CuO/Al sparklers

[brimstoned]

I've been doing a little experimentation with small amounts of copper thermite. My goal was to make a crackling star for tiny mines easily.

I calculated ratios based on:

 

3 CuO + 2 AL --> Al2O3 + 3 Cu

 

which indicated 82% CuO and 18% Al; the result was about 50 gm.

This mixture was diapered in with an additional 10% of smokeless powder ( I've a can of Hodgen Lil'gun I don't use much for reloading) and poured into a small polypropylene

tub with 50 cc of acetone in the bottom. Time, stirring and a little more acetone resulted in a slurry slightly thicker than pancake batter.

Some of the mixture was poured in quarter-sized quantities on a thick glass sheet to dry, later to be broken into smaller bits for star mines (sample pieces make a bright, low-frequency DE effect, easy to ignite).

The thin bamboo skewer I used for agitation rapidly dried with about three inches of the composition and looked surprisingly like a sparkler, I dipped it a second time and let dry.

After about four hours ignition produced large bright sparks combined with small, low-toned thuds, fairly slow burning. If I can get a camera going, I'll try to get shots of the next try, I found the effect quite interesting!

BTW, Al was -425 mesh American bright flake.

Edited August 30, 2012 by brimstoned

[AdmiralDonSnider]

Interesting, keep us up to date!

[ExplosiveCoek]

It's a termite comp really, doesn't Fe2O3+Al look familiar ? You can make some good bangs with the compo you posted, regarding that your Al is fine enough.

[brimstoned]

It's a termite comp really, doesn't Fe2O3+Al look familiar ? You can make some good bangs with the compo you posted, regarding that your Al is fine enough.

 

Indeed, I believe I did mention thermite in the OP...does termite comp require the addition of dried insects?

 

Seriously though, a decade or so ago I was making up to 6" cylinder shells, I've had my share of "good bangs" but that does seem quite as important anymore.

I found my trunk of gear from years ago recently, and picked up the enthusiasm again: as the pyro budget is greatly reduced, small set pieces should extend my chems for quite awhile.

[ExplosiveCoek]

The good bangs was more of a reference that, since it could burn that fast, it might not be suitable for sparklers. Which would ideally burn quite slow

[brimstoned]

It does seem as though the NC is an inhibiting factor...curiously enough, the thinner film acts more like DE, slightly thicker strobes, thicker yet burns like a star comp.

[psyco_1322]

I had recently made some stars bound with dextrin, they burned bright and fast, and were a real bitch to get lit. Never put them in a shell, they took so much water to bind up and cut they cracked all over after drying. Black match taped to them would not even lit it, took some hot burning visco to ignite. I can't see a sparkler made with it lasting more than 2 or 3 seconds. I used dark Al for the stars.

[brimstoned]

I think the binding with NC makes a difference, as it provides its own oxygen. There is nothing present in your star mixture to oxidize the dextrin?

[taiwanluthiers]

If you bind with shellac, then it would have dried insect in it...

[Seymour]

I think the binding with NC makes a difference, as it provides its own oxygen. There is nothing present in your star mixture to oxidize the dextrin?

 

NC can only really provide enough oxygen for its self, if that. Even the propellant quality stuff is tweaked pretty hard to the carbon monoxide side of the oxygen ballance. Much of the stuff used for binders won't even be able to fully burn the carbon in it to CO.

 

If anyone else has done the lab demo where you ignite charcoal and CuO, they will also recognize that CuO can oxidize organics. Still, these bright thermite like stars are in my opinion best over fuelled with the Aluminium... not an environment for burning carbon, but when it's this hot and fierce, 4% dextrin won't be any obstacle.

 

I had recently made some stars bound with dextrin, they burned bright and fast, and were a real bitch to get lit. Never put them in a shell, they took so much water to bind up and cut they cracked all over after drying. Black match taped to them would not even lit it, took some hot burning visco to ignite. I can't see a sparkler made with it lasting more than 2 or 3 seconds. I used dark Al for the stars.

 

I did the same thing but with glitter type Aluminium, and they required the most steps of prime to light of any star I've made. Still, with dark Aluminium my CuO/Al powder mix lights easily with black match... I's expect normal colour star prime to have a good chance of lighting it.

[psyco_1322]

I think I used the 6:2 formula, which you cant tell the difference in the burn while in powder form. With a chunk of burning thermite that emits atomized copper, I don't think the dextrin minds where it's getting oxygen again.

[Seymour]

With a chunk of burning thermite that emits atomized copper,

 

Yup. I love the pink smoke trails from these things!

[brimstoned]

If you bind with shellac, then it would have dried insect in it...

 

I just looked that up...I didn't realize shellac was produced from dried insect secretions!

Edited September 9, 2012 by brimstoned