64 replies to this topic

[adamw]

What do you use it for where? In fireworks? It's a good fuel and makes bright stars! Or if you were meaning it's use in the 'real' world, the main use I know of is as a 'sacrificial anode' for protecting metalwork underwater, ie, it corrodes instead of your nice undersea pipeline.

[BigG]

Originally posted by crackerboy
What do you do with magnesium anyway? Besides using it as an emergency fire starter.

Magnesium has some amazing properties, which make it a big help in fireworks.

Adam already mentioned the usage as fuel. Magnesium does not require a lot of energy to burn, but releases more energy then any other metallic fuel used in pyrotechnics. It raises the temperature flame considerably. With the addition of magnesium, you can generate good colours from Nitrates (Nitrates are generally not energetic enough oxidizers to create good colour, but the addition of magnesium lift up the temperature high enough to improve/generate colour).

You can also create "nitrate flash" with magnesium - which while do not compete with chlorate/perchlorate breaking charges, can still generate quite a good break.

Magnesium/aluminium alloys (also called magnelium) burn in a vibrating flame that is responsible for some unique effects in stars.

Magnesium is EXTREMLY flammable. It is reducing agents that extract oxygen out of everything ? water, stone, even sand - which is why it is a serious headache for fire fighters. It you get a hold of it, keep in original drum and away from all igniting sources - including static.

BigG

[leniol]

Hah, hust got hold of 100g Mg powder from Labpak chemicals for 3.50+ delivery (7.50. :flames:)! Just though this might help.... I'd recommend thinking about what you 'need' it for - they might say no to I'm making fireworks.....

[al93535]

I made some magnesium powder, and I have a question for you guys. Can't I coat the magnesium in paraffin wax, or linseed oil, then use it in a star comp that uses water as a binder? Seems to me it would be fine because the magnesium is coated in a waterproof layer, thus would never contact the water. But I just wanted to make sure before I attempt this.
Thanks,

[adamw]

the suggested way is to use Potassium Dichromate. Here is some info from Skylighter:

This is a simple process, but you should wear gloves and a respirator when you do it. Read the MSDS for potassium dichromate and you'll see why. It is best to do this outdoors and away from any fire. Explosive hydrogen gas is given off during the reaction.

Add the potassium dichromate to warm water, stirring while you do. Make a saturated solution by continuing to add potassium dichromate and stirring until no more potassium dichromate will dissolve.

Slowly add the magnesium powder to the solution. You should see bubbling and fizzing as hydrogen gas is given off. Stir the solution until the bubbling stops, then add more magnesium. Continue adding magnesium and stirring until there is no more bubbling.

Pour the solution with the magnesium through a filter. Be sure and catch the solution in a container. Seal it and dispose of it properly. It is toxic and under no circumstances should be put down a drain into the public water system. Air dry the now coated magnesium sludge, then crush it into powder again.

[KNO3]

If it gives off H gas, then does it also produce Magnesium Oxide, contaminating the Mg? As i assume the Mg displaces the H in H2O forming H + MgO2? If so, could this decrease the reactivity of the Mg?

[Yugen-biki]

2Mg (s) + 2H2O (l) --> 2MgOH (aq) + H2 (g)

This will produce hydrogen gas, but I don't think that this reaction is the dominant one when coating Mg with K2Cr2O7. It is more likely something similar to:

Mg(s) + K2Cr2O7 (aq) --> K2CrO4 (aq) + MgO (s) + maby CrO2

[Mumbles]

It's almost agonising looking at these reactions you guys have posted.

Mg(s) + 2 H2O ---> Mg(OH)2 + H2

There is no set reaction for the dichromate/Mg interaction. Get ready because the following explanation will be highly chemistry based. I can see already one big misconception. This is that a layer of MgO or Mg(OH)2 is formed and this protects from corrosion. This is not quite the case. This layer will be combined to be refered to as the oxidation layer because I don't want to have to keep saying the names over and over. Well the oxidiation layer is not the same as Aluminum's, in fact they are very different. Al forms a strong bonded oxidation later. It is passive and non-porus. Al can withstand attack from concentrated HNO3. It forms the passive film of oxide, and the nitric acid is no longer able to get through it.

Magnesium on the other hand has a weak oxidation layer. It forms in multiple layers, and is not strongly attached to the metalic nucleus underneath. Because of this the oxidation layer is flaky, easily attacked, and does not provide proper oxidiation protection. If you put Mg in water, it would completely react. The addition of chloride(and probably other electrolyte) ions increases the attack speed signifigantly.

The dichromate addition does provides protection from water reaction, and chloride reaction. Because of this fact, it is obvious it does not simply provide an oxide layer on the Mg. If you have ever passivated Mg, you will know that you don't just soak the Mg in dichromate solution, and all is fine. You actually coat the Mg with the solution, and let it dry on the metal. this signifies that the dichromate (or derivitives of it) assist in the protection. Otherwise, we would just soak the metal, and use the remaining Dichromate to coat the next batch. Long story short, the chromium ions integrate as part of the oxidation layer. Inside the oxidation layer, spectromicroscopy has found Cr(III) ion, these come from the dichromate ion (Cr(VI) oxidation). The integration of Cr(III) ions, and Cr(VI) ions in addition to the oxidation layer makes a harder, less permeable layer. The same phenomenom is seen in Al. If Al is oxidised with dichromate, an even harder oxide layer is observed. The most resistant oxidation layers are found to be formed from pure metallic particles, not partially oxidsed ones. To get proper integration of the chromium ions, it needs to be combined during the formation of the layer.

As far as practical use of this. I would say as long as your Mg is still sparkly or shiny, it will be fine to coat. If you have old corroded Mg, perhaps washing with very dilute HCl, and water DIRECTLY before coating with the dichromate would be acceptable.

I almost forgot. Here is a journal article on this. If you don't understand it, as I'm sure there will be enough, just read the conclusion, points 2 and 4. It doesn't cover everything, but it will tell you all you need to know in a much more condensed manner. http://www.mse.eng.o...c/frankel69.pdf

Edited by Mumbles, 04 October 2005 - 08:18 PM.

[KNO3]

Nice, so the coating process is more complex than it sounds! Nice to get some hardcore chemistry going on. I understand most of that, but you are obviously very educated in chemistry, i know where to come if i have a question to do with chemisry. Its always good to learn someting new!

[Mumbles]

I posted this on another forum. There happens to be a member there who is a professional pyrotechnic chemist. I got most everything, but he did inform me on a couple of points. I knew some of it, but I will post it all here in bullet form because I didn't mention it.

• Some Mg is lost in this process
• Hexavalent (VI) Chromium still remains in the oxidation crust. This makes it still dangerous to breath in the dust. It also provides a sort of self healing effect should the layer become scratched.

• One aspect that people in the fireworks business seem to have missed, is that it is ineffective to treat magnesium with pure dichromate solutions. You also need an anion activator, for example acetate, formate, sulphate, chloride, fluoride, nitrate, phosphate or sulphamate. The activator corrodes the Mg metal and provides the hexavalent chromium with electrons to facilitate its partial reduction to trivalent chromium.

There is an article in Pyrotechnica XVI called "Corrosion Protection Of Magnesium Without The Use Of Chromates". This will probably provide more information than I can.

[paul]

QUOTE(By Crazy_Swede)
One aspect that people in the fireworks business seem to have missed, is that it is ineffective to treat magnesium with pure dichromate solutions. You also need an anion activator, for example acetate, formate, sulphate, chloride, fluoride, nitrate, phosphate or sulphamate. The activator corrodes the Mg metal and provides the hexavalent chromium with electrons to facilitate its partial reduction to trivalent chromium.

Isn?t this done by the water that previously reacts with the magnesium to corrode it, so the chromium can act ?!

[Yugen-biki]

QUOTE By Crazy_Swede

One aspect that people in the fireworks business seem to have missed, is that it is ineffective to treat magnesium with pure dichromate solutions. You also need an anion activator, for example acetate, formate, sulphate, chloride, fluoride, nitrate, phosphate or sulphamate. The activator corrodes the Mg metal and provides the hexavalent chromium with electrons to facilitate its partial reduction to trivalent chromium.

Quote by Paul

Isn?t this done by the water that previously reacts with the magnesium to corrode it, so the chromium can act ?!

Why should the cromate treatment methods of Mg written in books be wrong? Shimizu or Lancaster does not mention any thing about an "anion activator". Does this mean that the treatment is for nothing?! And the dichromate could just be mixed with the star composition?

Edited by Yugen-biki, 06 October 2005 - 02:22 PM.

[Mumbles]

Dichromate mixed with the star comp is far less efficient. It doesn't provide anywhere near the protection of soaking. If you look at the above explanation I made, it's quite obvious. Solid dichromate no matter how fine will not integrate into the Mg oxide layer to any appreciable degree.

As far as the corrosive agent, I always assumed that water would work. Perhaps because when coating the Mg is it more of a paste than a solid dispersed in a liquid, and would have a very high surface area for evaporation, it needs the extra corrosivity. In the next few months here I will be doing some tests. I have 6 methods to try, and the linseed is going to take a while to dry. I am using Ammonium Perchlorate mixed with the Mg in a test tube and covered with water with a pH indicator.

As for why the other books don't mention it, perhaps they are not aware of it. Since I am not the author, nor have I even confirmed that the anion activator helps, I can't say anything. This individual is the most knowledgable on pyrotechnic chemistry of anyone I know. I tend to trust what he says. My experiments will tell though.

Edited by Mumbles, 06 October 2005 - 10:52 PM.

[BigG]

Dichromate mixed with the star comp is far less efficient. It doesn't provide anywhere near the protection of soaking. If you look at the above explanation I made, it's quite obvious. Solid dichromate no matter how fine will not integrate into the Mg oxide layer to any appreciable degree.

As far as the corrosive agent, I always assumed that water would work. Perhaps because when coating the Mg is it more of a paste than a solid dispersed in a liquid, and would have a very high surface area for evaporation, it needs the extra corrosivity. In the next few months here I will be doing some tests. I have 6 methods to try, and the linseed is going to take a while to dry. I am using Ammonium Perchlorate mixed with the Mg in a test tube and covered with water with a pH indicator.

As for why the other books don't mention it, perhaps they are not aware of it. Since I am not the author, nor have I even confirmed that the anion activator helps, I can't say anything. This individual is the most knowledgable on pyrotechnic chemistry of anyone I know. I tend to trust what he says. My experiments will tell though.

I bealive simuzu does mention a dichromate solution - so I suspect that does means the inclusion of water - which might provide a corrosion agent. I am not sure why you use ammonium perc mixed with the MG??

[Yugen-biki]

I have done tests with my dichromate coated magnesium. I put a very small ammount coated Mg in a beaker with NH4ClO4 solution. I let it stand for a day and notised no reaction.
If ordinary Mg were put in a identical NH4ClO4 solution a lot of small boubbles formed. And adding a few chrystalls of dichromate made the boubbling stop.
I have no reason to doubt Shimizu. In the end he has used that method for industrial use.

BigG

I am not sure why you use ammonium perc mixed with the MG??

I use it for strobe.