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Looking for source for Mg (thermite)

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LAN_403

HV Enthusiast

Sun Jul 13 2008, 07:41PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
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Posts: 3068

Spent many hours trying to hunt this stuff down on GOOGLE, but not with much luck. I'm looking into making a mixture of thermite which requires -600 mesh Magnesium which is not too readily available. (The thermite will be used to ignite very large clustered rocket motors which require almost instantaneous and simulataneous ignition to ensure proper flight)

Figured, some of you Chem guys / gals may have some other sources that I may have overlooked for chem supplies.

Thanks!

Hon1nbo

Sun Jul 13 2008, 08:09PM

Registered Member #902 Joined: Sun Jul 15 2007, 08:17PM
Location: Pacific Northwest USA
Posts: 1042

what exactly is the thermite mix you intend to use? I would think that thermite (iron and aluminum, even with the magnesium powder added) would have too sporadic ignition timing, as the stuff is hard enough to light as it is...

I used to buy my thermite online, but then most suppliers went under, and the ones left are way overpriced, so just make some... get aluminum from an etch-n-sketch, iron oxide from rusty nails and whatnot, and shave some magnesium bars from a camping store, or for finer particle size you can buy it online, I get mine from united nuclear...

HV Enthusiast

Sun Jul 13 2008, 08:24PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
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DaJJHman wrote ...

what exactly is the thermite mix you intend to use?

Basically the mixture is as follows:

About 3:1 with 3 parts Mg (600 mesh) and 1 part Cupric oxide

Most mixtures of thermite (which uses aluminum etc...) are useless for igniting motors.

But the mixture above lights with a simple electrical match and practically instantly.

Chris

Sun Jul 13 2008, 08:47PM

Registered Member #8 Joined: Thu Feb 02 2006, 04:34AM
Location: Harlowton, MT, United States
Posts: 214

Why would you want to use magnesium? Aluminum can reduce just about any metal you'd want out of a thermite reaction, and since it has a higher boiling point, the temperature can go higher than a magnesium thermite, around 2500Â°C. If you're worried about it being too hard to ignite, you could just add a small amount of magnesium at the surface which doesn't necessarily need to be so fine. You could just grind it from a solid piece.

Also thermite probably isn't the best thing for simultaneous ignition of the motors. Chemical means tend to be slow and varied in reaction time. You'd likely be better off using powerful electric ignitors.

Shaun

Sun Jul 13 2008, 08:59PM

Registered Member #690 Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616

Try here:

But you'll have to sift through the tens of different types of magnesium. A quick scan of it indicates they have up to 1000 mesh! OF course they have to ship it mixed with larger grains...

HV Enthusiast

Sun Jul 13 2008, 09:57PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
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Chris wrote ...

Why would you want to use magnesium? Aluminum can reduce just about any metal you'd want out of a thermite reaction, and since it has a higher boiling point, the temperature can go higher than a magnesium thermite, around 2500Â°C. If you're worried about it being too hard to ignite, you could just add a small amount of magnesium at the surface which doesn't necessarily need to be so fine. You could just grind it from a solid piece.

Also thermite probably isn't the best thing for simultaneous ignition of the motors. Chemical means tend to be slow and varied in reaction time. You'd likely be better off using powerful electric ignitors.

Because, the other mixtures of thermite made from aluminum are extremely difficult to ignite. Thermite made from a magnesium mixture will light instantly with just a small igniter or electrical match. It is this reason alone that magnesium is used.

Thermite is the standard for simultaneous ignition of motors of this size. For the particular design i'm using, there are (4) motors in which the propellant slugs themselves are 4 inches in diameter and about 4 feet long, and the central core about 1.5" in diameter.

wrote ...

You'd likely be better off using powerful electric ignitors.

Thats exactly what i'm doing. I'm building my own electric igniter.

Remember, its all about safety. You can't have a 300 lb rocket going off with a 4 cluster arrangement and not have even one motor not ignite. Very bad.

For a single motor of this size, i'd use just a standard igniter dipped in themalite or some other pyrogen. But even in this case, it usually takes almost 5 seconds to ignite the propellant. The thermite mixture produces enough energy
to almost instantly ignite the propellant.

Basically, you need an energy flux to the propellant surface of about 100 cal/cm^2/s (420 watts/cm2) to ignite the propellant grain with 0.1second (This per NASA SP-8051).
The thermite mixture is designed to meet this requirement.

Plus its the standard by which most high power clusters are lit, so its already proven.

Hon1nbo

Mon Jul 14 2008, 12:04AM

Registered Member #902 Joined: Sun Jul 15 2007, 08:17PM
Location: Pacific Northwest USA
Posts: 1042

ok, understanding this, I would use a mixture of magnalium (magnesium/aluminum mixture, it will get the high temp while being easy to light... you can get magnalium off of ebay, or make it yourself... it might require some experimentation though...)

Hazmatt_(The Underdog)

Mon Jul 14 2008, 08:26AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

Cutting to the chase

1. Fire starter key-chain thing from WalMart or sporting goods store. It has a pyrite built in so you shave off some of the Mg bar and ignite it with the striker by a pocket knife.

2. Mg 1" rods used in swamp coolers used to be available at the hardware store as sacrificial anodes. they come in a little plastic tray package with a green ground wire attached.

Get yourself a 2nd cut or bastard file, I prefer the 2nd cut, and at least 12" long, 18" if you can find one, and "go to town".

Or if you're a thoughtful and careful person like I was and understand what you're dealing with, you can make a drum sanding colletion box to collect the dust. Bare in mind that I will not be liable if you hurt yourself with this method, it is very dangerous.

A reminder too, Mg shavings once under the skin cause blisters and boils that will not go away until the metal is removed, it is reactive under the skin.

Adrenaline

Mon Jul 14 2008, 01:27PM

Registered Member #235 Joined: Wed Feb 22 2006, 04:59PM
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Posts: 80

Skylighter has been good to me for sourcing this sort of thing. They only have up to 325 mesh that should be fine enough?

I have some 2micron powder at home, but it is pretty nasty.

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