Voryon Posted October 31, 2018 Posted October 31, 2018 Yes probably my NC solution contains some Water, but using the same solution to bind compositions with MgAl + all other typical firework chemicals, except NH4ClO4 or (NH4)2SO4, did never give such reaction. I've even bound the classical AP/Mg/xSO4 strobes without these issues, but to be fair in these comps only Dichromate treated Mg was used. So I still believe that the nature of the comp is somewhat unstable.
PyroGnome Posted October 11 Posted October 11 (edited) There might be a 2-step thing happening here with the Cu reacting with (NH4)2SO4 under the likely acidic conditions and forming the copper sulfate which is hygroscopic enough that it'll probably always be the preferred outcome since it can pull in its own water to be soluble in. That'll allow the MgAl some room to start forming Mg Perchlorate at sites where the alloy isn't perfect, aside from the extremely violent reaction that can get going with Mg or MgAl and copper sulphate (or many other copper salts). Apparently copper sulphate in water will practically explode if you throw any magnesium in. Here's that reaction with magnesium ribbon, just imagine it with powder: CuAl with a small amount of Zn is used as a strong reducing agent, CuAl probably isn't much better. Plain old Cu may or may not form a tetraammine complex with the ammonium sulphate depending on the solubilities, or it might be having fun with nitrocellulose which is a nitric acid ester and already has a negatively charged terminal oxygen while copper really wants to be +2. I'm not sure why coating MgAl isn't mentioned more in regards to NH4ClO4 though, it's just as reactive with Mg/Al as it is with Mg according to FAST. Edited October 11 by PyroGnome Accidentally hit enter
Crazy Swede Posted October 11 Posted October 11 In practice, there is a big difference in reactivity between MgAl and NH4ClO4 compared to Mg and the latter. But yes, without some kind of protection the shelf life is limited with MgAl.
PyroGnome Posted October 11 Posted October 11 BTW, here's Shimizu's non-AP strobe paper. They're Guanidine nitrate based. The downsides are that they all use lead tetraoxide in varying amounts, and potassium dichromate. The dichromate doesn't have to be ground though, and having it finer than ~60 mesh messes things up since it's being used to generate hot spots rather than as a protectant or overall catalyst, which removes around 95% of the awfulness of the stuff since it's usually in the right range when you get it anyway. When I last used any of it in parlon bound Mg stars (to compare those against the ones with just parlon / acetone binding at a later date) some of it solvated in acetone from the color so there's a possibility that it makes its way to the Mg anyway. Guanidine nitrate is fairly unreactive towards Mg and is used in combination with a Sulphate (which all of the formulas he lists contain) and dichromate to produce an ultra-permanent protective layer on Mg for use with ammonium perchlorate. They're bound with NC / acetone and it's not even specified whether the Mg is treated and for at least the 3 formulas containing parlon I personally wouldn't bother (and it might actually ruin the strobing if the Mg is treated with dichromate in this case) but linseed oil should probably be used if you're worried about it. The 4 formulas range from 1.1Hz to 0.7Hz and he mentions that 8mm (5/16") cubes are probably the largest that can be made with them. If you need larger they'd probably make nice cores for color changing stars without the compatibility issues of AP strobe mixes. Igniter was 35% >100 mesh Mg 65% CuO Red 54.6% Guanidine Nitrate 18.3% Mg 4.5% Parlon / Chlorinated isoprene rubber 13.6% SrSO4 4.5% Lead Tetraoxide (>200 mesh) 4.5% Potassium dichromate (36-60 mesh) Orange 54.6% Guanidine Nitrate 18.3% Mg 4.5% Parlon / Chlorinated isoprene rubber 13.6% CaSO4*1/2H2O 4.5% Lead Tetraoxide (>200 mesh) 4.5% Potassium dichromate (36-60 mesh) Yellow 59.8% Guanidine Nitrate 19.9% Mg 15% Na2SO4 0.3% Lead Tetraoxide (>200 mesh) 5% Potassium dichromate (36-60 mesh) Green 52.8% Guanidine Nitrate 17.5% Mg 6.1% Parlon / Chlorinated isoprene rubber 13.2% BaSO4 6.1% Lead Tetraoxide (>200 mesh) 4% Potassium dichromate (36-60 mesh) I would think these would work with MgAl as well, but Mg will probably give better color purity as usual and this isn't a situation like with AP where it would be quite as concerning. Parlon wasn't used for the yellow because sodium doesn't need a chlorine donor. An interesting observation is that the required amount of lead tetraoxide seems to be directly related to the amount of parlon in most of the formulas, so I'd guess that the 0.3% in the yellow formula is the minimal amount required to create the strobing effect without the parlon acting as a low-value fuel. One last note is that when I saw the MgAl / Cu combinations, which I haven't seen anywhere before, I got a funny feeling in the pit of my stomach, so I did some digging around. If enough AP gets into solution with 20%+ ammonium hydroxide (which will be there in some quantity if there's humidity) and copper reacts, the tetraamine copper perchlorate complex is formed; it's not a super ugly compound as those things of which we don't speak go but you really don't want it in your stars / rockets either... and like I suspected that stuff shouldn't be let near hexamine which I haven't seen in AP blue strobes either. I found a fun tin-cure silicone (like GE II advanced but without the tin catalyst premixed) made by Alumilite (High Strength I) that appears to be suitable for the same purpose as the caulk but is a two part mold-making mixture with high hardness after cure for a silicone rubber. Using that would make mixing everything easy and eliminate the dangers of pressing a flammable elastic substance, assuming it would still work when not a mess of air bubbles and uneven particle distribution. 😉 The platinum silicones can't be used, they'll fail to cure in the presence of both amines (Ammonium perchlorate is probably out) and nearly any amount of sulfur along with various other things that are probably present in some amount in most pyro chemicals. Shimizu_non_AP-strobes.pdf
PyroGnome Posted October 11 Posted October 11 14 minutes ago, Crazy Swede said: In practice, there is a big difference in reactivity between MgAl and NH4ClO4 compared to Mg and the latter. But yes, without some kind of protection the shelf life is limited with MgAl. How limited... Just wondering, I'm always trying to get an idea on those things but can never really quantify it. FAST has some rather strange reactivities in the tables that don't match what I've seen but I tend towards "worse than advertised" whenever I think of AP for some reason. I might seem like I have some odd concerns (considering I don't mind using chlorates) sometimes but that's sort of a "devil you know" thing. That mess with the tetraamine copper perchlorate I mentioned in the post above is an example I've never seen brought up anywhere (mainly because I wasn't looking) and is probably unlikely in practice. But it's one of those instances where you don't want unlikely to become an "oopsie", probably more so than most of the comps we usually work with. Sadly the only blue strobe with rocket potential worth touching is probably the GN / AP / Cu, or more research into the silicones. I plan on using shimizu's Guanidine Nitrate / Ammonium dichromate / metal sulfate coating method when I finally make some strobe rockets out of either metal. If that lasted 8 years with AP/Mg strobe stars laying out on a workbench I'd expect it could protect rocket comp longer than I'd trust the tubes in ambient humidity. I also thought it might be fun to make some strobing hummers / strobing go-getters (maybe have them whistle at first like the rockets but much shorter to burn off fuel so they don't strobe into the ground 1/2 mile away) but those definitely need to be able to last a while... at the rate I get dragged away by needing to eat or sleep or any of those other silly inconveniences it's more a matter of not being able to press enough for a 5" shell before the first layer of inserts starts going bad if I don't use something that's at least medium-term stable. I'll have to suck it up and use the AP eventually because strobe rockets are one of my favorites and there's not an alternative in that case (guanidine nitrate alone unfortunately has bad characteristics for rockets in general with the chamber pressure influencing burn rate far too much according to the semi-pro rocket hobbyists), but in the meantime I'll keep looking for one. The availability of the SO4 ion in this situation is my main concern. I've not seen ammonium sulphate used in pyro before... anywhere. It seems as though metal powders could get ugly with it even at a non-solvated interface. Maybe that's just me or I'm forgetting something because most of my inorganic chemistry is ancient compared to organic.
Crazy Swede Posted October 14 Posted October 14 On 10/11/2024 at 1:36 PM, PyroGnome said: How limited... Just wondering... ...The availability of the SO4 ion in this situation is my main concern. I've not seen ammonium sulphate used in pyro before... anywhere. It seems as though metal powders could get ugly with it even at a non-solvated interface... Your first question is impossible to answer since it depends on the RH and temperature the pyrotechnics are stored at, how the complete formula looks like and the shape and size of the magnalium particles (the less specific area, the slower the effects of corrosion will show). Regarding sulphates, both BaSO4 and SrSO4 are practically insoluble and do not pose a problem as long as non aqueous binding systems are used. Soluble sulphates, like Na2SO4, are of course worse but the cation seems to contribute to this, CuSO4 probably being the worst due to the combination of low pH and catalytic action of the copper ion.
PyroGnome Posted October 17 Posted October 17 I kinda figured. Any real life experience with motors going bad would be appreciated though. With protected Mg or Mg/Al and nitrocellulose binding my gut feeling is that they'd last a while (not years for sure, and not most blues) and it's possible the tin silicone blues will last longer if the perchlorate is fully incorporated into the polymer chain like it looks like it will be. I found the source of ammonium sulphate being used in blue strobes on Skylighter's website where they were apparently taken from one of the Jennings-White AFN articles. If those are like his other papers they were primarily designed to produce the best blue color purities first and all else second. In relation to this thread I noticed that the Jennings-White Strobe Chemistry paper from JPyro Issue 20, Winter 2004 says: Quote The use of magnesium aluminum alloy (magnalium) instead of magnesium, in combination with ammonium perchlorate, goes a long way in reducing the probability of an unintended exothermic reaction. However, magnalium and ammonium perchlorate, in combination with some other materials, have also been known to heat up in the presence of water.[21] Non-aqueous binding generally solves the problem, nitrocellulose being popular for strobe stars. 21) C. Jennings-White, “Ammonium Perchlorate/Magnalium Blue Star Systems”, Western Pyrotechnic Association Newsletter, Vol. 2, No. 6, 1990. If anyone has the old WPA paper it might be helpful in determining what he was talking about, but I haven't seen the ammonium sulphate in newer formulas including the above strobe paper (although that paper was more about seeing what could strobe) so that might have been one of the "other materials", but without the earlier paper that's just a guess. That line is also interesting since it implies that water binding can be used in some formulations but that's not on my shortlist of things to try. Anyone from the WPA know if they sell or have an archive of their old papers? In Shimizu's paper in that other thread regarding magnesium coating with the dichromate / guanidine nitrate / sulphate mixture, he tested ammonium sulphate for that portion and it inhibited formation of the passivation layer (coating formed but spalled off) so I'd hazard a guess from that that it's not good for plain dichromate coating outside of that guanidine nitrate system either and probably not for plain old metals.
PyroGnome Posted 3 hours ago Posted 3 hours ago To answer my own question a bit, a paper by D. Juknelevicius et. al tested various AP / TMAN blue strobes and used AP/MgAl 40-80 mesh/BaSO4/Potassium Dichromate (60/25/15/5) as a reference. Magnalium wasn't treated, the dichromate was just part of the mixture where it could treat the MgAl in-situ to some degree if the mix got wet but acts as a catalyst regardless. They consolidated pellets from 1g of comp, 13mm in diameter, 4-4.5mm high, with a dead weight of ~4500lb (2000kg). No binder was mentioned / used for most of them. They age tested them in a humid environment at 32-46F for 30 days... it wasn't mentioned whether this was because the temps in Lithuania are fairly cold for the majority of the year (although they rarely reach midwest US levels lol) The reference MgAl mix showed near zero degradation after a month. The mixes using copper oxide, which was the majority, developed blue spots on the pellet surface. The mix using copper metal turned completely blue. Usually those changes are related to formation of copper complexes, apparently. The mix with basic copper carbonate didn't have a change in color mentioned. The color changes were only cosmetic (complex formation doesn't really change the elemental makeup after all) and all of them still strobed. Anyway, it's comforting to know that it probably takes a good amount of time before anything really stupid happens. I'd expect rockets to last longer given the lower surface area-> size ratio unless the tubes themselves have a really high moisture content. While I was looking, I found a 1930s German strobe / falling leaves type effect (although Germany loves strike-on-box firecrackers so it might have just been that type of thing) in a 70s Wasmann presentation that might be one of the most horrifying mixtures I've ever seen... I don't know which territory Germany occupied in 1930 but Martinikas doesn't translate from German, and it just translates to Martinis from Lithuanian according to google, which seems wrong too: "Martinikas" For preparation cardboard was coated with a dispersion of this composition in water, and dried. The substance is ignitable by friction and burns with a rattling noise. The frequencies measured were 2 - 3 cps. 34.7% Bole white (This is a type of clay) 31.4% Water 12.9% Gum arabic 9.6% Calcium carbonate 6.6% Potassium chlorate 4.8% White Phosphorous Because of the toxicity of white phosphorous it was banned almost immediately after it showed up. I'd bet that a box of these suckers is worth a fortune, it'd be a miracle if any exist that haven't caught on fire on their own yet. Anyway the rest is a light read of a 3 page section but has some odd & interesting formulas and more importantly some refs and information on tuning the strobe frequency within huge ranges. Red, green, and white that are all 7% AP or less as written with strontium / barium nitrate and potassium perchlorate as oxidizers with a note that seems to indicate the AP can be wholly replaced by one of several other gas generating oxidizers / additives... nice since AP is expensive compared to almost everything else in a strobe mix, and a mention that they're tunable from 0.5Hz to 50Hz by varying a copper chromite catalyst from 0.03% to 0.1%. There's also a set of "acoustic strobe" formulas designed purely for loudness that don't use ammonium perchlorate at all, but they do need a weird resin binding system with PEDN (di-nitrate), dinitroglycerin, or meso-erithritol converted into acrylates, and the oxidizers are barium / strontium perchlorate which don't run cheap. These can be tuned by changing ratios from 0.1Hz to 1000Hz.
Recommended Posts