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a safer flash powder formula


r1dermon
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normally, in the industry in which i work (fireworks manufacturing), we're using a mixture of Al, antimony, a very small percentage of sulfur, and a large portion of KClO4 for our salute composition.

 

recently, someone posted a video online about something named "blue" aluminum. as many of you probably know, flash powder is incredibly dangerous to mix and to be around in general...and in the quantities we mix (up to 40lbs through a screen at a time), the results of an accidental reaction due to static or friction, or what have you, would be absolutely catastrophic. well, this "blue" aluminum appears to create the same results as standard flash powder when confined to a container, (plugged tube, or pasted shell...etc...), but in the open, it is practically inflammable. there's barely an indication of any small reaction occuring under the burning presence of a torch.

 

my question is, i've recently discovered that formulas have been created (and patented) which utilize Pentaerythritol as the main fuel, supplemented by a bit of Al, with the same KClO4 as the oxidiser. i've also seen compositions using terephthalic acid as the major fuel source in a binary composition which creates the same results.

 

my major questions are, WHY. why do these compounds react violently when under pressure, but practically not at all, when unconfined, even when mixed with a high powered oxidiser. my second question is, the reaction clearly accelerates exponentially as more pressure is available, so with that in mind, does that mean eventually this compound would produce the same brisance that an HE compound would produce? and lastly, assuming the reaction can be controlled (as far as pressure is concerned), i assume it would be possible to control the tone of the actual "boom" it produces, simply by changing tensile strength characteristics in the vehicle utilized for containment (the mortar shell).

 

thanks for any info.

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normally, in the industry in which i work (fireworks manufacturing), we're using a mixture of Al, antimony, a very small percentage of sulfur, and a large portion of KClO4 for our salute composition.

 

recently, someone posted a video online about something named "blue" aluminum. as many of you probably know, flash powder is incredibly dangerous to mix and to be around in general...and in the quantities we mix (up to 40lbs through a screen at a time), the results of an accidental reaction due to static or friction, or what have you, would be absolutely catastrophic. well, this "blue" aluminum appears to create the same results as standard flash powder when confined to a container, (plugged tube, or pasted shell...etc...), but in the open, it is practically inflammable. there's barely an indication of any small reaction occuring under the burning presence of a torch.

 

my question is, i've recently discovered that formulas have been created (and patented) which utilize Pentaerythritol as the main fuel, supplemented by a bit of Al, with the same KClO4 as the oxidiser. i've also seen compositions using terephthalic acid as the major fuel source in a binary composition which creates the same results.

 

my major questions are, WHY. why do these compounds react violently when under pressure, but practically not at all, when unconfined, even when mixed with a high powered oxidiser. my second question is, the reaction clearly accelerates exponentially as more pressure is available, so with that in mind, does that mean eventually this compound would produce the same brisance that an HE compound would produce? and lastly, assuming the reaction can be controlled (as far as pressure is concerned), i assume it would be possible to control the tone of the actual "boom" it produces, simply by changing tensile strength characteristics in the vehicle utilized for containment (the mortar shell).

 

thanks for any info.

 

This not a mechanistic answer, so may not satisfy you.

 

Solid propellants, like flash powder, gun propellants and solid rocket fuels are normallly modeled empirically using the burn rate equation:

 

[math]R = cP^n[/math]

 

where [math] R[/math] is linear burn rate, [math] c [/math] is a constant [math]P[/math] is pressure and [math]n[/math] is known as the "pressure exponent" or just "exponent".

 

This equation is approximate, no more, and the "constants" are only approximately constant over a limited regime. In particular, when burn rate vs pressure is plotted on a log-log scale to deternime the exponent, the curve sometimes kinks exhibiting what is called a "slope break".

 

Now, the combustion is stable when n<1, but when n>1 pressure, and burn rate, increase unstably. Gun powders, for instance typically have exponents >1 and pressure s limited by the very short time involved. Rocket propellants have a slope of, say 0.6, and burn stably. Your flash powder probably has a high exponent.

 

One possibility with "blue aluminum" is an oxide coat on the particles that breaks under high pressure, and likely under high dP/dt, exposing more actual fuel to the oxidizer. This is purely speculative since I don't know what "blue aluminum" is. I do know that the morphology of aluminum particles has a significant effect on burn rate.

 

Before using that stuff, some closed bomb combustion tests on small amounts of mixed flash powder would be in order. Also in order would be the standard impact, ABL friction and ESD sensitivity tests.

 

 

KIDS: DO NOT TRY THIS AT HOME. This is dangeerous stuff. Professionals only.

 

This web site is supposed to be the source for information on blue aluminum. I found some discussion in the forum, but little "meat". My impression from the video was of a group with little safety discipline.

Edited by DrRocket
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