Sciencemadness Discussion Board

Purpose of thermite

averageaussie - 30-4-2023 at 15:43

Hello all,
I am new to this forum so excuse me if I don't know any unwritten rules, but what is the purpose of a thermite reaction? I know in a lot of them carbon is used as a reducing agent, but couldn't you just use a stronger reducing agent like aluminium or magnesium instead of making a mini volcano? just feel that it would be a lot safer.

Rainwater - 30-4-2023 at 16:12

I use it as a quick and easy welding method for grounding electrodes, Structured steel, and demo work.
Different compositions for different applications. But essentially the same.

Admagistr - 30-4-2023 at 16:18

You can also use it to produce various metals with high melting points and those that are difficult to reduce from their oxides, but the resulting metals are not very pure.You can produce chromium, iron, molybdenum, tungsten, manganese, nickel,...

Herr Haber - 30-4-2023 at 16:19


Carbon is not used in a thermite reation. A metal such as Al, Mg, or a 50/50 % alloy called MgAl. Aluminium is most common. You can use others if you are rich :)
"Safe" here depends on a lot of factors:
- Your particle size
- Your oxide.

There are ways to tame the reaction.
You definitely will want to watch the whole series The Gayest Person on YouTube made on exotic thermites:

Johanson - 30-4-2023 at 17:17

averageaussie, please be careful if you are messing around with thermite as a hobby. I just had a student get seriously burned doing thermite in class. Thankfully he was sent immediately to an excellent burn center nearby, and is recovering. He got 2nd degree burns on several parts of his body, and spent several days in hospital.
My advice: use a very long wicking mechanism. Do not use a magnesium wick that can accidently tip over into the batch, or melt and drip into the batch while lighting it (that's what happened here). You can use cheap aluminum powder opposite either red iron oxide or manganese dioxide, but run the wick completely out of the container and a few inches away before lighting the end, and then move a safe distance away. Even then, it can be unpredictable. Just food for thought....

j_sum1 - 30-4-2023 at 20:20

Purpose of thermite.

  • Welding railroad tracks
  • Reducing exotic elements and/or low-tech creation of alloys
  • Education: there is a lot of good high-school level content related to thermite reactions. Including stoichiometry, yield calculations, managing safety. And at a higher level, determining reaction feasability, calculating entropy and enthalpy change of reaction, calculating maximum reaction temperature, manipulating reaction kinetics etc etc. I know I learned a lot through thermite reactions myself: things that have proved very valuable in other contexts.
  • Fun. I mean, what's not to love?

    Of course good safe ignition methods are important. A sparkler is a good method. My standard is to use Mg ribbon and to ignite that with a little pile of potassium permanganate and a dribble of glycerol. It takes roughly 30 seconds for the Mg to ignite and then a few more seconds for the reaction to start. That is plenty of time to clear the area and gives good visual cues of what is going on.

    Herr Haber - 30-4-2023 at 20:33

    Sparklers give you a good delay and work well with coarse reagents.
    With 63 micron atomized Al (worst possible shape) and similar size Fe2O3 a simple visco fuse will work. This particle size will definitely erupt in a volcano :)
    You can use low density thermite to ignite coarser thermite.

    Conure - 30-4-2023 at 23:36

    Can carbon (graphite, charcoal) alone produce a self sustaining thermite reaction ?

    [Edited on 1-5-2023 by Conure]

    averageaussie - 30-4-2023 at 23:48

    I would like to thank everyone for pitching in on my post, and personally thank Herr Haber and Johanson for correcting me and showing their concern for my safety respectively. I would like to reassure everyone that I will not be touching thermite until I have MUCH more experience in chemistry.

    I would like to elaborate on my original question; why would someone use thermite to reduce a metal such as silicon or manganese using aluminium as a reducing agent, when you could use a stronger reducing agent such as magnesium or chlorine with an aqueous solution of a metal oxide?

    I am aware that Silicon dioxide is very insoluble, so a silica thermite makes sense for getting elemental silicon. however something like manganese thermite confuses me, why is the heat from the thermite not interchangeable with a stronger reducing agent, and vice versa? why can copper be reduced in a solution, but not other metals? Surely the use of a strong reducing agent such as magnesium or chlorine would work?

    j_sum1 - 1-5-2023 at 01:59

    Chlorine is an oxidiser not a reducer.
    Not all redox reactions can take place in aqueous solution.
    Elevated temperatures can make many reactions feasible that cannot occur at low temperatures.
    High temperature aids reaction kinetics too.
    Aluminium is a pretty good reducer. Mg is stronger, but not generally necessary.

    My advice is to watch a few videos and do some reading. Then give it a go yourself. They can be done quite safely. Just choose a suitable outdoor location. Watch out for flammable items. And of course ignite safely and stand clear.

    Herr Haber - 2-5-2023 at 20:33

    Aluminium is used for the simplest reason on earth: cost
    Mg as j_sum1 says is not generally necessary.

    You seem to be confused on a few things but if you're interested in an industrial example where molten magnesium and chlorine are used you might want to research the Kroll process.
    There are a few cool videos on titanium and zirconium metallurgy on Youtube related to this process.
    One below, there are plenty others with more sparks :)

    [Edited on 3-5-2023 by Herr Haber]