Understanding Metal Powder Particle
Size and Shape
Fireworks makers: Right now, as you look at the metal powder options on the Skylighter chemicals list, you are probably asking yourself: "what is the difference between spherical and spheroidal metal powders?" Or, for that matter, "what does it matter that a particle shape is granular, or flake, or atomized?"
Particle Shapes 101:
Keep in mind that particle shape is not the only factor influencing how a metal powder will perform in a firework composition. The particle size of the metal powder, whether it is coated or not, and other factors are just as important as particle shape.
Particle shape matters mostly because of its impact on pyrotechnic composition reactivity. Think about it. Which is easier to light, a 3 x 3-inch piece of paper or a 3 x 3-inch piece of plywood? Chemically theyíre almost the same thing. But the little, bitty edge of the paper is a lot easier and faster to light than the edge of the plywood. And thatís what separates the flake particle shape from the atomized-ease of ignition.
No matter what fireworks device you're trying to make, your success will depend in part on using the right metal powder particle shape. So pay careful attention to the type of metal powder prescribed in your composition. If particle shape or size is not specified, and you are new to making fireworks, then itís a good idea to ask someone knowledgeable. Using the wrong one might be a waste of time and money, or could even be dangerous.
The following photographs show the most common metal powder particle shapes used in making fireworks. The scale on the bottom of each photograph shows a 200-micron long scale for your reference (that means 200 millionths of a meter, or a little bigger than a grain of fine, salt.
Flake-shaped aluminum metal powder particles (magnified 100 times)
Notice how "edgy" the metal powder flakes are. These thin edges heat up and ignite faster than the rest of the metal powder particle. Flakes, because of this edginess and the fact that they offer the greatest surface area, are generally the most reactive metal powder particle shape when used in a pyrotechnic composition.
Granular-shaped ferro-aluminum metal powder particles (magnified 100 times)
Granular (ground) metal powder particles have a characteristic, gravel-like particle shape. Like flakes, they have a lot of sharp edges, too. But they do not offer as much surface area, and so will not be quite as reactive as flake metal powders.
Atomized metal powder particles come in two basic particle shapes: those that are almost perfectly round called spherical, and those that have irregular, rounded shapes, called spheroidal.
Atomized, spheroidal aluminum metal powder particles (magnified 200 times)
Notice that spheroidal metal powder particles also have "edges," those irregularly shaped extensions you see in the aluminum photograph above. But because they are rounded, they are not as reactive as the flake and granular metal powders.
Atomized, spherical titanium metal powder (magnified 100 times)
Atomized, spherical aluminum metal powder (magnified 500 times)
Spherical-shaped metal powder particles range from being perfectly round, shown in the titanium photo above to almost-round, as shown with the aluminum particles. These are the least reactive particle shapes of all, with very few, if any edges to take fire.
So, the bottom line is that all metal powders are not created equal. Whenever you are creating a new pyrotechnic composition, choosing the right metal powder fuelís particle shape is critical. And if one particle shape does not work in a given formula, consider which particle shape might be the best for your particular application. If in doubt, give us a call. We can nearly always steer you to the right one.
If you have any doubt what particle shape your metal powder is, you can check it yourself. Radio Shack sells inexpensive high-powered magnifiers. We use two, one with 30-power magnification, the other with 100-power.
For more information on metal powders, their particle shapes and sizes check out our article "How Particle Size and Shape is Defined."
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