Sciencemadness Discussion Board

Spontaneous Ignition

Armistice19 - 17-11-2010 at 19:14

I'm sorry to bother you smarter and more intelligent peoples of the forum, however I am obviously at a lack of preventative safety knowledge. After purchasing my first ball mill a couple weeks ago I began milling some aluminum for flash composition. Each time I milled the material for multiple days in hope of reaching "air-float" German Dark. At first I opened my mill to view my new creation only to realize that now that it had been exposed to oxygen it was now burning in the air. I tried a second time, however this time I allowed the media and material to cool down for a bout an hour and a half. It was my assumption that the spontaneous ignition was due to the heat caused by friction of constant milling for long periods of time. I opened my mill and thankfully this time my aluminum powder did not spontaneously ignite.....immediately. It wasn't until I began sifting, and separating the aluminum away from the media that bright glowing embers slowly began to appear and before I knew it I was rolling up my favorite carpet and putting it on the side of the road for the garbage men to retrieve the next morning. The newspaper that I was using to accumulate the sifted aluminum powder was now melted and infused by heat onto my carpet from the ensuing blaze. If this happens again then I am going to have to reconsider weather or not this particular hobby is really for me. In all honesty the safety of me and my family if of utmost concern, and because of this I am very close to giving up on this sort of thing all together.

Sedit - 17-11-2010 at 19:35

I have never performed such an experiment so this is all theory, if im wrong someone will correct me without a doubt.

How about milling it with some sort of inert solvent so that its oxygen reactivity never really becomes an issue until the solvent dries. It would hinder sifting operation though but given the fine partical size I don't feel that sifting will ever be a good idea with such finely divided Aluminum. Even if you manage to have it not go up in flames you will still end up with heavy oxide contamination.

crazedguy - 17-11-2010 at 19:48

idk what your trying to do the best way to make flash is to buy the preground Al flake and perchlorate and mix on a sheet of paper
dont forget to make a static wrist band that ties into the wall plus use static spray
ball milling is better left to the factory just buy the Al powder its sometimes 14 bucks a LB

Armistice19 - 17-11-2010 at 20:25

I could easily mill my next batch with a solvent as my current ball mill is manufactured with liquid milling in mind. It is composed mostly of neoprene, and it certainly makes an airtight seal after the seal, lid, washer, and nut are secured tightly into place. As for crazedguy, I certainly understand that aluminum powder can be purchased and is readily available online from chemical pyrotechnic suppliers, however pound for pound there really does not exist a more economically friendly way of obtaining high grade aluminum powder.

crazedguy - 17-11-2010 at 20:41

wouldnt the particle size be reduced because of friction and if you use a solvent the friction would be reduced maybe stopping the milling
i dont really know much about milling just have a lot of experience with flash powder

mnick12 - 17-11-2010 at 21:01

I have heard of incidents similar to this, some causing quite a bit of damage. A particular incident I recall reading a few years back was an experienced pyrotechnic hobbyist, who wanting some ultra fine magnesium, milled some coarser granules to get the desired particle size. Upon opening the ball mill the magnesium dust instantly ignited causing a massive fireball with alot of heat, miraculously the man escaped with only mild burns.

Anyway I would suggest you do this: I assume you are starting with Al foil and milling it down over the period of a few days. I would suggest that you open the ball mill and let the Al powder remain in contact with the atmosphere for an hour or two. Do this once or twice a day until you are done milling. While this may seem counterintuitive it really isnt, aluminum is actually quite a reactive metal and when exposed to O2 it forms a layer of Al2O3 which protects it from further oxidation. So heres what I suspect is going on, as you mill the Al you destroy the passivating layer while at the same time increasing the surface area by alot. So when you finally so expose the ultra-fine Al to atmospheric O2 it rapidly begins to form Al2O3, and after a certain point enough heat energy is released to ignite the Al.

So hope that helps, and be careful.

franklyn - 17-11-2010 at 22:33

My two cents - don't mill so fine. Unsifted your material will have a range of
grit sizes spanning from around 400 on down to dust that will suspend in air.
To obtain a visual reference of grit sizes see how those look in sand paper.
There is no benefit and some detriment to going beyond 600 # grit , since
the greater exposed surface area means more oxygen bound to the material.
Spontaneous ignition means that it has not been passivated , in other words
the powder surface is raw aluminum which heats from reacting with air. The
lapidary drum ball mill is I expect hermetically sealed when it runs. The only
available air contained within it's small volume is quickly consumed as the
grains are fragmented to expose more surface and much aluminum will remain
with no oxidized surface. When first opened pour in some drug store variety
70 % rubbing alcohol to protect and cool the material by evaporation. Spread
out the powder on a cookie pan stirring and turning at intervals to dry , as
it does it will develop the oxide layer. When it is dried and free flowing it
can then be sifted to separate the finer material from the courser grains
which can be milled some more.

.

Sedit - 17-11-2010 at 23:36

It does seems counter productive franklyn, Your suggesting he create a messload of the oxide to protect the Al which is what he is trying to avoid. If the heat is generated then the oxide is formed, end of story. What he needs to do is protect the HIGHLY reactive particulate without interference from atmospheric oxygen which is leading to the issue at hand.

Inert atmosphere would be great but in this case a huge pain in the ass to say the lest. Better to possibly try extreme cold to slow reactivity and with winter comming it should be simpler then it sounds

Next person that say to buy a reagent that someone wishes to synthesize I might just have to cyber slap BTW. Your wasting our time here at science madness 99.9 % of the time

Shit yall are gonna make me have to clean out my ball mill which is contaminated with Lead right now so I stayed away but this topic just bugs me because I know I could do it right yet never have.



All in all, Avoid the sifting for the moment and perform your seperation mechanically under a solvent by hand if needed else you will have the reactivity issues come into play.

Is it really needed to have a very precice partical size that its worth risking the eintire batch?

franklyn - 18-11-2010 at 00:44

@ Sedit
Scratch aluminum and the exposed surface becomes oxidized within minutes.
A fine powder without surface oxidation will combust in air with minimal prodding.
This is only useful as a reagent and suicidal for pyrotechnic applications.

.

hissingnoise - 18-11-2010 at 02:59

Quote:
In all honesty the safety of me and my family if of utmost concern, and because of this I am very close to giving up on this sort of thing all together.

To prevent its ignition, freshly milled Al should be exposed to air very gradually.
Opening the lid on an airtight container allows air to contact the powder much too suddenly.
After milling, air should be allowed to leak slowly into the container for some time before opening.
This will prevent the sudden oxidation that would heat the Al to ignition.



quicksilver - 18-11-2010 at 06:39

Quote: Originally posted by franklyn  
@ Sedit
Scratch aluminum and the exposed surface becomes oxidized within minutes.
A fine powder without surface oxidation will combust in air with minimal prodding.
This is only useful as a reagent and suicidal for pyrotechnic applications.

.


This is right on the money.

But a few questions have not been answered and some information is missing. I have milled Al quite some many times with this phenomenon not occurring once.
This problem does NOT have to occur. But much more information needs to be determined.

What was used as milling media?
What was the source of the original Al?
What was the mill container constructed of?
What was the speed of the mill RPM and did was the unit closed to air?
How long did this milling continue unabated?
Was any other materiel used in the mill & was there any materiel added to the Al?


Generally speaking continual milling with no pausing for a moment to open the mill container invites certain problems. Steric Acid used as a mild lubricant is generally standard. Milling media should be altered during the process as what may have been appropriate for tearing the foil and shearing process is not the best for further reduction.

One does not allow the continual mill process to continue uninterrupted for several days on end. The media should be altered. A mild lubricant in very tiny amounts utilized.

If Al foil is used the first step is to reduce it prior to milling and make sure it is really pure and uncoated. Buy the cheapest foil available: it generally does not have a coating of any sort. Then use a scissors to cut that into small sections and place into a blender: this will chop it in to tiny (round) sections that work very well with the STARTING mill process. Use hard surface media first to created a flake shape. Add a very tiny amount of steric acid or similar. Run the mill for 24 hours and open [the container]. Run the mill for 36 hrs and open again. Run the mill for two days max and open each time. Initially heavy glass marbles or brass spheres work very well. Eventually smaller (.5 inch) lead balls are appropriate for extremely fine Al.

NEVER allow the mill to run without opening. Never use a media that may contain other materials (stone, etc). Never use a container that has not been cleaned completely! Slower speeds are actually more effective than faster.
Using foil is a slow process. Floor sweepings from milling is generally very fast materiel to mill. Differing aluminum result in differing outcome. Some is VERY brittle and will granulate rather than flake, eventually getting extremely fine and weeping and surface lubricant. Exposing Al to air allows the oxide to exist: sealing it throughout the process will not.

Mistakes can be overcome IF the process of any synthesis is examined in detail. Energetic materials (Energy experiments in general) are unforgiving. The more research beforehand limits mistakes provided you understand the process and what is happening.
Milling pure Al is dangerous and that is why oxidation is allowed to occur. Keeping the Al from mixing with other materials is also a "no-no", that why everything is cleaned.

With no exaggeration I would say I have milled well over 40lbs of Al & about 10lbs of Mg and not had this problem occur. I have gotten some of the finest Al I have ever examined (under a microscope) via standard methods. This process CAN be done very safely. You MUST examine what you are doing that is causing this to occur! It may be as simple as not opening the container at intervals. Try 12-24 hours continually. Make SURE that everything is unadulterated.
All too often the Al sold on eBay (especially) & by some pyro dealers are adulterated with carbon (often as high as 25%). This is NOT due to some "foil-paper burning process" but simple greed. The older process had perhaps 2-5% carbon that appeared attached to the flake Al. There also was a Al powder than had some Teflon. This was from sweepings from two factories and a great deal of powder made from it. It was extremely dangerous but the opening of the containers allowed oxidation to build and even though the Teflon was there, limited tragic incidents resulted. It was unusually reactive to say the least!!!

-=Work in safety=- NO ONE HERE WANTS TO SEE YOU HARMED! And what's more, you CAN achieve a very safe working condition. It is never a good idea to conduct work in the home. but if no other place is available, never leave anything unattended. If you need to leave. Turn off the mill. If it takes a few more days: so what? Keep you weight levels down until you understand any problems that may occur. Be strictly aware of any fire danger.
You MAY be doing everything correctly and sparking from some source (motor brushes) MAY be the cause of a flash of air-float Al that you simply didn't realize!!! Ask questions: people will treat you with respect. No one wants to see you harmed or your stuff fucked up...



[Edited on 18-11-2010 by quicksilver]

condennnsa - 18-11-2010 at 08:10

Quote: Originally posted by franklyn  
@ Sedit
Scratch aluminum and the exposed surface becomes oxidized within minutes.
A fine powder without surface oxidation will combust in air with minimal prodding.
This is only useful as a reagent and suicidal for pyrotechnic applications.

.


wikipedia says : "Metallic aluminum is very reactive with atmospheric oxygen, and a thin passivation layer of alumina (4 nm thickness) forms in about 100 picoseconds on any exposed aluminium surface.[5] This layer protects the metal from further oxidation."

Actually the practice in the pyro community is to keep opening the mill jar at regular intervals. If, for example you mill for a week, make a habit of opening the jar every 12 hours at least, leaving it open for about a minute or two. this will create the oxide layer on the fresh surfaces, but won't lead to ignition temp, as you would get from the huge surface area of 1 week milling time.

nitro-genes - 18-11-2010 at 08:59

Add 3-5% of a viscous silicone oil before milling (Other oils, like motoroil makes your rubber drum swell like crazy) and after milling is done, take the drum from the rollers and leave it (STILL CLOSED!) somewhere outside for 3-4 days or so. The very small amount of oxygen that is able to get into the drum will passivate the aluminum in a controlled way. Another thing that I used to do is simply opening the lid and quickly closing it again for a couple of times. Be carefull though not to produce a dust cloud while handling the drum, as once happened to me! :o

Despite these difficulties I still think milling in an nearly airtight drum is better. If continuously the aluminum is passivated-depassivated by erosion-etc you will probably end up with pure aluminum oxide pretty quick...:)


[Edited on 18-11-2010 by nitro-genes]

The WiZard is In - 18-11-2010 at 09:03

Quote: Originally posted by Armistice19  
I'm sorry to bother you smarter and more intelligent peoples of the forum, however I am obviously at a lack of preventative safety knowledge. After purchasing my first ball mill a couple weeks ago I began milling some aluminum for flash composition. Each time I milled the material for multiple days in hope of reaching "air-float" German Dark. I am very close to giving up on this sort of thing all together. [snip]



First "air float" is applied to charcoal. German Dark info at the
end.

Ye old Aluminum Powder and Pastes "The Tale of the Powdered
Pig" Reynolds Metals Company, 1957. And I suspect a zillion
web sites.

Hammered aluminium powder is lubricated w/
"stearic acid is commonly used, although tallow, olive oil, rape
seed oil or other oils may be employed."

Wet ball milling — "An inert liquid such as mineral spirits is also
added ...."

----------
Extracted from:

A Buyer's Guide for Aluminum Metal Powders
Ken L. Kosanke
PGII Bulletin 27 & 28 November, 1981 & December, 1982

Back issues available from the PGII [ www.pgi.org ]


1) The number one question concerns the definition of the very general descriptive
terms -- dark, light and bright. I think these are poor terms and their use should be
avoided. They are much too general and can mean quite different things to various
people. These differences (between kinds of aluminum powders) can be very signifi-
cant. Even subtle differences, not detectable by eye or feel, can produce significantly
different pyrotechnic effects (more on this later).

Dark USUALLY refers to very fine flake aluminum, with finer flake USUALLY appearing
darker. This is a consequence of light reflecting off the more numerous irregular particle
surfaces. However, an exception is "German dark" aluminum. Here most of the dark
color is from the presence of carbon, resulting from its manufacturing process more on
this later). There are at least three grades of German dark, all appearing quite dark, but
all having different particle sizes. Obviously in this case, darkness of appearance is no
guide t particle size. It has also been reported in the literature that some manufacturers
add carbon black to their products. Again, darkness is no guide to particle size.

To MOST pyrotechnists, bright, not light, is the opposite of the attribute dark.
USUALLY, bright refers to flake aluminum's, but the flakes are large enough (if free of
carbon) to appear shiny (bright). Bright flake aluminum can still be very fine and very
reactive.

Light USUALLY refers to atomized or finely ground aluminum's. The particles of
aluminum have more of a 3-dimensional character than flakes. Unfortunately, light
atomized aluminum can be as dark appearing as dark flake aluminum.

Confusion can be avoided by substituting more descriptive terms, such as "flake" and
"atomized", along with an indication of particle size, for the ambiguous dark, light and
bright. Possibly the one exception I make is the use of the term flitters, which are very
large flakes usually in the range of 8 to 14 mesh.

The third manufacturing process leads to flake aluminum. Here aluminum particles or
foils are either rolled or hammered into very thin flakes. In either event, a lubricant must
be added to the aluminum to prevent the flakes from sticking together and onto the
rollers or hammers. Stearic acid (stearin), a fatty organic acid, is a common used
lubricant. The presence of the lubricant often gives flake aluminum a slippery feel, and
is the reason it resists mixing with Water in star compositions. It also causes the powder
to appear shiny, and protects it from oxidation. One significant variation in making flake
aluminum accounts for essentially all of the dark color in dark German aluminum. Here
little or no lubricant is used. Instead the aluminum is rolled on or between very thin
sheets of low ash paper. After the rolling process, the material is heated in an inert
atmosphere, turning the paper to carbon.

nitro-genes - 18-11-2010 at 09:07

It is better NOT to use stearic acid in combination with flake aluminum! With stearic acid, the end product is impossible to handle without particles of aluminum floating all over the room, leaving silvery dust on everything! :)

The point of the paper process is not to turn it into carbon later btw, but creates a aluminum carbide coating that protects it from further oxidation.

[Edited on 18-11-2010 by nitro-genes]

The WiZard is In - 18-11-2010 at 11:23

Quote: Originally posted by mnick12  
I have heard of incidents similar to this, some causing quite a bit of damage. A particular incident I recall reading a few years back was an experienced pyrotechnic hobbyist, who wanting some ultra fine magnesium, milled some coarser granules to get the desired particle size. Upon opening the ball mill the magnesium dust instantly ignited causing a massive fireball with alot of heat, miraculously the man escaped with only mild burns.


Ball-mill-1.jpg - 889kB Ball-mill-2.jpg - 847kB Ball-mill-3.jpg - 813kB

This is your basic thermite® type reaction. A standard lab demo
is to burn Mg ribbon in quartz sand. See also —

William D Jones
The Magnesium + Cab-O-Sil Fiasco
Reprinted in : The Best of American Fireworks News V
(The Best of AFN series can be had from http://www.fireworksnews.com/



---------
donald j haarmann
rec.pyrotechnics
December 8, 2005

"Lloyd E. Sponenburgh" <LLoy...@mindspring.com
|

| I suspect is was a combination of a localized ignition of a small amount of
| Mg between the balls, along with atomized Mg from the agitation of the
| balls, and (*possibly*) a silane reaction with the SiO2 (Cabosil) in the
| jar.
|
| I've run Mg in a jar only once -- ONLY once, and I was not milling it. I
| got severely injured. I, too, had Cabosil mixed with the magnesium.
|
| LLoyd

Silane! Buff and Wöhler's Siliciuiumwasserstoffgas (siliciuretted hydrogen)! I have my
doubts. The only source of hydrogen being moisture and just how the water would be
decomposed remains a question. Burning magnesium and cabosil perhaps could in the
presence of moisture release a combination of any of the 6 silicon hydrides, however,
absenting a lot of water the amounts would not be significant. It is, however, well known that
the mechanical treatment of chemicals can increase their reactivity.

Dropping ball upon balls ... the point contact area cannot be great (I have at this time been unable
to find a equation or table of sphere point contact areas vs. diameter) therefore, a lot of energy
can be generated over a small area by the impact of two balls.

Armistice19 - 18-11-2010 at 16:21

I use value time aluminum foil to start with, its about 75 cents a roll and its perfect for my applications. I take the foil and fold it over itself several times before I tear it into smaller pieces. I then use a blender to obtain finer granules. The granules are then put in the mill and let go non stop for 7 days. (I realize now that milling for this long continuously is a life threatening mistake.) My ball mill is composed of 2 air-tight neoprene containers, and my media is non sparking Lead-Antimony balls. The RPM's on my ball mill is 60 AT MOST. From now on I will need to be exposing my aluminum powder to oxygen on a regular basis while milling. I have plenty of 100% pure silicone oil around the house which I could use as an added safety measure.

BromicAcid - 19-11-2010 at 14:59

I had a similar experience with silver thermite going up on me and causing third degree burns over a good portion of my body... not fun. It really brought back the memories to read that post WiZard.

Armistice19 - 19-11-2010 at 18:39

So I opened my second container today after leaving it open a crack overnight. It did not spontaneously ignite. However my lead-antimony media was toast. It was lumpy and had distorted shape. At first I thought it was simply coated with lumps of aluminum powder but I soon realized the problem was much more permanent. The lumps were very solid and had become infused with my media. I suppose this might have also been caused by too much continuous unstopped milling. Since I am working with my oxidizers and fuels separately, I think that Alumina cylinders will be my next choice of media. Also what benefits come from adding lubricant to my aluminum during milling?

FrankRizzo - 19-11-2010 at 19:37

The problem with Lloyd's accident report in AFN as posted by The Wiz is that the "dilutent" that Llyod was mixing with the magnesium was an *OXIDIZER*. Magnesium will steal the oxygen off of many materials that one might normally think to be inert. In this case, cab-o-sil is chemically SiO2...note the two oxygen molecules ready for action.

Commercial aluminum, even the "dark" aluminums, are lightly stearin coated to prevent spontaneous ignition during mfg.

oxidizer? we don't need no stick'n oxidizer

The WiZard is In - 20-11-2010 at 11:48

Quote: Originally posted by FrankRizzo  
The problem with Lloyd's accident report in AFN as posted by The Wiz is that the "dilutent" that Llyod was mixing with the magnesium was an *OXIDIZER*. Magnesium will steal the oxygen off of many materials that one might normally think to be inert. In this case, cab-o-sil is chemically SiO2...note the two oxygen molecules ready for action.

Commercial aluminum, even the "dark" aluminums, are lightly stearin coated to prevent spontaneous ignition during mfg.



Tell the WiZ (Donald J Haarmann)
American Fireworks News
Number 19 March, 1983

Dear WiZ: I have, after a 25-year hiatus returned to fireworks, my renewed interest
in which coincided with the arrival of last year's tax refund. I promptly ran amok,
ordering a pound of this and that and soon had a fine collection of pyro chemicals. I
felt confident that I could, on a moment's notice, whip up any formula published.
Wrong. As luck would have it, when Jerry Pulice's Whistling Titanium Rocket article
was published (AFN #9) 1 found I lacked 10-28 mesh titanium and had only 100
mesh or some very coarse sponge which I had obtained from Jim Finckbones’ Mega
Tech (of whom it can be said, here is a pyro who has paid his dues).

The problem of reducing the 4 mesh sponge to 10-28 mesh seemed a simple
problem of running it through my kitchen blender. So I proceeded to dump the entire
pound in the blender and start it on Speed 1 (my blender has seven speeds).
Click-it-ter, click-it-ter, click, snap, crack, ting-ting; it would seem that a little higher
speed was in order. So, on to No. 2, then 3, now 4 and then 5 and WHAT-HO, along
with the click-it-ters, snaps, tik-tik, bang-bang, clinks and rattles, there were little
white sparks going around in circles, along with the titanium, when HOLY
PYROPHORIC BATMAN – the-the-the inside of the blender just lit up like a light
bulb! Now the top has blown off and titanium dioxide smoke and finely divided Ti is
issuing forth. It rapidly became a race to turn off the blender and at the same time
keep my laundry bill to a minimum.

Hummmmm, no doubt a fluke so this time I tried it again, but using a three-foot
dowel rod to push the buttons. All was OK.(even fine) until once again Speed 5 was
reached and once again FLASH-POP SMOKE. All of which leads me to write to my
WiZ with my plaintive question: WHY ME?

signed G. R. Phlegmone

Dear Phle: The answer to your question is less obvious than would appear. It would be
simple to put it down to "just another nut job", however we pyros as a group are given
to mixing together finely divided, highly reactive metals, along with strong and not
particularly stable oxidizing agents. Then, not being satisfied, we add fuels like gums
and charcoal. And for the height of folly, we put a match to it!

There is, of course, a rationale to all this: fireworks are fun.

Now as to what happened and what to do about it, the following may be of some
use/interest. As you have astutely observed ' titanium, along with several other metals,
is pyrophoric, that is, they are 1) capable of producing a spark when struck (as with a
blender blade), 2) burning in air spontaneously (indeed, some months ago a well known
pyro was burned when some Ti powder ignited as he was pouring from one container to
another). What probably saved you was the limited amount of oxygen available in the
blender and when the heat from burning raised the air pressure add blew the top off,
the powder was dispersed sufficiently so that the reaction was not sustained.

Now things to do. You could Simply buy coarse Ti but then I would be out of a job and I
need the money. Being a Wizard ain‘t cheap. Now, as the Ti is rather reactive with air,
we have the choice of either removing the air by placing the blender in a vacuum
chamber (shouldn't cost more than a couple of grand) or of placing the blender in a
cabinet and displacing the air with an inert gas such as krypton. This is simpler than the
vacuum chamber but lacks elegance.

What is needed is an inert gas that could be poured into the blender to displace the air;
as luck would have it, there is such a gas, sulfur hexafluoride. Not only is it inert and
non-toxic, but it is five times heavy as air.

There is the eternal problem: where to buy it? The Sears catalog doesn't list it and a
quick check of the J.C.Whitney catalog failed to reveal it. So. we have to call out the
heavy artillery, that is, to barter. If you live in a "closed" state and have access to Class
C, you have a great item to barter.

Now SF is commonly used as an insulator in high voltage work, so grab a handful of "C"
and truck over to your local power plant with a big plastic bag and trade for some. If you
choose to buy it, at $10.30 a pound in 10 pound lots liquefied in a steel cylinder, you
should have about a 7,000 year supply. If you don’t like the plastic bag idea and you
are a physics fan, the fact that the critical pressure of the gas is only 2,206 kPa & 21
deg. C. will be of some use:

When you get it home, pouring it into the blender will be a bit of a chore as it is
colorless . You will have to fall back on by-guess and by-gosh or if you have one
handy, a Schileren set-up will be useful. If you decide to use this method, please drop
me a note so that I can check the horizon for smoke now and then.

[Who would put titanium in a blender? I’ll never tell!] /djh/


djh
----
Hudson Maxim
Dynamite Stories 1916

DEDICATION
INTRODUCTION
To the actors in the comedies and tragedies of real life without whose efforts and
sacrifices the stories could not have been so interesting and true, this volume is with
grateful acknowledgments most respectfully dedicated. As the parts played by the actors
were not rehearsed, the performances have required a little retouching in the interest of
the reader, the author having subordinated history to story rather than story to history.


franklyn - 22-11-2010 at 22:51

Quote: Originally posted by The WiZard is In  
The Magnesium + Cab-O-Sil Fiasco
Reprinted in : The Best of American Fireworks News V
The Best of AFN series can be had from http://www.fireworksnews.com

http://www.sciencemadness.org/talk/viewthread.php?tid=14884#...

This has all the earmarks of a Texas tall story. While the intrepid victim
may well have been singed , credibility is lost with embellishment.


" My mill jar was a one gallon capacity PVC jar "

" The mill jar was still on the mill with the quite, green white glow of
burning magnesium emerging from it's mouth. I put out the jar fire
with dry sand "

" The jar - was burned to ruin by the fires inside "

" A welder's helmet was hanging in the line of fire - it was charred
almost to destruction.

" I poured cold water over the burns for a couple of minutes until
fires caught my eye. There were several small fires burning in and
around my milling shack."

- Although PVC is intrinsically fire retardant because of it's
relatively high flash point ~ 435 ºC and 57% of it's weight is Chlorine,
the heat of a magnesium flare would liquefy and ignite the container
with napalm like combustion. Even with the shack open , 2 minutes
is the mean time for flashover and conflagration of everything. The
events as described don't correlate intense heating with little fire.
http://www.chemexper.net/specification_d/chemicals/supplier/...
( It should be noted that PVC , magnesium , and a nitrate salt constitutes
tracer composition for rifle ammunition )
http://tinyurl.com/366allw
http://tinyurl.com/393fprh


" my arm had third degree and second degree burns. The left side of
my face was a mass of very shallow third degree burns. The delicate
new skin below was sore and pinked , but otherwise healthy."
- Although the writer goes to extensive detail of his injuries no where
is there any mention of the scabbing which must necessarily occur to
be consistent with what is claimed.
- Third degree burn means total loss of skin requiring grafts to replace it
and hospitalized in an intensive care burn center.


" I went through Special Forces training in the Navy "
- Huh ? Special Forces is an army outfit. Generically " Special Forces "
refers to Navy Seals also but it is seldom referred to as such , and while
many military branch facilities provide interservice training , basic survival
skills are service specific.

" They also taught us how to recognize shock in one's self , and
how to treat it."
" the next day I saw a doctor - " Damn Lloyd ! You could have died !
I've seen people die from shock with less than this ! "
- Shock is the medical term for excessive blood loss. Had the ' doctor '
received Special Forces training also he would have known that.

.

bbartlog - 23-11-2010 at 04:15

Seems like nitpicking. Sure, he may not in fact have had third degree burns to the extent claimed. His 'couple of minutes' might have been only 15 seconds - who knows how someone's perceptions of time would be affected in that situation?

As for the rest, it seems like
- the SEALs might not have existed under that name at the time that he would have trained
- almost the entire reaction would have occurred outside the PVC jar (that being where the oxygen was), limiting its involvement
- 'shock' does not necessarily imply blood loss; you sure can get shock from being badly burned; and even if there is some narrow medical definition that meets your criteria there's no reason a doctor couldn't have been speaking colloquially.

In short it seems like you're grasping at straws to throw doubt on a perfectly plausible story.

watson.fawkes - 23-11-2010 at 05:43

Quote: Originally posted by franklyn  

This has all the earmarks of a Texas tall story. While the intrepid victim may well have been singed , credibility is lost with embellishment.

" My mill jar was a one gallon capacity PVC jar "
The fellow who relates the story is the author of the book Ball Milling Theory and Practice for the Amateur Pyrotechnician. In it he describes the construction of mill jars from PVC plumbing pipe and standard fittings. His one gallon jar has a main body of 6" diameter pipe, 8" long.

grndpndr - 23-11-2010 at 12:06

FWIW Franklin has some valid observations.2nd/3rd degree burn victims of the degree described aren't sent home with antibiotic cremes etc to care for themselves.Home care and recovery:o
I wont bore you with military terminology/history but rest assured a Navy SEAL would never refer to himself as SF and vice versa.
I cant comment on the rest of his story but the military and injury parts of the story sound like artistic license to me.:D

[Edited on 23-11-2010 by grndpndr]

[Edited on 23-11-2010 by grndpndr]

quicksilver - 29-11-2010 at 11:06

Most possibly. However for an author like Spoonburger to write a "mia culpa" of that nature is quite something. He has contributed to a great deal of energetic / pyrotechnic oriented material in organized and printed sources for many years.
The thing that strikes me is his recollection of pain which in an odd sense is a good thing as serious 3rd degree burns generally kill those nerves. I also have milled Mg, however I had always be quite careful of the milling media & to always make damn sure the device(s) were grounded.
Again, from my experience, Mg mills finer and finer in a granulated form; not crushing into flakes or similar shapes. In fact I have seen Mg SO fine as to be difficult to ignite if not separated quite a bit; almost forming a solid in it's fine particulate form.
It's likely that Loyde got it right on the money. That the dry silica formed a static phenomenon with the movement of the mill and that was all that was needed.

Once, quite some many years back there was an aluminum that was available for a short time that had a coating of Teflon! This was some of the most reactive aluminum I had ever seen; perhaps the most. As the story goes it was pulled from some floor sweepings of an aerospace industry plant & was milled once in a large quantity with both lead and Lignum Vitae (Iron Wood) croquet balls in a cement mixer. Perhaps the reason it did not cause a disaster is the combination of media and lack of air seal.
It most certainly DID have it's hand in many problems during it's sale to the public.

Included below is an interesting patent that uses either terephthalic acid (the better result) or pentaerythritol (less effective) to create a flash powder that claims not to be explosive without containment but with containment is an extremely powerful explosive mix. This (if true) would add a HIGH element of safety to both burst charges or simulators - virtually any area where an extremely loud explosion is needed but safety is primary.



Attachment: _6521064-flash.pdf (44kB)
This file has been downloaded 848 times

[Edited on 29-11-2010 by quicksilver]

nitro-genes - 30-11-2010 at 15:57

Very interesting, I was sceptical at first, having seen only peak pressures mentioned in the patent, but total impulse also seems twice as high as with regular FP.

Unconfined, the 72.9/18.5/8.6 composition is nearly impossible to light, even with a gasburner. Loosly packed in sealed cardboard tube and lighted by fuse it burns slowly (though very steady!) with yellowish/white flame. The cardboard tube (quick test) probably didn't provide enough pressure to make DDT. That is the only serious drawback I can see, maybe intermediate PE contents/higher Al could be used to overcome this high pressure thresshold for this comp. to work. Another thing would be using chlorate instead of perchlorate or adding a catalyst like Fe2O3. Haven't tessted this yet, though the comp. with perchlorate seems amazingly inert.

So whats the deal here? IIRC they mentioned sublimation of the PE? Would other polyols qualify as well? Erythritol, sorbitol, etc?

The WiZard is In - 30-11-2010 at 18:47

Quote: Originally posted by quicksilver  

Included below is an interesting patent that uses either terephthalic acid (the better result) or pentaerythritol (less effective) to create a flash powder that claims not to be explosive without containment but with containment is an extremely powerful explosive mix. This (if true) would add a HIGH element of safety to both burst charges or simulators - virtually any area where an extremely loud explosion is needed but safety is primary.



Flash compositions of some types will cause explosions in the
lightest of containers even sometimes in just a few turns of paper
but it also happens that these compositions are extremely brisant
and sensitive. Horrifying mixtures of potassium chlorate, pyro
aluminium, sulphur and barium nitrate have been employed and
should be avoided at all costs. Mixtures of the perchlorate, sulphur
and bright aluminium are safer and appear to be used extensively
in the U.S.A. and Japan, but even these would be considered
dangerous by many of us in Europe. In fact the more common
European technique is to use a strong paper tube with a
composition consisting simply of potassium perchlorate and dark
pyro aluminium.

Rev. [The Master Blaster Pastor]
Ronald Lancaster Fireworks: Principles and Practice


djh
----
Pyrotechnics don't have
to be a dying art. /djh/

nitro-genes - 1-12-2010 at 01:38

Even 70/30 KClO4+DG Al by itself is pretty sensitive, both to static discharge and friction. Put a few mg's in a mortar and see how easy it flashes from the resulting friction. The PE addition somehow makes the composition nearly completely inert when unconfined, the difference is really quit dramatic and not even remotely comparable with "regular" flash. I was suprised to see the steady burn rate of this composition at all.

quicksilver - 1-12-2010 at 07:17

I had thought the patent interesting as I had not seen something of this nature before with such emphasis as to gain a full patent. The selection of terephthalic acid to a 70/30 is what interests me most as there may be factors such as the gaseous by product of (terephthalic acid) making for ignition perhaps even enhancing it; but in it's solid state being a retardant to combustion.
Obviously the need for understanding what happens to terephthalic acid during a burning process would determine why (or if) this patent fills it's promises.

Personally I would not waste reagent-grade pentaerythritol on something like this but the garbage in drums that is often sold (in the vinyl paint and coating businesses) is a different story. However in today's climate of fear and stupidity I would not attempt to buy a can any longer. Terephthalic acid unfortunately is not available in a low technical grade (TTBoMK) but I don't think it's too pricey.

[Edited on 1-12-2010 by quicksilver]

Mumbles - 1-12-2010 at 13:31

Quote: Originally posted by mnick12  
I have heard of incidents similar to this, some causing quite a bit of damage. A particular incident I recall reading a few years back was an experienced pyrotechnic hobbyist, who wanting some ultra fine magnesium, milled some coarser granules to get the desired particle size. Upon opening the ball mill the magnesium dust instantly ignited causing a massive fireball with alot of heat, miraculously the man escaped with only mild burns.


When I read that I thought of another accident actually than Lloyds. It happened to Bob Forward, but I am not sure if it was Mg or MgAl, but I lean toward magnesium. The accident actually didn't happen when he opened the mill, but rather when he was dropping or pouring the dirty media back into the uncleaned jar.

Lloyd is a person well versed and well respected in pyrotechnics, so I will let his story be. I do have a bit of an issue believing the jar was still intact. I had a pretty major accident recently with much cooler burning materials, and PVC a fair distance away was melted very severely.

With regard to milling of aluminum both stearic acid and oleic acid are fairly common with nearly every type of flake aluminum, even the blackheads and dark aluminums. I've seen the aluminum carbide theory mentioned before, but have never heard anything that would convince me one way or the other if it is just carbon/stearic acid, an aluminum carbide protective surface with a highly scattering surface, or a combination of both that gives the dark color and protection. There is certainly some fatty acids in there though. I've also heard some people claim the aluminum carbide improves reactivity. A drum of Eckart #5413-H reads the following though:

Aluminum >/= 90%
Aluminum Oxide < / = 4%
Stearic Acid < / = 2%
Carbon < / = 2%

I'm curious as to why you'd try using lead to mill aluminum. Even hardened lead is softer than aluminum. I'd imagine this would result in fairly significant lead contamination of the aluminum powder. Most who try to make their own flake aluminum, or reduce the size of MgAl, use steel. Again, I'd leave the glass marbles out. It's pretty clear you're trying to use this to make flash, and abrasive materials are not something I would want to be adding.

nitro-genes - 1-12-2010 at 15:25

I go with the increased reactivity of the aluminium carbide coating, it seems that even with nanopowders like ALEX, a coating of palmitic acid is enough to prevent further oxidation of the aluminum upon storage.

Interesting stuff these nanopowders, I've been thinking about a way to produce them OTC for a long time. Commercially they are made by explosive evaporation in inert surrounding gas, particle sizes go as low as 100 nm. Lots of potential in pyrotechnics, HE and rocketry...

--> http://www.nanosized-powders.com/en/35/

Mumbles - 1-12-2010 at 23:01

The reason I've always been suspicious of the aluminum carbide theory is that every intentional preparation of it utilizes far higher temperatures than would be experienced if just charring the paper off. You'd also think you'd be able to see yellow crystals on the surface. Not to mention it decomposes with moisture, so I would imagine any aluminum carbide that may would be decomposed within at most a few months of it's production.

quicksilver - 2-12-2010 at 07:31

I also can attest to the problem w/ using lead as a medium. I stopped after a single day. However the result will yield some substantial reduction at that point but the contamination is something that occurs no matter the material if metallic. However, in hindsight, I am not sure the level may be as great as it may initially seem as the surface of the lead become coated with Al particulate & the crushing / shaving effect may be more than direct contact. But I always want to opt for purity so I dismissed it.

Even brass had some contamination and the problem of introducing copper elements into anything that may contact a perchlorate/chlorate is a serious one. Glass appears to be a fairly decent material but finding anything but large marbles is tough. Personally I don't mill unless I am going to be doing a fairly substantial amount as I have the setup for it and it just seems a waste to mill much less than a pound
I also think that the "open" or free volume in a mill can contribute to problems as well as a more full mill may utilize the "shaving effect" to an advantage.

There is a factor that is often unconsidered; & that is that direct contact of medium and milled material is often much. much less than most people think. The shaving or crushing effect is often what takes place and for that, the medium needs weight. Even glass is quite light unless the volume is fairly large.

The preparation is (IMO) one of the significant agendas of working this effectively. The "water and cut foil" prep in a blender had been the better of many as it has an element of safety and size reduction is fairly good if a blender used is one that could stand up to long runs. If that is not available; the user needs to be satisfied with a much lessened rending of the foil.
The best starting material I had found was floor sweeping due to that "shaving factor" so as to produce a granular mater prior to further rending & flattening. The problem of cleaning up from contamination of dirt and debris is one that is very tough to avoid but (IMO) worth the effort as you generally have several pounds to work with at minimum. I had once totally forgotten to place the milling medium in the mill when I was first beginning to ball mill materials and found that the simple act of tumbling the floor sweepings had a great result. Therefore it's just my opinion that with Al (and perhaps Mg) the actual SAME material is the best milling media one can use! Several large cubes (or best; spheres) of Al may actually be the best if time is not a factor. The problem occurs when the mill uses a volume area that doesn't allow for a distance fall. A 6" diameter doesn't allow a "dropping" of the media and milled element to take place to gain a crushing effect.

There is a remarkably thin (viscosity) oil available which is a synthetic used for pump lubricant that is really the only thing I have used in the past. A tiny bit goes a long way. In it's refined state it's used as microscope oil due to it's remarkably thin viscosity (it only had a "mil-spec number" as I remember but it is common as a pump oil referred to as "ultra fine". 2-3ml per lb of Al is MORE than enough & once the mill has been turning for a few days the majority will adhere to the walls and be left behind from the product.

The draining of the water from the initial blender rending will allow enough oxide to develop prior to milling. And in the case of floor sweepings, there should be enough oxide there after a day of more air exposure.

It occurred to me that Loyde must have known that a true "outside ground" of the whole unit is a demand that has to be met. A third prong ground of the motor just doesn't cut it. The whole unit needs a real full ground of "rod in earth" type. I think he even had written that!
There had been some discussion of using a conductive container in a mill (paint can) rather than rubber, etc as it could be grounded more effectively. I have never tried that as an experiment I was not willing to risk the consequences.

[Edited on 2-12-2010 by quicksilver]

The WiZard is In - 2-12-2010 at 09:50

Quote: Originally posted by quicksilver  
I also can attest to the problem w/ using lead as a medium. I stopped after a single day. However the result will yield some substantial reduction at that point but the contamination is something that occurs no matter the material if metallic. However, in hindsight, I am not sure the level may be as great as it may initially seem as the surface of the lead become coated with Al particulate & the crushing / shaving effect may be more than direct contact. But I always want to opt for purity so I dismissed it.



I would note in passing commercial producers of milled aluminium
anneal it before milling w/ steel balls. Aluminum is tooo soft as manufactured.

At no extra charge —

GOLD-BEATERS SKIN. This skin is prepared from the external or peritoneal
coat of the cæcum or blind gut of neat cattle. [Neat cattle — from whom is obtained “neat’s foot
oil”. /djh/] The workman separates and turns over the portion which encircles the
junction of this pouch with the rest of the intestines, and draws it off inverted form
the other coats to the length of 25 or 30 inches. It is then immersed a short time
in a weak solution of potash, and is cleaned by straying upon a board with a
knife. When thus well cleaned and by soaking in water, the piece is stretched
upon a kind of frame from 40 to 50 inches in length and 11 inches wide, and
made up of two uprights held together by two cross-pieces having longitudinal
groves two and a half line in width. The surface of the membrane which was
outside in the animal, is placed in contact with the upper part of the frame ; it is
stretched in every direction, and is glued to its rim. Another membrane is then
stretched above the first, with its external surfaced placed upwards, and is
attached to it by glueing around the edges. When dry, the membranes are
separated by running a sharp knife along the groves. Each strip is then glued up
a frame similar to the first one, but without a grove, and is washed over with a
solution composed of alum 1 ounce ; water, 2 quarts.

When the surface is dried, a sponge dipped in a concentrated solution of fish-
glue in white wine, rendered aromatic by cloves, nutmegs, or camphor, is passed
over it. When this coating is dried, it is covered with a coat of white of eggs, and
the strip is cut into pieces 5 ½ inches square, which are then smoothed out under
a press, and make up into leaves.

A body is given to the pieces of gut ; that is, they are moistened with an infusion
of cinnamon, nutmeg, or other warm and aromatic ingredients, in order to
preserve them ; an operation repeated after they have been dried in the air .
When the leaves of the skin are dry, they are put into a press, and are ready for
use. After the parchment, velum, and gut-membrane have been a good deal
hammered, they become unfit for work, till they are restored to proper flexibility,
by being placed leaf by leaf, between leaves of white paper, moistened
sometimes with vinegar, at others with white wine. They are left in this condition
for three or four hours, under compression of a plank loaded with weights. When
they have imbibed the proper humidity, they are put between leaves of
parchment 12 inches square, and beat in that situation for a whole day. The are
then rubbed over with fine calcined gypsum, as the vellum was originally. The
gut-skin is apt to contract damp in standing and therefore dried before being
used.

GOLD-BEATING……. 2 pages.

Ure’s Dictionary of Arts, Manufactures, and Mines: Containing A Clear
Exposition of their Principles and Practices.
By Robert Hunt, F.R.S.
Longman’s, Green, and Co. 1878
Volume 2, p. 727-728.100


Ball milling aluminium

The WiZard is In - 2-12-2010 at 09:54

Found this in the depths of my HD.

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.

Ball milling book or two

The WiZard is In - 2-12-2010 at 10:09

I shelve — and you may find interesting.

A treatise on the internal mechanics of ball, tube, and rod mills
Horace Edgar Rose, Ralph Major Edward Sullivan
Constable, 1958 - 258 pages
(Not found @ google.com/books)

Amazon.com pop'd up these :—

High-Energy Ball Milling: Mechanochemical Processing of Nanopowders by M. Sopicka-Lizer (Hardcover - Jul 7, 2010)
Buy new: $239.95

Mechanical Alloying And Milling (Dekker Mechanical Engineering) by C. Suryanarayana (Hardcover - Sep 28, 2004)
Buy new: $219.95 $188.26

Excerpt - Table of Contents: "... 11 2.1. Introduction 2.2. Historical Background 2.3. Development of High-Energy Ball Milling 2. ..." Surprise me! See a random page in this book.

Mathematics and Control Engineering of Grinding Technology: Ball Mill Grinding (Mathematics and its Applications) by L. Keviczky, M. Hilger, and J. Kolostori (Hardcover - Mar 31, 1989)
Buy new: $239.00

Bet it's a real page turner! Not.

[Edited on 2-12-2010 by The WiZard is In]

franklyn - 2-12-2010 at 11:37

So the gist is - you can beat our prices , but you can't beat our balls ?
I think I'd rather have a lap dance to bump and grind aluminum.

.

watson.fawkes - 2-12-2010 at 12:15

Quote: Originally posted by franklyn  
I think I'd rather have a lap dance to bump and grind aluminum.
I think I'd prefer a crotch that wasn't on fire.

The WiZard is In - 2-12-2010 at 12:17

Quote: Originally posted by franklyn  
So the gist is - you can beat our prices , but you can't beat our balls ?
I think I'd rather have a lap dance to bump and grind aluminum.
.


Ah a Big Apple residence — you must be thinking of the
Melody Theater long gone from W 48th Street.

Wiki-P Lap dance and follow the obvious links for more info.

Ball Milling Speed and Load

The WiZard is In - 2-12-2010 at 12:33

Rose and Sullivan

Ullmann's B2 5th ed.




Ball-mill-Ullmann-2.jpg - 335kB Ball-mill-Ullmann-1-800.jpg - 384kB Ball-mill-Rose-800.jpg - 240kB Ball-mill-Ullmann-3.jpg - 358kB


djh
-----
How I came to have volume A1-26
and B1-8 of the 5th ed of Ullmann's?
eBay. Found it at a price I could justify
and close enough that the shipping wasn't
a deal breaker. As with most of what I
buy on eBay I was the only bidder.

I inquired of the seller - where did you get
this brand new set? He was a commercial
photographer and the publisher sent him
the set for an ad. and didn't want it returned! A
complete set was ca. US $12 000!

After several years of effort I found the 27 & 28
volumes at a reasonable price.

For chemistry I prefer K & O. I own the 3 and 4th
ed. I have looked at the 5th or latter ed but prefer
the earlier eds. Someday I'll find the 1st ed for a
good price.

quicksilver - 3-12-2010 at 06:51

-=OT blurb=-

Now the PRICES of texts on energetic materials and associated sciences is a whole topic in itself. I too, have attempted to put together a functional collection of books over the years and at this moment I would say without exaggeration I have at least $2500-30000 in books I've bought (striving for a decent deal at each turn) and working used book sales and library sell-offs.
Lap-dances: Hell, you could get a month of Happy Endings for the money it would take to get some of the more recent publications. And although I know we have already discussed Albris and other used book sellers; I do have a method that MAY help one or two of you get some more textbooks at a decent price.
Contact a "Librarian's Association" in a smaller community (they are general county-oriented groups of working-level librarians who join together to attempt to pull more money for their own branches) and tell them you are looking to BUY books in specific categories in rough condition and that you are a "continual source" to buy off these type of books. - YOU WILL GET CALLS BACK! They are hungry for money and they really don't see any value in what (to many of us) would be a gold-mine of information. That's how I got most of the PATR. Usually the names are (County name) Librarian's Association, or collective, or something damn similar & will take a bit of hunting but they may be listed or on-line.

franklyn - 3-12-2010 at 13:49

@ The WiZard is In

You are seriously afflicted with bibliophilia. No doubt
you haunt the stacks of the Strand on 11th street.

Regarding
" As with most of what I buy on eBay I was the only bidder. "

Ever lose out on an opportune find on Ebay ?
You might try sniping.
Gixen is a last moment bid entry service that's free.
I've had good results , the logon is not private but
no charges of unauthorized use have surfaced.
www.gixen.com

.

quicksilver - 3-12-2010 at 14:49

He's not the only one; I caught it (bibliophilia) back in the UseNet days when a certain person used to post there quite often. But seriously; you (Franklyn) have found some GREAT stuff online. I know because I still hunt and some of the links you've found have slipped right through my fingers... :-)

Armistice19 - 8-12-2010 at 17:31

Recently I purchased three boxes of chrome plated steel milling media (50 balls each box). I also took the advice that all of you have so kindly posted and bought 1lb of stearic acid as well. With these new products I will attempt the same synthesis and post the results. Thank you for all of your assistance.

[Edited on 9-12-2010 by Armistice19]

quicksilver - 9-12-2010 at 07:02

Just as an aside Skylighter is selling a rock tumbler (a common ball mill design) for $79, which (if it is the same as the Harbor Freight unit made in China - they appear the same.....) actual cost is $29.
Rock tumblers are attractive due to low cost, completed assembly and rubber containers. But they are tough to really ground properly & will always be totally air-tight. These are not always seen as advantages.
Ball milling should be done out of doors, they should be grounded as well as possible (the whole unit: not just the motor or frame) & a tiny amount of "breathing" is a positive thing; stopping large amounts of hydrogen or other gases from building. They should also be worked with remotely: even if that simply means along extension cord. When stopped; they should be allowed to come to a "resting period" for a few moments. This settles the crushed material and allows the ground to do it's job. dielectric and conductive elements can even produce a capacitive phenomenon to a slight degree and a moment's resting is a safety issue that has some dividends.

gregxy - 9-12-2010 at 10:36

It would also be interesting to investigate if aluminium carbide is what makes the "dark german" powder better.

Perhaps someone could:
1. Grind Al foil in an air tight container for several days
2. Add powdered graphite, lampblack or charcoal without letting much air in.
3.Continue grinding.
4. Stop grinding and carefully introduce air.

Another alternative would be to grid with steric acid and then
roast the product without air to pyrolyze the organic coating.

Mumbles - 9-12-2010 at 22:48

I really doubt that the mechanical grinding would impart enough energy to form aluminum carbide. You'd probably end up with nothing you couldn't get from an unethical reseller of aluminum. I also have a feeling that trying to burn off a stearic acid coating would make quite a mess, as it would fuse first before pyrolysing.

If you want to test this aluminum carbide theory, I'd imagine you'd perhaps want to wash the coating off of a powder, and try to roast the aluminum powder with a little graphite using conditions known to generate aluminum carbide. You could then do some tests side by side with the decoated powder, and the powder which has been roasted.

quicksilver - 10-12-2010 at 09:29

The unethical agenda of "Indian Dark" (the most common one where they adulterate with carbon) was actually caught by about 4 or 5 people. I think I may have been one of them.
I had bought some years back and it just felt odd. Putting in a microscope reveled that the carbon was not attached; the way it would have been from the old fashioned burning foil-paper. & there was MUCH too much carbon. A fellow who I used to trade with contacted me and wanted to trade for some straight rolled rocket tubes that I wanted. I didn't want him to get the idea that I was screwing him so I said what I believed. He got a sample from me and said he had never seen anything like that before (it was sold by a large pyro supplier AND a very large specialty importer).
I took a tiny sample an used an oil lens at 1000x and it became very clear that the carbon was never attached and was an obvious (air float) wood carbon. One guy continued to sell it off but the large supplier would not sell it and made a really big deal out of it with the importer. It's all gone now as that was years back. It was way too obvious as it actually settled if you had the right equipment.

Getting back to carbide: I think it would be just too dangerous to work that in a ball mill. I think it may be possible to do on a very small scale in a lab environment but I believe it's too reactive enough to attempt to use impact as a manner of mixing.
There has been several "odd" highly reactive Al powders. Frankly I think some of the tragedies may have been a result of those. The Teflon / Al powder was really a death mix as was the commercial Al powder that had an adulterant of brass powder in it. (copper and a per / chlorate is a serious issue).
When the CPSC first put the clamp down the prices went from 4-8 USD a pound to $15 & there was a lot of money to be made. But when the final civil action looked like it was going to hold, that was when people started to make fast money from it.

[Edited on 10-12-2010 by quicksilver]

Free Reading.

Armistice19 - 12-12-2010 at 16:49

The Wizard Is In, Thanks for the book info. I already found a free copy of "Mechanical Alloying And Milling" on Scribd.com

http://www.scribd.com/doc/3629131/Mechanical-alloying-and-mi...

Excellent reading material!!

As I mentioned earlier I had found my lead media to be deformed and chunky, also the mix was very warm after milling. I'm not sure about it but page 43 talks about deformation of powders due to heat caused by kinetic energy. I think this might explain the particular incident.

"Temperature rise during milling The intense mechanical deformation experienced by the powders leads to generation of crystal defects and this plus the balance between cold welding and fracturing operations among the powder particles is expected to a&#128;ect the structural changes in the powder. Another important parameter, the temperature experienced by the powder during milling, dependent on the kinetic energy of the balls, can also determine the nature of the final powder product. If the temperature generated is high, the associated higher di&#128;usivity (higher atomic mobility) leads to processes resulting in recovery (and recrystallization). In such a case, a stable phase, e.g., an intermetallic, would form. On the other hand, if the temperature is low, then defect recovery would be less and an amorphous (or a nanocrystalline) phase would form. The temperature of the powders during milling can be high due to two di&#128;erent reasons. Firstly, as mentioned above it is due to the kinetic energy of the grinding medium. Secondly, it is possible that exothermic processes occurring during the milling process generate heat. But, in practice, when the temperature of the powder or the milling container is measured, it is probably due to a combination of these two factors. Additionally, one can intentionally raise the temperature of the container, but this would not be considered here. Let us now consider the temperature rise during MA, due to the kinetic energy of the grinding medium, either observed experimentally or calculated using some appropriate theoretical models. The intentional raising of powder temperature to study the structural changes in the mechanically alloyed powder has been partially discussed in Section 4.3.10 and will be further discussed in the individual sections on Solid Solubility Extensions, Intermetallic Phase Formation, Amorphous Phases, and Nanostructures. A comprehensive review on the temperature e&#128;ects during mechanical attrition has been prepared by Koch [203], which also contains details of the different models used for these calculations. The macroscopic temperature of the vial (or powder) has been measured with thermocouples in some cases. A maximum temperature of 40±428C was recorded [203] when the experiments were conducted with no balls in the container; even with 13 balls in the SPEX mill, the temperature rise was noted to be only about 508C. Hence, it was concluded that most of the temperature rise comes from the motor and bearings. Some investigators have, however, reported very large temperature rises. The data available on the measured temperatures is summarized
in Table 6."


(Click the Link and scroll to page 44 to view the table)

It seems conventional ball mills can reach up to 90 degrees C. That sounds about right since my media and powder were very warm to the touch after milling. I may reduce the amount of media in order to lighten the load. This in turn should cool down the motor, also using chrome plated steel media should create less kinetic energy. Hopefully this second go round will turn out beautifully.







[Edited on 13-12-2010 by Armistice19]

Stocking stuffers

franklyn - 12-12-2010 at 20:12

http://www.harborfreight.com/3-lb-rotary-rock-tumbler-67631....
http://www.harborfreight.com/dual-drum-rotary-rock-tumbler-6...
http://www.amazon.com/Diameter-Chrome-Steel-Bearing-Balls/dp...

.

Armistice19 - 13-12-2010 at 20:28

Wow, I wish I hadn't bought my materials already. Those are really good prices, it seems I've been overspending. That rock tumbler looks exactly like my ball mill. Perhaps I've been severely ripped off :(

Armistice19 - 28-4-2011 at 12:30

I tried once again to synthesize aluminum powder with the new information and suggestions from all of you. The experiment went as followed...

VARIABLES:

Aluminum granules and stearic acid were placed in a neoprene air tight ball mill with chrome plated steel media. The ratio was 10/1 media to filling by weight. The filling was 97% Aluminum and 3% Stearic acid by weight. Mill was run 24 hours at a time, then turned off. Once turned off the containers were removed from the mill and allowed to sit for 2 hours. After this the containers were opened and allowed exposure to the air for another 2 hours before being resealed and put back on the mill for another 24 hours. This process was repeated for 4 weeks without any problems.

RESULTS:

A semi-fine bright reflective powder was obtained. This Aluminum powder was mixed with finely powdered store bought potassium perchlorate in a plastic container that had been sprayed with "Static Guard". The ratio was 30% Al to 70% KCLO4. Batches of 1gram, 5grams, and 30grams were ignited separately with American Visco waterproof fuse. All of the tests had the same result. A very bright, slow burning, thick smoke producing lameness.

HYPOTHESIS:

Too much stearic acid caused lack of sufficient friction in the ball mill to create a fine enough aluminum powder for rapid deflagration. Experiment will be repeated with the exact same variables except a 0.5% to 99.5% ratio of stearic acid to AL by weight.

...Thoughts comments?

hissingnoise - 29-4-2011 at 03:04

Results might be better using thin aluminium foil and hardened lead media!

Armistice19 - 30-4-2011 at 16:18

I was using hardened lead antimony in my previous batch, and I actually am using thin aluminum foil. It had been cut into very small pieces and then put through a blender and ground into fine granules. Anyway, I was told that using chrome plated steel would be an efficient media because of its hardness compared to aluminum, where as lead is softer than aluminum. I expected better results this time. It seems that I have gotten rid of the spontaneous ignition problem, but only at the expense of the aluminum itself. I still think it was the stearic acid concentration.

Armistice19 - 7-5-2011 at 10:22

This morning I used a cheap 200 mesh brass sieve to sift through the previous "lame batch" of aluminum powder. After sifting I obtained ~24g of 200 mesh aluminum. This was then mixed with ~55g store bought powdered KCLO4. The result was a majestic "WOOSH" that closely resembled store bought black powder which I had handled in the past. This further supports my original hypothesis that the aluminum was not fine enough due to the lubricating effect of having too much stearic acid in the mill. I am hoping that this new batch containing only 0.5% stearic acid by weight will reach a much higher mesh and possibly even produce an report whilst uncontained.

CHEAP LAB SIEVES!! ---> http://www.sheffield-pottery.com/SearchResults.asp?Search=si...

hiperion42 - 7-5-2011 at 11:05

I found the use of tin snips or scissors to break the foil
down one level to be quite inefficient.
So i started using a paper shredder with confetti cut to
produce 4 x 23mm rectangles which works good.
Getting it down further to 1 x 1mm stage i introduced the
confetti into a blender which i turned on for about 2min at max speed.
The resultant product is a great starting point for introduction into
the ball mill for milling with alumina media.
The only problem is that after blending 1 role of aluminum foil confetti the
blender is fatally injured and has to be replaced.
Does anyone else have blender woes?

[Edited on 7-5-2011 by hiperion42]

quicksilver - 7-5-2011 at 14:42

Cut prior to putting it in a blender. When I played with that it was OK on the blender IF I cut them up 1st. Basically what you're doing with the shredder.
The concept is to get them in a position where the ball mill can have a object to tear into. The blender should produce a size that's damn near perfect for that.
It's the final result that counts however and if you're getting a good result w/ a shredder; so be it. A "lab-level" blender is a great deal better designed than one from a kitchen. It's not worth you ruining your stuff.

hiperion42 - 8-5-2011 at 02:59

The blender was a cheap one so i am curious how a more
expensive one will hold out.
On the picture from foil to confetti to 1mm level using paper
shredder and blender.

4566767.jpg - 353kB

quicksilver - 8-5-2011 at 04:50

It appears appropriate to me; it should mill quite well. I should add that I used a variety of medium in the mill and did get some fairly excellent results. But it is something that is best done outside and with a ground on the motor or metal frame of the mill. There's less chance of static outside and the "puff" of sub-micron Al won't hover above the opened container. I found it was optimum to work with as large as weight unit as was feasible at one time due to the time element in milling. The one issue I had was with Mg becasue that material granulated finer and finer; it didn't flake. It needed a well thought out means to work with it once it past a certain point (about 8um) it would settle into a near solid, it was so fine.

hissingnoise - 8-5-2011 at 05:09

Quote: Originally posted by Armistice19  
Aluminum granules and stearic acid were placed in a neoprene air tight ball mill with chrome plated steel media.

I assume you mean that the inside of the jar was neoprene-coated since a neoprene jar would be too soft for powdering metals.
An airtight jar would mean that minimal oxidation would occur and a lubricant would be unnecessary.
In this case grounding too, wouldn't be required . . .

Armistice19 - 8-5-2011 at 12:18

Here is the ball mill that I purchased, http://www.pyrocreations.com/inc/sdetail/11955/11959

Note the description:
"6 Lb capacity DOUBLE Barrel ball mill. Perfect size for milling 2 different comps at once in separate drums. (2 barrels measures 4.75" high x 4.5" in diameter).
Grind most materials into a fine powder in just a few hours. Includes 2 single 3 lb. Neoprene barrel with quick-seal, leak proof closures (spark resistant) Heavy construction and easy to use and built to last a lifetime. Liquid can be used in the barrel without any worry of leakage. Continuous-duty fan-cooled motor that should never give problems. If used on 220 volt a power converter must be used."

Also for everyone having trouble with their blenders if you have several hundred dollars to spare you might want to waste it on one of these.... WILL IT BLEND? "BlendTec" the indestructible blender----> http://www.willitblend.com/

Armistice19 - 6-6-2011 at 13:06

Good news folks. Excellent results were acquired with the new variables introduced. Very fast burning flash powder was synthesized after the stearic acid content was changed from 3 wt.% to 0.5 wt.%. Instead of a slow "woosh" a nice quick "POOF" and the flash powder was instantly gone. For those who would like to know here are the variables to my successful experiment.

Media to filling ratio:
-10/1

Filling composition by weight:
-AL 99.5%
-Stearic acid 0.5%

Milling time:
-4 weeks with breaks every 8-24 hours to allow open exposure to oxygen.

Sieve size:
-200 mesh brass

Conclusion:
-These variables make a nice fine aluminum powder for flash compositions but in my opinion 4 weeks is too long for most milling projects, and on top of that it is very very difficult to sift through a 200 mesh brass screen. Next time I will be using a 15/1 media to filling ratio in order to speed up the process, also I will be using a 120 mesh sieve.

Refinery - 28-2-2014 at 16:45

Does fine aluminium react with acetone? This is because I want to remove the paraffin/stearic acid from the powder. What would be best method to dry the powder after purifying? Would heating it in container with back-pressure valve over hot water bath allow acetone vapors to escape but prevent air from entering?

But 900 grams of balls for 100 grams of aluminium powder and 4 weeks milling time to produce only fair results? Oh god, I was aiming for something like 60:40 filling rates at maximum of 1-3 days.

[Edited on 1-3-2014 by Refinery]

Bert - 28-2-2014 at 17:55

It's the necromancer!

The ball mill chosen was far too narrow. Mill efficiency goes up dramatically with increased jar diameter- That "6lb. ballmill" is actually just two 3lb. (tiny!) mill jars on a double length roller system.

Charge is not determined by WEIGHT. Charge is determined by VOLUME. Mill jar should have been exactly 1/2 full of media, charge to be ground should fill up the interstitial space between the pieces of media, no more. Overfilled jar makes for a much slower grind-

Cheap acetone isn't too pure, acetone is also hygroscopic and needs to be dried before use in several pyrotechnic applications I know of, particularly where it contacts Mg or high Mg alloys. Molecular sieves work for that, so would various anhydrous chemicals that take up water as they hydrate and aren't soluble in acetone.

Refinery - 1-3-2014 at 13:35

Hmm, but does it actually matter if there is 3% of paraffin in aluminium if it is used in pyrotechnics?

Btw, does anyone have any ideas of cheap and easily available grinding media? I've been thinking of cutting cylpebs from 10-15mm steel rod, but the steel is obviously pretty soft and it might be consumed in the process. I might also get carbon steel which I could temper into good hardness but the rods are pretty expensive. Any sources of ceramic balls that would be tensile enough for milling?

Dornier 335A - 1-3-2014 at 13:49

Yes it matters. Even small amounts of oil or similar will slow down flash powders considerably.

I have used glass marbles as grinding media in a small ball mill. They work surprisingly well and look like new even after 50 hours in the ball mill.

Refinery - 1-3-2014 at 16:05

Well, that's bad.

Any ideas how to dry acetone moisten aluminium powder without igniting it? What if I mix a small amount of carbon with it at the begin of milling, would it protect the aluminium enough or would it be washed off the surface by acetone? Best way would be to use inert atmosphere with argon, but darn I dont have the welder(yet) as a reason to buy a cylinder. :P My best idea so far is back-flow valve and hot water bath to allow acetone evaporation but prevent air letting in.

My only intent to use paraffin is because one journal found that by mixing 3% of it with aluminium will decrease the particle size from coarse (0.5-2mm) to 20-50um in 6 hour period and without paraffin the flakes were reduced only to 500um. This time saving is so high that it becomes even fundamental.

[Edited on 2-3-2014 by Refinery]

Bert - 1-3-2014 at 19:30

Quote: Originally posted by Refinery  

Btw, does anyone have any ideas of cheap and easily available grinding media?[/


If you live in the USA, get enough nickles to 1/2 fill your ball mill jar. Non sparking, fairly non reactive (better than steel, anyhow!) and they work pretty well. If you get different media later, clean them and return to the bank!

If you want ceramic media, it's a common industrial item. Google is your friend!
Hint: It's often used by people making glaze for ceramics.
http://m.ebay.com/itm/400301684295?nav=SEARCH


Stearin wax was the lubricant of choice for milling flake Aluminum. Parafin? Do you mean the wax, or what is called kerosene in the USA?

[Edited on 2-3-2014 by Bert]

DubaiAmateurRocketry - 2-3-2014 at 02:42

Talking about the ignition,

I find the color of a propellant has a effect on the burn rate, maybe largely. If you have a transparent binder(PU/HTPB/GAP), it will burn fast. I am unsure of the reason but I came up with one. And if the propellant is dark colored (adding 1% carbon power/ asphalt/ pen ink) it will burn much slower(few mm/s) for some reason. Modern energetic composite propellant's burn rate is too fast, sometimes few centimeters per second. Too fast for many application(a half meter wide rocket/missle will finish its fuel maybe in less than 10 seconds). Therefore I wonder if there are any dark colored liquid energetic materials.

Bert - 2-3-2014 at 08:50

Quote: Originally posted by DubaiAmateurRocketry  
Talking about the ignition,

I find the color of a propellant has a effect on the burn rate, maybe largely. If you have a transparent binder(PU/HTPB/GAP), it will burn fast. I am unsure of the reason but I came up with one. And if the propellant is dark colored (adding 1% carbon power/ asphalt/ pen ink) it will burn much slower(few mm/s) for some reason.


If a solid propellant is transparent to infrared and/or visible light, energy will be transmitted into a fuel grain's interior by light from the burning surfaces in addition to the energy transfer by conduction from the burning surfaces. Increaseing the energy fed back into a grain will obviously increase burn rate, and in extreme cases can cause a grain to catastrophically fail. (KABOOM!)

Carbon black is commonly used as you describe to reduce light penetration into fuel grains. It's cheap and has some fuel value.

As far as dark colored liquid propellants: The infrared absorption profile of liquid fuel droplets sprayed into a combustion chamber certainly MATTER in regard to their speed of reaction. But unless the combustion chamber and tankage are transparent, light energy can't pre-heat propellant before it enters the combustion chamber in a way analogous to solid fuel.

If you WANT your fuel/oxidizer pre-heated, route it through a cooling system built into the walls of your combustion chamber & expansion bell (regenerative cooling).

,

[Edited on 2-3-2014 by Bert]

DubaiAmateurRocketry - 2-3-2014 at 08:57

Yes thats my explaination for this phenomenon too. A dark colored binder should reduce the large amount of radiation from the combustion to penetrate the transparent binder and pre-heat the next layer of propellant so it will be easier to ignite. Therefore ending in slow burn rate.

In my opinion, bitumen/asphalt is better than carbon black since it is a liquid and is miscible with most liquids, such as PU.

Bert - 2-3-2014 at 09:50

You know of the original asphalt based "composite fuel", GALCIT 53 propellant?

For well characterized, storage stable mil spec propellant, carbon black is likely going to be a cheaper & easier material to obtain in consistent quality than asphalt. Uniform performance is KEY with solid propellant- Every oil field is different and lots of odd things rode along with those hydrocarbons we wanted.

Have you got Richard Nakka's books on composite fuel & engine design?

http://www.nakka-rocketry.net/#Quick


Re-inventing the wheel is fun, and good training-

DubaiAmateurRocketry - 2-3-2014 at 11:42

Quote: Originally posted by Bert  
You know of the original asphalt based "composite fuel", GALCIT 53 propellant?

For well characterized, storage stable mil spec propellant, carbon black is likely going to be a cheaper & easier material to obtain in consistent quality than asphalt. Uniform performance is KEY with solid propellant- Every oil field is different and lots of odd things rode along with those hydrocarbons we wanted.

Have you got Richard Nakka's books on composite fuel & engine design?

http://www.nakka-rocketry.net/#Quick


Re-inventing the wheel is fun, and good training-


GALCIT53, yes thats some old stuff, but yeah. Potassium perchlorate's burn rate wont be slowed down by any other binder.

The reason I said asphalt so that there is more binder content. even 1% liquid can help with the viscosity a bit and allow more mixing and higher density in the end :) For uniformity of performance, just get the same asphalt product from same supplier hehe.

Nakka's site is very useful and some of his sites on theories are very useful for calculations. His book should be a lot of help on motor designs, however I have been concentration on the fuel and not the motor, ill eventually study that.