Miscellaneous: Flash powder

Flash powder is a pyrotechnic composition which is composed of an oxidizer and a metallic fuel. The deflagration of this composition is very fast and is often accompanied by a loud report, especially when it is compressed. Nowadays, it is often used in fireworks. Historically, it was used to create flashes in photography. Flash powder is also used in the domain of military technology, because of its property to create a great amount of noise and light (infrared radiation as well). This is also useful in the production of missile decoy flares which are used to deflect missiles that scan the infrared spectrum in search for a target.

There are many different flash powder compositions, which are based on different oxidizers. The most commonly used oxidizers are potassium perchlorate, potassium chlorate, potassium permanganate and potassium nitrate. Since there are many fuels that the mentioned oxidizers can be mixed with, it is clear that there are many different formulas for the production of these compositions. Here we will mention a few chosen compositions, one per each of the mentioned oxidizers:

Formula 1: 70% potassium perchlorate, 30% aluminium or magnesium powder

Formula 2: 67% potassium chlorate, 33% aluminium or magnesium powder

Formula 3: 42% potassium permanganate, 24% aluminium or magnesium powder, 34% sulphur powder

Formula 4: 50% potassium nitrate, 30% sulphur powder, 20% aluminium or magnesium powder

When using the chlorate formula, one must have in mind the general chlorate rule - one should avoid getting chlorates in contact with sulphur, sulphides and sulphates at all times. When using compositions based on potassium permanganate, one should make sure that such compositions don't get in contact with moisture, as it can make permanganate based compositions unstable. Bacuse of that, it is best to keep them in dry and tightly sealed containers. With a few rare exceptions (involving KClO₄ based compositions), most of the flash powder compositions show some kind of sensitivity, and many of them are sensitive even to friction and shock. Because of that, one must be very careful with compositions of this type. Also, production of larger amounts of flash compositions is not recommended.

To demonstrate a simple flash powder, we used the formula 3. In case of the mentioned formula, one needs to prepare potassium permanganate, aluminium (or magnesium), powdered sulphur, a scale, grinder and a mortar and pestle.

Although potassium permanganate is not even close to the sensitivty of potassium chlorate, one should powder KMnO₄ by using a mortar and pestle anyway. Since we didn't have a classic mortar and pestle at the time, we improvised a bit. Sulphur and aluminium were separately powdered by using an electrical grinder.

After the grinding, the needed mass of every substance was measured on a scale, according to the percentages given by the formula 3. The substances were then added to a smaller container in which they were first gently mixed by swaying the container. Aftar that, the mixture is added to a transparent plastic bag. This bag is then closed, and the composition is mixed by slow and gentle hand motion. After a short period of time, when the desired homogeneity is reached, the pyrotechnic composition is finished.

As we already mentioned, flash powder should not be made in larger amounts. Flash compositions must be stored safely, and in the case of permanganate based compositions, they should be stored in a dry place and in a tightly sealed container. Concerning the pyrotechnic properties, they mostly depend on the level of fragmentation of component particles in the composition.

On the picture above, one can see the result of ignition of a small amount of flash powder on the tip of a knife.