Geezer Posted September 15, 2016 Posted September 15, 2016 How long can I store stars or comets? I am working only with KNO3 and charcoal based stars and was thinking about making some now for use during the winter. It is my understanding that iron/steel can rust and contaminate/degrade stars containing that material so I guess Fe/Ti is out. Any others I need to be concerned about? AL? Mg/AL? Ti?
NeighborJ Posted September 15, 2016 Posted September 15, 2016 (edited) I'm no chemist but I'd not be concerned with the storage of any of those metals. The enemy of corrosion is moisture, so as long as the stars are bone dry, they should not degrade. That's not to say I haven't had stars go bad. I've had D1 stored away too early before it was completely dry and when opened 2 months later it smelled strongly of ammonia and it no longer worked as a glitter but still burned. The mgal is the one which looses it's reactivity over time but it can do this even without being bound in a star. If you wish to store certain comps long term it is a good idea to treat each metal with its appropriate coating ie,iron-linseed oil, aluminum-boric or steric acids, mg-potassium dichromate. I've heard of bp still working after unexploded ordinace was located from the civil war and it was sealed in iron shells. So given the absence of moisture, I'd say charcoal stars can be stored long enough to outlive you. Edited September 15, 2016 by NeighborJ
dagabu Posted September 15, 2016 Posted September 15, 2016 ...The mgal is the one which looses it's reactivity over time but it can do this even without being bound in a star... Hmmm, what? Did you have an issue with MgAl? I have MgAl from 2006 that is just as "fresh" as it was the day I made it.
NeighborJ Posted September 16, 2016 Posted September 16, 2016 Dag I'm sure the lost reactivity of my old mgal was something I did wrong. Unless it was the other chems I had who knows.
dagabu Posted September 16, 2016 Posted September 16, 2016 I would imagine it was since both Mg and Al are stable with a passivization layer to keep them from further degrading.
Mumbles Posted September 16, 2016 Posted September 16, 2016 Mg does not form a stable passivation layer the same way that Al does. It's more porous and flaky and allows the metal underneath to keep degrading. I'm not sure about MgAl. If you look at older barrels of it though, you can notice the top becoming more grey and less shiny. It does degrade at least a little bit. Except for Mg stars and stars with uncoated steel or iron I wouldn't really worry as long as they're stored well.
dagabu Posted September 16, 2016 Posted September 16, 2016 Thanks Mum, you are the in house chemist! It looks like I have coated mine with chromate back when I made it to passivate it, there is a distinct yellow tint to the MgAl. I honestly cannot remember if this was treated or not but a decade later, the canister full is still shiny and bright.
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