Intro: Making German Dark Aluminum Powder From Foil
This is an instructional for manufacturing your own homemade German Dark Aluminum powder. Homemade aluminum powder may not be as good as Eckart aluminum powder; however it is practical for use in pyrotechnics. German Dark Aluminum powder is a particular aluminum powder that has charcoal added to it to prevent oxidation while milling. Not only does charcoal prevent aluminum from oxidizing into aluminum oxide as it mills, it also makes the aluminum powder more reactive bringing about an acceptable product for pyrotechnics. German Dark Aluminum powder is a key ingredient in many pyrotechnic compositions especially in low grade explosive compositions such as flash powder. German Dark Aluminum powder can range from a coarse grade such as 100 mesh to a super fine grade such as 7000 mesh. The finer the grade of the aluminum, the more reactive it is.
Willow charcoal (1 tablespoon)
Ball mill (or rock tumbler)
Measuring tape or ruler
Scissors (or your hands)
Step 1: Measuring the Aluminum Foil
First, what you’ll need to do is use your scissors to cut ten 18 inch long pieces of foil.
Step 2: Shredding the Aluminum Foil
Next you need to shred the sheets of foil in a paper shredder. If you’re not able to access a paper shredder then tear the sheets of foil into small pieces as done in the picture.
Step 3: Adding the Charcoal
After shredding your Al foil, fill the barrel 3/4th of the way with you foil shreds and add 50-60 1/2” chrome plated steel balls. Next use a measuring spoon to measure 1 tbsp of willow charcoal. The charcoal needs to be in a powder form for measuring, so you can use a mortar and pestle to grind up your charcoal. The ball mill will grind the charcoal into a much finer powder along with the Al. You’re free to use a different charcoal other than willow charcoal so long as that type of charcoal burns well and does not interfere with the burning of the aluminum; gardening charcoal is a desirable charcoal to use.
Step 4: Ball Milling the Aluminum Shreds
Now that you have included your charcoal it’s time to ball mill for approximately 20-25 minutes. You need to add the foil shreds portion by portion because the shreds are fluffy and adding all of them at once including the media would leave no room in the chamber for crushing. So after 20-25 min of milling, your first portion of Al shreds should be flattened. Include more Al shreds and repeat the process until all of the shreds are in the barrel. This process at the beginning of milling doesn’t take very long.
Step 5: Milling Results
The top picture was taken one night after milling and the others were taken two nights apart.
Step 6: Final Product
Two nights later I have my final product. The mesh size is unknown but it took eleven nights of continuous ball milling to transform the aluminum foil into a fine powder. It’s optional to keep ball milling to obtain a finer powder than as pictured, however eleven days or nights is the goal for an adequate German Dark Al powder.
Step 7: Warning:
It is very important to expose the aluminum to fresh oxygen every 5-8 hours. If you fail to do so your aluminum powder may spontaneously ignite in air after you open up the barrel. This happens because the aluminum slowly consumes all of the available oxygen in the grinding chamber, so if you don't periodically open the container through the grinding process the very fine powder may spontaneously ignite in the sudden abundance of oxygen. Unlike my German Dark Al, professional grade German Dark Al (such as Eckart) has a stearin coating that evidently prevents ignition by air. When aluminum powder is moistened with water it spontaneously heats. If your product were to ever flare up DO NOT use water to extinguish the fire for it will react even worse. Smother it with a suitable dry powder such as sodium bicarbonate (NaHCO3, baking soda). The solid coats the fuel and smothers the fire.
I myself have had an accident with a different pyrophoric metal. I ordered 100 mesh magnesium powder and ball milled 60g of it for a faster burn rate for when I mix it with one of my oxidizers. When I milled the Mg for an extended period of time without disturbing it, it flared up when I finally did open up the barrel to see how it was doing. The powder didn’t flare up violently, and thank God it didn’t because I was in my room at the time, so I was able to see that the Mg powder was a darker color and appeared to be a finer mesh. I knew not to put the fire out with water so I dumped my product and media out on the grass in my backyard. As I emptied the barrel, the Mg powder REALLY flared up into an intense blaze due to the magnesium having already flared up and the sudden abundance of oxygen. I singed the hairs on my right arm, scorched my steel media, and freighted my grandmother sitting on the bench. I would have used sodium bicarbonate to extinguish the fire but I didn't have any readily available at the time. However, the hairs on my right arm, steel media, and grandmother all eventually recovered from the incident. Later, I tried ball milling the magnesium again except this time I checked on my powder every 5-8 hours exposing it to fresh oxygen. My final product resulted in a fine Mg powder.
Step 8: Testing the Final Product
I performed two different flash tests, both with the same ratio, oxidizer, and catalyst (70% potassium perchlorate/30% German Dark Al) except the flash test in the top picture has Eckart German Dark Al and the flash test in the next picture has homemade German Dark Al.
The flash powder test with the Eckart Al had a faster burn rate than my homemade Al. It gave a clean thump rather than a poof with lots of sparks like the flash powder containing my homemade Al. Both flash powders were very fast except one was faster than the other and gave off far less sparks. Both flash powders are excellent charges for deafening salutes or flash bangers or celebration sticks or flashlight crackers or whatever the heck you want to call them.
Step 9: Note:
-I advise that you wear safety glasses while working with aluminum powder.
-It’s possible to use high-alumina for media rather than steel. It should result in a faster milling time.
-For clean up I recommend that you use a towel, some cleanser, and a little water to clean out the barrel. You need the coarse detergent to rid the fine aluminum powder coat from inside the chamber. You do not want any remaining Al particles to contaminate your next element or compound that you may be ball milling.
-I’ve done some research on lead media and came across a thread on bombshock.com explaining why lead balls should not be used for crushing metal or any hard chemical. Apparently if the content in your chamber is not friable the lead will contaminate your product during the milling process. Unlike steel, lead is a soft yet heavy metal and if you try to grind a non friable substance then it is likely that your final product will have a darker tint due to lead particles being chipped off the media and milled into a fine dust. The fine lead dust is also very toxic and is a considerable hazard to your health.
-I recommend that you buy Lloyd E. Sponenburgh's booklet “Ball Milling Theory and Practice for the Amateur Pyrotechnician” if possible. It’s loaded with helpful information and even has thorough instructions on constructing your own ball mill.