Coating Fine Magnesium Against AP

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Edited by PyroSkitz, 11 December 2012 - 10:22 AM.

How clean was your Mg?? All passivation processes work best on a metal surface that's free from grease and oxidation. I've not tried the molybdate/phosphate process, but am doing some experiments at the moment with a vanadate process, I'll let you know how I get on.

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Edited by PyroSkitz, 11 December 2012 - 10:22 AM.

What's the spec of the Mg? And what process was used to coat it? Any processing to de-clump after coating?

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Edited by PyroSkitz, 11 December 2012 - 10:22 AM.

Hey guys, I need a bit of advice, at work we are currently making a new smokeless pyrotechnic range, we need to add 10% fine magnesium into a mix with ammonium perchlorate, we coated the mag with potassium di-chromate, sadly this still didn't stop the reaction when damped down! (presumably because di-chromate is soluble in water)

does anyone know of any other coating that we can use apart from above? (not linseed or acaroid)

i have read in Hardt's "pyrotechnics" that you can use Ammonium metamolybdate and dihydrogen phosphate, has anyone ever heard the process used in doing this or even done this them self?

any feedback for this would be greatly appreciated, hope to hear back from you guys soon :-)

The dichromate is not there to create a coating of the dichromate as such, It is there to passivate the surface (i.e form a low solubility surface treatment, you will notice that the mag takes on a green hue). So I guess you may not have properly coated the material. Anyway, how will you get on with having dichromates in products from a legal standpoint? R45, R46, R49 etc or whatever the GHS system code is for these now.

Have you thought about other oxidisers such as Guanidine Nitrate?

How about pre passivated mag there are plenty of commercial pyro suppliers that offer it (I know the one you use does).

G

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Edited by PyroSkitz, 12 December 2012 - 10:14 AM.

extremly fine, cant discuss microns as its company info, dichromate coating was the process, and sieved afterwards to de clump, so im not too sure why the process still got hot when wetted with amonium perchlorate? is it possible to up the dichromate coating when coating the magnesium? maybe we didnt use enough??

It's tricky to help if you're unwilling to give even the most basic details. 'dichromate coating' doesn't detail the actual process used. I've only heard of people running into issues when trying to coat extremely fine (1000mesh) Mg, using odd processes to coat or using a weak solution.

Is there barium or strontium nitrate in the mixture as well? These are known to strip off the dichromate treatment and render it useless against AP. You should also know that even dichromate isn't 100% effective against AP. It still exhibits a minor reaction according to Shimizu. You might want to try using dichromate in the wetting water, as this can sometimes help. Also, you may want to see if you could substitute MgAl for the Mg to reduce the problems.

Using a very fine Mg may require more dichromate due to the higher surface area. The method presented in shimizu is for 50g per 1 kilo of Mg. I don't know what mesh size this is for, but I'd guess at finest it'd be 200 mesh or so. You don't mention how fine the material is, but the 1000 mesh that Creepin_Pyro mentioned would have probably 30x the surface area of 200 mesh.