20 replies to this topic

[cooperman435]

I believe this method was actually electro plating of ali onto some carbon based sheet (paper) which could be removed by heating as to already begin with a very thin section of ali in the first place.

[digger]

I believe this method was actually electro plating of ali onto some carbon based sheet (paper) which could be removed by heating as to already begin with a very thin section of ali in the first place.

Do you have any reference to this process? Is it used today? Seems it would be rather expensive compared with milling atomised aluminium powders (which is what atomised powders were originally developed for).

[Mumbles]

Here is at least one patent. It's obviously more expensive, but I believe gives a finer product than simply milling. It appears that laminating it to the paper first allows one to get the Al foil finer in the first place. I've read this method (perhaps without charing) is used to produce gold leaf. A lot of information I find on this method seems to come from other people, while well respected, without references.

http://www.freepaten...om/3894693.html

[cooperman435]

Yeah my memory fails as to where this "info" came from and Im in mo way standing by it, just adding to the convo :-)

[digger]

Here is at least one patent. It's obviously more expensive, but I believe gives a finer product than simply milling. It appears that laminating it to the paper first allows one to get the Al foil finer in the first place. I've read this method (perhaps without charing) is used to produce gold leaf. A lot of information I find on this method seems to come from other people, while well respected, without references.

http://www.freepaten...om/3894693.html

Interesting

The only reason I ask for references is that. The supplier I use to buy my drums from(dedicated supplier to the European fireworks industry) says that there is allot of myth associated with the production of the al powders. He says that there is little difference in performance of many of the powders and they are almost exclusively produced by the process of wet milling atomised aluminium (there are a couple of grades used exclusively in the European industry that are very expensive, but he does not rate them much above mepco 000 (which is very good by the way)). This does ring true as it is possible to get very fine atomised powders which would take very little milling to get suitable results.

I just don't see why it would be produced in any other way industrially the technology is well developed and is straight forward. (the atomised process is the one that most producers quote on their websites). It is after all a low cost product when compared to specialty pigments which may use more interesting processes to get specific results. The only reason I can see that there would be carbon in al powders is as a cheap cutting agent (which I would not put past some).

I understand that some think that carbon is there to increase heat absorption. I think that this sounds like a wild stab in the dark to me, given the speed of the reaction and the fact that the thermal conductivity of carbon is far lower than that of aluminium (hence actually being a hindrance rather than a help).

There you go rant over

[Mumbles]

The only reason I can think of for the extra work, is that it's necessary for the finer material. Carbon is a biproduct, not an adulterant, at least in the quality material. There is a certain level where you can't reduce the powder any finer without laminating it back together even with steric acid. There are several patents on modifying the conditions to get it finer, by cooling the drum, or special fatty acid lubricants. I don't recall if it is mentioned in the patent I provided, but one of the ideas for the high reactivity of powder made by this method is that it forms some Aluminum carbide during roasting. It is well known that foils can only be made so fine by machines we have. For instance, aluminum foil used in the kitchen is ran through the roller two sheets at a time on the last run to give the thinness required, thus the one shiny and one matte side. It's not burned off, but below is a method for making gold leaf by hammering gold foil which is sandwiched onto paper to make it finer without relaminating.

http://www.tallogold...af_process.html

You also have to take into account that these powders primarily have military applications, where no expense or level of labor is spared for exactly what they want. In the US, these powders are probably still $5-6 or so per pound on the pallet to container size. It gets up to $8-10/lb on the single barrel scale.

I understand that there are all sorts of misconceptions with regard to aluminums, such as that German blackhead aluminum is even manufactured in Europe.

Edited by Mumbles, 27 July 2010 - 05:27 PM.