29 replies to this topic

[Yugen-biki]

There is no alterative to dichromate.
Shimizu has tested a lot of other things, but found only potassium dichromate to work. Or Ammonium dichromate in combination with guanidin nitrate and magnesium sulfafe. The alternative is to use MgAl, the dichromate is still needed but it is less reactive with NH4ClO4, and the coating results doesn't need to be as good.

[karlfoxman]

There is no alterative to dichromate.
Shimizu has tested a lot of other things, but found only potassium dichromate to work. Or Ammonium dichromate in combination with guanidin nitrate and magnesium sulfafe. The alternative is to use MgAl, the dichromate is still needed but it is less reactive with NH4ClO4, and the coating results doesn't need to be as good.

I thought so, if there was a safer alternative i am sure it would be used. Its nasty stuff but then if you wear the correct gear and respect it then the risk is reduced.

Edited by karlfoxman, 29 August 2005 - 08:58 PM.

[Yugen-biki]

I allways freek out when handeling K2Cr2O7. I wash my hands several times and shower even if I use proper protection.

But the strobe is so beautiful

[Valec]

Well, I had a look at Hardt's Pyrotechnics today, and I found some information regarding the treatment of magnesium which might be interesting:

Ammonium perchlorate mixtures are not
immune from spontaneous combustion. Unwanted reactions are particularly
common in mixtures which contain magnesium, and the best way to prevent
them is to bind the whole star with nitrocellulose. In addition, the magnesium or
magnalium must be given a surface treatment to protect it against corrosion. The
most common method employs potassium dichromate. For every lOOOg of metal,
50g of potassium dichromate is dissolved in 300 ml of hot water. This solution is
intimately mixed with the metal, and the latter then dried by heat, with frequent
stirring to prevent formation of lumps220. Additional dichromate is added to the
composition to buffer it against reaction. Since potassium dichromate is an irritant
poison, an alternative coating method using ammonium metamolybdate
[(NH4)6Mo7O24] and ammonium dihydrogen phosphate [(NH4)H2PO4] has
been recommended2. This is reported to give corrosion protection superior to
that afforded by dichromate treatment.

What do you think? Did anyone try this already?
The dihydrogen phosphate isn't too expensive, it's about 30?/kg in Germany.

[Valec]

Did anyone trying using the phosphate oder molybdate?

(Sorry for the additional post, I clicked 'reply' instead of 'edit').

Edited by Valec, 05 September 2005 - 11:50 AM.

[Yugen-biki]

This sounds very interesting.

ammonium metamolybdate [(NH4)6Mo7O24] and ammonium ihydrogen phosphate [(NH4)H2PO4] has been recommended

Which book is this, "Pyrotechnics" By Alexander P. Hardt, Ph.D.? Does he write how it is done? Or where can one find the process?

[Valec]

Yes, it's Alexander P. Hardt's "Pyrotechnics". The quotation I posted can be found on page 153.
In the Bibliography, a source for this information ist given:

Alenfelt, Per. 1995. "Corrosion Protection of Magnesium without the Use of Chromates,"
PYROTECHNICA'XVI (August, 1995), pp. 44-49. Pyrotechnica Publications,
Austin, Texas.

Anyone got access to this publication? Probably it will give more information about the exact process of coating.


P.S: I had kept some APC strobe stars outdoors (in an airtight container) for 7 months now, without any coating of the magnesium.
Today, I had a look at them and I was surprised as there was very very little smell of ammonia and they still seemed to work.At least those ones made with real coarse magnesium, the others were a bit difficult to ingnite and didn't really strobe but rather flash once and stop burning again.
Maybe I should give them a good prime and try them "in the wild".

Edited by Valec, 14 April 2007 - 08:41 PM.

[Mumbles]

As far as that quote in Hardt. Does it say anything more about the ammonium coating? Specifically what I am looking for is if they are both acceptable seperatly, or if it only works in conjunction. I suppose if no body knows, I may investigate into a copy of Pyrotechnica 16.

[Yugen-biki]

OK, Thanks Valec.

I think that I'll use the K2Cr2O7 for now and maby buy needed litterature later.

[Valec]

Somewhere else in the book (under materials->magnesium) there are a few more sentences:

Protective coatings effective in mixtures containing no ammonium salts include
linseed oil, paraffin, and polyester resins. The standard treatment for magnesium
to be used with ammonium salts is coating with potassium dichromate217. The
toxicity and carcinogenicity of the dichromate ion should be borne in mind.
Alenfelt2 has recommended an alternative surface treatment using ammonium
metamolybdate and ammonium dihydrogen phosphate.

But as far as I see, that's all, nothing more precisely. Sounds like if you need both which would make it more expensive. But in my opinion it's worth the price to stop working with the dangerous dichromate.

Edited by Valec, 08 September 2005 - 11:35 AM.

[Bonny]

I have been reading quite a bit here about treating mg with linseed oil when milling and for storage. After milling,when heating it to dry the oil, should the linseed oil be smoking out of the pan? Or is that too much heat. Is it best to just let it air dry? i did some 100 mesh mg and dried the linseed oil off in a pan (smoking), the only problem is that now my mg is clumpy...

Anyone???

Edited by Bonny, 07 May 2007 - 08:45 PM.

[starseeker]

Somewhere else in the book (under materials->magnesium) there are a few more sentences:

But as far as I see, that's all, nothing more precisely. Sounds like if you need both which would make it more expensive. But in my opinion it's worth the price to stop working with the dangerous dichromate.

Hi,
i have made some 60,40 magnalium this weekend and after reading these post i was wondering if it is sufficient to just treat it with linseed oil if i am only going to use it in kno3,pott perc comps bound with 25% alc,
many thanks,
Vince.

[Frozentech]

Hi,
i have made some 60,40 magnalium this weekend and after reading these post i was wondering if it is sufficient to just treat it with linseed oil if i am only going to use it in kno3,pott perc comps bound with 25% alc,
many thanks,
Vince.

You shouldn't need any treatment at all for MgAl with KNO3 and KClO4. It's mainly when you get into Mg with aqueous bound comps, or Mg and MgAl with NH4ClO4 that you need to be concerned.

[starseeker]

You shouldn't need any treatment at all for MgAl with KNO3 and KClO4. It's mainly when you get into Mg with aqueous bound comps, or Mg and MgAl with NH4ClO4 that you need to be concerned.

Thank you frozentech,
i thought rather safe than sorry!
Vince.

[Bonny]

[quote name='Bonny' date='Apr 12 2007, 08:10 PM' post='33329']
I have been reading quite a bit here about treating mg with linseed oil when milling and for storage. After milling,when heating it to dry the oil, should the linseed oil be smoking out of the pan? Or is that too much heat. Is it best to just let it air dry? i did some 100 mesh mg and dried the linseed oil off in a pan (smoking), the only problem is that now my mg is clumpy...

Anyone???

Anyone???