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Crackling Stars


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#16 BigG

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Posted 12 January 2004 - 09:30 AM

Lead by itself does not work. Get red lead from any pottery supplier.

#17 Phoenix

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Posted 12 January 2004 - 06:32 PM

That's what I thought. The red lead is an oxidiser, and presumably a very reactive one as the lead is pretty eager to drop the oxygen onto whatever it's in contact with, and if that happens to be as reactive as MgAL..CRACK.

#18 Stuart

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Posted 12 January 2004 - 07:21 PM

Dont suppose MgAl can be bought from anywhere or alloyed easly at home?

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#19 lord_dranack

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Posted 12 January 2004 - 08:38 PM

I believe that pencil sharpeners were at one time made on MgAl-there were reports of them exploding when held in a Bunsen flame. I don't know if they still use this...

I wonder if pure Mg would work, or would it be too reactive?

#20 tajmiester

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Posted 12 January 2004 - 08:39 PM

I saw a page about it once, try doing a search on google. Basically you get a REALLY hot charcoal fire going, melt the two and mix...

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#21 Phoenix

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Posted 12 January 2004 - 10:03 PM

I've seen this page somewhere too (It was probably the same one). I wanted to try it myself, as the idea of a really brittle metal that can be used in so many ways was very appealing. However, my search for magnesium did not turn up anything useful looking (only large scale industial suppliers - nothing "friendly")

OTOH, aren't power too housings sometimes made from Mg or MgAl? If it was pure Mg, it's clearly just a matter of alloying it with some Al. I suppose If the housing was a MgAl alloy it would not be a brittle one and you'd have to do some alloying yourself. I'll definately take a look next time I'm shopping at the tip.

Edited by Phoenix, 12 January 2004 - 10:03 PM.


#22 phildunford

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Posted 13 January 2004 - 10:54 PM

If you want a lump of magnesium, get a 'sacrificial anode' for steel hulled boats in fresh water.

not tried them myself but this companay do a .3kg one for ?15.

pcs boats

Go to their on-line shop and search for magnesium. - can't deep link 'cos it's a database.

Should think any decent sized ships chandlers would do these...
Teaching moft plainly, and withall moft exactly, the composing of all manner of fire-works for tryumph and recreation (John Bate 1635)
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#23 Stuart

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Posted 14 January 2004 - 07:17 AM

Cheaper one at the bottom if you search magnesium. 1.5 kilogram for ?16.99. Even if the bar through it weighes half a kilo (which I dout), your getting more magnesium for your money

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#24 tajmiester

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Posted 14 January 2004 - 09:44 AM

Found it!!! The information about making MgAl is on Dexters site at:

http://www.redhouse....rspage/mgal.htm

Tris

#25 Stuart

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Posted 14 January 2004 - 07:12 PM

Is MgAl soft? I couldnt imagin it being harder than Al as the Al and Mg atoms are similar sizes

Stuart

#26 alany

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Posted 15 January 2004 - 07:02 AM

Is MgAl soft? I couldnt imagin it being harder than Al as the Al and Mg atoms are similar sizes

It depends on the alloy. The 50:50 alloy is quite hard and brittle and can be broken up with a hammer or even a mortar and pestle (better to use an iron one if you have one, say an iron pot and bar). It is easy to break up 50:50 MgAl into -60 mesh is just a few minutes, a ball mill with ball bearings will do lots to -200 mesh in only an hour or so.

#27 Stuart

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Posted 15 January 2004 - 07:08 AM

Has anybody on the forum ever tried making it as this sounds interesting. Might just have to give it a go :-)

Stuart

#28 Steve

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Posted 19 January 2004 - 11:30 AM

Leadoxide or bismuthoxide are surely the safest. But they are friction sesitive in the same way like Fe(III)O and Al are.

Iron oxide and Al friction sensitive? i thought they were pretty hard to set off, unless you are thinking of the same mix as i am which involves some sort of burning mix along with iron oxide and al, which crackles (although not as impressivly as proper lead/magnalium microstars)

Please enlighten me

Steve

p.s. I'll grab that (Fe2O3/Al crackle) formula and post it as soon as the internet works again at home and i've got my formulas to hand.
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#29 Yugen-biki

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Posted 19 January 2004 - 02:53 PM

From Shimizu The art, science and technique page 326:

Thermit

Red iron aliminium composition
Al (fine flake) 45%
Red iron oxide 55
Red thermit
Minium 80% (does he mean minimum maby?)
Ferro-silicon 20

Please note these compositions, esecially the red thermit, are a little sensitive to friction.


I have tried making the Red iron aliminium composition using talcum iron(III)oxide and atomised Al. This was really hard to ignite just like flash made from Atomised Al :rolleyes: !
When using 25micron Al flake the friction sensitivity hightens for sure but how much I don?t know. You have probably nothing to fear...

#30 lord_dranack

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Posted 19 January 2004 - 03:55 PM

Are copper oxides ever used in crackling compositions? I think I saw one on the net somewhere, or I could just be making this up... :)




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