Flash Powder
Background
Flash powder is used in many pyrotechnical, magic, and
theatrical demonstrations; should be used with extreme care
and be avoided if the same effect can be achieved by some
other means. It will detonate if confined by even a few
layers of newspaper and is hazardous due to its sensitivity
to friction, static and heat and becomes a lot more sensitive
when wet.
Having said that, flash powder is probably one of the most
widely used compositions in the pyrotechnic industry. It
is used to produce dazzling visual effects, loud cracks
and bangs, as a bursting charge and as an ignition charge
for other compositions.
Composition
There is a huge number of possible compositions, all of
which will produce a slightly different effect and have
different characteristics. Below is just some of the possibilities.
These are here as examples only, you should not carry these
out unless you have accurate information about the safety
of each.
| Ingredient |
Formula |
Standard |
US Army |
Nitrate |
Green |
| potassium perchlorate |
KClO4 |
70% |
64% |
|
43% |
| aluminium powder |
Al |
30% |
|
20% |
|
| aluminium dark flake |
Al |
|
22.5% |
|
|
| aluminium dark pyro |
|
|
|
|
36% |
| sulfur |
S |
|
10% |
30% |
|
| antimony sulfide |
Sb2S3 |
|
3.5% |
|
|
| potassium nitrate |
KNO3 |
|
|
50% |
|
| barium nitrate |
Ba(NO3)2 |
|
|
|
21% |
|
As you can see, there is a huge amount of room for variation.
Here is some information on varying the composition of
flash powder.
Oxidiser/Fuel Ratios
It is possible to have as much as 75% oxidizer all the
way down to 38%. Basically, the more oxidizer: the faster
it will burn and the less light given off; the more aluminium:
the slower it will burn and the more light it will give
off. A good rule of thumb is to have proportions falling
within these specifications: 40-70% oxidizer, 20-40% aluminum,
20-30% sulfur or antimony trisulfide (if you are going to
use it at all).Just to give you an idea of the variation
which is possible, I have seen successful flash powder made
from magnesium filings (that's filings not powder) and potassium
permanganate.
Magnesium
It is possible to use magnesium instead of aluminium, however
you should take care when using magnesium as it can cause
the composition to spontaneously explode when stored (you
should avoid storing flash powder in the first place).
Sulfur/Antimony Trisulfide
These two chemicals are added for two reasons:
As an ignition promoter, that is, to lower the ignition
temperature of the composition
To deepen the noise which is made from a crack to a boom.
This phenomenon is not fully understood.
You should not use potassium chlorate (or any chlorates)
when using sulfur to a composition as the sensitivity is
increased by up to ten times.
Oxidizers
The most common oxidizers are potassium perchlorate and
potassium chlorate. It is advised that you use the perchlorate
rather than the chlorate as it is much safer, and the noise
from a composition containing chlorate is at best only slightly
better than that from a composition containing perchlorate.
Equations
The equation of flash powder will vary greatly depending
on the composition. Basically there will be aluminium oxide,
some chlorine dioxide and maybe some potassium chloride.
