10 replies to this topic

[Plays with Fire]

Hey all, I've read many times here that water/moisture can cause Al compositions without boric acid to spontaneously ignite and I was wondering if the same was true for Mg compositions?

If so, would boric acid prevent this in Mg, like it does in Al?

Also, can dextrin + water be used as a binder for compositions containing Al (and compositions containing Mg if the answer to my first question is yes) if the proper amount of boric acid is used, or should one still not purposely add water?

Much Thanks,
Plays with Fire


P.S. I searched for the words magnesium and water together and got no matches.

[portfire]

i dont think magnesium and water spontaneously ignites but it reacts with steam and gives off hydrogen i think

[adamw]

Did you ever do any chemistry at school? Think about simple terms of reactivity in metallic elements: magnesium is more reactive than aluminium!

You can use magnesium in compositions bound with water if it is coated, with for example dichromate or a physical inhibitor such as linseed oil.

[Plays with Fire]

You can use magnesium in compositions bound with water if it is coated, with for example dichromate or a physical inhibitor such as linseed oil.

I've searched under as many terms as I can think of that might find a post/thread about how to actual coat metallic powders yourself, but alas I come up empty. Has anyone coated stuff themselves instead of buying it coated?
If so, I'd be intrested to learn how. I can't imagine that it's just pouring the linseed oil in and mixing!

With no intent to harm myself or others ,
Plays with Fire

[Phoenix]

I remember reading on rec.pyrotechnics that boric acid should NOT be added to magnesium comps. This was a while ago, so you might want to check that yourself.

[adamw]

You may find this useful:

http://www.ukrocketr...owtopic=573&hl=

[Give_me_APCP]

I've never heard that moist aluminum could spntaneously combust...

But now I'm interested in this.

Is this really something to worry about? When we mix flash it is outdoors on site, but often very humid (this is better for non-static conditions of coarse). Should we be worried about the fine Al in the humid heat? What about moisture content of the oxidizer ehen they are mixed?

[adamw]

The data that I have on alu / water reaction gives a timeframe of several days - nothing to worry about considering the comparatively little amount of water in the atmosphere.

[Chyros]

As for magnesium; when it it comes into contact with water (not steam or ice as far as I know), it will very slowly give off hydrogen bubbles. Increasing the area of contact (eg powdering it) will increase the rate of reaction.

[Plays with Fire]

As for magnesium; when it it comes into contact with water (not steam or ice as far as I know), it will very slowly give off hydrogen bubbles. Increasing the area of contact (eg powdering it) will increase the rate of reaction.

I am curious about this reaction. Is it: Mg + H2O = MgO + H2 ?

If powdered Mg was dropped in water, would the reaction take place at a dangerous speed?

I would like to see such a reaction; is there a safe way to do it (eg. remotely activated and away from all people/property/flammables)?

Sincerely,
Plays with Fire

[Chyros]

I am curious about this reaction. Is it: Mg + H2O = MgO + H2 ?

Sounds reasonable, I can't see what other reaction it could be...

If powdered Mg was dropped in water, would the reaction take place at a dangerous speed?

I would like to see such a reaction; is there a safe way to do it (eg. remotely activated and away from all people/property/flammables)?

I've never tried this reaction at all, but I know that if you put in magnesium ribbon, the bubbles form only very slowly. I don't think powdering it will make it form bubbles at super speed but safety doesn't hurt. If you want to do it from a distance you could either suspend something burning over the container with water and make it act like a pilot flame, or you could place a bigger container upside down over it with a big hole in it and light the hole from a distance (this would increase the "bang" you'd get). If you find the powder reaction is much too slow, you could consider electrolysing some magnesium ribbon suspended in the water (this would speed up the reaction and add oxygen to the reaction, making it bang even louder).