Nitrate and Aluminum

[aa92td]

Ok i've got a question for you guys.

I've been made some Al Streamer stars from bp (80%) and Al (20%)

something like a month ago.

now yesterday i made 5" Ariel shell and loaded him with these stars,

but i dont remember if i made the star composition with boric acid.

lets say that i didnt put boric acid and I'm planing to shot the shell next week , how much its dangerous?

[50AE]

It depends of the aluminium particle size and the conditions. If the inside of the shell is dry (it should be), it's safer. The reduction occurs when the composition is damp/wet. If your aluminium particles are bigger, the chance of ignition is lower.

[BLAST420]

where is the danger? Just black powder and Alluminum?? This is new information to me. i thought fireworks (large shells too) can be stored for years and years!!

[oskarchem]

The problem is between the oxidiser and the reductor; The oxidiser being KNO3 and the reductor Al, a reaction occurs between the two chemicals, creating heat, and it was ignite.

[psyco_1322]

Umm you've had these stars for a month, what makes you think that putting them in the shell will make them go bad? If anything was going to happen it would have been within 24hrs of making them.

[Mumbles]

Yes, if they are dried(which they should be), they will be fine. Excessive storage(years), especially with exposure to the elements can make them go bad over time. 1 month is certainly not nearly long enough. The bad reactions happen with moisture. If they're dry, they've already degraded as much as they will.

[Niter]

where is the danger? Just black powder and Alluminum??

 

 

Under the influence of moisture, aluminium reduces the potassium nitrate to potassium hydroxide and ammonia. Potassium hydroxide and aluminium, under the influence of moisture, undergo a greatly exothermic reaction to form potassium aluminate and hydrogen gas. This may cause the temperature to rise faster and faster and even ignite the composition.

 

So what you need is acidity in your composition to reduce the initially formed alkalinity. Boric acid is typically used, but any acidity compatible with the composition would do the trick.

[50AE]

Can I use citric acid instead of boric then ?

[Niter]

Yes and no, but to be very sure, better not.

 

Citric acid usually comes as a monohydrate. So if you introduce citric acid, you introduce a bit of moisture to your composition. If there's a more hygroscopic salt in there it might steal the moisture and becomes hydrated itself, which might give trouble.

 

On the safe side, you might want to use Ascorbic acid, which doesn't suffer this disadvantage. For Nitrate/Aluminium compositions Ascorbic acid would probably be a good choice, but remember that it, unlike boric acid, is a reducer.

 

If it ain't broken, don't fix it. If you can use boric acid, do so. If you don't have boric acid then in a nitrate/aluminium mix adding ascorbic acid is much better than adding nothing at all.

[50AE]

Mine is a monohydrate. Thanks for the info.

[jadesource]

You can get boric acid at the doller store cheap they sell it as roach killer. I use it all the time works great also if you make a 4% gum arabic solution it makes a great binder and it is also acidic which works just like the boric acid does.

[carbonhalo]

Roach/ant killer here is Borax (Sodium tetraborate)

[Mumbles]

I've seen a few different products around. Generally if you look at a couple of stores you might be able to find something that is 100% boric acid. I started getting it from pottery supply shops, but the last OTC bottle I had was 99+% boric acid with some roach pheromones in it. I was worried it was going to start a roach infestation in my shop.