Difference in Aluminum

[TYRONEEZEKIEL]

As far as aluminum goes, I believe the reactivity goes from

 

bright -> American Dark -> German Dark -> Indian Blackhead being most reactive.

 

This concept puzzles me greatly. How can Al be black? It is a silvery metal.

 

Also, Al=Al how can one be more reactive than the other minus particle size/surface area. With this said, are the black aluminums really pure aluminum, or are they an aluminum salt, or compound?

Edited June 7, 2009 by TYRONEEZEKIEL

[Seymour]

As far as aluminum goes, I believe the reactivity goes from

 

bright -> American Dark -> German Dark -> Indian Blackhead being most reactive.

 

That seems right, however there is much debate over, for example, if Indian is indeed better than German. I would not treat it as fact.

 

This concept puzzles me greatly. How can Al be black? It is a silvery metal.

 

Firstly, this stuff is ridiculously fine. We are talking about many of these flakes being not much wider than a wave of light. This obviously means that they do not reflect so much! Secondly, their preparation involves roasting the Aluminium with a small percentage of an organic material. This is converted largely to lampblack which will, even in such small quantities darken it slightly.

 

If you get a small pinch of the powder and rub it along a surface it becomes a lighter grey as the flakes line up and for a sort of 'sheet'.

 

Also, Al=Al how can one be more reactive than the other minus particle size/surface area. With this said, are the black aluminums really pure aluminum, or are they an aluminum salt, or compound?

 

They are Aluminium, not a salt. They often (perhaps usually) have a coating of stearic acid to prevent the powder from becoming pyrophoric. Other than this, the small carbon content there are no significant impurities.

 

You mentioned particle size and surface area. There is the key.

[Ralph]

aluminium is only nice and silvery when protected from oxygen in the air if not if oxidises to a dull grey colour and when you look at your finer mesh uncoated aluminium powders you will notice they are a dull grey unlike bright flake which is shiny.

 

as Seymour said it there is alot of debate about which is better German or Indian dark if you were to compare the best of both german being 3 micron and indian being 2-4 micron i doubt you would actually notice a difference. (i and most of the Australian pyros use indian pyro100 which is 2-4 micron and we all love it (i supply it))

 

the reason for the differences in reactivity is all about 2 things the first being weather it is coated or not now uncoated aluminium is actually in coated with aluminium oxide (due to natural oxidation) bright flake is thickly coated in stearic acid and dark flake has a very thin layer of carbon and stearic acid (for shipping purposes it is classified as uncoated). When a composition is ignited if it contains one of these aluminiums the heat either provided by a fuse, match, lighter, prime, burst or what ever is igniting it must first get through the layer coating it in the case of dark flake there is almost no layer to speak of and the ignition of the metal particle is almost instant but with bright flake and uncoated aluminium forms they must first heat it suficently to "get to the aluminium"

 

and now for the one every one talks about first surface area. the surface area determines how easy it is to ignite and how quickly it can react. a flake has a very large surface area and a sphere has pretty much the minimum possible surface area (an easy way to show this is to take a piece of paper and light it than compare this to a tightly rolled ball of paper). the surface area is also determined by how small these shapes are the smaller the particle size is the greater the surface area per unit mass

[Mumbles]

I would generally consider all blackhead aluminums relatively equal. Any slightly better or poorer performance will be hard to discern. Given their main uses, it's not going to matter anyway. There are german dark aluminums that are not blackheads. There is one on the market, Ekhart 10890, that is a pretty close replacement for 809 American dark, which is no longer made. I use this in slow flash that I use to boost some of my bursts.

 

The process of making dark aluminum involves gluing a foil to a sheet of paper, and further pounding it with a stamp mill with some stearic acid. The paper give extra mass, and prevents it from being fused together. The paper is then burned off, leaving the characteristic black color. A drum of blackhead I saw had the following analysis:

 

Al >/= 92%

Al2O3 = 2%

Stearic Acid = 2%

Carbon = 2%

[TYRONEEZEKIEL]

so the color of the aluminum has to do with its ability to reflect light.. nvm thats how color in general works. its particle size and shape is what dictates that factor right?

 

 

 

I would generally consider all blackhead aluminums relatively equal. Any slightly better or poorer performance will be hard to discern. Given their main uses, it's not going to matter anyway. There are german dark aluminums that are not blackheads. There is one on the market, Ekhart 10890, that is a pretty close replacement for 809 American dark, which is no longer made. I use this in slow flash that I use to boost some of my bursts.

 

The process of making dark aluminum involves gluing a foil to a sheet of paper, and further pounding it with a stamp mill with some stearic acid. The paper give extra mass, and prevents it from being fused together. The paper is then burned off, leaving the characteristic black color. A drum of blackhead I saw had the following analysis:

 

Al >/= 92%

Al2O3 </= 2%

Stearic Acid </= 2%

Carbon </= 2%

 

 

where did the glue go?

[Mumbles]

The glue gets burned off too.

[TYRONEEZEKIEL]

so that accounts for the carbon correct? alongside the paper?

 

Couldnt I do this at home? or are there specific criteria to follow?

[Swede]

so that accounts for the carbon correct? alongside the paper?

 

Couldnt I do this at home? or are there specific criteria to follow?

 

It apparently has been done, but it is dangerous. There have been noted accidents whereby a guy opens a mill jar, and the inrush of oxygen-rich air can cause a fire or explosion --> maiming or death. Plus, it apparently takes weeks of milling. Not recommended at all when you consider the reasonable price of the commercial product.

[TheSidewinder]

If I correctly remember what I've read about the Blackhead process, it's actually "charred" in an oxygen-free (or at least very oxygen-reduced) atmosphere, to prevent oxidation of the Al.

 

I don't think that can be easily done at home, if at all.

[TYRONEEZEKIEL]

true words. Leave it to people who have the means to do it correctly and safely.

[bigbuck]

ok so if i had a rormula that called for american dark aluminum 809 (its a bright white illuminating star) can i use indian blackhead? the formula as follows

barium nitrate 54

aluminum,american dark 809 20

potassium nitrate 10

sulfur 8

dextrin 6

boric acid 2

so can i use indian blackhead from HCS ???

if so will fence post prime do the trick for a single layer prime??

thanks!!

Edited August 14, 2016 by bigbuck

[OldMarine]

I think that's Ofca's illuminating white formula and I recently tried it with mixed results. The Indian black will work in place of the 809.

These stars require step priming to light reliably. I tried several prime comps with a layer of rough BP over them and none worked well. The step priming worked like a champ though.

[bigbuck]

step prime with 50/50 star comp and bp and then just bp correct? thanks for the help

[OldMarine]

I used 75/25 comp/monocapa then 50/50, 25/75, 100% prime then a layer of BP. It may have been overkill but it worked great.

These stars are very hard to ignite but boy are they bright!

Edited August 14, 2016 by OldMarine

[Mumbles]

Indian blackhead will probably work. The stars may speed up a bit compared to the intended aluminum though. Be careful with the star mixture, it's basically a flash powder before it's bound. The best replacement for the old US Bronze 809 is probably Eckart 10890. It's a coarser flake than indian blackhead, and comparable to 809.

[bigbuck]

i actually found some 200 mesh bright flake today that i am going to try out

[WSM]

Years ago, I read the MSDS for German black aluminum, and they listed the carbon content as 11%.

 

I think it's possible that the carbon can be milled with the aluminum to protect it and speed the rate of reaction (or retard the reaction less than stearic acid). The carbon may help keep oxygen away from the fresh aluminum surfaces by some mechanism I don't understand yet.

 

I guess the fastest speed flash I've seen was using dichromate-treated 325 mesh magnesium, mixed with KClO₄ that was ball-milled with <1% Cab-O-Sil. It was so quick it didn't burn the paper it was on, just make an audible "Pop" and it was done. I called it "Hyperflash" and treat it very carefully. F.or safety, I'd usually make it in less than two gram quantities (one tenth of a gram would reliably "Pop").

 

A bright and loud, small report is possible using KClO₄, black aluminum and treated, fine magnesium. Be aware that it can and will bite so use it cautiously, and in very small quantities. Most of my research was over 30 years ago, so that should be taken into consideration before assuming I'm recalling this accurately.

 

WSM

[Arthur]

There is the problem that aluminium doesn't mill to fine particle sizes, it will also agglomerate. So there is a limit to the productivity of milling. To improve on the minimum milled size available various methods including incorporating with paper and or charcoal are used. The additives and process methods are designed to make the metal mill and shear and prevent it re-agglomerating. Only if there is a steady mass use for a product will it remain "in production" and a process's properties (hence product) may change if variables occur in the feed materials or even the manual operatives change.

[bigbuck]

any special precautions when rolling Ofca's illuminating white formula other than the norm? also formula calls for boric acid, should it be mixed in solvent or will incorporating it in dry be sufficient?

[OldMarine]

I was told by the Pyro Gurus to use it in solution. It doesn't distribute through the mixture enough when added dry. I did that with my second batch and they were great.

[bigbuck]

thats kind what i was thinking but wasen't sure,thanks for clarification om!

[braddsn]

Bigbuck, all of the water that I use for pyro I keep stored in a 5 gallon jug, with boric acid dissolved in it. That way, no matter what process I am using it for, I never have to worry about a reaction. And as for priming, with hard-to-light comps like the one you mentioned, white flitter, white strobe, etc, I prime 2 layers, first layer is 50/50 star comp/bp, then final layer is bp. Make sure each layer of prime is thick, at least 1mm for each layer. I also add 5% silicon to all of my bp that I use for prime.

[WSM]

Bigbuck, all of the water that I use for pyro I keep stored in a 5 gallon jug, with boric acid dissolved in it. That way, no matter what process I am using it for, I never have to worry about a reaction. And as for priming, with hard-to-light comps like the one you mentioned, white flitter, white strobe, etc, I prime 2 layers, first layer is 50/50 star comp/bp, then final layer is bp. Make sure each layer of prime is thick, at least 1mm for each layer. I also add 5% silicon to all of my bp that I use for prime.

 

Chemically, aluminum breaks down in an alkali environment; magnesium breaks down in an acid environment. Your treated water is okay for compositions with aluminum in them, but not a good idea for compositions with magnesium included.

 

WSM

[vikram11]

aluminium is only nice and silvery when protected from oxygen in the air if not if oxidises to a dull grey colour and when you look at your finer mesh uncoated aluminium powders you will notice they are a dull grey unlike bright flake which is shiny.

 

as Seymour said it there is alot of debate about which is better German or Indian dark if you were to compare the best of both german being 3 micron and indian being 2-4 micron i doubt you would actually notice a difference. (i and most of the Australian pyros use indian pyro100 which is 2-4 micron and we all love it (i supply it))

 

the reason for the differences in reactivity is all about 2 things the first being weather it is coated or not now uncoated aluminium is actually in coated with aluminium oxide (due to natural oxidation) bright flake is thickly coated in stearic acid and dark flake has a very thin layer of carbon and stearic acid (for shipping purposes it is classified as uncoated). When a composition is ignited if it contains one of these aluminiums the heat either provided by a fuse, match, lighter, prime, burst or what ever is igniting it must first get through the layer coating it in the case of dark flake there is almost no layer to speak of and the ignition of the metal particle is almost instant but with bright flake and uncoated aluminium forms they must first heat it suficently to "get to the aluminium"

 

and now for the one every one talks about first surface area. the surface area determines how easy it is to ignite and how quickly it can react. a flake has a very large surface area and a sphere has pretty much the minimum possible surface area (an easy way to show this is to take a piece of paper and light it than compare this to a tightly rolled ball of paper). the surface area is also determined by how small these shapes are the smaller the particle size is the greater the surface area per unit mass

Hi Ralph , just a quick doubt, could you just clarify what you meant by pyro100? is it a specific brand or is it just a generic classification?? thank you