FrankRizzo

What's the particle size of the MgAl in your formula, Seymour?

Without a lubricant and a carrier solvent, you will not even achieve less than 20micron particles by ball milling. Once the particles get to a certain mass/cross-section ratio, they begin to impact weld with one another, and particle size cannot be reduced further. Lubricants (like stearic acid) dissolved in a carrier solvent will reduce this effect enough to bring the material down to 2-5micron, but will never achieve nano-sized particles (0.01micon).

Commercial nano aluminums are produced by a high-energy electric discharge through a thin aluminum wire in an inert atmosphere (helium, argon, sometimes nitrogen). The wire superheats (evaporates) from a solid to plasma. As the plasma particles contact the inert gas atoms of the chamber, they cool down and condense back to nano aluminum particles. The pressure in the vessel is controlled during the process to favor smaller particles. This is not something you're going to do in the garage successfully.

Here's an updated reference for those of you looking to make one of these easy P2F assemblies:

The author took the time to put one together (and take it apart!), and found that the working diameter of the piston inside the ram is ~43mm (1.70"). This gives a P2F multiplier of ~2.3X (1000psi gauge = 2300lb force). Again, this isn't a perfect representation of the force applied, but will enable consistency (most important).

http://www.wichitabu.../ptof/ptof.html

But the video clearly shows a spiral forming not just a spiral shape expanding which means it has to be made from a rotating point ejecting stars rather than just a shaped burst.

No, it's much simpler than that. The inner spiral pattern expands with the burst...the stars further from the center are propelled with more force from the expanding gas envelope. The stars that make up the blue sphere after the spiral has burned-out are just layer along the inner surface of the shell and coated in a thick layer of a dark prime so they don't appear until later. Does that make sense?

I think there's a post on rec.pyrotechnics that details the construction of these shells. I'll do some searching and get back to you.

Edit: The shell referred to in the rec.pyro post is a significant upgrade of the basic technique that you saw in the YouTube video, but using precisely rolled color-changing stars. It will blow your mind.

A still frame from John Reilly's video:


The actual video: http://pyrotechnics....24jud02_low.wmv
The relevant discussion: http://groups.google...1f3b25fcd0f887/

That's a "snail" shell. Both halves of the shell are filled with burst, then the stars are loaded in a spiral fashion at the equator where the two shell halves come together. To keep the pattern from shifting during handling, the stars are usually wrapped in a thin tube of tissue paper placed in the desired shape. It's much the same as making a smiley face or heart shape. Cheers!