Best uses for hexamine

[Siegmund]

I seem to have bought some, several years ago, planning to do... um... something with it, but I can't remember what. I imagine to try a new blue (but only KP not AP on hand.) Now it's sitting there on my shelf, just begging to be put in something.

 

Anyone have any favorite formulas requiring hexamine but not requiring AP?

 

For that matter - is there a simple list of circumstances under which one should use hexamine instead of red gum or shellac or whatever?

[Arthur]

Hexamine is a good fuel for blues.

[SharkWhisperer]

Gorski cited Gary Smith's Perc-based blue & violet rubber stars on the Skylighter website, both of which use 5% hexamine in place of hotter MgAl fuel, and neither of which use AP. Link is : https://www.skylighter.com/blogs/how-to-make-fireworks/rainbow-rubber-stars?_pos=1&_sid=365830b2b&_ss=r . Think I saw a green barium nitrate-based flash that contained hexamine in one of the formularies, but it really didn't catch my attention.

 

I'm about to try crosslinking phenolic resin with it as an NC binder/fuel substitute for dragon eggs/crackle, since my phenolic resin (there's many many types) didn't overtly dissolve in acetone as I expected. However, I've read elsewhere that this x-linking reaction requires heat to propel the reaction. Anybody know whether hexamine x-linking of phenolic resin proceeds at room temp, just at a slower rate, or not at all?

 

If I don't see success with current uses, then it'll meet my last couple of pounds of AP for some nicely saturated blues for the 4th!

 

I haven't worked with it much, but it's supposedly rather hygroscopic.

 

It's also the precursor for RDX, but those details prolly belong in the HE section.

[Mumbles]

I consider hexamine less of a traditional fuel. To me it's more of a flame enhancer. It is a fuel, but I haven't seen it used a lot as a primary fuel. Generally it's used in conjunction with something like red gum, shellac, phenolic resin, etc. Maybe to a lesser degree with metals. It is cooler burning, so it tends to lower the flame temperature. This is probably why I haven't seen a ton of use of it with metallic fuels. It may just not be able to make that big of a difference. When it decomposes, it makes pretty much all gas. Nitrogen, carbon dioxide and steam. This helps to cool things down, but it also helps to expand the flame envelope. If you try two formulas side by side with and without hexamine subsituted in, the hexamine version has a higher liklihood of having a bigger flame and possible a cooler, more saturated color.

 

It does also crosslink phenolic resin. I've looked into the temperatures a little bit, but not as thoroughly as I'd like. There is a lot of information out there on it. Hexamine is prepared from formaldehyde and ammonia. When it gets hot, it can break back down into these components. There is suggestions that crosslinking can come from methylene bridges from the formaldehyde portion, or dimethyleneamino bridges somewhat from the ammonia portion. It realistically is probably a mixture of both. This general reaction is used in a lot of industrial and commercial products, plywood and other structural composites are probably the most well known applications The temperatures a lot of people use to "crosslink" phenolic in pyrotechnics are actually quite low. Whether it happens at room temperature, it's hard to say. There's both the question of if it happens, and how long it takes. Most literature I've read recommends a temperature of at least 150F/65C. I've seen conflicting reports as to whether you need to get the hexamine to start decomposing, or if you need to get the resin to soften/melt to get the crosslinking to happen. Crosslinking comes with concomitant production and elimination of water. Most patents you come across run the crosslinking at a temperature in excess of 212F/100C to help drive this off and force the crosslinking. I have an article by Jim Widmann on this below. I have seen him suggest that even higher temperatures may be desirable since publication of that though.

 

Jim Widmann has some information on crosslinking here: https://www.dropbox.com/s/bwb066i83ca2wo8/Pheno-Hex%20Binding%20ISF%202015.docx?dl=0

[rellim]

Spanish Blue formulas #1 and #2 call for 4% hexamine.

The pyro dictionary gives a green formulation:

55 Barium Nitrate 10 potassium perchlorate 10 hexamine 12 Magnalium 7 red gum 12 parlon 4 dex.

[Siegmund]

"Flame enhancer rather than traditional fuel" would explain why it's seen so rarely on its own, but almost always in combination with some other organic fuel.

 

Have spent a good bit of the afternoon digging through a bunch of ancient blue-comp threads on here, looking for things that might benefit from trying it - hopefully without turning them into Kitchen Sink Blue #2. Heh.

[Richtee]

You can cook a hotdog with it. Or a steak if ya got enough.