pyrojig Posted January 7, 2013 Posted January 7, 2013 I had a concern that just came to mind. Im not quite sure but in my experience with chlorate comps, it seems best to avoid acidic conditions ( such as sour paste, or resins that contain trace acids). While working with a purple and yellow round star comp( which contained 2-8% of Magnalium , I experienced the heating of the comp (like nitrate/ Al stars) . My first reaction was to add a dilute solution of boric acid to the comp to reduce the hydrogen sulfide gas and heat being produced . The mix was to be pressed by hand in a star pump. . My concern: Is there enough acid in this dry comp to create unwanted reactions,sensitivities , and or worse " spontaneous ign".? The boric acid treats AL not Mag, So what does one do to reduce reactions of comps that contain Magnalium ?
Mumbles Posted January 7, 2013 Posted January 7, 2013 In my experience, magnalium is attacked by Boric acid. As for the chlorate issue I don't know if it'd be a big problem. Boric acid isn't a conventional acid in that it doesn't produce hydrogen ions, it absorbs hydroxide. The production of chloric acid, which can decompose into chlorine dioxide is generally thought of as the major detrimental reaction. I don't think that boric acid is strong enough to do this. It certainly isn't strong enough to protonate bicarbonate into carbonic acid. To protect magnalium, some of the commercial operations I'm familiar with use potassium dichromate solution to wet the mix.
pyrojig Posted January 8, 2013 Author Posted January 8, 2013 (edited) Thanks Mumbles .I was figuring it was going to be K-dichromate due to the mag content. But figured since there was the chance the alloy was more resistant to the oxidation. The magnalum is pretty fine stuff, maybe in the ballpark of 300-400mesh. So heating is almost inevitable in comps bound with water. Dichromate is toxic, but a crucial need with mag comps that have any hygroscopic oxidizers, or are water bound. I just had to double check with you guys for a confirmation.I have had success with using it, in the past, but that was with a Perch comp.Blesser White strobe. I was going after more of a shimmer effect using a ultra-fine Magnal , and milled perch. This comp did heat up very warm to the touch, but never to a extreme point that lead me to worry. I did add the boric acid to this comp. and it did help to a extent. The strobes worked great , not as fast as I hoped for but very nice. Edited January 8, 2013 by pyrojig
AdmiralDonSnider Posted January 8, 2013 Posted January 8, 2013 I heard that the dichromate is a skin absorber so go sure to wear adequate protection even if it´s in solution. The shimmer effect is said to be based on anhydrous magnesium sulphate if I remember correctly. But this seems to be an AP application.
WSM Posted January 8, 2013 Posted January 8, 2013 I heard that the dichromate is a skin absorber so go sure to wear adequate protection even if it´s in solution.The shimmer effect is said to be based on anhydrous magnesium sulphate if I remember correctly. But this seems to be an AP application. ?, I'd say especially if it's in solution. Dichromates are nasty... but useful. Wear appropriate PPE's and wash thoroughly after handling them. Also avoid breathing the smoke of burning compositions containing it (stand upwind if burn-testing any stars or compositions with a dichromate component). From my research over the last ~30 years, I think the shimmer effect is due to the MgAl mixture. I say mixture because MgAl isn't a true alloy, but an inter-metallic mixture. I've observed that magnalium mixed with certain oxidizers are prone to burn vibrationally (i.e., strobe). Mixtures of magnalium and barium nitrate or magnalium and ammonium perchlorate certainly exhibit this phenomenon when mixed with an NC lacquer and dried (though they won't neccessarily burn continuously on their own [as is], they do burn vibrationally). WSM
AdmiralDonSnider Posted January 8, 2013 Posted January 8, 2013 From Hardt Table 15-17: "Formula 3 may be given a faster frequency by replacing the barium sulfate with anhydrous magnesium sulfate. The resultant fast strobe is sometimes called a "shimmer" effect." Good point on the dichromate protection; it was just my desire to stress that this material can be harmful in a state other than airborne and inhaled particles.
pyrojig Posted January 9, 2013 Author Posted January 9, 2013 Thanks you guy's.. I did read that section of Hardt for the faster shimmer effect using the Mag-sulfate. I imagine to get your Mag sulfate ( epson's salt) dry I;d just dry at 200f in the over for a half hour or so. I am fully aware of the toxic nature of this great salt ( K-dichromate) .Is there a ratio of Mag-to-Al that serves this purpose better (WSM)? My alloy is the 50/50. Would adding more fine al to the comp create a offset to the Magnalum >creating a faster frequency ?
psyco_1322 Posted January 9, 2013 Posted January 9, 2013 (edited) I've tried some "Twinkling" stars that had a really fast strobe rate, you might try some. http://www.cannonfuse.com/store/pc/Pyrotechnic-Formulas-Stars-d27.htm Scroll almost to the bottom, the first green one there does make a fast flittering strobe effect. Edited January 9, 2013 by psyco_1322
Mumbles Posted January 9, 2013 Posted January 9, 2013 One thing I should mention with the Magnesium Sulfate is that it has somewhat poor storage stability. Even sealed in with NC inside of other sealed containers, people in the industry have mentioned that they don't last for more than a few months before being noticeably degraded. Drying MgSO4 is a pain as well. 200F is nowhere near enough. To drive off all the water requires at least 250C (note the different units). If you heat it too fast or too hot too quickly, it will dissolve in it's own water of hydration giving you a hard caked product. I've been told that if you heat it around 150-200C for an hour or so before ramping the temperature up to drive off the rest of the water this can be avoided. In any case it's wise to remove the product, crush it back to a fine powder, and give it a final heating at 250-300C to drive off any residual water.
pyrojig Posted January 10, 2013 Author Posted January 10, 2013 That is a shame. Its seams with a good binder like nc it would last longer( maybe with anhydrous acetone) .Would parlon serve and extra protection v.s. NC? I cant imagine it would, but thought I'd throw that out there. You do have a point of the drying of Mgso4. I will give your advise a shot .
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