823 replies to this topic

[Karl Mitchell-Shead]

No chlorine donor, ok the colour wasnt brilliant but clearly visible

[CCH Concepts]

my comment about negative explosives was over looked, am i asking about a banned subject here or just not alot of people have come across them before?

[pyrotechnist]

I love the idea of negative flash, sounds safer than normal flash and also doesn't contain the dam bright flash associated with it, depending on sulphate used etc.

[seymour]

my comment about negative explosives was over looked, am i asking about a banned subject here or just not alot of people have come across them before?

It can be quite frustrating when you post on a forum and you get no replies, but it is a reality of the way things work unfortunately, and I doubt that there are any members who have not made posts and waited for a reply that never came.

While it does not mean that people are interested, it could be that people are interested but have nothing to contribute. Older members are also quite likely to have posted about, or read about negative explosives at some point in the past, since they are a topic that has popped up every few months for the last few years on the firework forums.

Personally, while I find such compositions interesting, they do not get me all that excited because of the use of Mg.

(4) In practical use it is necessary to protect the noise unit which contains the magnesium sulfate/magnesium mixture from moisture.

That, in my opinion, is what will stop Mg based negative explosives ever being widely used, and why I will continue to use Perchloeate/Aluminium for flash powders. It does not corrode, and while the sulfate/Mg mixture may not be as sensitive as the perchlorate/Aluminium mixture, the idea of fine magnesium with a water-attracting sulfate seems like a situation where the precautions to get it to work and be safe far outweigh the benefits that the composition gives.

[pyrotechnist]

MgAl seems to work also

[Mumbles]

You could also try using a non-hygroscopic sulfate, such as strontium or barium sulfate. Hydrated CaSO4 works fine too. I doubt you'd get much of a color, but if you were worried, a mix of barium and strontium will make a white color anyway. I don't know what you're talking about with "and also doesn't contain the dam bright flash associated with it, depending on sulphate used etc. " The flash is still going to be blindingly bright. It is the Metal oxide that really makes the bright light.

One caveat associated with the negative explosives is that they are notoriously hard to initiate. You have to use a booster or ignition charge of the more sensitive 70/30 to get them going in some cases.

Another saluting mix that is said to be safer is an Ammonium Perchlorate and aluminum mixture. I have no idea why this would be any better than KP. However, this carries with it some risk. Ammonium Perchlorate is known to be able to be detonated. I've heard many people say that AP based mixtures are louder, and this may be why.

[CCH Concepts]

does the negative explosive have to use Mg, cant another metal be used such as Al. the little i have read didn't go into the chemistry behind the reaction. my assumption was it was a displacement striping the 4O from the sulfate.

[MDH]

Yes, but you would have to omit magnesium and copper sulfate. The other sulfates will work with aluminum.

Did anyone I try the calcium sulfate flash I recommended several pages back?

[CCH Concepts]

i havnt tried it, intended to. but my workshop got quite damp over the winter, so i decided all chems best left sealed and wait for the summer before i start experimenting again.

out of interest was a right that this is a displcment similar to thermite? the sulphate acting like the FeO?

[Mumbles]

Not quite a thermite, in the sense that no metals are produced. I believe someone posted an equation above where the sulfate gets reduced to the sulfide, and the metal forms it's oxide.

[CCH Concepts]

so its not as simple as the higher reactivity metal displacing the lower.
would there be any way of getting at all the oxygen, that reduces it from 4 to 2 atoms, could the other two not be reacted?
or is this due to bonding i see sulphide is two atoms are double bonded and 2 are sigle bonded.

i would be interesting to see if this could be reduced down to

CaSO4 + Mg = S + Ca + 4MgO

i appolgised for any spelling mistakes i cant use the spell check at work.

[Mumbles]

Forming CaS or MgS would be more energetically favorable, so I have my doubts.

[CCH Concepts]

by that do you mean the sulfur will react with the magnesium before the oxygen will so you will never get 4MgO

[Potassium chlorate]

I'm more interested in sending a mole to Malta and gathering their colored flash secrets.

You can make incredibly nice green flash either with barium chlorate and magnalium or with barium chlorate, magnesium, potassium chlorate and PVC, though this flash isn't very safe, of course;

Ba(ClO3)2 50-65%
MgAl 35-50%

or:

Ba(ClO3)2 36%
Mg 46%
KClO3 11%
PVC 7%

Both will be incredibly green even in broad daylight.

[Mumbles]

What I mean is that it will go CaSO4 + Mg ---> CaS + 4 MgO

Forming Ca + S + 4 MgO wouldn't be as energetically favorable as forming CaS. It would take a bunch of extra energy to break it apart into Ca + S. Calcium Sulfide is more stable than Magnesium Sulfide, so even with excess Magnesium, you couldn't form MgS and Ca metal.

Edited by Mumbles, 05 April 2010 - 03:40 PM.