Milling Mg powder

[JTO]

I have half a kilo of Mg shavings, which I turned into small chips in a blender. I am going to make it into powder in a ball mill with steel balls. Because I have read about its pyrophoricity, I am going to have the mill running outdoors. Also, the lid of my mill has a 10mm hole in it which I normally cover with tape, I think I can easily aereate it by opening the hole for a couple of hours at a time, perhaps turning the mill a little once in a while. I might even leave the hole completely open, and tilt the mill, which is rather long, so that the hole end is elevated, allowing continuous venting. My question is, I read that one can passivate Mg powder with linseed oil. How does one do that? Would it be possible to add the linseed oil to the mill during the milling already, instead of after the milling is done? How much oil? Are there other substances that one could use for passivation?

[SharkWhisperer]

Probably not a great idea to try milling Mg with hobbyist equipment and no prior industry experience. Commercial Mg powder is manufactured under stringently controlled atmospheric and temperature conditions that you could not hope to reproduce. You're making guesses about ventilation holes and guessing when milling reactive and pyrophoric powders is just asking for problems. Even outside, you eventually need to approach that mill. And eventually you need to open that jar. A half kilo of Mg powder burning could instantly cause some very very serious damage, even from a few meters away. We all take chances with energetic materials, but I don't think you're going to find too many people on this site that mill their own Mg, if any, and the idea probably won't be met with encouragement. For good reason.

 

IF you need pure Mg powders, then just buy it. $15/pound or so. Atomized, granular, or flake. Which physical form of Mg do you need by the way? Which form would milling produce? They don't behave identically. That said, there are really only a very few advanced fireworking applications where Mg cannot effectively be replaced with much safer magnalium, which is even cheaper.

 

Regarding passivation, there's plenty of threads here on the topic and a search function that works well.

 

Save your Mg chips for firestarters.

[JTO]

Thanks, SharkWhisperer! What I am going to do is that, wearing a face shield and welder's gloves, I am going to take a sample of a gram or few of the contents through the vent hole every once in a while, without opening the mill. Then I am going to test its reactivity using instructions I found at passfire.com. Only after I've ascertained that it is safe to open, I am going to do so. The Mg cannot burn inside the mill because if it did, it would almost instantly become deprived of oxygen. Now that I think about it, I might even vacate the mill through the vent hole a small quantity at a time, which would certainly be safe. Also I am probably going to leave it pretty coarse, or alternatively remove it in parts to get several different mesh sizes. I am certain I can pull this off safely, the worst thing that could happen is that my mill gets destroyed. My main issue is with passivation with linseed oil. I do not know whether it makes any difference whether one uses pressed oil or the boiled variety. Also, I do not know whether it can be added in small quantities during the milling process, or whether it needs to be added to the finished product. This information I am unable to find in any of the threads.

 

Probably not a great idea to try milling Mg with hobbyist equipment and no prior industry experience. Commercial Mg powder is manufactured under stringently controlled atmospheric and temperature conditions that you could not hope to reproduce. You're making guesses about ventilation holes and guessing when milling reactive and pyrophoric powders is just asking for problems. Even outside, you eventually need to approach that mill. And eventually you need to open that jar. A half kilo of Mg powder burning could instantly cause some very very serious damage, even from a few meters away. We all take chances with energetic materials, but I don't think you're going to find too many people on this site that mill their own Mg, if any, and the idea probably won't be met with encouragement. For good reason.

 

IF you need pure Mg powders, then just buy it. $15/pound or so. Atomized, granular, or flake. Which physical form of Mg do you need by the way? Which form would milling produce? They don't behave identically. That said, there are really only a very few advanced fireworking applications where Mg cannot effectively be replaced with much safer magnalium, which is even cheaper.

 

Regarding passivation, there's plenty of threads here on the topic and a search function that works well.

 

Save your Mg chips for firestarters.

Edited August 3, 2021 by JTO

[SharkWhisperer]

Thanks, SharkWhisperer! What I am going to do is that, wearing a face shield and welder's gloves, I am going to take a sample of a gram or few of the contents through the vent hole every once in a while, without opening the mill. Then I am going to test its reactivity using instructions I found at passfire.com. Only after I've ascertained that it is safe to open, I am going to do so. The Mg cannot burn inside the mill because if it did, it would almost instantly become deprived of oxygen. Now that I think about it, I might even vacate the mill through the vent hole a small quantity at a time, which would certainly be safe. Also I am probably going to leave it pretty coarse, or alternatively remove it in parts to get several different mesh sizes. I am certain I can pull this off safely, the worst thing that could happen is that my mill gets destroyed. My main issue is with passivation with linseed oil. I do not know whether it makes any difference whether one uses pressed oil or the boiled variety. Also, I do not know whether it can be added in small quantities during the milling process, or whether it needs to be added to the finished product. This information I am unable to find in any of the threads.

 

Gotta look a little harder. Boiled linseed oil. Home Depot/Lowes/Ace/Amazon. Be careful. The risk greatly exceeds the reward.

 

Coating Mg is an obnoxious pain in the ass. Half the reason I have had pounds sitting on a shelf for years untouched. MgAl does 95% of what Mg can do. Safer. And cheaper.

 

Here's some information. This is not to be misconstrued as enthusiasm for your project, because I offer none.

 

https://www.amateurpyro.com/forums/topic/3802-coating-mg/

 

https://www.amateurpyro.com/forums/topic/13957-magnesium-treatment/?hl=%2Bboiled+%2Blinseed&do=findComment&comment=190685

[JTO]

Thanks SharkWhisperer! I read the threads and one of the comments actually contains the pdf file which I referred to earlier, and which explains the reactivity tests using various substances and various coating, and it was actually posted by you, last April. There is a store that sells boiled linseed oil about 2km from where I live. I will post an update here once the project is done, to share my experiences, and also to inform you about whether I had to explain my neighbors that the bright flash they saw was just a meteor that hit my yard.

[FrankRizzo]

JTO - What's your use for this Mg powder you're working on?

[JTO]

There are probably hundreds of recipes at pyrodata.com which call for magnesium powder. I am probably going to make a bunch of different mesh sizes (remove them from the mill at different stages) and experiment making some stars. I might for example make ones with Al (which I already have made in several different mesh sizes, finest of which was initially pyrophoric) and ones with Mg, it would be interesting to compare them. Naturally I am going to ascertain the safety of the Mg powders before I use them. I am probably going to see if small quantities react with various substances, water, kno3, kcl03 at least, as instructed in "Coating Magnesium.pdf" which can be found online. What do you think, an interesting project, no? Do you have any suggestions about passivation with linseed oil? Extremely annoyingly, the pdf says that part 2 of the document will address passivation with linseed oil, but there is no part 2 anywhere to be found :-)

Edited August 3, 2021 by JTO

[SharkWhisperer]

There are probably hundreds of recipes at pyrodata.com which call for magnesium powder. I am probably going to make a bunch of different mesh sizes (remove them from the mill at different stages) and experiment making some stars. I might for example make ones with Al (which I already have made in several different mesh sizes, finest of which was initially pyrophoric) and ones with Mg, it would be interesting to compare them. Naturally I am going to ascertain the safety of the Mg powders before I use them. I am probably going to see if small quantities react with various substances, water, kno3, kcl03 at least, as instructed in "Coating Magnesium.pdf" which can be found online. What do you think, an interesting project, no? Do you have any suggestions about passivation with linseed oil? Extremely annoyingly, the pdf says that part 2 of the document will address passivation with linseed oil, but there is no part 2 anywhere to be found :-)

It's just coating and allowing it to dry. Use 3-5% by weight boiled linseed oil, depending on how fine your Mg is (finer=more surface area to coat). Screen mix several times through the smallest-mesh screen that it will realistically go through without too much force, so it is uniformly distributed--an uncoated surface is a reactive surface. Spread it out and let it dry completely in a safe place under ambient conditions--may take up to a week depending on starting materials, amount/quality of oil, environment, and how thick your pile of comp is. You can mix it around from time-to-time if your pile is thick to try to speed drying. After drying, screen it again to remove any residual clumps. Put it in a jar.

 

Done.

 

Read about linseed oil and how oil-soaked rags are a fire hazard. Read the MSDS. Much modern stuff is not actually boiled flaxseed (linseed) oil, but contains chemicals to enhance drying. Do not dry your Mg in the sun. Do not accelerate drying in a heated drying box. Linseed oil can react exothermically with atmospheric oxygen. It's started many a woodshop/apartment/house afire. Suggest you take a look at this video:

[FrankRizzo]

JTO - Skip the magnesium milling and make a 50/50 magnalium alloy and process that instead. It's much easier to process (extremely friable) and much less likely to have a pyrophoric accident.

[JTO]

FrankRizzo, when you say "make a 50/50 magnalium alloy", do you mean milling Al and Mg together? That would not be actual Magnalium because Magnalium is an alloy, whereas milling the two together makes a powder with two kinds of particles, Al and Mg, right?

JTO - Skip the magnesium milling and make a 50/50 magnalium alloy and process that instead. It's much easier to process (extremely friable) and much less likely to have a pyrophoric accident.

 

[JTO]

Thanks ShartWhisperer, I was aware of the autocombustion potential, but it was still awesome to actually see it in the clip. I have, at home, a fairly massive brick and mortar wood-burning stove, which has an oven compartment in it, closed with a heavy cast iron door. During the winter I used the stove for heating, but this time of year it is idle. I think I am going to do the drying in small batches, say 100g, and spread the powder thinly on, say, a glass plate. Then I am going to put it inside the oven compartment, close the door and remove any combustible materials that might be in the vicinity of the stove. Also I am going to leave the chimney damper open. Also, I did some googling, and it seems that "boiled" linseed oil always contains siccatives (agents which make it dry faster). I guess that is an advantage rather than a drawback, because presumably you want it to cure in a reasonable time. I'll keep you updated of the project :-)

 

It's just coating and allowing it to dry. Use 3-5% by weight boiled linseed oil, depending on how fine your Mg is (finer=more surface area to coat). Screen mix several times through the smallest-mesh screen that it will realistically go through without too much force, so it is uniformly distributed--an uncoated surface is a reactive surface. Spread it out and let it dry completely in a safe place under ambient conditions--may take up to a week depending on starting materials, amount/quality of oil, environment, and how thick your pile of comp is. You can mix it around from time-to-time if your pile is thick to try to speed drying. After drying, screen it again to remove any residual clumps. Put it in a jar.

 

Done.

 

Read about linseed oil and how oil-soaked rags are a fire hazard. Read the MSDS. Much modern stuff is not actually boiled flaxseed (linseed) oil, but contains chemicals to enhance drying. Do not dry your Mg in the sun. Do not accelerate drying in a heated drying box. Linseed oil can react exothermically with atmospheric oxygen. It's started many a woodshop/apartment/house afire. Suggest you take a look at this video:

 

[SharkWhisperer]

FrankRizzo, when you say "make a 50/50 magnalium alloy", do you mean milling Al and Mg together? That would not be actual Magnalium because Magnalium is an alloy, whereas milling the two together makes a powder with two kinds of particles, Al and Mg, right?

 

Yes, I believe he means it is safer for you to experiment with molten metals and magnalium alloy making than to mill magnesium under poorly controlled conditions. I might agree.

 

And yes, milling the two metals together does not make the alloy, just a mixture of powdered metals with Mg reactivity and Al-nitrate-water concerns, so you probably wouldn't have done yourself any favors :+\

 

Though I appreciate the challenge of making your own chems, even powdered Mg, you could be doing so many other fun things with that time. Mg is easy to purchase without the hazard of making it and it's not that expensive https://www.pyrochemsource.com/Chemicals-M_c_18.html . You still need to coat it if you're damp-mixing it with most any oxidizer, though. MgAl has a gadzillion more uses than Mg, can satisfactorily replace Mg in many cases, and is cheaper than Mg if you don't want to turn your back yard into a smelting factory to play with molten metals and make your own. And you don't need to coat MgAl with linseed oil (pia) or dichromate (unnecessary toxicity exposure risk).

 

So....that was another voice conferring concern over your planned Mg milling and suggesting an alternative.

[JTO]

Thanks SharkWhisperer! I live in the EU and it is kind of hard to acquire many materials here. For instance we have an EU directive which bans the sale of "precursors" of explosive to private individuals, and that list contains such crucial chemical as potassium chlorate and perchlorate, and many others. So I am making my own (KClO3), which is fortunately very easy. I am pretty sure that I could order powdered Mg from, say, Amazon.de, but I like to make my stuff by myself whenever possible. The Mg shavings I bought from Aliexpress (China) about 6 months ago.

[FrankRizzo]

JTO - My apologies for the delay. Yes, alloy the two, not simply mix. Tentacles and myself wrote a fairly simple treatise on the process years ago. If you need more info, please read through that document. Magnalium 50/50 alloy is very friable and is easily ball milled to a fine powder. It is slightly less dangerous than the same process with pure magnesium, though does require the utmost care.

[JTO]

An update to my Mg milling process - it has failed :-) Not because of to the safety concerns which you brought up, but because the stuff is impossible to mill. After 20 days of 24/7 milling with steel balls, the powder is still so coarse that I can easily see individual particles. Strangely it is black in color. I made a test with 0.25g of the powder plus 0.75g KClO3 and even lighting it with a propane torch was somewhat difficult. When it started burning, it lasted for about 2s and the fire was just barely self-sustaining. I am going to save it in case I want to experiment with some kind of sparkling compositions (ideas?) but I don't think I'm going to try to continue with the milling.

 

Yes, I believe he means it is safer for you to experiment with molten metals and magnalium alloy making than to mill magnesium under poorly controlled conditions. I might agree.

 

And yes, milling the two metals together does not make the alloy, just a mixture of powdered metals with Mg reactivity and Al-nitrate-water concerns, so you probably wouldn't have done yourself any favors :+\

 

Though I appreciate the challenge of making your own chems, even powdered Mg, you could be doing so many other fun things with that time. Mg is easy to purchase without the hazard of making it and it's not that expensive https://www.pyrochemsource.com/Chemicals-M_c_18.html . You still need to coat it if you're damp-mixing it with most any oxidizer, though. MgAl has a gadzillion more uses than Mg, can satisfactorily replace Mg in many cases, and is cheaper than Mg if you don't want to turn your back yard into a smelting factory to play with molten metals and make your own. And you don't need to coat MgAl with linseed oil (pia) or dichromate (unnecessary toxicity exposure risk).

 

So....that was another voice conferring concern over your planned Mg milling and suggesting an alternative.

 

[SharkWhisperer]

An update to my Mg milling process - it has failed :-) Not because of to the safety concerns which you brought up, but because the stuff is impossible to mill. After 20 days of 24/7 milling with steel balls, the powder is still so coarse that I can easily see individual particles. Strangely it is black in color. I made a test with 0.25g of the powder plus 0.75g KClO3 and even lighting it with a propane torch was somewhat difficult. When it started burning, it lasted for about 2s and the fire was just barely self-sustaining. I am going to save it in case I want to experiment with some kind of sparkling compositions (ideas?) but I don't think I'm going to try to continue with the milling.

 

 

Well, nobody can say you didn't try (even if not recommended). The black could be from lead if you used lead media (even hardened sheds some) or from a rubber coating coming off of your mill jar (depending on your jar type; common in the smaller hobby mills).

 

Personally, I have a lot more things to do with my store-bought MgAl that I could do many of in the 20 days (!!!) that your mill ran. Just would never bother.

 

Depending on the final sizing, which you can determine by screen sorting, your metal is likely good for some fireworking uses. Sort it out and see what you actually have. Then it'll be easy to come up with a plan for it.

[JTO]

Thanks for your reply and suggestion! My mill is made of a stainless steel can originally made for storing spaghetti, about 30cm long and maybe 9cm in diameter, with a couple of kilos of steel balls. Ergo,the black color is unlikely to have come from the mill. I made it at minimum budget, the can is from a charity shop, and as a motor I used the motor, gear, chuck and thyristor speed regulator from an old Makita cordless drill that I bought for 20 euros because the batteries (which I did not need) were dead. I have been successfully milling extremely fine Al powders with it, one batch even got so fine (pyrophoric) that it started spontaneously burning when I opened the can :-) I immediately closed it to deprive it of oxygen, and was able to passivate the powder by exposing it to air in a controlled manner. During this process it was pretty cool to observe that the powder became so hot, on its own, that I got minor blisters on my fingers, as it was developing an oxide layer on the particles, even though nothing visible was happening. Naturally I did this outdoors. I have also been milling softer materials such as charcoal and KClO3 which only take a short time to mill, with good success. The Mg powder is my first unsuccessful milling project.

 

Well, nobody can say you didn't try (even if not recommended). The black could be from lead if you used lead media (even hardened sheds some) or from a rubber coating coming off of your mill jar (depending on your jar type; common in the smaller hobby mills).

 

Personally, I have a lot more things to do with my store-bought MgAl that I could do many of in the 20 days (!!!) that your mill ran. Just would never bother.

 

Depending on the final sizing, which you can determine by screen sorting, your metal is likely good for some fireworking uses. Sort it out and see what you actually have. Then it'll be easy to come up with a plan for it.

 

[SharkWhisperer]

Thanks for your reply and suggestion! My mill is made of a stainless steel can originally made for storing spaghetti, about 30cm long and maybe 9cm in diameter, with a couple of kilos of steel balls. Ergo,the black color is unlikely to have come from the mill. I made it at minimum budget, the can is from a charity shop, and as a motor I used the motor, gear, chuck and thyristor speed regulator from an old Makita cordless drill that I bought for 20 euros because the batteries (which I did not need) were dead. I have been successfully milling extremely fine Al powders with it, one batch even got so fine (pyrophoric) that it started spontaneously burning when I opened the can :-) I immediately closed it to deprive it of oxygen, and was able to passivate the powder by exposing it to air in a controlled manner. During this process it was pretty cool to observe that the powder became so hot, on its own, that I got minor blisters on my fingers, as it was developing an oxide layer on the particles, even though nothing visible was happening. Naturally I did this outdoors. I have also been milling softer materials such as charcoal and KClO3 which only take a short time to mill, with good success. The Mg powder is my first unsuccessful milling project.

 

 

I'm not sure what worries me more: A) you milling Mg in the first place, or hearing about how you screwed the lid down on a jar full of Al dust that spontaneously caught fire, risking a burst jar with flaming Al in your hands/face. Glad it went out... Your black Mg shall likely remain a mystery.

[JTO]

It was actually not the airborne al dust that autoignited, but the surface of the powder itself. The powder is so fine that it flows like liquid when you tilt the jar, or at least did initially. The burning was a kind of an orange glow, like you might get when you ignite steel wool, and radiated heat. One good thing about the mill is that the milling container and lid are stainless steel, they cannot melt, except under quite extreme temperatures. After that I have milled a couple of more batches of al, but left those slightly coarser (micrometer size?) so that there is no sign of pyroforicity.

 

I'm not sure what worries me more: A) you milling Mg in the first place, or hearing about how you screwed the lid down on a jar full of Al dust that spontaneously caught fire, risking a burst jar with flaming Al in your hands/face. Glad it went out... Your black Mg shall likely remain a mystery.