Molten Metal LED Display pt2
As promised, here’s some video of my recent fun with Wood’s Metal. Thanks to Phil for recording this.
Some basic stats:
LEDs: 54
Resistors: 40
I’m still testing different materials to find some combination that will prevent the metal from sticking to the container. Acrylic by itself doesn’t do so badly (far better than glass at least) but there’s still significant stickage. What I would really like is to find something that will let the metal flow and move somewhat like mercury.
A friend recently suggested that I just use mercury but it’s far too toxic for my tastes. I’d be one spill away from turning my lab into a Superfund site.
Other things that I’ve tried:
| Worked well for a while but then turned white and powdery. I suspect that it slowly cooked. | |
| Mineral Oil | Worked marginally well but didn’t prevent enough sticking |
| Water | Less effective than the mineral oil |
| Silicone Lube | Epic Fail. Actually, this had the curious property of making the metal stick evenly to everything it touched, lining my container with a thin sheet of metal. Might be useful if it wasn’t the exact opposite effect I was going for. |
Based on accounts I’ve read online, I suspect I may never find a ‘lube’ that makes acrylic perform the way I want. A common experience (and similar to what I’ve been seeing) is to find something that works for a while but then fails.
I may have to resort to simply lining the bottom of my container with teflon.
nice video! i would think that polyethylene or polypropylene would work well as a container, no? teflon sprays are not hard to find though. also from the video it looked like you had a fair bit of oxidation/crap on the surface, removing this should significantly improve flow, i’m not sure how fast it re-accumulates though – if it is fast then you have little hope in an oxygen environment.
if you are concerned about toxicity then i would suggest field’s metal, which does not have either lead or cadmium as wood’s metal – and has a lower melting point besides. mcmaster sells it. cadmium is quite toxic!
There’s an interesting story regarding that oxidation you see. That was my first guess as to what it was too — oxidation — but I no longer think that’s what it is. For a while I was careful to always have the metal submerged in water or mineral oil in an effort to prevent that grey and black gunk from building up. Yet neither the water or mineral oil seemed to help and the gunk built up as fast as ever (possibly faster). I even tried using mineral oil that I first outgassed in a vacuum to remove most of the dissolved oxygen. This had little effect.
However one experiment I did suggested that oxidation may not be the explination. I melted some metal in the open air and let it sit for 30 minutes. When I came back, the surface of the metal was just as shiny as it was when I left… no signs of corrosion whatsoever. If it was oxidation, I would expect a crust on the surface.
My current theory is that the gunk is actually some of the constituent metals crystalizing and falling out of solution. Wood’s metal is a mixture of four types of metals: Bismuth, Cadmium, Lead, and Tin. The lowest melting point of those four metals belongs to Tin at 450 degressF. Yet Wood’s metal melts at 158 degreesF. Thus I suspect what is going on with the gunk is that small momentary concentrations of some of the component metals are forming just long enough for the atoms to get together, crystalize and fall out of solution. Indeed, I’ve tried heating some of the metal up to around 600 degreesF and that does seem to get rid of most of the gunk (not to mention create a load of very toxic fumes.. I used a respirator when I did this).
I’ve since found that keeping the temperature up a bit beyond 158 degreesF seems to help minimize the gunk. If I end up doing some sort of dynamic display where the metal is pumped around, I’ll probably design into a part where the metal gets heated up well beyond its metling point and mixed.
As for the container goes, I’ve ordered a sheet of clear Teflon (FEP) with adhesive backing from McMaster (part no 5805T11). I’m thinking that if I lay that down on the bottom of my acrylic container that should give me a really good non-stick surface. We’ll see.
As far as Field’s metal goes, that was my first choice when I started this project. Unfortunately, Indium, one of the key component elements in Field’s metal, has become staggeringly expensive in the whole recent commodities surge of the past few years. It was selling for something like $25/kg in November of 2006 and is now selling for around $600 – $700/kg on ebay (or as much as $2000/kg from metals vendors).
Interesting experiment! Have you tried using a ferro-fluid? These are fluids with a high iron content used for visually revealing the fields on a magnetic striped card, and other interesting effects. Check YouTube. My thinking is that these room temperature fluids will do the job: not reactive or toxic. They do use a (possibly flammable) solvent that evaporates to deposit the iron on magnetic fields. This means that the led array would have to be in a sealed container to prevent fire and the solvent from evaporating.
Good luck with this – I can see a led “waterfall” effect of leds in a clear plastic tube that has the fluid flowing downward, and pumped back up to the top. RGB the leds and add fiber optic to make a cool cascade.
Have you considered gallium? It melts at 30C/85F and is more or less nontoxic. Don’t know about it’s conductivity but it is used in semiconductors.
The failure with the Silicon lube should not put you off.
Odds are if the container was made of silicon you would have had a more successful outcome.
I suggest getting one of those flexible silicon baking trays popular in kitchen shops these days. They are made from silicon and will withstand 200C in an oven. so no chance of melting.
A smooth surface would be better than a rough surface – the rough surface is common in bakeware because it makes releasing the cake easier but this is not your problem.
Silicon doesn’t like to stick to anything except silicon.
Gallium would be great except that it’s really quite expensive.
Ah, more importantly I’ve found that apparently gallium loves to stick to stuff.
If you’re trying to lubricate acrylic, give fabric softener a try. Seems to work for acrylic fabrics….
hey. why don’t you use gallistan? maybe because you never heard of it?
http://www.geratherm.com/en/technologie_galinstan
“the enviromentally-friendly mercury substitute” sounds perfect for your needs.
Galinstan Examples of Applications
* clinical thermometer in medical technology
* micro-relay and �tools in medical technology
* high-performance lubricant for cathode-beam tubes (MRT, CT)
* magnet-fluid technology in the area of metallurgy
* cooling agent for high-performance engines in the automotive field
good luck and keep on going with the good work
Galinstan has a number of the same inherent issues as gallium… namely that it’s very expensive and also it tends to wet and stick to stuff. See: http://en.wikipedia.org/wiki/Galinstan
Colloidal silver. Or forgo the whole “liquid metal” thing and just use salt water to achieve the same effect.