18 replies to this topic

[Mumbles]

Chemistry is my passion. I got lucky enough my passion overlaps quite a bit with my hobbies.

Anyway, I've never had a problem with MgAl reacting in any composition I've used. I've also been under the impression that the Mg portion will react preferentially over the Al portion. Dichromate in the wetting water is probably the easiest solution. I personally wouldn't go to this length unless I noticed a problem though, mostly because I really don't like dichromate. Mg doesn't have the problem that it will reduce nitrate to ammonia to my knowledge, but it's still a water based solution with salts and will at the least be attacked by the water. There was also some talk about there being a best of both worlds situation with MgAl. As in the Al portion strengthens the passive oxide layer to prevent reaction, and if any water did get through, the Mg would act as the "sacraficial anode" of sorts. The difference in oxide layer strength is a main player in the reactivity difference between Al and Mg. Thats completely heresay though, and I really don't have reliable facts one way or the other. All I know is that MgAl seems to be relatively stable in compositions.

I don't have a copy on hand. Does lancaster specifically mention boric acid as an acid that attacks MgAl, or just references weak acids in general? Boric acid itself is kind of a weird substance, and isn't what you would normally think of as an acid, as in giving up hydrogen ions. I could go into significantly more detail, but it's not really neccesary. It's an acid in the sense that it accepts hydroxide ions. I don't think it would react with Mg anymore than water would. If you don't trust me, mix boric acid with sodium bicarbonate. It doesn't fizz as far as I remember. Fizzing requires protonation of the HCO3- ion to H2CO3, which then decomposes to CO2.

B(OH)3 + OH(-) ---> B(OH)4 (-)

Yes, you can use sulfuric acid to prepare boric acid just the same as you can use HCl. I like HCl better personally, but any strong acid will be just fine. Just for filtering and reactivity's sake, it might be better to use diluted acid. Adding concentrated acid may give a false negative result as the water would become too warm, and the boric acid not precipitate immediately.

Anyway, I find the most efficient use of boric acid is to dissolve it in the water I use to wet the composition with. I keep a gallon jug of it around. Not only do you use less boric acid, it also provides better protection as it is much more intimately mixed. Boric acid has to be in solution anyway to provide any sort of protection. At room temperature, you can dissolve roughly 5-6% by mass in water. I've used the boric acid soln even when not necessary, such as when I run out of distilled water or something like that. It doesn't hurt colors or effects at all.

[portfire]

I don't have a copy on hand. Does lancaster specifically mention boric acid as an acid that attacks MgAl, or just references weak acids in general?

quoted from Rev.Ronald Lancaster's book 'fireworks Principles and Practice'

"MgAl is attacked by weak acids (e.g., boric acid) and sodium oxalate and, to a lesser extent, by other firework chemicals. It is, however, protected by potassium bichromate, which is often used for this purpose."

Sorry i couldn't go into more depth on the subject.

Dean

[t1tan]

Chemistry is my passion. I got lucky enough my passion overlaps quite a bit with my hobbies.

Anyway, I've never had a problem with MgAl reacting in any composition I've used. I've also been under the impression that the Mg portion will react preferentially over the Al portion. Dichromate in the wetting water is probably the easiest solution. I personally wouldn't go to this length unless I noticed a problem though, mostly because I really don't like dichromate. Mg doesn't have the problem that it will reduce nitrate to ammonia to my knowledge, but it's still a water based solution with salts and will at the least be attacked by the water. There was also some talk about there being a best of both worlds situation with MgAl. As in the Al portion strengthens the passive oxide layer to prevent reaction, and if any water did get through, the Mg would act as the "sacraficial anode" of sorts. The difference in oxide layer strength is a main player in the reactivity difference between Al and Mg. Thats completely heresay though, and I really don't have reliable facts one way or the other. All I know is that MgAl seems to be relatively stable in compositions.

I don't have a copy on hand. Does lancaster specifically mention boric acid as an acid that attacks MgAl, or just references weak acids in general? Boric acid itself is kind of a weird substance, and isn't what you would normally think of as an acid, as in giving up hydrogen ions. I could go into significantly more detail, but it's not really neccesary. It's an acid in the sense that it accepts hydroxide ions. I don't think it would react with Mg anymore than water would. If you don't trust me, mix boric acid with sodium bicarbonate. It doesn't fizz as far as I remember. Fizzing requires protonation of the HCO3- ion to H2CO3, which then decomposes to CO2.

B(OH)3 + OH(-) ---> B(OH)4 (-)

Yes, you can use sulfuric acid to prepare boric acid just the same as you can use HCl. I like HCl better personally, but any strong acid will be just fine. Just for filtering and reactivity's sake, it might be better to use diluted acid. Adding concentrated acid may give a false negative result as the water would become too warm, and the boric acid not precipitate immediately.

Anyway, I find the most efficient use of boric acid is to dissolve it in the water I use to wet the composition with. I keep a gallon jug of it around. Not only do you use less boric acid, it also provides better protection as it is much more intimately mixed. Boric acid has to be in solution anyway to provide any sort of protection. At room temperature, you can dissolve roughly 5-6% by mass in water. I've used the boric acid soln even when not necessary, such as when I run out of distilled water or something like that. It doesn't hurt colors or effects at all.

Very informative and helpful post, thank you for the information.

[YT2095]

sorry for my Away time, the line was borked for 6 days, but I`m back now

basically do Not use Borax in place of Boric acid, A) Unless you like Yellow colored fireworks (Sodium contam), and you don`t want it to do the same job as Boric acid does.

Yes you Can get the acid from it sure, but it`s a lengthy process that will give a low yield (you need to scrub ALL sodium ions out!).

Nitric or Hydrochloric acids are the best to use (their sodium salts are quite soluble), you`ll want to do Several washes with these and several Fridge coolings to grow boric acid crystals.
Happily Boric acid isn`t all that soluble whereas the Sodium salts are

also using HCl or HNO3 you can heat your crystal to a high heat to dive of the residual acid traces without worry of thermal decomp to the boric

Edited by YT2095, 10 April 2008 - 05:13 PM.