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wink.gif posted on 2-9-2015 at 09:54
Mixing fine powders


Hello, guys. What is the best method to mix fine powders, that can be done for safety issues in the open? I thought about stiring them in classic beaker by wooden stirring rod, but...

They are sensitive to friction. So some magnetic stirring by specialized mixer is probably out of the question... however how can I mix them well then? And preferably safely.

Any ideas?

[Edited on 2-9-2015 by x_blaster_x]
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[*] posted on 2-9-2015 at 10:00


Can you be more certain of what is being mixed. It could matter greatly. Can they be moistened?



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[*] posted on 2-9-2015 at 10:01


Diapering is a very common technique to mix friction sensitive powders, see the numerous threads on the subject on this forum. Essentially, it involves pouring the powders to be mixed in a beaker, or on a creased piece of paper, then pouring this mixture, which is not yet homogenous, into another container. It is then poured repeatedly back and forth between these two containers until the desired consistency is attained. Alternatively, for mixtures which aren't friction sensitive, use a ball mill. What compounds are you mixing? That will help you get an answer most suited to your situation.



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[*] posted on 2-9-2015 at 11:22


Sodium chlorate with powdered aluminium. It is considered to be friction sensitive, but I have no idea to witch extent. Since it should go boom, then I have no idea, if it can be moistered or not.
Will not NaClO3 react with watter?

Pouring small amounts between two beakers sounds reasonable. That should not explode, but dunno, if that could mix the parts properly, so the result is usable for fireworks and not just burn...
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[*] posted on 2-9-2015 at 13:09


My mixer...

ej6a90.jpg - 162kB

The group of 4 pushbuttons select pre-set mix modes, (1) one turn forward, half turn reverse, (2) two turns forward, one turn reverse, (3) five turns forward, five turns reverse, (4) 10 turns forward, ten turns reverse. Each pattern is repeated until the button nearest the voltage regulator is pressed (reset).

Truth be told, only one mode is required, the one forward, half reverse, as this mixes very quickly and completely. The pot controls the stepper speed from 15 to 75 RPM, any faster and the powders tend to not cascade, any slower than 15 is boring and noisy, but has the added bonus of the stepper vibration adding to the intimate mixing.

The tin can is a holder for the cardboard mixing cup, the plastic ring at the top of the can provides friction to hold the cup so when the stepper reverses, the powders own momentum coupled with the cup now moving the opposite direction underneath adds to the mixing intimacy in a huge way.

This is "diapering" at its finest

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[*] posted on 2-9-2015 at 13:13


Use plastic measuring jugs with handles so you do not have to wrap your hands around the explosive material.

Not sure if that introduces a Static disharge initiation problem though.

Personally i would not do any of this.

There are Great lengths people go to to get a good Bang, yet i value my hands too much to get this kind of Bang.




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[*] posted on 2-9-2015 at 13:22


To be honest, if you are not sure whether NaClO<sub>3</sub> can be moistened and are worried that it might react with water, you have not done nearly enough research on the properties of the components nor on the mixture.

It is extremely hygroscopic and to be able to work with this mixture you are going to have to put some thought in how to to keep it dry as you work with it. I really hope you are not planning on storing this.
Adding any water during mixing will leave you with a muddy result that will be near impossible to dry again. If you try, you probably won't have much of the original aluminium left by the time it is dry.




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[*] posted on 2-9-2015 at 13:31


Quote: Originally posted by aga  
Use plastic measuring jugs with handles so you do not have to wrap your hands around the explosive material.

Not sure if that introduces a Static disharge initiation problem though.


Static discharge is always a problem and plastics can support this. This is basically flash powder if you are going to mix it use paper scoops and just mix it slowly by hand. Also if you do not know how reactive chlorates are or what type of aluminum you have you need to be very careful.

I mix anything this sensitive binary and allow the movement of the items to mix the chemicals. I also use PERchlorate though its more stable. If you have not experienced the power of flash powder you do not know to fear it. Do not use anything glass or PVC because if it explodes they will not be able to remove the pieces from you via xray.

[Edited on 2-9-2015 by szuko03]




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[*] posted on 2-9-2015 at 14:58


If it's Wet, just heat it up under a Flame.

What could Possibly go Wrong ....

That is Sarcasm : Do NOT even try that.




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[*] posted on 2-9-2015 at 15:12


Quote: Originally posted by aga  
Use plastic measuring jugs with handles so you do not have to wrap your hands around the explosive material.

Not sure if that introduces a Static disharge initiation problem though.


If you want to go this route - mix by hand but have stand-off handles - I suggest making the mixing container out of cardboard or papier-mache (a very useful and often ignored material, use diluted white glue for very durable builds).

I like the mixing motor scheme above. Better not be close when conducting dangerous operations.
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[*] posted on 2-9-2015 at 16:15


I don't often do energetics, but when I do mix up a flash powder, I do so in a container that I made by folding and taping a piece of paper together. I stir it gently with a wooden dowel, and tip it back and forth while shaking it carefully to mix it. And I never make more than a few grams at a time. That amount of mixing is enough to make a decent flash powder that will burn very quickly and leave little to no solid trace behind.



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[*] posted on 2-9-2015 at 20:04


I read a study once from the 1950's (in the US) by a professional chemist of the accidents that had occurred in recent years among amateurs. Of course in those days if you blew yourself up it was your own fault, nobody hired lawyers to try to blame someone else. Anyway, there were several really bad accidents surveyed, including some deaths. Every single one of them involved potassium chlorate.



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[*] posted on 2-9-2015 at 21:37


Quote: Originally posted by Varmint  
My mixer...


I like that. The only modification I'd make, however, would be to add either a timer that shuts it off automatically (and preferably also allow for a delayed start), or the ability to just turn it on and off remotely. This way, when you're dealing with highly friction-sensitive mixtures, at no point during the mixing process would you actually have to be near it.
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[*] posted on 2-9-2015 at 22:18


Two things I dislike are threads started with such a vague misleading description of the true intent (especially a dangerous one), and the obvious fact no prior searching was done first. In this very sub-forum was a recent thread actually titled "Potassium chlorate with metal powders". In it are two books with much information on the subject. Foremost being you do not use a Chlorate (especially Sodium), only a Perchlorate (Potassium) which itself has been purified and tested to be sure no minute amounts of Chlorate contamination are present. Even then this is very dangerous to experiment with, the best advise is don't. This cannot be stressed enough when Sodium Chlorate is used.

http://www.sciencemadness.org/talk/viewthread.php?tid=62415#...

http://www.sciencemadness.org/talk/viewthread.php?tid=28901#...




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[*] posted on 3-9-2015 at 03:49


Darkstar:

I don't disagree with your suggestions, my concern lies with the fact that you will actually have to do something with the composition once mixed.

Ergo...

If I'm dealing with a composition that I can't explicitly trust to mix perfectly safely under nothing more than it's own weight, I won't be dealing with that composition at all.

One thing missing from the post above is the air-float filter. I use a square of toilet paper held in place by the same type of plastic ring as the cup to can friction fit, this prevents any composition from escaping the confines of the cup. The last thing you want is a steadily building dusting of composition on the electronics that suddenly flashes over and ignites due to a spark.

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[*] posted on 3-9-2015 at 08:37


Oh, and to clarify, I was referring to mixing aluminum and potassium perchlorate in my previous post... I wouldn't handle chlorate like that.



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[*] posted on 4-9-2015 at 12:25


My Buddy Dr. Crazyfingers usta do this kinda stuff all of the time.

He was very familiar with all of the pertinent precautions.

Still, I don't call him Dr. Crazyfingers fer no reason.

He is currently endowed with less than 10 fingers total. And, of those he does have, some are fractional fingers.

I suggest intensive research before embarking upon such experiments.

Maybe Energetic Materials is a better area to query in?
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[*] posted on 4-9-2015 at 13:35


First of all, at all times, wear shrapnel rated eye protection and a respirator as needed. Trust me, inhaling powdered Potassium Nitrate is NOT fun, and I doubt Perchlorates of any kind are anymore-so.


When I mix flash powders, I do it in the following method:

1)Place one piece of standard printer paper on scale
2)use powder scoop to measure out required weight of reactant 1
3)alter amount as needed, ie, if you've got too much, scoop it back up till it's right.
4)repeat previous with a FRESH piece of paper and clean scoop for reactant 2
5)pour one reactant off it's paper onto the other
6)gently "roll" the edges of the paper into a U shape, moving the "center" left and right, mixing the powders across the surface
7)as needed, use a thin plastic or wooden tool to break up larger clumps and remix with paper rolling method
8)once thoroughly mixed, fold paper to form a funnel, and gently pour the mixed powder into a casing

If your powder does not fit on one sheet of paper comfortably, you are making too much at once.


Oh, and while I'm at it, do you have a rough blueprint for that thing Varmint? Perhaps a copy of the software? I've screwed around with Arduino's before and I'm interested in getting a couple to make a few various handy devices, and that looks like it would be REALLY handy for some of the stuff I do.

[Edited on 4-9-2015 by James Ikanov]

[Edited on 4-9-2015 by James Ikanov]
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[*] posted on 4-9-2015 at 13:47


Given that Arduinos are really cheap and easy to program, has nobody thought of building a remote-controlled mixing station/lab to do all this dangerous stuff at a distance ?

Robotic arms etc are freely available on ebay, for little $.




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[*] posted on 4-9-2015 at 19:54


I'd be glad to help as I understand the consequences of mixing gone wrong, and I firmly believe this represents the safest method possible.

The only improvement with regard to safety would be to get rid of the tin can, and get a cardboard tube with thinner walls, both of which would tone down debris if something ever managed to go wrong. You'd just need to develop a means to hold the cardboard cup firmly yet easily detachable.

As you can see, it really is an Arduino of sorts, in that it is running the ATMEGA328P chip, and you probably recognize the "FTDI" port on the left edge of the board near the display.

So, you can obviously replace everything but the stepper drive (Polulu A4988), and the LCD interface (if you even care for a display), with a bone stock Uno R3. The display is interfaced via I2C and a 8 bit port expander, but you can reduce complexity here by just buying a 16x2 LCD with an I2C LCD "Backpack" and adjust the code to account for the various backpack wire mapping schemes.

The power supply is a salvaged PC Laptop supply that provides 18.5V for the stepper drive (required for high torque) but please note this is too much to feed to an Arduino power input, which is why my implementation uses a 7805 to provide the 5V for the MCU and display. You'll need to do something similar so you don't burn up your Arduino.

The stepper itself is the Adafruit 200 step per rev (1.8*) motor, these are $14, and can be had cheaper elsewhere, but I don't mind supporting Adafruit on some things, they put a lot of effort into making this kind of tech available to the average Joe. I'm a design engineer by trade, so 95% of this comes naturally for me, the hard part is C++ and all its (valuable) abstraction. I could do this stuff 10x faster writing in assembler, but why not learn all I can while I'm at it? (Life mission: Learn)

So, digest that for a while, and let me know if you want to turn it into a project. Again, I'd love to help, but I'm not going to just toss everything over the fence and see if it goes anywhere, show some interest/results of your research given the collection of hints embodied here, and we'll take steps together.

Sound reasonable?
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[*] posted on 4-9-2015 at 20:26


Oh, forgot to mention, your breaking up clumps with ANYTHING while the 2 or more components are together is an outrageous risk. I use extremely fine mesh screens, one for each component. Each component gets screened/sifted at a time onto clean separate paper, and the physical interaction begins only while pouring each separately into the mixing drum.

Once its mixed and ready to be utilized, now is the time to use best practice and ground yourself, handle the cup with caution, etc, etc...

Yes, I'm aware that these compositions are meant to be lofted into the air by explosive force, but anything you can do to avoid friction/impact/static means everything when it comes to safety.

AGA: While I clearly understand the safety aspects, I'm just not comfortable placing the seeming majority of the focus on the mixing as I've outlined here. It would be beyond easy to make the mixing remote, even advisable, but when people keep mentioning mixing as a key danger point, I believe it casts the wrong image, the real focus is how it is utilized once mixed. What sense would it make to treat the mix as somehow "safe" just because the mixing is over?

To that end, the ultimate in safety is to fuse, load and seal the device with the components inserted separately (unmixed), then use the mixer with a device clamp that allows you to rotate the device itself to achieve the mixing. Good practice is to leave 40% or more free space in a device, this leaves plenty of room for that mixing, and if you can get any safer by any means, well, that should be standard practice.
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[*] posted on 4-9-2015 at 22:17


Quote: Originally posted by Varmint  
While I clearly understand the safety aspects, I'm just not comfortable placing the seeming majority of the focus on the mixing as I've outlined here. It would be beyond easy to make the mixing remote, even advisable, but when people keep mentioning mixing as a key danger point, I believe it casts the wrong image, the real focus is how it is utilized once mixed. What sense would it make to treat the mix as somehow "safe" just because the mixing is over?


I think the main advantage of remote-controlled mixing is not so much that it makes the entire process (mixing, handling, usage) "safe," but that it simply makes it that much safer. Yes, you still have to handle the mixture once it's mixed; however, at least now there's one less step in the process for you to have to worry about something going wrong. Like you said earlier, just having some dust from previous mixtures on your electronics is enough to ruin your day; it's really just about removing as many of these sorts of variables as possible, reducing the number of chances for you to be injured (or worse) during the process. Considering the nature of playing around with sensitive energetics, a freak accident caused by something completely out of your control is inevitably going to happen at some point or another given enough time, so why not make every effort to ensure that you aren't going to be around when it does?

Anyway, with that said, I do agree with you that the main focus should be on handling the mixture after it's mixed, not while it's being mixed. If something is going to go wrong, chances are that's when it's going to happen. (assuming the proper precautions were taken during mixing, obviously)
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[*] posted on 9-9-2015 at 09:51


Quote: Originally posted by Varmint  


So, digest that for a while, and let me know if you want to turn it into a project. Again, I'd love to help, but I'm not going to just toss everything over the fence and see if it goes anywhere, show some interest/results of your research given the collection of hints embodied here, and we'll take steps together.

Sound reasonable?


Absolutely.
I'll stew on that for a while and get back to you. Most of my experience is really limited and not as in depth as might be useful, but hopefully this won't be outside the realm of plausibility for me.
Almost everything I've done so far has been very KISS oriented but it'll certainly be an interesting exercise at least. If it works out I've got a few other projects that you might or might not be interested in.
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[*] posted on 9-9-2015 at 17:48


OK James, we can take this to U2U unless anyone else is interested in which case a new thread might be in order.

Let's see if we get any joiners.

Here's a minimalist approach, pretty close to 4cm x 5cm.

20qm161.jpg - 219kB

Could be a stirrer, could be a mixer, could be any number of core functions that use a stepper motor.
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[*] posted on 9-9-2015 at 18:18


Sorry I use pics or sil labs stuff, I would favor maybe IR coms rather than radio but then again there are some great cheap IC2 modules about with good range. depends just how sensitive the material is.
Another suggestion maybe earth the container and use a belt from the motor to the cup rotator.

[Edited on 10-9-2015 by Little_Ghost_again]




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