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Registered Member #3395
Joined: Thu Nov 04 2010, 08:42AM
Location: Christchurch, New Zealand
Posts: 193
I'm having trouble igniting a mixture of thermite using magnesium ribbon. I made sure the iron oxide mixture was dry and had very little water content by heat drying it, and my aluminium powder is reasonably fine. It was ground with a coffee/seed grinder and the result was a mixture of very fine dust but the majority of the powder particles are about 0.5mm in size.
I understand the surface area of the aluminium powder has to be very high, so perhaps my powder needs to be even finer?
Registered Member #902
Joined: Sun Jul 15 2007, 08:17PM
Location: Pacific Northwest USA
Posts: 1042
You may try shaving some magnesium into a powder and have it at the base of the ribbon entry.
I personally stopped using magnesium years ago due to reliability and safety concerns. I currently use an ignition mixture from United Nuclear for lighting my thermite. I dip electronic rocket ignitors from Aerotech in it. (I use Aerotech since you can get insulated leads easily, and thermite is conductive).
Registered Member #54480
Joined: Sun Feb 15 2015, 01:02AM
Location: Kennebunk ME
Posts: 7
Try using a simple sparkler. Recently I was experimenting with this and I thought my ratios were off but the problem ended up being my ignition source was just too low. 99cent sparklers make great fuses.
Registered Member #230
Joined: Tue Feb 21 2006, 08:01PM
Location: Gracefield lower Hutt
Posts: 284
The sparkler idea is good one your problem is that the aluminium is not fine enough you need explosive grade Al powder ie sub micron particle size then even a match will ignite it.
Registered Member #902
Joined: Sun Jul 15 2007, 08:17PM
Location: Pacific Northwest USA
Posts: 1042
johnf wrote ...
The sparkler idea is good one your problem is that the aluminium is not fine enough you need explosive grade Al powder ie sub micron particle size then even a match will ignite it.
Sparklers have safety issues as well. They are chaotic, and throw too many metal flakes before the flame reaches the base of the sparkler. If you have made the Al that fine and it is actually explosive, then regulation issues come into play in most jurisdictions as well.
Registered Member #61428
Joined: Sat Jan 14 2017, 12:39PM
Location:
Posts: 50
johnf wrote ...
your problem is that the aluminium is not fine enough
Exactly right. The simplest method I have seen for getting from what you have to "fine enough" is with a ball mill. Either the drum tumbler type or the type where a turnstyle-like rotor pushes 4 large steel balls around a circular race filled with the powder. (I don't know the specific name of the second type.)
It probably wouldn't hurt to mill your oxide too.
FYI, Copper thermite is even more energetic than iron.
Registered Member #135
Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735
I think you guys are overlooking the obvious here.
When you have Al powder that is not pure Al, like 6061 its hard to burn because of the alloying metals, so you make it burn easy!
You make up your thermite with an excess of iron oxide, then mix in the magnesium powder. The Magnesium consumes some of the iron oxide, but it gets it going, enough so that you can use a butane torch to light it. Just make sure you get the hell away fast.
Registered Member #61400
Joined: Sun Jan 01 2017, 01:01PM
Location:
Posts: 33
Thermite reaction starts when some of the aluminium melts. Sparklers are fine because sparks don't have enough heating capability to do that. I've found that the most convenient method to start common thermite is potassium permanganate with a bit of glycerol. That is if you don't have some commercial ignition mixture. If half a teaspoon of permanganate fails to start a thermite there is something badly wrong with the mixture.
Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
I remember setting off thermite in high school. I wound up putting a crater in my street road. It melted through everything. Anyway, the aluminum and rust were as fine a baby powder. I set it off with a magnesium ribbon without a problem. Once it starts you can not stop it until the fuel runs out.
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Difficulty igniting Fe2O3/Al thermite mixture
