same temperature as
ice, although if you add 1% antimony and 1% bismuth, that will lower its melting point maybe another 10 degrees. My lead-free solder in 5% antimony,
so I've just been using that as my tin source. But even better, try putting a blob of it on aluminum, then using some tool to scratch the aluminum's
surface through the gallium. There won't be an immediate reaction, but if you tilt the aluminum and the galinstan sort of looks like it's sticking to
a specific spot on the aluminum, then just wait, there will be one. Once you notice the reaction and get bored of it, add water to make it more
interesting.
|
|
|
Harristotle
Hazard to Others
Posts: 138
Registered: 30-10-2011
Location: Tinkerville
Member Is Offline
Mood: I tink therefore I am
|
|
Thanks for both sets of feedback Melgar and MrHomeScientist.
MrHomeScientist:I didn't coat anything with Ga2O3, but the bead is in 0.5M NaOH, which forms the electrolyte of the cell.
Melgar: When I spill galinstan, I have found that if I rub sunscreen ( an oil emulsion) that I can completely wipe up the spill with a tissue.
I demonstrated this to one of my ex students: I showed him the galinstan and he spilt some on his super expensive new laptop. An awkward look of
horror crossed his face as he looked at the lovely anodised case and the silver splash, and processed the significance of all the nasty you tube
videos about aluminium cans and gallium. I had cleaned it all off within 20 seconds (including the run to the pantry to get the sunscreen) - no
residue, and no ill effects. This is a trick worth remembering - skin moisturiser will probably do as well.
An update of the project can be seen here (redesigned cell, eliminated the possibility of gas production driving movement etc) - the arduino is making
the blob beat. I have put an explanation and a link to the source code on github too!
https://www.youtube.com/watch?v=4TBBPrjubc8
|
|
|
Melgar
Anti-Spam Agent
Posts: 2004
Registered: 23-2-2010
Location: Connecticut
Member Is Offline
Mood: Estrified
|
|
Yeah, any solvent less polar than water does a decent job of cleaning it up. Dilute acids work too. If some got on an anodized aluminum laptop, it
could easily sit there for months without reacting. Anodized aluminum has an even thicker oxide coating than regular aluminum, and even getting
regular aluminum to alloy with galinstan or gallium can be difficult. Also, anodized aluminum is usually not commercially pure, since it has other
metals added for strength. These other metals tend to interfere with gallium's ability to penetrate into the aluminum, and reactions between
structural aluminum alloys with galinstan tend to fizzle out quickly.
|
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
