Re: Burn rate of ammonium perchlorate based mixtures.

On Mar 5, 11:36 am, mikes2653 <mikes2...@xxxxxxxxxx> wrote:

They need to be distinguished because a heat of decomposition can be
negative (as Conkling indicates for potassium or barium chlorate) but
initiation energy can still be positive (if it was not, the compound
could not exist under standard conditions). Initiation energy is a
matter of concern only at the start of the reaction. Heat of
decomposition is relevant over the entire course of the reaction.
Whether a redox reaction will be pyrotechnic or not is dependent upon
whether the sum [(heat of decomposition of oxidizer in Kcal/mole X
number of moles of oxidizer) + (heat of combustion of fuel in Kcal/
mole X number of moles of fuel)] is positive or not. This can be
helpful in predicting the reaction rate, but does not tell the whole
story.

Yep. Would it be accurate to say that this equation is primarily
useful in evaluating the ability of a fuel/oxidizer mixture to engage
in a stable pyrotechnic reaction?


Something as simple as the particle size of the ingredients may
be more influential. It tells us relatively little about ease of
ignition. This is, as I earlier noted, largely affected by such things
as the melting points of the composition's ingredients.

Yes. Particle size and melting points of fuels and oxidizers tell us
much more about ease of ignition than do thermodynamic factors.
Particle size can exert great influence on speed of burning as well.

It seems to me that one thermodynamic factor, that being the heat of
decomposition of oxidizers, is fairly useful in predicting the
sensitivity of a pyrotechnic mixture to mechanical action. Is this a
correct observation?

As for making the simple complicated - do you want to make fireworks
or are you just interested in theory? If it's the former, let me
suggest on the basis of long experience that a lot of the science of
pyrotechnics is rather remote from everyday application, and will not
repay in practical results the effort required to master it. I have
run into quite a few people over the years who have been distracted by
playing with the chemistry of formulae to the point that they have
never learnt how to make reliably functioning shells, rockets, etc. It
is not just a question of 'whatever turns your crank,' unless for you
this is purely an armchair pursuit and you do not intend to make any
actual fireworks. Mastering the craftsmanship required is necessary to
safety; mastering the science is not.  It is easily possible to adjust
compositions to give the results you want without extensive
thermodynamic calculations.

My pursuit of pyrotechnic knowledge is at this point an "armchair
pursuit." I used to make fireworks, (I was quite sucessful in making
small skyrockets that carried "payloads" of cut stars, both color and
charcoal. I was most sucessful with small rockets, but I also have
made decent fountains, wheels, and small starmines). At this point in
time, I am just interested in theory.

.

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