# What is thermite? **URL:** \ **Category:** Factual Questions\ **Created:** [November 3, 2005, 8:24pm UTC](https://boards.straightdope.com/t/what-is-thermite/329346 "2005-11-03T20:24:23Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Strinka](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/strinka/32/512_2.png) [@Strinka](https://boards.straightdope.com/u/Strinka)\ **Post date:** [November 3, 2005, 8:24pm UTC](https://boards.straightdope.com/t/what-is-thermite/329346/1 "2005-11-03T20:24:23Z")
That’s it. ---
**Author:** ![Ike\_Witt](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ike_witt/32/283_2.png) [@Ike\_Witt](https://boards.straightdope.com/u/Ike_Witt)\ **Post date:** [November 3, 2005, 8:29pm UTC](https://boards.straightdope.com/t/what-is-thermite/329346/2 "2005-11-03T20:29:13Z")
[Thermite](http://columbia.tfd.com/Thermite+process). Seems like powdered metal for use in incindiary devices. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [November 3, 2005, 8:30pm UTC](https://boards.straightdope.com/t/what-is-thermite/329346/3 "2005-11-03T20:30:01Z")
Thermite is a combination of (usually) finely-ground aluminum metal powder and powdered metal oxide, normally iron oxide. When heated, the metal oxide gives off oxygen, which reacts with the aluminum to produce aluminum oxide and pure metal plus a great deal of heat. It’s used for cutting operations, and also in solid rocket engines. ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [November 3, 2005, 8:37pm UTC](https://boards.straightdope.com/t/what-is-thermite/329346/4 "2005-11-03T20:37:08Z")
I saw a show on one of the ‘educational’ channels. The premise is that scientists go to some remote location, they’re given tasks to accomplish, and they do them. In one episode a scientist made some thermite. I don’t remember why. ISTR they were looking for a heat source, but thermite is a little bit of overkill. Or they may have been trying to weld something. Whether that was the task or not, they did weld some metal with the substance. Interesting stuff. Of course, interesting stuff is often dangerous. ‘Do not try this at home.’ (And I haven’t.) ---
**Author:** ![Strinka](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/strinka/32/512_2.png) [@Strinka](https://boards.straightdope.com/u/Strinka)\ **Post date:** [November 3, 2005, 8:51pm UTC](https://boards.straightdope.com/t/what-is-thermite/329346/5 "2005-11-03T20:51:09Z")
Ah. Thanks! ---
**Author:** ![silenus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/silenus/32/166_2.png) [@silenus](https://boards.straightdope.com/u/silenus)\ **Post date:** [November 3, 2005, 8:57pm UTC](https://boards.straightdope.com/t/what-is-thermite/329346/6 "2005-11-03T20:57:50Z")
😃 > [@Johnny L.A.](#): > > Of course, interesting stuff is often dangerous. ‘Do not try this at home.’ (And I haven’t.) I have! Well, not “at home” exactly. But we did make thermite in my high school Chemistry class. Made a real nice spot-weld on a steel plate, and cut right through some 1/4" angle-iron. White-hot doesn’t begin to describe it. ---
**Author:** ![Rodd\_Hill](https://avatars.discourse-cdn.com/v4/letter/r/3ab097/32.png) [@Rodd\_Hill](https://boards.straightdope.com/u/Rodd_Hill)\ **Post date:** [November 3, 2005, 9:11pm UTC](https://boards.straightdope.com/t/what-is-thermite/329346/7 "2005-11-03T21:11:03Z")
Thermite was the active ingredient in most WW2 incendiary bombs. Here’s a Luftwaffe one, with an explosive head: [http://www.warbirdsresourcegroup.org/LRG/b22ez.htm](http://www.warbirdsresourcegroup.org/LRG/b22ez.htm) There was a History or Discovery Channel program about a year ago with one of the few remaining Special Air Service “originals.” They re-enacted how they blew up German aircraft in North Africa with thermite bombs (IIRC, a small HE charge would open up the wing fuel tank, then the thermite could ignite the fuel). He was quite the character, as you might imagine; this octegenarian playing with bombs! 🙂 ---
**Author:** ![gotpasswords](https://avatars.discourse-cdn.com/v4/letter/g/c57346/32.png) [@gotpasswords](https://boards.straightdope.com/u/gotpasswords)\ **Post date:** [November 3, 2005, 9:20pm UTC](https://boards.straightdope.com/t/what-is-thermite/329346/8 "2005-11-03T21:20:51Z")
I’ve seen it used to weld continuous rail for a train line. Thermite’s actually pretty common for this. Thermite puts out gobs of heat and welds rail quite nicely. It’s quite a spectacle as well - Once they light it, it spits sparks and smoke for a few minutes. Smells about as bad as you’d expect it to. 😃 ---
**Author:** ![Jurph](https://avatars.discourse-cdn.com/v4/letter/j/50afbb/32.png) [@Jurph](https://boards.straightdope.com/u/Jurph)\ **Post date:** [November 3, 2005, 9:34pm UTC](https://boards.straightdope.com/t/what-is-thermite/329346/9 "2005-11-03T21:34:36Z")
> [@Q.E.D.](#): > > It’s used for cutting operations, and also in solid rocket engines. Terminology nitpick: only liquid-fueled rockets have “engines”. When I was doing ballistic missile research, we were very specific to call the solid boosters “motors”. Estes has blurred the common vocabulary with their model rocket motors, which they market as “engines,” but most rocketry texts (and all propulsion engineers) retain this distinction in their language. Also, modern solid motors – at least in ICBMs – tend to only use powdered aluminum (and not iron or a mixture), since the main purpose of metal in your propellant is to add reaction mass and heat capacity. It probably has something to do maximizing surface area and heat capacity and minimizing mass. I don’t know enough of the reaction chemistry to give specifics, but aluminum is better than iron for the task, so including a mixture would be sub-optimal. ---
**Author:** ![Kevbo](https://avatars.discourse-cdn.com/v4/letter/k/e47774/32.png) [@Kevbo](https://boards.straightdope.com/u/Kevbo)\ **Post date:** [November 3, 2005, 9:36pm UTC](https://boards.straightdope.com/t/what-is-thermite/329346/10 "2005-11-03T21:36:36Z")
The iron oxide is iron oxilate I think (may be getting this mixed up with jewler’s rouge though) which has an extra oxygen atom or two over garden variety rust. The aluminum has a greater affinity for the oxygen than the iron, So in the burning, the aluminum scavanges the oxygen, leaving iron… so the iron oxilate/oxide is reduced to molten iron. ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [November 3, 2005, 9:43pm UTC](https://boards.straightdope.com/t/what-is-thermite/329346/11 "2005-11-03T21:43:14Z")
> [@Jurph](#): > > Also, modern solid motors – at least in ICBMs – tend to only use powdered aluminum (and not iron or a mixture)… Speaking of which, what was the name of that rocket fuel plant in Nevada that blew up a couple/few years ago? And what was it that was touched off my the welding sparks? ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [November 3, 2005, 9:48pm UTC](https://boards.straightdope.com/t/what-is-thermite/329346/12 "2005-11-03T21:48:34Z")
I’ve made thermite with plain old rust (iron oxide) and aluminum powder. Manganese dioxide plus aluminum also works. Around here, they use it to break up ice jams on the river in spring. ---
**Author:** ![Jurph](https://avatars.discourse-cdn.com/v4/letter/j/50afbb/32.png) [@Jurph](https://boards.straightdope.com/u/Jurph)\ **Post date:** [November 3, 2005, 9:51pm UTC](https://boards.straightdope.com/t/what-is-thermite/329346/13 "2005-11-03T21:51:57Z")
> [@Jurph](#): > > It probably has something to do maximizing surface area and heat capacity and minimizing mass. I don’t know enough of the reaction chemistry to give specifics, but aluminum is better than iron for the task, so including a mixture would be sub-optimal. [And now I know.](http://www.aerospaceweb.org/question/propulsion/q0246.shtml) The aluminum serves as a low-mass heat sink, absorbing heat and evening out the burn rate of other propellants. By slowing down the rate of reaction, it controls the explosion of the propellants and increases the efficiency of the nozzle. Farther down the article lists some of the trade-offs (e.g. you need a conical nozzle to reduce friction losses) but the benefits are great. As for the Nevada plant, [here’s](http://www.chemaxx.com/explosion1.htm) a good summary. They call the stuff that exploded “rocket fuel” which is technically incorrect – it was ammonium perchlorate (NH[sub]4[/sub]ClO[sub]4[/sub]), which is an oxidizer. The drums they stored it in were polyethylene, and the combination of a strong oxidizer inside a flammable hydrocarbon drum was an accident waiting to happen. A welding spark touched off one drum, and ka-POW. Weirdly enough, it was supposed to be stored in aluminum drums. On one hand, aluminum’s a good idea, because it doesn’t catch fire as easily. On the other hand, once it does catch… :eek: ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [November 3, 2005, 9:57pm UTC](https://boards.straightdope.com/t/what-is-thermite/329346/14 "2005-11-03T21:57:30Z")
> [@Jurph](#): > > As for the Nevada plant, [here’s](http://www.chemaxx.com/explosion1.htm) a good summary. 1988? I didn’t realise it happened so long ago. ---
**Author:** ![Harmonious\_Discord](https://avatars.discourse-cdn.com/v4/letter/h/74df32/32.png) [@Harmonious\_Discord](https://boards.straightdope.com/u/Harmonious_Discord)\ **Post date:** [November 3, 2005, 10:11pm UTC](https://boards.straightdope.com/t/what-is-thermite/329346/15 "2005-11-03T22:11:12Z")
I read a article in the 1904 archives of the local paper. It was about how this new method of welding rails together would allow for much cheeper joining by unskilled labor. I don’t see how using thermite without injuries would be unskilled. I think they should have said consistant welds by moderately skilled labor. ---
**Author:** ![Jurph](https://avatars.discourse-cdn.com/v4/letter/j/50afbb/32.png) [@Jurph](https://boards.straightdope.com/u/Jurph)\ **Post date:** [November 4, 2005, 12:21am UTC](https://boards.straightdope.com/t/what-is-thermite/329346/16 "2005-11-04T00:21:48Z")
> [@Harmonious Discord](#): > > I read a article in the 1904 archives of the local paper. It was about how this new method of welding rails together would allow for much cheeper joining by unskilled labor. I don’t see how using thermite without injuries would be unskilled. I think they should have said consistant welds by moderately skilled labor. Remember that using a deep fryer is considered “unskilled” labor, too, but the first week you use one, you _will_ get burned. And really, laying the powder down and then touching a long, burning punk to it has got to be safer and easier than using any gas or electrical welder. ---
**Author:** ![Harmonious\_Discord](https://avatars.discourse-cdn.com/v4/letter/h/74df32/32.png) [@Harmonious\_Discord](https://boards.straightdope.com/u/Harmonious_Discord)\ **Post date:** [November 4, 2005, 12:34am UTC](https://boards.straightdope.com/t/what-is-thermite/329346/17 "2005-11-04T00:34:39Z")
> [@Jurph](#): > > Remember that using a deep fryer is considered “unskilled” labor, too, but the first week you use one, you _will_ get burned. And really, laying the powder down and then touching a long, burning punk to it has got to be safer and easier than using any gas or electrical welder. The method was to form a temporary mold around the ends, fill it with thermite, and then light it. The mold was removed after cooling and the rail filed down to the correct dimensions in some way. I think they should have said consistant welds by moderately skilled labor, because someone just off the street would quickly be injured. Think how the railroads at that time took people off the laying crews and had them do some dynamiting. ---
**Author:** ![enipla](https://avatars.discourse-cdn.com/v4/letter/e/54ee81/32.png) [@enipla](https://boards.straightdope.com/u/enipla)\ **Post date:** [November 4, 2005, 1:03am UTC](https://boards.straightdope.com/t/what-is-thermite/329346/18 "2005-11-04T01:03:14Z")
Rust and aluminum dust? And you can use it to weld? 4,500 degrees? Could a simple paste be made, and be used to weld two pieces of steel together? I’m thinking about a commercial product. I’ve got a wire feed welder, but thermite sounds like it would be very handy for a small quick job. Maybe it’s too dangerous to sell to the public [looks out window at 500 gallon propane tank and 4-20lb propane bottles]. There is lots of dangerous stuff out there. I can buy gun powder in bulk. It can’t be that easy. ---
**Author:** ![Bosda\_Di\_Chi\_of\_Tricor](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bosda_di_chi_of_tricor/32/16845_2.png) [@Bosda\_Di\_Chi\_of\_Tricor](https://boards.straightdope.com/u/Bosda_Di_Chi_of_Tricor)\ **Post date:** [November 4, 2005, 1:12am UTC](https://boards.straightdope.com/t/what-is-thermite/329346/19 "2005-11-04T01:12:26Z")
> [@enipla](#): > > Rust and aluminum dust? > > And you can use it to weld? > > 4,500 degrees? > > Could a simple paste be made, and be used to weld two pieces of steel together? I’m thinking about a commercial product. I’ve got a wire feed welder, but thermite sounds like it would be very handy for a small quick job. > > Maybe it’s too dangerous to sell to the public [looks out window at 500 gallon propane tank and 4-20lb propane bottles]. There is lots of dangerous stuff out there. I can buy gun powder in bulk. > > It can’t be that easy. Ummm…do not do this at home. _ **REALLY!!** _ :eek: :eek: :eek: ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [November 4, 2005, 1:29am UTC](https://boards.straightdope.com/t/what-is-thermite/329346/20 "2005-11-04T01:29:27Z")
> [@enipla](#): > > It can’t be that easy. It’s not. The stuff is hard to ignite (usually a Mg ribbon or ignition mix), and you end up with a big pile of white hot aluminum oxide in addition to your iron. If you try using it for small projects, you’ll quickly find that the molten iron loses heat too fast to make a decent joint. [Next page](https://boards.straightdope.com/t/what-is-thermite/329346.md?page=2)