FLASH POWDER
by Infallible Prodigy

Introduction:

Flash powders, generally speaking, include any oxidiser/metal fuel often with the addition of other chemicals to modify burn rate and sensitivity. Standard flash powder is a mix of 70% KClO4 (Potassium Perchlorate) / 30% Al (Alumnium Powder - 600 mesh). Flash finds a use in many consumer fireworks for producing a loud report as well as a salute filler for amature pyrotechnists.

Safety:

First, I would just like to give you a sense of the power of flash powder. 50 grams or less on a flat surface, completely unconfined, when ignited will produce a very audible explosion instead of just a flash. It is an even smaller amount for Magnesium based flashes. A few grams in an open ended cardboard tube (walls about half a centermetre thick) will shatter the tube and make a very, very loud bang. 3 grams contained in an M-80 type casing will remove several fingers and disfigure a hand if ignited while being held. So, be careful, and only attemp making it if you are thouroughly experienced with slower burning powders such and Black Powder.

Flash powders can be very sensitive compositions, depending on the mesh (particle size) of the metal powder, the intimacy of the mix and the addition of other chemicals. Good flash can be initiated by a single spark, friction, heat, static discharge and shock. Many accidents have resulted from people not taking it seriously, and treating it like it is harmless. But that is not to say that it is unusable because of its sensitivity, as long as it is treated with respect, it is unlikely that an accident will occur.

Many flash compositions will call for the addition of Sulfur or Antimony Sulfide to be added for lowered ignition temperatures and faster flame propagation. But this also increases the sensitivity of it. Sulfur has a low caloric output, so it requires only a small amount of energy (whether that be heat or kinetic) to be ignited when mixed with an oxidiser.

But, in other instances, substances such as stearin will be included in the formula (coating the metal powder). Stearin will de-semsitize the mixture to some degree by providing a barrier between the oxidiser and the metal powder, lowering the chance of spontaneous ignition and increasing the amount of energy required to ignite the mixture

The sensitivity of the flash powder will be determined by the following things:

The oxidiser - The oxidiser plays a large role in whether the composition will be sensitive or less so. Unstable oxidisers (Oxidisers that decompose from only a small input of energy, or have incompatabilities with other substances) such as KClO3 (Potassium Chlorate) and KMnO4 (Potassium Permanganate) will make faster and more powerful flash mixtures than more stable oxidisers, but will be prone to accidental ignition, whereas more stable oxidisers will provide slower burning and weaker flash powders, but more stable.

The mesh (particle size - The higher the number, the finer the particles) of the ingredients - A general rule in pyrotechnics, is that the finer the ingredients, the faster the reaction, but also the more sensitive the mixture. Take, for example a block of iron and a pile of iron powder, both left out in the rain and the environment. After a while, if you were to come back to the two, you would see that while on the iron block, only the very surface has corroded, the powder has corroded completely. This reaction, like pyrotechnic compositions, relies upon surface area. The block only has the surface of the very outside of itself, while the powder has many times the surface area, due to the division of the particles which creates more area. So, using 600 mesh Alumnium powder over 400 mesh will be the difference between good, and excellent flash, but also safe (as possible) and unstable flash.

The shape of the metal fuel - Each particle of metal powder will have a certain shape, and this plays a part in how sensitive the flash is. Flake alumnium is the fastest burning and least stable, because of its huge surface area. Granulated powder works, but not as well and spherical powders work poorly because of a small surface area in proportion to the mass of the particle. Again, I am going to ask you to take an example. Take three pieces of paper - Scrunch one up tightly into a ball, as tight as possible. Crunch the second one up, and scrunch it into a looser ball. Leave the third as a sheet. Now take a flame to the edge to each piece of paper. The flat (flake) un scrunched page will catch fire easiest, followed by the loosely scrunched ball, and then after a long while, the tight ball will light. This example applies for metal powders also. Flake aluminium will produce very powerful and fast flash while spherical will produce slow, bright burning weak flash.

The reactivity of the metal fuel - Some metals ie Magnesium, are more rective than metals such as zinc, iron and alumnium, and therefore will produce more powerful and more sensitive flash. To work at the same level as flash made from a reactive metal, the less reactive metal will have to be more finely divided to produce a faster reaction. Because they are more reactive, they will also take a lot less energy to ignite, making a more sensitive mix.

The addition of other chemicals - Adding sulfur will produce faster, but more sensitive flash.

Some general rules for safely handling flash:

NEVER grind any flash mixture! Always mix via the diaper method (explained below)

Only add accellerants if the metal powder is under about 500 mesh, or cannot be ignited by flame or fuse.

Never mix more than 10 grams of flash if you are inexperienced, and even if you are experienced, no more than 50 grams.

Never use flash in a metal casing. There is no need for metal, paper casings work perfectly. Metal just increases the chance of being injured.

The hotter burning the mixture, the better it will work in a salute.

Wear a dust mask, safety glasses and thick gloves! I know it may sound stupid, but fine aluminium powder can be picked up by the wind and inhaled, which your lungs will not appreciate. Glasses and gloves are self explainatory.

Try to wear cotton clothing, and if possible use static guard (spray) before mixing.

NEVER, and I mean NEVER mix Chlorates with Sulfur, Sulfides or phosphorus. It will lead to a very unstable mixture, that will most likely spontaneously ignite.

Finding the pre-cursors:

~ Oxidisers ~

KNO3 - Potassium Nitrate - Can be found as a fertiliser, at chemists, as a stump remover (grants brand) as a soot remover for chimneys, to prevent you from getting an erection :) . It goes under the names of Potassium Nitrate, Pot. Nitrate, Saltpeter and K-Niter.

KClO3 - Potassium Chlorate - Can only really be found at chemical suppliers these days, and can be made through a few methods (do a google search!). KClO3 is a very restricted chemical and doesn't find much use outside of pyrotechnics.

KClO4 - Potassium Perchlorate - Even harder to make and find than KClO3. Also can only really be found at chemical suppliers, but can be made through a few, very, expensive methods.

KMnO4 - Potassium Permanganate - Available from chemists, agricultural stores, sears and pet stores. Amongst other things it is used as a water purifier (If memory serves) and goes by the name of Condys Crystals.

~ Metal Powders ~

Al - Aluminium - Can be found in a variety of places. If you reside in the US, it can be purchased through chemical suppliers and EBay. Also found in metallic paints, boat paint, has applications in fibreglass and can be made through a few methods. 600 mesh is the best for flash, and below 325 mesh will not work.

Mg - Magnesium - Chemical suppliers, but most likely you will have to make it by sanding down solid magnesium, which is found as emergancy fire starters at camping stores as well as sacrificial anodes.

Zn - Zinc - EBay, chemical suppliers and can be made through a few methods. Can be found as galvanising paint and galvanising spray paints.

~ Additives ~

S - Sulfur - Can be found at most gardening stores, some chemists and hardware stores.

Pyrotechnic Suppliers:

www.pyrocentral.com - Owned by a member of the backyard ballistics forum - Order there! http://www.skylighter.com - Probably the biggest pyro store http://www.firefox-fx.com/ www.pyrotek.org http://www.dawntreader.net/info.html http://www.wolterpyrotools.com/index.html http://www.pyrosupplies.com/ http://www.pyro-pro.com/ http://www.lortone.com/ http://www.unitednuclear.com http://www.cannonfuse.com http://www.discountpyro.com/index

There are more, but I will leave it up to you to find them :)

Mixing up flash:

Because of the sensitivity of flash powders, a wise pyrotechnist will always use the diaper method (explained below) to mix his flash, so as to prevent as little friction and shock as possible.

The Diaper Method - Get a large sheet of newspaper and spread it out on a flat surface outside. Now, weigh out your flash chemicals and pour each ingredient through a ~40 mesh seive (to remove any lumps) onto the middle of the paper. Now gently lift up each corner of the paper, lifting the chemicals, and causing them to fall back over themselves. Continue this until the mixture is of a uniform grey consistancy. Your flash is no ready for use. That is all it takes to make good flash powder - NO grinding neccesary. It is best to spray yourself with static guard before mixing, and to use only tools that will not spark or generate static. Also, if possible, have yourself grounded.

Flash Compostions:

All compositions from Wouter vissers collection of pyrotechnic compostions - I havent asked for permission, but I hope I would get it if I did.

Various Perchlorate Based Flashes:

Potassium Perchlorate.............................50
Aluminum..........................................23
Sulfur............................................27

Potassium Perchlorate.............................70
Aluminum (dark pyro - 600 mesh flake).............30

Potassium Perchlorate.............................65...70%
Aluminum...................................rest (up to 100% Higher % Al results in stronger flash)

Potassium Perchlorate.............................3
Aluminum, 400 mesh................................3
Sulfur............................................1

Potassium Perchlorate.............................80
Aluminum..........................................27
Sulfur............................................3

Potassium Perchlorate.............................64
Aluminum..........................................23
Sulfur............................................13

Potassium Perchlorate.............................72
Aluminum..........................................28

Various Nitrate Based Flashes:

Potassium Nitrate.................................50
Sulfur............................................30
Aluminum..........................................20

Barium Nitrate....................................4
Alumium (fine mesh)...............................2
Sulfur............................................1

Potassium nitrate.................................3
Potassium perchlorate.............................3
Dark aluminum (USB 809)...........................3
Barium nitrate....................................1
Antimony sulfide (CN).............................1
Sulfur............................................1
Dextrin...........................................1/2

Permanganate Based Flashes:

Potassium Permanganate............................12
Aluminum..........................................7
Sulfur............................................10

Potassium Permanganate............................3
Alumnium..........................................2
Sulfur............................................1

For more flash compositions visit http://come.to/pfp - the PFP database.