Trouble with thermite

[Brightthermite]

So I have been trying to mix up some thermite (in a 3:1 ratio) using 500 mesh 30 micron AL and iron oxide I made my self by soaking iron pipe and filtering the water.

 

When I light my thermite it goes of more or less like flash powder. I'm confused as I tried actually making flash powder using this aluminum and potassium nitrate and it would not even ignite. I check to see if the potassium nitrate may have been the problem by making a very small batch of magnesium flash powder with it and it detonated fine. So this leads me to believe it is the aluminum but I don't understand why it reacts so violently with the iron oxide.

 

So if someone could please help me with my thermite it would be appreciated!

Edited June 21, 2017 by Brightthermite

[DesertCatUSN]

I'm a newbie, but I read elsewhere here that flash is actually K Perchlorate and Al mix, not Al and K Nitrate. Why don't you just buy your iron oxide? It's super cheap. Also, doesn't some thermite have a lot of Mg in it, which is more difficult to ignite with low temperature flames? Your Al is very fine. Isn't it more coarse in thermite? Maybe that's why it reacted so violently, the fineness of the Al powder. I'm not an expert or really experienced at this, but I thought this might help based on my readings. I'm sure someone with more expertise wii correct my errors and assumptions, but perhaps these ideas will help. Roger

[lloyd]

Cat,

There are perchlorate, chlorate, and nitrate flash mixtures. It's not incorrect to call a mixture of KNO3/Al 'flash', because it's one of the several alternatives.

 

Now... if you hear or see someone write "7:3", that's referring to potassium perchlorate/aluminum flash powder. It's the 'standard' salute powder for modern fireworks.

 

Lloyd

Edited June 23, 2017 by lloyd

[Brightthermite]

I'm a newbie, but I read elsewhere here that flash is actually K Perchlorate and Al mix, not Al and K Nitrate. Why don't you just buy your iron oxide? It's super cheap. Also, doesn't some thermite have a lot of Mg in it, which is more difficult to ignite with low temperature flames? Your Al is very fine. Isn't it more coarse in thermite? Maybe that's why it reacted so violently, the fineness of the Al powder. I'm not an expert or really experienced at this, but I thought this might help based on my readings. I'm sure someone with more expertise wii correct my errors and assumptions, but perhaps these ideas will help. Roger

[Brightthermite]

I thought the aluminum may have been too fine as well but I did some research that says it's nearly too large for any type of flash powder but just big enough for thermite. So I have no idea at this point I'm very confused.

[lloyd]

We use "German blackhead" or "Indian dark" aluminum for flash. It must be _extremely_fine_ flake to work well in lightly-contained items.

 

Lloyd

[Brightthermite]

Yeah I now know it's too coarse for flash, but I don't understand why it will flash with iron oxide.

[lloyd]

Did you consider that iron oxide can behave as a catalyst?

L

[Brightthermite]

That may be what is happening, because when my "thermite" ignites there is no molting iron left or residue left at all. I guess I'm just shocked that iron oxide works better to oxidize or induce a reaction from my aluminum then potassium nitrate does. Thank you for the help tho!

[Arthur]

An important feature of the thermite reaction is that NO gas should be produced. With nitrates gasses will be produced and these will carry heat away slowing the reaction, The Iron oxide/aluminium reaction produces no gas so all the heat stays at the reaction zone to propagate the reaction.

[dave321]

i think therMATE may include barium nitrate and sulphur to make it easier to ignite,

just out of interest.

[Brightthermite]

That makes sense. I guess the only thing I'm left wondering is why there is absolutely no product of the reaction left, no iron or anything.

[DesertCatUSN]

I've seen both Iron and Copper as the primary metallic oxide for thermite. Can most oxides of metals make a thermite mix, like Lithium, for instance? How about nickel/cadmium or lead? Just thinking (scary), I have a bunch of old rechargeable batteries that have died, but contain metals. Would that even make sense, or way too much trouble? Or could I extract the metals from those batteries (big, 18V +) and use them for coloring in pyro mixes. Just seems a shame to not use them for something. Thanks. Roger

[Mumbles]

Flash and thermite are essentially the same reaction. It's a metal plus an oxidizer. In thermite (aka the Goldschmidt reaction) the oxidizer is usually a metal oxide. In flash, the oxidizer is traditionally an oxygen evolving salt.

 

Whether or not a thermite reaction will proceed is based on reduction potentials. By choosing a metal and an oxide totally at random, you can pretty much determine whether or not it will react by looking at an Activity Series. http://wps.prenhall.com/wps/media/objects/1053/1078773/tools/bl04tb04.html The metallic fuel must be higher on the list than the oxide to proceed thermodynamically. Additionally the larger the difference, the more violet. Thus why Al + Fe2O3 can be tame, but Al + CuO can be pretty violent. Lithium oxide basically wont work with anything.

 

You can also use this to determine potential interactions in water wet stars. It explains why soluble copper salts for instance are incompatible with traditional metals like aluminum and magnesium.

 

The no solid products is an issue with reaction rate. If you use a coarser metal powder/granule size it will proceed slower. Fine Al basically vaporizes or sprays the metal into the air, while a coarser powder can be used in the more traditional sense to create molten iron.

[DesertCatUSN]

According to the chart you referenced, Lithium is the most easily oxidized. Is that why Li Oxide won't work with anything, it is at the top of the Activity Series, so no other metal will react, as they're all lower? And would that mean Barium or Calcium with CuO would cause an extremely violent reaction? Or are they so reactive that a mixture would self ignite (bad)? Just out of curiosity, is there, or does anyone, even use some type of Au or Pt oxide, since they're so non-reactive? Finally, would Hg Oxide be extremely reactive also, but isn't used due to toxicity?

[Mumbles]

That's correct about litihum. Mixing lithium oxide with any other metal will not produce metallic lithium. As far as I know, the only way to make it is via electrolysis. It only takes a couple of volts, which doesn't seem that impressive for it's very reactive nature. The more reactive the metal, the more inert the oxide (usually).

 

The violence of a reaction has to do with the difference between the metal and the oxide more or less. So yes, a mixture of calcium or barium with copper oxide would be quite violent. It's probably worth noting that both of those metals react with water and oxygen in the atmosphere too though, so it might eventually self ignite. Magnesium is about the most reactive useful metal.

 

The underlying principle behind the activity series is the oxidation potential of the metal. Some activity series will list these. Lithium is probably around -3.0 V for instance and decreases as you go down the table. Hydrogen is at 0 V. This means that the metals below hydrogen actually have positive potentials. If you know much about electrochemistry or potentials, this means that the metals are actually more stable than the oxide. Anything lower on the activity series than hydrogen will actually thermally decompose into the metal and oxygen. Silver, gold, mercury, etc. all do this. Given this, I don't know how well they'd work in thermites. The oxide might decompose before it really starts reacting.