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Author: Subject: Making metal powders
plante1999
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[*] posted on 22-9-2012 at 04:22
Making metal powders


In an home chemistry lab very often metal powders are needed. Example are Tin powder, Zinc powder or aluminium powder. In this thread I would like to discus about home chemist way to make metal powders from metal ingot. At the time I'm more interested to make tin powder, but many other metal powder's are used like aluminium powder for phosphorus production.

Thanks!

[Edited on 23-9-2012 by plante1999]




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Hexavalent
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[*] posted on 22-9-2012 at 09:58


I usually buy my metal powders, but for coarser stuff I get access to filings from the workshops (in the engineering department) at my school. This can probably be done in an amateur environment, e.g. filing down the ingot over a container. I have heard of people using blenders on aluminium, but how well that works and how safe it is, I've no idea.



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[*] posted on 22-9-2012 at 10:00


A file works well for creating small amounts of course magnesium or zinc powder.



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[*] posted on 22-9-2012 at 12:01


Quote: Originally posted by plante1999  
In an home chemistry lab very often metal powder's are needed. Example are Tin powder, Zinc powder or aluminium powder.


Pure metal powders are often hard to get, especially if analytical purity or any special grade stuff is needed.

The easiest way is usually go to the self and get the preferred stuff, or call Sigma and get a bottle of what is preferred


But I know that in a home lab this is aint so easy... So let's see.

I know someone who had made Al "powder" from Al foil with a blender. It wasn't at the quality of the "german black pyro Al", ut it was fairly good for flashpowder and thermite reactions. So this could be method no. 1.

Method no. 2 is also used in industry, it works with soft metals (even with Al), they make a relative large ball mills, they put a lot steel spheres in it and some of the metal what is need to milled. It will produce a really-really small grain size powder, the only problem that the steel spheres could spark and metal powders could ignite... So fill the ball mill with Ar or N2.

Method no. 3 could be electrochemistry, with well plated electrodes and proper current perfect metal powders could be made (powdered lithium is produced this way).

And my last method, no. 4 could be used for platinum, palladium, gold, ect. some metals could be reduced into metallic form from solutions with reducing gases like CO, SO2 and like these. With this method highly active metal powders could be made.

P.S.: method no. 5 also fits in the above category, because salts e.g. iron-oxalate could be reduced at elevated temperatures to pyrophoric iron.




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elementcollector1
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[*] posted on 22-9-2012 at 12:13


Al: Possibly drill, cut ingot, ball mill result
Mg: Drill ingot, ball mill result
Less reactive metals: Chemical reduction of salts




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[*] posted on 22-9-2012 at 14:01


For Al and Mg a somewhat common method among pyro's is to construct a device with a rotating drum pasted with sandpaper. The metal ingot is pressed against it. The drum is partially immersed in a bath of water or oil which prevents dust, keeps the temperature down, keeps the paper from clogging and in the case of oil provides some protection against oxidation.



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[*] posted on 22-9-2012 at 14:24


My main problem with sandpaper was always that some "sand" will get into the metal powder what was made by that way. And the separation of a fine powder from a few percent of sand.... Nightmare.



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elementcollector1
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[*] posted on 22-9-2012 at 14:31


Which is why the ball mill works so much better with turnings. I tried sandpaper for quite a while, and it was terrible. Hardly anything produced.



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plante1999
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[*] posted on 22-9-2012 at 14:57


So in short we have at the time:

Ball mill for soft metal's like aluminium, reported to work very well.

A file for small amount of material, reported to work well.

Sandpaper, reported to work but give unpure metal powder, unsuitable for chemistry.

Coffee grinder/blender, reported to work but give coarse product.

(electro)Chemical reduction of noble metals, no report.

Reducing gas reduction of oxide, worked with iron oxide for me.


We need more ways and and more try at the procedures!

[Edited on 22-9-2012 by plante1999]




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[*] posted on 22-9-2012 at 15:11


Not easily done at home, but possible if you are determined: another method is to pour the molten metal onto a rapidly spinning disc. It will spray the metal around and it will break up into tiny droplets that solidify in flight.
Other methods of atomizing molten metal are in use such as breaking up a flow of metal with an ultrasonic actuator or impinging a jet of pressurised gas onto it.




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[*] posted on 22-9-2012 at 15:44


phlogiston, I don't think that's entirely within the reach of the home chemist, and potentially dangerous what with the molten metal, the spinning mist of molten metal, and the potential pyrophoricity of the result. Also, that produces spherical powders, whereas we think flakes are more suited to the task (having more surface area).

As for chemical reduction, it works better the nobler the metal is. For example, copper works extremely well in this process, as does bismuth. Sodium and magnesium, for obvious reasons, work poorly. Aluminum fares little better. Lead, tin, and indium would presumably give good results, having similar reactivity to bismuth.

Electrolysis: Only works well for a few different metals. Copper and silver work well. More reactive metals could be made by making the bath molten, but you'd have to keep the temperature below the melting point of the desired metal and above the melting point of the salt for it to even possibly work.

Ball mill: Good
File: Good, takes forever to get anything useful
Drill: Especially good in tandem with the ball mill
Sandpaper: Bad, impure result and takes forever
Coffee grinder: Good, useful for most demonstrations where an oxidation coating is not unwanted.
Blender: Not so good, only really useful for making smaller flakes (which can then be ball milled).
Chemical: Good, but only in certain cases
Electrochemical: Good if you monitor the bath each and every 5 minutes for a number of days until desired result is achieved
Reducing gas w/oxide: Never tried. Presumably, it would work well, but I can't say for sure.




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[*] posted on 22-9-2012 at 17:09


1) Aluminum Paint is basically an emulsion of ball-milled aluminum paste is oil & resin. If oil could be leached out using a suitable solvent then you can have the residue as almost pure aluminum flakey powder.

2) Long ago I have read in physics text book that if tin metal is cooled sufficiently then it becomes so brittle that it just crumbles in a powder. My attempt to do so by putting small beads of tin metal in the freezer of our household refrigerator failed probably because the temperature (-20 Deg C) was not low enough.

There even was a story in that book about an expedition to the north pole was put to great inconvenience because tin in their soldered metal containers gave away due to extreme cold.

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elementcollector1
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[*] posted on 22-9-2012 at 17:35


Yes, that's due to allotropy. One allotrope of tin is bright, shiny and generally more rotund, and the other is gray, flaky and not as nice-looking. Then, once the tin heats back up, it turns back into the other allotrope, while still very flaky. This could generate some nice tin powder. I don't think any other metal does this quite as easily, if at all. The Wiki throw states that pure tin will transform into this allotrope at 13.2 C, while impurities can lower this to well below 0, or make the transformation impossible. 99% Sn solder would be a good choice for this, I think.



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[*] posted on 22-9-2012 at 17:46


Gray tin is a funny thing. While thermodynamically favorable below 13.2C, it needs a kick in the pants to start. There are some preps in Brauer, I believe involving ammonium hexachlorostannate solution. More typically, you just need to seed white tin with a bit of gray tin.

Small amounts of certain other metals also have powerful inhibitory effects.




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[*] posted on 23-9-2012 at 01:53


I have just read a report on preparing ultrafine copper powder by the reduction of copper sulfate using ascorbic acid as a reducing agent, and might try it soon. I'm on my phone at the moment so I can't provide a link, but IIRC it was by a researcher called Songping-Wu.



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[*] posted on 23-9-2012 at 03:08


Quote: Originally posted by elementcollector1  
Yes, that's due to allotropy. One allotrope of tin is bright, shiny and generally more rotund, and the other is gray, flaky and not as nice-looking. Then, once the tin heats back up, it turns back into the other allotrope, while still very flaky. This could generate some nice tin powder. I don't think any other metal does this quite as easily, if at all. The Wiki throw states that pure tin will transform into this allotrope at 13.2 C, while impurities can lower this to well below 0, or make the transformation impossible. 99% Sn solder would be a good choice for this, I think.



Isn't this what caused Napoleon's troops to freeze to death on the march out of Russia? Their tin buttons crumbled allowing their clothes to pop open and the subzero winter did the rest.
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[*] posted on 23-9-2012 at 04:25


This page (possibly from a member)
http://members.pyroforum.nl/gamekeeper/metal_grinding_machin...
Gives some good advice including plans and comparisons for a powder grinder.




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[*] posted on 23-9-2012 at 04:54


Quote: Originally posted by Hexavalent  
I have just read a report on preparing ultrafine copper powder by the reduction of copper sulfate using ascorbic acid as a reducing agent, and might try it soon. I'm on my phone at the moment so I can't provide a link, but IIRC it was by a researcher called Songping-Wu.


Aluminium can also be used to displace the copper, downside is it takes a couple days. Once you're done, filter and wash with HCl to clean the copper of any oxide and remove any leftover aluminium.
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[*] posted on 23-9-2012 at 05:14


You can make large quantities of very fine iron powder by reducing its oxide using hydrogen. It works for copper, too, and I think many other transition metals in very fine mesh form can be obtained that way.
Sometimes carbon(II) oxide can be used, but hydrogen is easier to isolate. Be careful, almost all freshly prepared fine metal powders are pyrophoric. It's best to use a low quality cork for closing reaction tubes and just leave the powder for a few days. Traces of oxygen seeping through the cork reduce the activity of the powder's surface.

Many metals can be reduced using organic reducers in aqueous solutions, but then it's the concentration that dictates the mesh size, and it's not a quick procedure for making a lot of powder relative to the vessel size.

Iron and lead oxalate upon heating give iron and lead (and lead(II) oxide, but higher temperatures prevent large quantities from forming) so finely dispersed that their active surface is extremely large. Be very careful because if it catches fire, it looks like a piece of coal, glowing dull red. It's very hot. It's a metal on fire, so don't play with it.

Sodium can be dispersed by rapid cooling of vigorously stirred melt in kerosene (preferably in a closed, oxygen deprived atmosphere). The more intensive the stirring is, the finer the grains become. Ultrasound probes could disperse it into real powder. Of course, it would be extremely reactive and would be useful for organic chemisty, but under inert gas conditions. That's not something an inexperienced amateur should perform.
Stirring has to be done with an overhead stirrer, and not a magnetic one, because sodium is paramagnetic and will coalesce under rotating magnetic field.
I've made such fine grain before and because I don't have inert gas cyllinder at home, I had to resort to purging the vessel using kerosene vapor. Traces of oxygen exist in non degassed kerosene, so the product always looked dull violet-gray.

I suppose calcium could also be dispersed in a ball mill like magnesium, but I'd purge oxygen out using argon or I'd end up with calcium and quicklime powder instead.



Quote: Originally posted by Fossil  
Aluminium can also be used to displace the copper, downside is it takes a couple days. Once you're done, filter and wash with HCl to clean the copper of any oxide and remove any leftover aluminium.


You can never get reasonably pure copper that way. You get grains that contain aluminium inside. It's always contaminated because once the aluminium grain is covered by copper, the reaction stops - its surface is sealed shut. Unlike hydrogen reduction of iron(III) oxide, the end product is not porous because its units are joined by metallic bonds.

However if aluminium poses no problems for future plans, it's fine.

[Edited on 23-9-2012 by Endimion17]




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[*] posted on 23-9-2012 at 07:32
Copper powder


Found this on lambdasyn. The page should load fine, it is translated with Microsoft translator.
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[*] posted on 23-9-2012 at 08:09


I have previously made tens of Kg's of powdered metals like copper and iron and even some nickle via the electrochemical route when i was playing with sintering.

The trick is to use an extremely small cathode to create a ver high current density on the surface. and run the cell at such a large over voltage (and subsequently large current) that there is very vigorous gas production on the cathode this will help the metal granuales fall off and keep the partical sizes small.

Ive have never tried this with zinc but id guess that with some agitation to break up the zinc sponge it would work quite well.

It may even work with Aluminium if a sutible electrolyte can be found.
I have tried with acetone/aluminium chloride and ethanol / aluminium chloride and managed to get a few ma to flow at about 20-30 volts i ended up with perhaps a half a gram of grey powder on the cathode. this fizzed when put into NaOH so it might have been Al powder.


I have allso reduced Copper Sulfate with brown sugar (I don't think there's anything special about brown sugar its just what i had at hand) I don't know the exact chemical reaction.

in a 200ml beaker
I created a hot saturated solution of CuSO4. added about 40 grams of brown sugar heated untill just about boiling then i added about half a gram of NaOH granules. the beaker rapidly fizzed up and turned bright orange.

the resulting copper powder after washing/settling and decanting several times was extremely fine and alittle conductive if pressed firmly.

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[*] posted on 23-9-2012 at 08:19


Oh incidently a few Kg of powdered iron in water will create a visible quantity of hydrogen bubbles that go's for days

I ment to make a h2 candle that worked that way but forgot bout it :)
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[*] posted on 23-9-2012 at 11:24


I didn't think iron was reactive enough to produce hydrogen from water. Even magnesium only works at elevated temperatures.



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[*] posted on 23-9-2012 at 11:33


I find the file suitable for small quantities. Reduction is a good option though.



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[*] posted on 23-9-2012 at 15:58


Think about a 1" tubing, which at one end, on top, you plug a CO2 extinguisher tank, and at the other open end you put a flat closure with screw adpter. Screw the closure as to allow for the thinnest squeeze possible, in a preliminary test with water. Then do another test with molten lead. If successful, it will work for most metals in the melting range of your burner.
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