strange properties of boric acid

[stormyweathers]

i recently tried a few experimental comps using boric acid, trying to get a green color.

 

Here are my findings:

if you completely saturate melted parafin wax, it burns with a nice green color and crackles the whole time, but it doesnt burn very consistently.

I imagine if BP were mixed into it, it would work better.

 

a 1:2 ratio of boric acid to BP yeilds an interesting mixture

it wont burn at all

so i added about 4 more times tthe volume of BP and it was still hard to light.

during combustion, tons of bubbles with a smell of hotdogs shot out.

 

does anybody know what these bubbles are?

[it burned considerably slow, about 10s for 3 g]

[NightHawkInLight]

If a boric acid green is possible, you are unlikely to get it with a nitrate based composition. Certainly not with mere BP. Perhaps with a magnesium composition you could achieve a hint of color.

 

Perchlorate or chlorate are what you should be experimenting with.

[stormyweathers]

what properties of chlorate/perch and magnesium are more conducive to a boric acid green than a nitrate?

[NightHawkInLight]

Nitrate in general is VERY poor with colors. Most are not even possible to produce.

 

Chlorate and Perchlorate however are much better due to chlorine content and some other properties. Perch being safer to use, so I recommend that over chlorate. As far as Mg, it just seems to work very well with colors for one reason or another. Perhaps the high heat generated by it burning easily vaporizes coloring salts. I don't know for sure.

 

That said, I do not believe a good green with boric acid is possible or it would have been done before. That doesn't mean not to try it, it's just the sort of project I like to take on. Just know that you better do your research or you don't stand much of a chance.

[Arthur]

Flame colours depend on the flame environment. In alcohol flames which are very cool boric acid makes nice colours so with paraffin wax it will be similar, but with BP like comps it will not make colour. Some colourants need a hot flame, some a medium flame and some a really cool flame (all in flame terms! "cool" is still far too hot to touch!) That's why star formulae are so finely tuned to optimise temperature and colour, and why "systems" may not be best for all colours.

 

Are the notes from the Kosanke's pyrotechnic chemistry course available?

[Mumbles]

I like the effort, but I think your work may go to waste. I would love to be proven wrong though. If I didn't have to mess with barium to get nice greens, my life would be much happier. The key piece of information here is the color emitting species. With most colors it is the mono-chloride, which is why we add chlorine donors. In this case, the emitting species are borate esters.

 

Here is a picture of a boric acid flame. It's pretty transparent as you can see. An alcohol flame is quite vividly colored, as I am sure you know. The difference is borate esters are formed in the alcohol, but not in the natural gas. An interesting experiment might be to dissolve it in a non-ester forming solvent to see if it is still colored. This will discern between the ester vs. flame temp arguement.

 

http://jchemed.chem.wisc.edu/jcesoft/cca/c...HTM/FLAME/1.HTM

 

Something to try might be formation of solid borate esters. This might not be the best choice though, some are just as poisonous as barium nitrate. If you want to try to form the esters in situ in the flame, plenty of red gum might be an option, I hear it has lots of alcohols and acids in it. Nitrocellulose may also be promising.

 

BP as a base isn't going to work. I don't know of any colors outside off white and potentially orange that can even be made with potassium nitrate. I really don't know why it doesn't work. Metallic fuels all burn hotter than KNO3. I think a lot of it has to do with chlorine. Chlorate and Perchlorate decompose to KCl primarily while releasing oxygen, which is pretty much flame transparent. KNO3 decomposes to K2O primarily, which gives off a strong white light.

 

Good luck, and keep us posted.

[optimus]

Flame colours depend on the flame environment. In alcohol flames which are very cool boric acid makes nice colours so with paraffin wax it will be similar, but with BP like comps it will not make colour. Some colourants need a hot flame, some a medium flame and some a really cool flame (all in flame terms! "cool" is still far too hot to touch!) That's why star formulae are so finely tuned to optimise temperature and colour, and why "systems" may not be best for all colours.

 

Are the notes from the Kosanke's pyrotechnic chemistry course available?

 

Here you go:

 

http://books.google.co.uk/books?id=Q1yJNr9...;q=&f=false

[psyco_1322]

You might have a try at saturating chlorowax with boric acid, just to see if it differs. I have some I could play with if you don't have some. I think I might try some boric in NC to see how that results.

 

Here is something that just blew my mind:

 

Right before the convention, I started putting together some thoughts about a larger Lampare rocket header to make when I got there. It's kinda been my thing every year to make them and it really gets peoples attention. This year was a 3L (~.8 gallons) header. The idea was 3L of Trimethyl Borate, the green alcohol flaming stuff people like to play with. So I contacted the man in charge of making the motor for the the beast and began making a mock-up, testable header. Fill the bottle up, dumped in a load of boric acid and tested to make sure it was saturated in green color. The break was 75g of whistle in the nice cone that's made into the bottom of the bottle. Went out, set it up, lit, video'd, retired, and watched. Booommm! and a nice fireball erupted...except...it was orange. A huge orange fireball came from 3L of green burning alcohol crap. Ok...so you start thinking and the only thing you can point your fingers at is that whistle...the sodium must have killed the color! Except there is no sodium there, if it is, it's purely minute amounts from chemical contamination. The whistle was made with potassium chlorate and potassium benzoate with a few percent of red gum....so who wants to explain this to me?...why my green was orange? I did shoot the header, and then another...very epic. I just used some Coleman fuel and then the second one was a mix of many things that were gathered from around the manufacturing tent.

[NightHawkInLight]

I very much doubt it was the sodium. I am almost certain that the orange color comes from a higher temperature of combustion due to a fine mix with the air; As opposed to colder burning in the more oxygen depleted area directly above the surface of the liquid. The color is likely close to the natural burning color of the alcohol, slightly changed because of the additives. I'd bet the break has nothing to do with it. It's just burning to hot.

[stormyweathers]

psyco, i dont have any chlorowax, so let me know if its worth using.

 

 

but the main purpose of my tinkering was to get a green burning candle out of cheap materials

[or any color for that matter]

[Mumbles]

I honestly wouldn't waste your time with chlorowax. It's seems like it's everyone's first inclination to add chlorine to a flame to improve the color. It doesn't help if the color emitter isn't a monochloride to begin with, or the chlorine can't kill any blackbody emitters though.

 

If I were going to go about this, I'd add some oxidizer to the wax:boric acid mixture. Ammonium Perchlorate would be my first choice, but potassium chlorate may work as well. Adding in some clean burning fuels may help to promote the color production. Things like hexamine, or perhaps red gum or shellac.

 

Stearin (Stearic acid), is pretty closely related to wax, although it is a relatively pure compound. It used to be a fairly widely used formula in blues, which are notoriously hard to make. I'd treat this as a similar type of challenge. Below is a blue lance formula, and a proposed green variation based on boric acid. The mix would be pretty crumbly and not castable, but it should compress into pellets on it's own.

 

Potassium Chlorate 16

Copper Acetoarsenite (Paris Green) 5

Stearic Acid (Stearine) 2

Polyvinyl Chloride (PVC). 0.5

 

 

Potassium Chlorate 16

Boric Acid 5

Wax 2.5

[psyco_1322]

I honestly wouldn't waste your time with chlorowax. It's seems like it's everyone's first inclination to add chlorine to a flame to improve the color. It doesn't help if the color emitter isn't a monochloride to begin with, or the chlorine can't kill any blackbody emitters though.

 

Crap...what was I thinking when I said that. In that case the chlorine would be near useless.

 

I tossed a bit boric acid into some NC lacquer the other day. If I remember it tonight, I'll let it dry out and see what it burns like.

 

I'm a bit confused on the formation of Trimethyl Borate. If it forms when you add boric acid to methyl alcohol, then when it evaporates what happens? I know it leaves some white solids behind, which I presume to be boric acid, but what happens to the TMB? Any insight Mumbles?

[NightHawkInLight]

Crap...what was I thinking when I said that. In that case the chlorine would be near useless.

 

I tossed a bit boric acid into some NC lacquer the other day. If I remember it tonight, I'll let it dry out and see what it burns like.

 

I'm a bit confused on the formation of Trimethyl Borate. If it forms when you add boric acid to methyl alcohol, then when it evaporates what happens? I know it leaves some white solids behind, which I presume to be boric acid, but what happens to the TMB? Any insight Mumbles?

"Trimethyl borate, or boron trimethoxide, has formula B(OCH3)3. It is a clear liquid. It melts at −34 °C and boils at 68-69 °C. It decomposes in contact with water. It is flammable and burns with a green flame."

 

So says Wikipedia. It doesn't look good for use in pyrotechnics since it is a liquid at any reasonable temperature. The only way I can think of to use it for a green flame in a solid star is to synthesize a solid chemical compound that partially decomposes into TMB or a similar compound when heated. Perhaps even a minor chemical variation to TMB that would form a solid compound at room temp yet still burn green. Given, I don't know enough chemistry to know for sure if that is even possible, let alone how to go about it.

[Mumbles]

That was my general idea, form it in situ. Well, I was going with the assumption that other related compounds make green too, given his experiments with wax.

 

Hmmmmm, I wonder if Polyvinyl alcohol would do the trick. That would be a very promising thing to try. Perhaps bound with NC to serve as a binder initially for proof of concept. After than oxidizers and fuels can be added.

[psyco_1322]

Well it burned a bit of NC last night. I think I put too much boric acid in there and it kinda retarded the burning, so I'm giving it another try. I did see a hint of green in the flame as I was lighting it....so...maybe there is hope Maybe try dissolving the NC in methyl alcohol and adding boric...hmmm. Ideas.

 

Thanks for that bit of info NightHawk. It doesn't really answer my question as to the formation and what happens as it evaporates. I read that wiki page, the other uses list is kind of weird sounding.

 

Mumbles,

This thread might be better off in the Chemistry section with the direction it's going.

[Mumbles]

Two problems.

 

#1 Methanol will evaporate

#2 Good NC isn't soluble in alcohol

 

While looking up other stuff while I was trying not to do school work, methylcellulose might be the key. Methylcellulose is NOT CMC, and doesn't have a great deal of sodium in it. It would serve as a binder, a fuel, and a methyl ester source.

[asilentbob]

Remember that highly chlorinated compounds tend to be flame retardants, so mixing boric acid into chlorowax... probably wont burn straight right off the bat. I like mumble's idea of adding hexamine. The hexamine cooking tabs are just pressed hexamine with a few percent wax to help bind them and they burn with a mostly clear blue flame. I'd start with a very low percentage of chlorine donor to start. Ideas could be like hexamine/boric acid, hexamine/wax/boric acid, hexamine/boric acid/oxidizer, etc...

 

TMB, TEB, etc are all generally formed in solution when dissolving boric acid in an alcohol. Its very much an equilibrium. While you can fractionally distill it off carefully... water vapor in the air and such will always make there be a bit of an equilibrium going on between water, boric acid, the alcohol, and the boric acid esters (mono, di, tri)... hence trimethyl borate for example will have an equilibrium going on with atmospheric water, and any that happens to be in it already... to form back boric acid and the alcohol... Since its all equilibrium all the time the residue of boric acid that is left over should be slightly less than the original mass of boric acid used. It could be deceiving though because it wont be dry and there could possibly be unforeseen other chemicals around, perhaps trapped in the boric acid crystal lattice.

 

Some alcohols come with denaturing agents, and a few are probably sodium compounds. Personally I don't think this is what was behind the orange fireball... but I dunno.

 

If your going to be playing around with boric acid a lot, you could try dehydrating it in a furnace of some sort to get other boron compounds to play with.

[NightHawkInLight]

Two problems.

 

#1 Methanol will evaporate

#2 Good NC isn't soluble in alcohol

 

While looking up other stuff while I was trying not to do school work, methylcellulose might be the key. Methylcellulose is NOT CMC, and doesn't have a great deal of sodium in it. It would serve as a binder, a fuel, and a methyl ester source.

I love this thread. If it weren't for the next MPAG shoot being just around the corner and having just started on one lonely multibreak shell, I'd be all over experimenting on this. I like your thinking there Mumbles.