A self-fueled liquid metal motor | Hacker News Reader

A self-fueled liquid metal motor

newscientist.com

80 pointsfreefrancisco11 comments

This was posted the other day, but surprisingly sank unnoticed. Here's a repost of the comment I left then:

O.o The micro pumping and capillary action are extremely interesting, but seeing how it deforms in response to an electrical current is just eye-popping. Naturally I want to see what happens if you send AC signals rather than static DC...at the least I would expect something similar to the behavior of ferrofluids on a speaker cone, eg https://vimeo.com/65815077 or even suspensions of cornstarch: https://www.youtube.com/watch?v=dS9LNBQE2Jw which has a handy how-to at the end. The supplementary material is available free even though the article is paywalled and is a great read. http://onlinelibrary.wiley.com/doi/10.1002/adma.201405438/su.... The alloy is described here: https://gmwgroup.harvard.edu/pubs/pdf/1014.pdf According to the supplementary, the aluminum flake 'fuel' is not consumed but breaks up into tiny fragments and eventually diffuses to the surface, causing the reaction to tail off. This seems like fairly fundamental research.

The shape it makes when electricity passes through it reminds me more of Lichtenberg figures: http://www.wikiwand.com/en/Lichtenberg_figure

Oh definitely, that's what I'd expect when you just pump electrons in it with DC. But alternating current should lead to interference patterns of some sort.

Music is Afrola by Bird Creek. To me, it made the video much more engaging.

Indeed. Visions of Feynman doing a record with Fela Kuti are passing through my mind right this instant.

Reminds me of those little soap-chip powered toy boats we made as kids.

When placed in a solution of sodium hydroxide, or even brine, and kept in contact with a flake of aluminium for "fuel", it moves around for about an hour.

So not quite self-powered.

We took "self-powered" out of the title.

Chemist here: I think that's overly editorial. If there were an air-burning engine made of aluminum, which consumed itself for motive force, we might describe that as self-fueled. In general the reducing agent is considered fuel and the oxidizer is assumed; a motor that oxidizes aluminum using hydroxide is not that different from one that oxidizes it using oxygen.

Edit: The flake of aluminum fuel physically gloms onto the motor, and aluminum will normally form an oxide that would prevent hydroxide (certainly brine) from reducing it. It's not a 'mere' fuel that's physically driving the droplet, there's a single reaction happening. My hunch is that's where the tin comes in.

Thanks for the great comment! We put 'self-fueled' back in the title.

Pretty sure the tin is just to help get the low temperature eutectic of Galinstan. I am pretty sure mercury would work just as well, but children and grad students don't get to play with Mercury much any more.

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