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Author: Subject: Magnesium powder from magnesium ingots
IndependentBoffin
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[*] posted on 10-6-2011 at 01:16
Magnesium powder from magnesium ingots


Hi guys,

I've been checking shipping regulations re: magnesium powder and it is difficult to ship sub-mm magnesium powder without licenses in terms of time, expense and paperwork.

The most expedient way of getting hold of magnesium powder is by buying pure magnesium ingots (fairly large - about 4 litres in volume per ingot) and turning that into a powder. No paperwork is needed for buying magnesium ingots.

Can anyone suggest a time/cost efficient and safe way of turning these ingots into < 200 micron powders on a laboratory scale (say a few kg per week)?

The most obvious route is ball milling but judging by spontaneous ignition accidents that occasionally happen even when milling aluminum, magnesium will be even more hazardous.

Also, the process of converting 4L magnesium ingots into forms suitable for milling is not without hazard. My workshop machinist has some experience working with magnesium alloys and he says it is a real hazard to work with.

Thanks.




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[*] posted on 10-6-2011 at 03:08


This video (http://www.youtube.com/watch?v=3Se750W6Lm0) shows how to make small quantities of magnesium powder. Someone in the comments section suggested to use a slowly-spinning belt sander with a piece of magnesium continually pushed against it to generate larger amounts of Mg powder. I'm not sure if the powder produced is fine enough, though.



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IndependentBoffin
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[*] posted on 10-6-2011 at 04:04


Yeah I saw those too but personally I found this video a bit better quality and more informative:
http://www.youtube.com/watch?v=JeMeRhgKFsk

It seems the first pass against a steel file gives ~200 micron powders. I don't know what the particle size (or purity) will be if you use sandpaper.

The quantities involved are very small though. A belt sander is a nice idea.

What about making a cheese grater out of steel and rubbing the ingot against that to get shavings, and then putting those shavings in a ball mill?

The ball mill will need to have fresh air flushed through it to passivate the metal powder so it doesn't become pyrophoric.




I can sell the following:
1) Various high purity non-ferrous metals - Ni, Co, Ta, Zr, Mo, Ti, Nb.
2) Alkex para-aramid Korean Kevlar analogue fabric (about 50% Du Pont's prices)
3) NdFeB magnets
4) High purity technical ceramics
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[*] posted on 10-6-2011 at 05:48


Wouldn't the belt sander contaminate the Mg powder with Aluminum Oxide?



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[*] posted on 10-6-2011 at 07:46


When I needed some magnesium turnings, a drill press was the best thing I found to do the job. It worked pretty well really, though it is inefficient because you can't drill 100% of the metal easily. The leftovers could be recast or broken up some other way though. With a big drill bit you could easily get 1-3kg of turnings in a day, extrapolating from my experiences with it. I don't think you'll be able to avoid ball milling though if you want fine powder. Why worry about flammability? Just flush the mill drum with Ar or He if you have them. Butane or propane would work too, but you'd have to be more careful that it was sealed well, etc..
I was under the impression that if you grind it up fine in air it ends up with a large fraction of MgO contaminating it, especially if the process is a high friction one that heats the resulting powder.

[Edited on 10-6-2011 by 497]
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[*] posted on 10-6-2011 at 07:51


Quote: Originally posted by Phosphor-ing  
Wouldn't the belt sander contaminate the Mg powder with Aluminum Oxide?


Yeah that was what I was thinking, but it really depends on the wear rate of magnesium to the wear rate of the belt. Magnesium is a fairly soft metal but I still don't know what purity will be coming out from the sanding approach.

Hence why I thought some mechanical operation to grate shavings off a large Mg block - perhaps even under water - followed by ball milling is best.




I can sell the following:
1) Various high purity non-ferrous metals - Ni, Co, Ta, Zr, Mo, Ti, Nb.
2) Alkex para-aramid Korean Kevlar analogue fabric (about 50% Du Pont's prices)
3) NdFeB magnets
4) High purity technical ceramics
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[*] posted on 10-6-2011 at 08:33


Quote: Originally posted by Phosphor-ing  
Wouldn't the belt sander contaminate the Mg powder with Aluminum Oxide?


Don't use non-clogging sanding belts they are coated with
stearate's to prevent clogging. Use zirconium belts (they are
generally blue in colour) and are designed for use on metal plus
they last a long time.

Oh - keep a "Class-D" extinguisher at hand just in case ....!

http://www.labsafety.com/CLASS-D-Combustible-Metal-Fire-Exti...

Or perhaps a Fire Grenade.

http://www.antiquefireextinguisher.org/

If you use one — please report back what happens when CCl4 hits
burning magnesium...!
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[*] posted on 10-6-2011 at 20:17


Magnesium will react somewhat with water, so if you choose to mill, under oil would be better. If you use some sort of grinding wheel dipped in the oil and mount the block of magnesium to a hinge and apply force with a spring or weight so that it is constantly pushed into the grinding wheel, you can even automate the process slightly. Though you can also make a really big mess. Some sort of hard metal file mounted on an oscillating sander could be interesting. Either way, you need to keep the metal cool. Dripping oil should work well, and if you plan the choice of oil out well, a simply solvent wash should clean it all up quickly.

If the use is pyrotechnics, a 50/50 magnesium/aluminum alloy is relatively easy to make and extremely brittle. You can use a BBQ coal starter and a tin can if memory serves correctly. Should be several videos on youtube with more than enough info. If not I know I have run across pages on several pyro's home sites.




So many ideas... too few dealing with chemistry.
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[*] posted on 11-6-2011 at 00:06


Quote: Originally posted by asilentbob  
Magnesium will react somewhat with water, so if you choose to mill, under oil would be better. If you use some sort of grinding wheel dipped in the oil and mount the block of magnesium to a hinge and apply force with a spring or weight so that it is constantly pushed into the grinding wheel, you can even automate the process slightly. Though you can also make a really big mess. Some sort of hard metal file mounted on an oscillating sander could be interesting. Either way, you need to keep the metal cool. Dripping oil should work well, and if you plan the choice of oil out well, a simply solvent wash should clean it all up quickly.

If the use is pyrotechnics, a 50/50 magnesium/aluminum alloy is relatively easy to make and extremely brittle. You can use a BBQ coal starter and a tin can if memory serves correctly. Should be several videos on youtube with more than enough info. If not I know I have run across pages on several pyro's home sites.


My workshop machinist said that in general he prefers to use water-based coolants rather than oil ones when machining, because oil based ones can add proverbial fuel to the fire. At least you know that water, while it may still support combustion of magnesium, is not a fuel in itself.

I presume the same principle applies to ball milling magnesium in oil. Also AIUI ball milling works by having very high contact stresses at the impact points between the milling balls and each other, or the wall. Having any dense fluid in there will dampen the impacts and reduce your milling efficiency.

It looks like fine magnesium powder sells for about USD$1-2 for 10g on Ebay. Being able to set up decent Mg powder production facilities would be a good cash cow to fund my inventing. In fact my metal suppliers told me of a facility in continental Europe which does just that: buys Mg ingots which have no bureaucratic obstructions and converts it into micron-sized Mg powder.

I wonder if sub-mm magnesium powder will have import/export restrictions if it is mixed with a suitable bulking agent that reduces it's flammability? NaCl is a possibility although separating it from the Mg powder will be a hassle. Another is polystyrene foam and Mg - although both are fuels the polystyrene can be easily removed with acetone.




I can sell the following:
1) Various high purity non-ferrous metals - Ni, Co, Ta, Zr, Mo, Ti, Nb.
2) Alkex para-aramid Korean Kevlar analogue fabric (about 50% Du Pont's prices)
3) NdFeB magnets
4) High purity technical ceramics
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[*] posted on 11-6-2011 at 07:59


This is true about the oil. I would wonder if silicone oils would work better. I have no experience in the matter.

I imagine for ball milling, if you start from curls or flakes with a lot of very heavy steel balls and just a small amount of oil, it might work ok. With aluminum the oil can help stop the particles from sticking together, but I don't know if that would be needed with magnesium. As well on the flip side, if you use oil the particles don't get the chance to build up a protective oxide layer which would normally happen while milling the metal without oil and opening the mill periodically to allow the metal to oxidize slightly and not become outright pyrophoric... but if coated in oil, I don't believe it would be an issue... until maybe the oil is washed off. Magnesium can probably be ball milled without oil just as aluminum can be, just being careful to open the mill and stir around the powder more frequently than with aluminum... giving time for the metal to form an oxide coating and the resulting heat to disperse.

Since contamination from grit when using grinding stones or sand papers is an issue... perhaps a hard steel "file" wheel could be fabricated and used in place of a grinding stone. The groves could be made in a variety of ways.

Magnesium ribbon/curls are sometimes used as a bulking agent by pyro suppliers, which the consumer screens out by hand. NaCl would not be appreciated. I imagine trace moisture would work to speed up the corrosion of the magnesium as well as making it useless for pyrotechnic colors. Polystyrene is a fuel, but it is also a fuel with a VERY high surface area... it is an interesting idea though. I wonder if the trace polystyrene left on the surface of the magnesium after extraction would make the magnesium clump up.




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[*] posted on 11-6-2011 at 09:32


Quote:
This is true about the oil. I would wonder if silicone oils would work better. I have no experience in the matter.

I imagine for ball milling, if you start from curls or flakes with a lot of very heavy steel balls and just a small amount of oil, it might work ok. With aluminum the oil can help stop the particles from sticking together, but I don't know if that would be needed with magnesium. As well on the flip side, if you use oil the particles don't get the chance to build up a protective oxide layer which would normally happen while milling the metal without oil and opening the mill periodically to allow the metal to oxidize slightly and not become outright pyrophoric... but if coated in oil, I don't believe it would be an issue... until maybe the oil is washed off. Magnesium can probably be ball milled without oil just as aluminum can be, just being careful to open the mill and stir around the powder more frequently than with aluminum... giving time for the metal to form an oxide coating and the resulting heat to disperse.


Oh...you were talking about a small quantity of oil. I was thinking submerged :D

Yes that might work. But bear in mind atomised aluminum used by the military has an intentional passivating oxide layer.

For military purposes atomised aluminum is made by injecting molten aluminum at high pressure through a nozzle into a noble gas atmosphere. However, a very controlled amount of oxygen is introduced into the atomisation chamber to produce a passivating layer.

I suspect, there is a reason why military manufacturers don't make aluminised explosives with no passivating oxide layer (even though the atomisation process can clearly allow for it) and instead just use oil. It is probably because aluminum with just a coating of oil for protection can be quite reactive and we do not know what kind of unintended reactions might happen between say TNT/RDX and metallic Al. Issues such as gas pockets, degraded shelf life, cracking, single displacement reactions by the Al, etc. may all come into play.

Having oil on the metal powder may not protect your pyrotechnic/explosive/binder mixture from pure Al, e.g. if the oil is able to dissolve in a liquid explosive matrix (e.g. AN-NM, while casting) or in a solid solution (borrowed this concept from metallurgy but I think it is valid here).

So my point is that an oxide passivating layer is essential for any sensible usage of metal powders. The questions are how you introduce it and how you keep it to a minimum.

Quote:

Since contamination from grit when using grinding stones or sand papers is an issue... perhaps a hard steel "file" wheel could be fabricated and used in place of a grinding stone. The groves could be made in a variety of ways.


Yeah that was why I was thinking about something like a cheese grater.

Quote:
Magnesium ribbon/curls are sometimes used as a bulking agent by pyro suppliers, which the consumer screens out by hand. NaCl would not be appreciated. I imagine trace moisture would work to speed up the corrosion of the magnesium as well as making it useless for pyrotechnic colors.


Yes, agreed.

Quote:
Polystyrene is a fuel, but it is also a fuel with a VERY high surface area... it is an interesting idea though. I wonder if the trace polystyrene left on the surface of the magnesium after extraction would make the magnesium clump up.


Despite being a fuel-fuel mixture, I think 1% Mg powder - 99% polystyrene foam by volume would not have the combustion properties of 100% Mg powder by volume.

Whether or not polystyrene adheres to MgO films over Mg substrates depends on the degree of adhesion between the two. I suppose this can be experimentally investigated by having a macroscopic form of Mg dipping it in polystyrene and then trying to wash it off with acetone.

If you can still attack the substrate metal with, say, dilute acids, then the polystyrene layer has been washed off for our intents and purposes.




I can sell the following:
1) Various high purity non-ferrous metals - Ni, Co, Ta, Zr, Mo, Ti, Nb.
2) Alkex para-aramid Korean Kevlar analogue fabric (about 50% Du Pont's prices)
3) NdFeB magnets
4) High purity technical ceramics
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[*] posted on 11-6-2011 at 09:50


For all those suggesting using files, They take way to long, use a saw, I use a sawzall(electric hacksaw) to get power when I need it then you can process this down to finer levels if you wish.

If you could find a way to put a file into a sawzall then it would save a great deal of time for you. I also find a dremel works well but then there is the issue of brushes in the motor which although has never been a problem yet could possibly ignite the powder. The biggest issue with Dremels is the air that blows out of them so if you have the pencil attachment I would no doubt use this instead since it would keep the motor and the fan feet away from your working area.





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[*] posted on 11-6-2011 at 13:19


Quote: Originally posted by IndependentBoffin  

Yes that might work. But bear in mind atomised aluminum used by the military has an intentional passivating oxide layer.

For military purposes atomised aluminum is made by injecting molten aluminum at high pressure through a nozzle into a noble gas atmosphere. However, a very controlled amount of oxygen is introduced into the atomisation chamber to produce a passivating layer.

I suspect, there is a reason why military manufacturers don't make aluminised explosives with no passivating oxide layer (even though the atomisation process can clearly allow for it) and instead just use oil. It is probably because aluminum with just a coating of oil for protection can be quite reactive and we do not know what kind of unintended reactions might happen between say TNT/RDX and metallic Al. Issues such as gas pockets, degraded shelf life, cracking, single displacement reactions by the Al, etc. may all come into play.


Forsooth! The reason atomized Mg and Aluminum are preferred
in pyrotechnics/explosives is that the partial size is constant.
Remember the Greek considered the sphere ... well I forget just
what - I'll use perfect.

With flake particles ... a particle that fits through a 40 mesh
sieve and is 0.001 mm long is 40 mesh, if it is 1 meter long
it is still 40 mesh. Spherical particles assure uniformness of
output.

Passivating layer. Pure aluminium will passivate itself. How
many here are old enough to remember the originally aluminium
storm windows? You had to clean them once a week with steel
wool or they would self destruct. It was not until better alloys
were developed that they became practicable.

Magnesium is not reactive in pyrotechnics/explosives excepting
for sulphur, Ellern mentions during WW II the Bosch had trouble
with this combination.

At no extra charge I be attaching a copy of the Mil Spec for
Magnesium. I see not reason to post the one for aluminium,
you can scope it out for yourselves.


Attachment: MIL-DTL-382D.pdf (114kB)
This file has been downloaded 512 times


djh
---
I remember when aluminium
cookware first came on the market
here in La US of A, the steel pot
manufacture started a rumor that
aluminium pots were poisonous.

Somewhat resurrected a few years
back when some claimed Alzheimer's
disease was caused by aluminium.

Then in the beginning some claimed
Legionnaires Disease was caused by
nickel poisoning. A classic case of
toooo good chemistry!
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[*] posted on 12-6-2011 at 10:49


Just remembered that some pyro flake aluminum is coated in stearic acid to prevent oxidation. I should have mentioned this in my previous post.

The main reason I'm wary of polystyrene is that there was an incident a few years back when it was used in a big long multi-break aerial shell at a PGI convention as a sort of filler I think, with very bad results. Or at least that is what I was told.

Wizard, would you happen to have some info on that? I believe they were 13+ breaks. However its been so long that my memory of it all is probably far off.




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[*] posted on 12-6-2011 at 11:22


Quote: Originally posted by asilentbob  
Just remembered that some pyro flake aluminum is coated in stearic acid to prevent oxidation. I should have mentioned this in my previous post.

The main reason I'm wary of polystyrene is that there was an incident a few years back when it was used in a big long multi-break aerial shell at a PGI convention as a sort of filler I think, with very bad results. Or at least that is what I was told.

Wizard, would you happen to have some info on that? I believe they were 13+ breaks. However its been so long that my memory of it all is probably far off.


Polystyrene bring's upon my mind no recollection. I will
post a query among at the collective.

Stearic acid to prevent oxidation.

No. Just a lube.

Aluminum Powders and Pastes
“The Tale of The Powdered Pig”
Reynolds Metal Company 1960

DEVELOPMENT OF ALUMINUM POWDERS
Use of thin metal foil or "leaf" for decoration and ornamentation dates back to early
Egyptian days when the art of overlaying wood, bone and other materials with gold or
bronze was developed. Through the ages this art spread over China, India and later
over Europe. Its height perhaps was reached in the fabulous extravagance of Louis the
14th in whose court the glitter of gold leaf reached world renown.

Gold particles were melted, cast into bars, hammered down into thin sheets. These
were reduced still further in thickness by interleaving with goldbeaters' skins and
pounding the pack with a heavy hammer, producing leaf only a few millionths of an inch
in thickness. In beating to thin leaf, certain particles broke off at the edges of the leaf.
The artisan soon found, however, that these particles could be stuck together with egg
white or other materials to look like a continuous leaf. Next step was to use such
particles to form a paint for ornamenting chinaware, porcelain enameled objects and
similar work.

Then leaf scraps were shredded by rubbing through a fine mesh screen to form a
powder that could be utilized in paints. However, such powder was expensive, so
similar powders were made from copper and bronze. Eventually base metal alloys
colored by heat treating, were developed to duplicate almost every tint of the rainbow.
"Silver bronze" powder was made either from tin or silver. Making powder from tin
involved certain difficulties, while silver was expensive.
Thus the advent of aluminum powder about 1890 resulted in rapid adoption by the
bronze powder industry. This pigment was called "aluminum bronze" even though not
made from a bronze alloy. Modern "aluminum bronze" pigments are made from high
purity aluminum.

Thus this reference to "bronze" has been carried down into today's usage by the metal
powder industry and is sometimes confusing to metallurgists not familiar with this
historical background.

Early Production Methods: Possibly the first metal powder was made by hammering
scraps of gold leaf or grinding in a mortar and pestle. Rubbing scraps of gold leaf
through a fine mesh wire sieve perhaps was next employed. These tedious manual
methods of the goldbeater, however, were replaced by mechanical methods around
the middle of the 19th century to give birth to the modern bronze powder art.
Today mechanical stamps or ball mills reduce the aluminum feed to powder by many
light blows. Ball mills are huge cylinders carrying a charge of aluminum powder and
steel balls. As the cylinder is revolved, the balls are caused to cascade down against
the inner wall, reducing the aluminum particles to flake powder by the multiple impacts
so produced.

Aluminum powder is also made by atomizing molten aluminum, allowing the molten
spray to harden in a blast of air.

Early Applications: Until the latter part of the 19th century, the cost of metal powders
limited their use largely to decoration and ornamentation of jewelry, chinaware,
porcelain enameled work and objects d'art.

With the development of the bronze powder industry and greatly reduced cost of the
powders, application expanded greatly.

A very fine powder was developed for striping or "lining" coaches and other vehicles.
The term "lining", referring to fine powders, is a carryover from this period.

However, "fine" powders of the older days were only 120-140 mesh. Now it is possible
to produce powders so fine that 99.99% of a sample will go through a 400-mesh screen
(although all official reports are based on quantity through a 325-mesh screen as this is
the finest screen certified by the U. S. Bureau of Standards).

The finest powders are usually furnished in paste form, (mixed with sufficient liquid to
form a paste), since the extra fine powders are easier to handle and use in this form.
Types of Powders: Aluminum powders can be divided into two broad classifications —
flake and granulated. The length or width of a flake particle may be several hundred
times its thickness; whereas the length, width and thickness of a granulated particle are
all of approximately the same order, the length dimension probably not exceeding two
or three times the thickness dimension. Flake particles are thus essentially flat, while
granulated are more or less spherical or sausage shaped. The different characteristics
and applications of the two types will be explained later in sections under those
headings.

MODERN PRODUCTION METHODS
First advance in production methods came with the substitution of mechanical means
for the laborious handwork of the goldbeater. Sir Henry Bessemer was so intrigued by
the possibility of making a profit of nearly $25 per pound by converting brass to "gold"
bronze powder that, after concentrating on the problem for several years, he finally
developed a satisfactory mechanical production method and profited greatly there from.
In fact, he dominated the market for many years.

While the problem of producing fine particles of metal mechanically is not difficult, it is
not so easy to give them the shape, brilliance and other characteristics required. As is
explained more fully under characteristics, page 62, the powder particles must be flat,
have smooth surfaces, be separated from each other and have surface characteristics
that permit one particle to slide over another easily (flow). Also the color must be right.
All these characteristics require certain things of the production methods. The best
quality powder appears to be that produced by a large number of light hammer blows,
affording the metal an opportunity to spread out, break off, work harden, etc. as will be
explained.

Today, three different methods of producing aluminum powders are in use at the
Louisville plant of the Reynolds Metals Company — the largest plant of its type in the
world. Flake powders for chemicals and explosives are produced dry by stamping or
hammering extremely thin aluminum foil. Pigment powders are produced as a paste by
ball milling granular powders in a liquid, and subsequent drying. Granular powder is
produced by atomizing molten aluminum. Each method produces a powder with
individual characteristics, so each method will be described in detail for a better
understanding of how to use the resulting product.

In addition to these, there are other methods of producing aluminum in finely divided
form. "Grained" aluminum consisting of rough irregular particles 1/64 to 1-inch in length
results when molten aluminum is stirred while it is solidifying. "Granulated aluminum" in
the form of flattened drops up to 1/2-inch in diameter are made by pouring molten
aluminum through a sieve into water. Shot is made in the same manner. The small
particles resulting from grinding and sawing operations also have certain uses.

Atomizing: In general granular powder produced at Reynolds is made by atomization.
Pig aluminum is melted in a furnace. As the molten aluminum flows through a small
orifice in the atomizing head, it strikes a stream of air. This breaks up the liquid
aluminum into many small particles to form a spray which is directed into a receiver.
There it solidifies or freezes to form fine particles, roughly teardrop or spherical in
shape. These particles then are blown on through the duct to a structure housing a
series of canvas bags for collecting the granular aluminum powder.
Stamping: Whereas production of powder by atomizing is a fairly simple process
involving essentially a single operation, producing the flake powder by stamping
requires a number of operations. Particle size in atomizing is controlled by air and metal
temperatures and by spray nozzle adjustment. In stamping, many more factors enter
the picture.

Thickness of original foil material; number, force and rapidity of the individual hammer
blows; number of hammering stages employed; type and amount of lubricant;
arrangement of air agitation and discharge; amount of polishing; etc. — all have an
influence. Also number and selection of screening operations between hammering
stages greatly affect the final product. It is these wide variations in the manufacturing
process that are employed in producing the many types of powder to provide exactly
the characteristics most suitable for each particular application, in the chemical or
explosive field. Reynolds powders stamped from foil are not supplied for pigment
purposes.

Raw material for stamped flake powder is largely in the form of foil from Reynolds foil
plants. The foil must be free from materials such as oil, grease, dirt, iron or other
substances. Also no aluminum alloys can be tolerated because they do not reduce
properly under the hammers, due to their high mechanical properties.
In order to remove the effect of work hardening during rolling and to make the material
as workable as possible, it is first cleaned and annealed; then cut up into particles small
enough to pass through a screen with ¾ -inch openings. Further reduction is by
hammering in stamping mills.

These stamping machines are of several different types. All have multiple hammers
raised by cams and allowed to fall to strike the steel anvil by force of gravity. Anvil and
lower end of hammers are enclosed to confine the powder. Additional material is fed
into the mill at frequent intervals while discharge is continuous. Material at this stage will
pass through a screen with 20 openings to the inch (20-mesh screen).

Lubricant is necessary to prevent the small particles from welding together under the
impacts from the hammers. Lubrication also facilitates spreading of the metal under
impact, thus increasing the rate at which large flakes are broken up into small flakes.
Stearic acid is commonly used, although tallow, olive oil, rape oil or other oils may be
employed.


Action of the hammers in beating out the metal into thinner and thinner flakes work
hardens or embrittles the material and so assists breakup. At the same time,
hammering one flake over the edge of another produces a shearing action that further
aids reduction of particle size.

Mills in the third stage usually employ more hammers, operate faster, produce a
greater number of lighter blows than the second group of machines. All mills are in
banks as shown in accompanying illustrations. These, like the other mills, are charged
at regular intervals (such as 1-hour) with the air discharge being continuous. Fourth and
fifth stages may be utilized for certain types of product, although particles from this third
stage will pass through 40 to 300-mesh screens, depending upon length of time in the
mill.

As will he further explained under characteristics, page 62, and under testing, page 66,
any particular powder rarely has all particles of the same size, unless specially made.
Most powders contain a certain amount of fines of a certain size range, with some
larger particles.

Grading: In any case, grading to size is an essential step in production. Grading is done
by screening through silk bolting cloth or wire sieves. A typical screen will be of 100-
mesh silk with a working area about 3 x 7 feet. As shown in accompanying illustration,
cloth spouts and covers are employed to prevent the fine powders from becoming
suspended in the air in the room. Material not passing through the screen is taken back
to the hammer mills and reworked. Various sequences of hammering and screening
may be employed. Tests for size, quality, etc. are made at every stage of manufacture.
See section on testing, page 66.

Polishing: For many applications where a brilliant characteristic is desired, the flakes
are actually polished by brushes in a drum. Illustration page 11 shows a typical polishing
room scene. Brushes usually revolve within the stationary drum.

Action during polishing is threefold. First a lubricant is applied to the surfaces of each
flake particle. Then the rubbing action develops heat which softens the lubricant or
polishing agent (usually stearic acid, a dry powder) and also helps distribute it over the
surface of the flake in extremely thin and uniform layers. Third, rubbing the flakes
between the brush tip and innerwall of the drum flattens and smooths out the flakes.
See further discussion under characteristics, page 62.

Wet Ball Milling: Most all aluminum pastes and some powders are made in ball mills.
High purity atomized aluminum powder is normally used as the raw material. It is
charged into a large cylindrical drum along with a lubricant, a suitable liquid and a
quantity of steel balls. The drum is placed with its axis in a horizontal position and
revolved. By adjusting speed of rotation, size and number of balls as well as amount of
aluminum charged into the drum, it is possible to produce an operating condition where
the balls "cascade" to provide a large number of hammer-like impacts as they fall
against the inner wall of the drum.

This action closely simulates the hammering in the stamping mills. This is desirable
since hammering produces a high quality powder characterized by a bright, glossy
surface that has the brilliance, luster and color desired. In ball milling, the lubricant is
used to avoid welding the particles together under impact. An inert liquid such as
mineral spirits is also added to form a carrier for the aluminum particles.

From the ball mills, the slurry goes through a filter to remove excess liquid. The filter
cake contains aluminum pigment with some mineral spirits. A metal content of 65-75
per cent gives a stable paste suitable for use in most coatings.

Driers may then be employed to reduce the spirit content still further or will completely
dry the mixture when dry powder is desired. Thus powder as well as paste can be
made in the ball mills.

The wide variety of powders and pastes described in this book are thus made by
various methods, different hammering sequences, types of lubricants, screening
sequences, etc. It thus becomes evident that making a high grade aluminum powder or
paste with characteristics precisely adjusted to the requirements of any particular
service is a task demanding the highest technical skill, long experience and ultra-modern equipment.


djh
----
Rape oil/Rape seed oil is currently not PC thus Cranola Oil.

Trivia - Rape in rapeseed comes from the Latin name for what plant?





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The WiZard is In
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[*] posted on 16-6-2011 at 15:15


Quote: Originally posted by asilentbob  

The main reason I'm wary of polystyrene is that there was an incident a few years back when it was used in a big long multi-break aerial shell at a PGI convention as a sort of filler I think, with very bad results. Or at least that is what I was told.

Wizard, would you happen to have some info on that? I believe they were 13+ breaks. However its been so long that my memory of it all is probably far off.


I have received two replies to my query —

------------
I think he was referring to the white expanded polystyrene
spheres, which compact well in slightly over filled shells
and when heated by the burst shrivel to tiny drops, so not
causing a fallout problem. Furthermore, the PS beads lower
the weight of the shell and make it more lift efficient...

-----------
I don't think he was talking about teflon if it was being used as a
sort of filler. Polystyrene is notorious for building up static charges
and it could have caused some type of accidental ignition this way.
However, without knowing any more details about the incident in
question, my take on this could be pure speculation.

NB - It's WiZard.



[Edited on 16-6-2011 by The WiZard is In]
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Neil
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[*] posted on 16-6-2011 at 15:50


Quote: Originally posted by The WiZard is In  

Rape oil/Rape seed oil is currently not PC thus Cranola Oil.

Trivia - Rape in rapeseed comes from the Latin name for what plant?



CANadian Oil Low Acid lacks the uric acid content that was previously irrelevant when rapeseed was primary grown for engine oil. Would you like a turnip with your oil? On British hunting forums they still regale each other with their shots made on fields of rape.



Magnalium is often used, as previously mentioned, in home milling operations because of it's brittleness. What about intentional hydrogen embrittlement?
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[*] posted on 17-6-2011 at 01:32
What's your price point?


I found a place that has a frequent sale of Mg powder for $20/lb with reasonable shipping costs. I just ordered one pound plus some AP as a test. I'll report back on my success.

And I'm still kicking myself for passing up a great deal just before I moved overseas. I was at the annual LDRS (High Power Rocketry's big launch. Highly recommended!). One of my rocket buddies had some Mg powder he wanted to sell. $50 for 5lbs!! I can't believe I passed that up.

Certainly in the future I'll be guided by that old classic line:

"It's better t have and not need, than to need and not have!"
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[*] posted on 17-6-2011 at 03:52


Quote: Originally posted by albqbrian  
I found a place that has a frequent sale of Mg powder for $20/lb with reasonable shipping costs. I just ordered one pound plus some AP as a test. I'll report back on my success.

And I'm still kicking myself for passing up a great deal just before I moved overseas. I was at the annual LDRS (High Power Rocketry's big launch. Highly recommended!). One of my rocket buddies had some Mg powder he wanted to sell. $50 for 5lbs!! I can't believe I passed that up.

Certainly in the future I'll be guided by that old classic line:

"It's better t have and not need, than to need and not have!"


What purity and particle size is your Mg powder?

Through my supplier networks I've been able to acquire 5kg of 180 micron spherical >99.7% Mg powder for USD$90/kg. Most of the cost is hazardous goods shipping by courier because you are not only paying for 5kg of powder but a few kg of distilled water to reduce the flammability.

A larger order or shipping by sea freight will reduce the cost substantially. By contrast my suppliers would sell me 99.9% Mg ingots sold on 1.25 metric tonne pallets about USD$10/kg. So there are clear cost advantages of buying Mg as ingots and grinding them down to your own powders, both in terms of cheaper non-hazardous freight and not paying to ship water.




I can sell the following:
1) Various high purity non-ferrous metals - Ni, Co, Ta, Zr, Mo, Ti, Nb.
2) Alkex para-aramid Korean Kevlar analogue fabric (about 50% Du Pont's prices)
3) NdFeB magnets
4) High purity technical ceramics
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[*] posted on 17-6-2011 at 09:12
Mg data...


The catalog says:

"Magnesium -325 VERY FINE MESH PLEASE NOTE THAT ALL CHEMICALS ARE SHIPPED IN A HEAVY DUTY PLASTIC BAG "

At $20/lb it's the best deal that I can find. My whole order was $100 with an added $18 for S&H. I can't wait to mix some propellant this summer. Now if I can just sneak my mother-in-laws Kitchen Aid mixer out to the barn...
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Panache
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[*] posted on 25-6-2011 at 17:24


What about ball milling in cryogenic
conditions say with ln2 using a pressure release valve.




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Intergalactic_Captain
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[*] posted on 26-6-2011 at 01:05


497 and Panache - You guys are taking a VERY dangerous path in your thought process. You DO NOT want to mill metals in an inert atmosphere - Doing so will only virtually guarantee the pyrophoric outcome. The idea of opening the mill to flush it with fresh air every so often serves to allow controlled oxidation of the newly exposed "raw" surfaces... Search APC and rec.pyrotechnics for mill-jar fireballs and you'll see why periodic opening is vitally important. If you never give the metal a chance to oxidize, the first time you open it will probably be your last.

...The nitrogen atmosphere is an interesting idea, as magnesium nitride forms relatively easily - However, anything like argon or propane/butane would more than likely leave you with pyrophoric magnesium.




If you see me running, try to keep up.
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