Aluminum powder

degarb · Dec 6, 2016

Years ago I bought arctic epoxy. Found it gone after half a build. Not very good thermally, probably as good as expected. Researching it was not silver, but aluminum. . I tried zinc oxide, but table shows not good thermal conductor. . Copper is 2x of aluminum, a aluminum, I recall. . However, bought copper powder, while I proved good thermally, still too expensive to be practical.

So, I bought bag of aluminum powder. But on arrival, thoughts of its danger arose. . I am first researching before opening. . So far, I might keep in a sealed zip lock bag, inside a plastic jar, inside a giant pickle jar, whose lid is rustproofed and outsides padded. And kept in detached garage. . Mixing into epoxy outside only. . I already use all the stuff of any meth maker for my work, so why not get into the terrorists tools?

Though I suspect this powder isn't suitable for termite, as you need a certain granular shape to catch more oxygen.

I hate to sign up and post in a fireworks forum for one storage question.

I have no nitrogen to dump on top.

Overall, it looks no more flammable or explosive than sawdust. . Yet when it goes, fire super hot and unstoppable. . Probably too dust finer and will hang in air longer. . If not still creepier.

Obijuan Kenobe · Dec 6, 2016

Magnesium powder might be scary (still need to light it with something hot), but I don't think you need to worry about Al powder. It won't spontaneously combust or anything.

obi

HarryN · Dec 6, 2016

Just store it in an empty metal paint bucket of sand or baking soda / baking powder. If it starts to get hot, baking soda (or better the powder) will release CO2 and slow it down. Sand is commonly used to put out metal and Li battery fires, not as good as the purpose built agents, but fairly decent.

In fact, a lot of R/C hobby people will charge their batteries in a bucket of sand to keep things contained "just in case". It is good, cheap insurance.

New, empty metal paint buckets are sold at places like HD / Lowes. Applying a label is easy.

Especially during the holidays when there is a lot more complex cooking, wiring, candles, etc. around, keeping some things like cat litter, sand, baking soda, and / or fire extinguishers to quickly knock down a small fire is a good idea.

scianiac · Dec 9, 2016

I would be most concerned when handling it to avoid static discharge, probably still not that much of a risk but can't be too safe. Have you considered silicon carbide? I've used it quite a bit as a thermal filler. It's relatively cheap, safe (just don't inhale it of course), non conductive so can be used for things like potting, and can easily be purchased in a wide range of meshs. Depending if you are trying fill a very small gap or a larger one you can mix in different meshs. So large particles mixed with smaller ones to fill in the spaces between the large ones are always best as long as the gap you are filling isn't too small so the larger particles add extra distance. The actual thermal conductivity is based on the crystal structure of which there are many for silicone carbide. For example 3C is 360WmK while 6H is 490WmK. 6H (alpha) is the most common so I think that's what most abrasives are made from. I can only imagine it's not used in commercial products because it would be murder on the processing equipment for little gain over other options.

degarb · Dec 11, 2016

Is silicon carbide sold by a sand blasting supply?

2 years ago, I bought a 50 lb bag of blasting soda. . I vaguely recall 30 bucks. . Similar to sodium bicarbonate. I personally didn't test flame fighting. But I filled up one 5 gallon pail and a half dozen clear peanut jars for around the house. My teen girl is stupidly allowed candles an insense in her room. . Not allowed to go for walks in woods alone; but, endangering lives of entire family as they sleep, is fine with the wife. . My teen reported the blasting soda did put out one fire in her room. . Wife, though, hides the extinguishers at every opportunity, as they don't go with the decor. . Easier to comply with wife than risk certain divorce court. . I need an artful, artistist fire extinguisher worthy of HGTV, and many designs, as she will grow tired every 6 months, move the furniture around and put the old artful extinguishers in the basement.

Anyway.... Sourcing and chemical similarity of blasting soda.
: am I on right track? . Or is blasting soda not good or half the price elsewhere?

I could mix some left over blasting sand, with my blasting soda, to leave enough soda for any new artistic fire containers I might one day hit upon. This would cost me little...
Unfortunately, to my mind and eye, the more practical the design, the more solutions to problems it solves, the more beautiful. While to most architects and designers, it is the opposite. . (My stomach turns when flipping past Project runway, or my local art museum whose building is a monstrous poor, useless design - unless wasting money and fighting roof leaks and wind storms is your goal.)

In my metal paint can, maybe I should break the pound into many small zip locks. In case on were to ignite during opening, it would be harder to ignite the rest.

degarb · Dec 11, 2016

I was water sand blasting old rusty iron railings, the spring before last. I started out using the black diamond. . I switched to landscaping sand (their purer form that I strained), as it worked just as well and cost far, far less, and didn't require a 55 minute round trip to outside the city. . My bet is that the black diamond was true silicon carbide.

I have two left over fives of the sand in my storage, which I would love to put to good use. Home depot Kinda rips people on sand. . Toys r us is more reasonable, as I recall. I just got lucky having a contractor only landscape supply practically across the road.

degarb · Dec 11, 2016

Hmmm http://m.harborfreight.com/50-lbs-m...a-65929.html?utm_referrer=direct/not provided

scianiac · Dec 11, 2016

I don't think any of those are silicon carbide. The black diamond I'm guessing is coal slag, a common blasting media that is more gentle than sand if I recall. And the soda is just baking soda. Neither would be a good choice thermal wise. Also of course be careful when blasting with regular sand, that's how you get silicosis, which is one of the reasons while blasting soda, slag, glass beads, etc are replacing regular sand. I bought my silicon carbide on ebay. I got some 600grit and some 120/240grit. For potting drivers I use a mix of the two to get optimal packing, for closer tolerance joints I just use the 600. I don't think it's a very common blasting media, at least that I've seen, it's more common for finishing harder metals. It's extremely hard.

degarb · Dec 12, 2016

Pardon my ignorance. . You build drivers at home or work? . How do you sintering the SiC? Do you press, or heat? What tools, and how doesn't it damage the electronics?

Back to my storage question. . I found a Christmas tin, buried the aluminum powder in it. . I dread mixing AL into the epoxy outside in 0 to 20 degree enough. I dread worse a 150 foot walk to retrieve it from my detached garage. . So, if basement caught fire, eventually eating through the tin and soda packing, are we talking high rise explosive, or just another problem upon many as your house burns up, gas pipes exploding?

scianiac · Dec 12, 2016

I have built drivers in the past and still do sometimes but it's often easier to just buy them. I do it for hobby and work (I sell modded flashlights). I don't sinter the SiC, that would be very hard. I just use it as a filler for various other materials, epoxy, silicone, Butyl rubber composites, etc. Whatever best suits the application. Those are used to pot drivers and generally thermally attach things.

Really there is probably little risk it will even combust. Unless you bought pyrotechnics grade alumnium it's probably safe. The pyro grade stuff is very fine, often in flake form, and has additives used to prevent oxide layers forming. Sitting still in a tin it may not burn even if lit. Handling it is when you have a risk, when it becomes airborn there is potentially enough exposed surface area to cause an explosion in just the right conditions. This is why if I were you I would take very good precautions against static discharge and other ignition sources when handling it. The zap from static discharge could be enough to ignite it in the air, again in the right conditions. And try not to get it airborn in the first place. Do you know the size of the powder you bought? Generally smaller than 40 mesh (420 micron) are where the hazard starts.

degarb · Dec 12, 2016

scianiac said:
I have built drivers in the past and still do sometimes but it's often easier to just buy them. I do it for hobby and work (I sell modded flashlights). I don't sinter the SiC, that would be very hard. I just use it as a filler for various other materials, epoxy, silicone, Butyl rubber composites, etc. Whatever best suits the application. Those are used to pot drivers and generally thermally attach things.

Really there is probably little risk it will even combust. Unless you bought pyrotechnics grade alumnium it's probably safe. The pyro grade stuff is very fine, often in flake form, and has additives used to prevent oxide layers forming. Sitting still in a tin it may not burn even if lit. Handling it is when you have a risk, when it becomes airborn there is potentially enough exposed surface area to cause an explosion in just the right conditions. This is why if I were you I would take very good precautions against static discharge and other ignition sources when handling it. The zap from static discharge could be enough to ignite it in the air, again in the right conditions. And try not to get it airborn in the first place. Do you know the size of the powder you bought? Generally smaller than 40 mesh (420 micron) are where the hazard starts.

500 mesh µ30 micron , he-he.

Still, not opened it. Outside, is a must. Never seen static electricity outside. Do I need to pound a pole in the ground and wear a metal wrist strap,attached to a metal wire? Could share with the Dog.

I need to lookup the thermal charactistics, etc, to see why you add SiC to silicone and epoxy. Watched big Clive add cornflower to silicone to make some good forms for epoxy led Christmas light diffuser.

I am thinking best setup would be zip bag of aluminum in tin of baking soda, inside metal paint bucket. Unsure if empty space is more heat insulation than sand around tin. Of course, sand on bottom to insulate there. Also,probably skip paint bucket and go for a Christmas popcorn tin. Great excuse to eat a tinful. And I must do it quickly, else the house may burn.

degarb · Dec 12, 2016

Maybe adding SiC to the epoxy, for density reasons? Is it really light weight? Good thermal but not near aluminum or copper.

I see on glass guy on YouTube using wine glasses on SiC to etch glass. Stumbled on last year when researching cirium oxide to buff out scratches in glass.

degarb · Dec 13, 2016

I have been pondering potting electronic board with delicate protruding components, where I may wish not to shroud inside, and wish to keep as lightweight as possible. All my lights are worn and carried on the person.

Probably spray polyurethane foam ground to size,but impractical as a can is single use. Considered artificial plant styrofoam that is easily moulded and glued on, where regular foam might be too heavy but less crushable. Also, considered light weight spackling, which may need a paint or caulk additive for strength. Haven't yet tested any ideas.

degarb · Dec 13, 2016

scianiac, are your drivers AMC based? You cap them on positive and vdd? Or something different?

scianiac · Dec 13, 2016

OK yeah that is some seriously fine stuff, would be careful with that. A grounding strap like you described would be a good idea. The metal storage strategy you described sounds good. I use the silicon carbide for the same reason you do, but also because it's non electrically conductive so it can be safely used as potting. While I don't know the exact thermal conductivity of this silicon carbide it's likely that it's 6H (alpha) type so has a thermal conductivity higher than copper. If it's some other form though it's still quite high in the range of aluminum. It doesn't have have any more of a thickening effect on silicone than any similar powder I think cornflower thickens it into a putty quicker, love big clive btw.

SiC is lighter than copper. As a thermal filler it's probably between aluminum and copper in overall effectiveness, copper's specific heat is better. But I don't feel safe covering electronics in copper or aluminium dust.

If you want to pot drivers for vibration and impact reasons as you described. I also like keeping EDC things super light but it's hard in a light, more mass in the head means more thermal mass which means longer runtime in turbo. Silicone, epoxy, duct seal mixed with SiC probably won't add that much weight unless the pill cavity is huge. If heat is not and issue and you just want a lighter potting you could just cover the driver in a thin layer of epoxy instead of filling the whole cavity. Weight and thermal conductivity just don't go together. Anything that will be super light will also be not very conductive. You could use glass micro balloons as a filler and it will be light but not very conductive.

You might want to try some potting with a duct seal based mixture. You can get it at the hardware store in a brick for a couple bucks. You just mix that with your filler of choice like you are mixing clay, just mix in as much as possible (start with a small batch as you'll get tired out otherwise). It's easier to use than epoxy and can be easily removed if you need to change, adjust or fix the driver. You can just pack it in the driver cavity and/or on the board and squish it in there.

I use all types of drivers, I've mainly built the various BLF driver designs. haven't had a need to design my own yet but a few current projects I think I will. But I use mostly FET+7135 and buck drivers in both personal and production lights. And as much as I enjoy building them it's just easier to buy them, building a few is fun, building 20 is much less fun. The potting is very important on the buck drivers both to dissipate heat and prevent the inductor from breaking if in an impact.

PhotonWrangler · Dec 13, 2016

It sounds like you're taking the right precautions, Degarb. Don't forget to wear a dust mask. Aluminum in the lungs is not a good thing.

degarb · Dec 14, 2016

scianiac said:
OK yeah that is some seriously fine stuff, would be careful with that. A grounding strap like you described would be a good idea. The metal storage strategy you described sounds good. I use the silicon carbide for the same reason you do, but also because it's non electrically conductive so it can be safely used as potting. While I don't know the exact thermal conductivity of this silicon carbide it's likely that it's 6H (alpha) type so has a thermal conductivity higher than copper. If it's some other form though it's still quite high in the range of aluminum. It doesn't have have any more of a thickening effect on silicone than any similar powder I think cornflower thickens it into a putty quicker, love big clive btw.

SiC is lighter than copper. As a thermal filler it's probably between aluminum and copper in overall effectiveness, copper's specific heat is better. But I don't feel safe covering electronics in copper or aluminium dust.

If you want to pot drivers for vibration and impact reasons as you described. I also like keeping EDC things super light but it's hard in a light, more mass in the head means more thermal mass which means longer runtime in turbo. Silicone, epoxy, duct seal mixed with SiC probably won't add that much weight unless the pill cavity is huge. If heat is not and issue and you just want a lighter potting you could just cover the driver in a thin layer of epoxy instead of filling the whole cavity. Weight and thermal conductivity just don't go together. Anything that will be super light will also be not very conductive. You could use glass micro balloons as a filler and it will be light but not very conductive.

You might want to try some potting with a duct seal based mixture. You can get it at the hardware store in a brick for a couple bucks. You just mix that with your filler of choice like you are mixing clay, just mix in as much as possible (start with a small batch as you'll get tired out otherwise). It's easier to use than epoxy and can be easily removed if you need to change, adjust or fix the driver. You can just pack it in the driver cavity and/or on the board and squish it in there.

I use all types of drivers, I've mainly built the various BLF driver designs. haven't had a need to design my own yet but a few current projects I think I will. But I use mostly FET+7135 and buck drivers in both personal and production lights. And as much as I enjoy building them it's just easier to buy them, building a few is fun, building 20 is much less fun. The potting is very important on the buck drivers both to dissipate heat and prevent the inductor from breaking if in an impact.

Excellent post.

Haven't yet measured electrical conductivity in even my Cu epoxy mixture. That isn't to say there isn't any, as my tests were a casual ohm meter check as a side curiosity, and probably didn't push probes very hard.

Only one reading of this thread,on the run. It seemed to me you were saying SiC thermal conductivity is between Al and Cu.?

Do own boards or cccv boards (though I want a cccv board that can jump my phone), need thermal potting? Naturally, in use, I will know, if something gets hot, I guess. Not noticed any heat at all on the pwm board. Not received my cccv boards yet from fast tech, though I have a uniden 18650 power pack I can employ, were I 100 percent confident it doesn't register current once cell reaches 4.2 volts. I got 3 cheap 2bay China chargers in spring, which I can measure current at 4.2 v cell. My intellicharger seems to mostly shut off at 4.2 maybe CV pulse. Using the cheap chargers only when no other option, even though all my cells are protected, except a few free ones I have in holder for emergency. Charge in cookie tins.

Now, on digikey the cccv chip is pennies, just add your own caps etc. Boards are like 2$, any good charger should be 8bay and have volt readout. If not on each bay, one volt meter on side you can use one hand to press cell into v , get voltage onto and off charger (2-3seconds max per cell)..... Making your own charger with magnets might not be too hard, if one knew a good choice for acdc transformers.

scianiac · Dec 14, 2016

Metals mixed into epoxy often won't be conductive until you add a ton of metal but even still I'm not going to risk it across the close pins of a driver. SiC's overall thermal performance I would say is about in between. It's thermal conductivity is higher than copper but it's thermal mass (specific heat) is more like aluminum and thermal mass is very important too, at least when you make really powerful flashlights.

Most boards like that probably don't need any potting unless you want to water proof them. Then again cheap Chinese electronics are known to sometimes use undersized components that get a little toasty.

degarb · Dec 15, 2016

scianiac said:
Metals mixed into epoxy often won't be conductive until you add a ton of metal but even still I'm not going to risk it across the close pins of a driver. SiC's overall thermal performance I would say is about in between. It's thermal conductivity is higher than copper but it's thermal mass (specific heat) is more like aluminum and thermal mass is very important too, at least when you make really powerful flashlights.

Most boards like that probably don't need any potting unless you want to water proof them. Then again cheap Chinese electronics are known to sometimes use undersized components that get a little toasty.

I wish to know a good source for micro glass beads and SiC.

In addition to the electronic stuff, for my headlamp builds, I wish to build the lightest, most practical firewall under the protected 18650 holder to protect the head. Also, for my wrist lights. Need padding, so silicone probably best rubber choice. Layering in strips of aluminum foil, which has reflective and a 660c melting point(silicone ignites at 1000c, I am told), while add nothing to weight-- is one idea in my head. Adding micro glass beads to the silicone, another idea. Adding borax to the silicone, as a cheap alternative to glass beads--which may be redundant, but I must think about this more. Adding fiberglass mesh, for whatever it might be worth. Maybe someone has better ideas.

Bondo polyester seems cheaper for resin than epoxy for potting.

I never have worked with fiberglass kits; but to me, look like a thin polyester resin with fiberglass reinforcement strips. The significance is this fiberglass could be used as filler or there could be sheet properties of fiberglass like shape, fireproof or weight.
www.instructables.com/id/Homemade-Flame-retardant/?amp_page=true?

https://www.wou.edu/las/physci/ch462/BouncingPutty.htm

http://makezine.com/projects/make-40/fond-o-bondo/

https://www.google.com/search?q=micro+glass+beads&oq=micro+glass

degarb · Dec 15, 2016

Actually, I am getting conflicting results googling silicone melting and ignition points. Some say it never melts and only ignites at 1000C, some say 300C melting with ignition point of 1400C.

GE has some junk called silicone 2. When I use that junk, it never dries for me. Probably how hard I squeeze it from tube....my point is that probably traditional silicone caulk all works the same. While silicone 2 may be doped and have a melting point. Hopefully, the case.

Aluminum powder

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