Ultralight Metallic Microlattices

[Enthalpy]

The kind of thingy that stimulates inventiveness, curiosity, and more...

http://www.sciencema...nt/334/6058/962

Science Magazine is pay-for-view, alas, and reports elsewhere are very incomplete:

http://latimesblogs....?track=lat-pick

 

From what I read elsewhere:

- This is a lattice of very small metallic tubes, made as a single part

- Newspapers call it a material, which it's not in a strict sense

- A frame of rods is first obtained, I understand by many crossed light rays that polymerize liquid MMA into solid PMMA

- Catalytic nickel is deposited on the solid frame after liquid MMA is flown away

- And the solid MMA frame is "somehow" removed from within the nickel hollow frame...

 

Unexpected:

- Catalytic nickel can be resilient, I thought it were always hard and brittle.

- They get a very low bulk density from tiny tubes, implying very thin tube walls.

I knew electrolytic nickel is used at 6µm wall, here electroless nickel must be thinner.

 

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If I see their truss properly, all tubes cross at 90°, which partly explains why the truss can collapse without breaking.

 

Other uses would need a stiff truss, which could be obtained by more tubes directions (more light beam directions) like 30°

http://en.wikipedia....iki/Space_frame

provided light stray reflections don't play crazy then...

 

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How they remove solid MMA from within long narrow nickel tubes must be tricky...

Has someone access to Science Magazine, please?

 

I could imagine, as a liquid etchant, to use dilute hydrogen peroxide, but it can't be very fast. A solvent must be even slower.

 

Or they first melt away the PMMA, then etch away the remnants.

 

Gaseous operation must both bring the etchant and remove the products faster. Possibilities?

- Ozone-enriched air?

- Dilute nitrogen tetroxide?

- Hot oxygen or chlorine at a very low total pressure. That must be fast.

 

If the PMMA frame can be made hollow, that is of tubes instead of rods, by circling the light beam that polymerizes the MMA, then the remaining through holes would let etch the PMMA frame hugely faster.

 

Marc Schaefer, aka Enthalpy

 

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And their trick with light beams looks like an excellent way to produce the heat exchanger I suggested there

http://saposjoint.net/Forum/viewtopic.php?f=66&t=2051#p23419

 

I wanted to make the frame by winding something around pillars for instance, but light beams would define many small aligned rods at once, and they can be automated. Some rods would extend to the sides, but they can be cut away before nickel deposition. Nice!

 

A little bit of MMA stkicking to PMMA and polymerized before nickel deposition would make smooth transitions between the rods, nice for strength and for flow.

 

With different light beam diameters or by circling the beam, varied nickel tube diameters are defined, which is all-important to make a heat exchanger with much exchange capability combined with a small pressure drop - just like blood vessels have varied diameters. In a simple case, tubes would be wide in the X direction, merdium in Y, and small in Z. Imagine a square pattern in the YZ plane: you could have fluid inlets at even rows and outlets at odd rows. Or more subtle schemes to obtain counter-flowing fluids.

 

Marc Schaefer, aka Enthalpy

Edited November 24, 2011 by Enthalpy

[Enthalpy]

Fun. I had suggested rapid prototyping, whose first machines used UV polymerization of MMA, to make the frame on which catalytic nickel is deposited. But as this was almost four years ago, I had forgotten it. Getting old.

http://saposjoint.net/Forum/viewtopic.php?f=66&t=2051#p23419

 

So the improvement by the Californian team is that

- They made it! Not the same as a paper description...

- Light seem to define long tubes directly along the beams. This differs from rapid prototyping.

- They have some practicable means to remove the frame once nickel is deposited...

 

Very nice achievement!