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Ammonium dichromate volcano experiment

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Hi,

I just want to report that several years before I tried to ignite these orange crystals (you know chemical volcano experiment, do not you?) with 650nm red and green DPSS modules. Without success - probably they do not absorb red and green.

This week I tried to ignite it with 5W mini-blaster made with NUBM44, SXD driver and 2 tiny 10440 cells - it "only" produces 5W 445nm output, but all works - the crystals decompose immediately into green Cr2O3 with fire splashes and cracking sound. Has anyone tried anything similar with other thermally unstable compounds?

It also ignites magnesium turnings but cannot do it with ribbon (thermal dissipation probably too high).
 

Benm

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Magnesium can be tricky: as a pure metal it's very shiny and doesnt absorb much light at all. When it tarnishes it goes dull and then black, absorbing much more light, but also protecting it from oxidation since this tarnish is a passivation layer.

For the ribbon: Try to cut into it from the side creating several strands. These will be easier to heat and also have some fresh metal exposed in the cuts, that might just be enough to set fire to it with a laser. Once it starts burning it'll happily keep doing that, and those fires are darn difficult to put out, so be careful.

If you need to put a magnesium fire out dump sand onto it - it will continue to burn under water and in CO2.
 
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Hi Benm,

Are you chemist, too?

Yes, I know about fire extinguishing, while working at Atofina, we had such a training every year. But the best way I heard of is pouring liquid nitrogen into fire - guys said that it can even extinguish burning LiAlH4.

Back to the burning subject, I would like to grow big crystals of (NH4)2Cr2O7 and NH4NO3 to see if laser could "burn" a hole in those or the crystals will "burn out" completely. Also interesting would be to try igniting Li metal with a laser because when ignited with a match it starts to melt and flow before it burns.

But I would not try this with diazonium salts or other perchlorates, because those space shuttle booster fuel crystals would explode for sure.
 

Benm

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I'm a chemist indeed.

Magnesium can 'burn' in a nitrogen atmosphere (converting it into magnesium nitride). This reaction is self-sustaining once lit. I'm not overly sure what will happen with -liquid- nitrogen. It could make it worse (like liquid oxygen set things on fire even though it's temperature is very low). It could also take away so much heat it goes out.

I've seen videos of magnesium burning in solid CO2 (between two slabs of it) and this results in carbon and magnesium oxide. The cold certainly does not put that out.

I doubt you could burn a hole through ammonium dichromate crystals. It doesn't melt, it just decomposes. I suspect that it will just decompose starting at the point you hit it, but there is no way to stop the rest of the crystal going off after that (well, quickly dunking it in liquid nitrogen might work here...).

It's worth a try though, i wonder if you can grow nice big crystals of ammonium dichromate. Since it's not that expensive it could be worth trying a slow re-crystallization with a seed crystal.
 




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