Project Logs

Collapse

• Impact Tester

  Michael Perrone • 03/28/2024 at 22:44 • 0 comments

  Bismuth and magnesium, somewhat like gold and aluminum, are considered dissimilar metals, so heating or melting these materials and expecting a good metallurgical bond isn't the best way to do things. That's where cold spray technology comes in: if you shoot metal powder at a surface fast enough, it can mechanically and chemically bond to the substrate without ever becoming a liquid.

  Image credit to VRC Metal systems

  But cold spray systems cost hundreds of thousands if not millions of dollars to own and operate - so is there something we can do instead? It turns out there is! If you concentrate large amounts of force over a small surface area, you can simulate cold spray or explosion welding

  (more images and details coming shortly)

• What is the Mg-Bi composite?

  Michael Perrone • 03/22/2024 at 18:48 • 2 comments

  Being relatively well-versed in metallurgy and to some extent chemistry, quite a few conventional explanations come to mind when I think of the magnesium-Bismuth composite

  • Firstly, the composite looks like it is produced electrochemically. Magnesium typically forms dendritic or feather-like structures as shown in the above image from Wikipedia during electrolysis of magnesium salts. If I were trying to reduce the formation of these dendrites in a battery for example, I might add some bismuth layers to redirect crystal growth and reduce dendrite formation, which could otherwise short out the battery. Supporting this argument, bismuth is often considered as an additive in magnesium batteries in many scientific articles to promote catalytic activity, provide reversible passivation, and improve magnesium battery efficiency and life cycle. [1], [2], [3], [4], [5]. It is certainly not beyond imagination (though it would require a water soluble bismuth salt that does not electrolyze easily, which is odd) that a magnesium-ion battery could have developed bismuth-magnesium layering during successive charge-discharge cycles, especially when considering article 3. And one could imagine such a prototype battery being used in 1947 by either the US or the USSR.
  • Alternatively, the bismuth lamination may be a prototypical form of anticorrosion coating, of the type actively being developed by Modumetal for more standard industrial metals and alloys like steel. In these materials, the bismuth layer might act as a chemically passive layer to potentially impede corrosion, but considering the galvanic interaction between the bismuth and magnesium, I'm not certain how well that would work unless the bismuth coating is largely free of holes - which could be challenging given what I've seen with magnesium electroplating... 
  • If Bismuth improves the catalytic activity of the magnesium, one could imagine a magnesium extractive metallurgical process utilizing bismuth in some way, occasionally replenished, in the electrolytic bath, to reduce the energy required for electrochemical production of magnesium metal. The stripes could indicate this occasional introduction of bismuth salts into the plating bath. Alternatively, the bismuth could be used to make sure the magnesium easily flakes off of the plating electrode when plating is complete, or again to prevent the formation of magnesium dendrites so that the magnesium extraction bath can run for longer between batches.

  But let's assume for a second that perhaps the composite was damaged by re-entry, weaponry or the crash-landing so it is not in its pristine state. It's certainly possible that the outermost Bismuth layer could have evaporated off in that scenario, and the magnesium could have been scarred in the way shown. What else might it be then?
  

  • Such a laminate could possibly impede magnesium combustion, which could be a very useful property in aerospace applications. I certainly noticed some protection going on when blowtorching some of the samples - the bismuth would oxidize when the magnesium would normally burn, inhibiting ignition somehow, despite forming what I imagine would be a thermitic composite. With bismuth having such a low melting point, I'm not sure how well this would work in practice: I would expect delamination at high temperatures when the bismuth melts.

  • Having personally played around with magnesium and bismuth electrochemistry in the past, I can attest that thin layers of bismuth on magnesium appear black, even if they are quite smooth (although perhaps the roughness was too small for my equipment to resolve) - so something interesting may be going on with optical absorption at the surface. Perhaps the composite indeed exhibits some interesting infrared and terahertz optical properties, as claimed online.
  • If the material happens to be a terahertz or phononic waveguide, it is possible that the material is also an exotic fuel or power source, considering that Peter Hagelstein's...

  Read more »

View all 2 project logs