Thermite
From HvWiki
Thermite is a mixture of a reactive metal and a metal oxide which when ignited produces a thermic reaction. The most common ingredients for home made thermite are aluminium and iron(III) oxide. The result of the reaction is aluminium oxide, molten iron, and a large amount of heat. The temperature of the molten metal can reach 2500 °C.
The balanced equation for the reaction is:
- 2Al + Fe2O3 → Al2O3 + 2Fe
The thermite mixture should be 25.3% aluminium and 74.7% iron(III) by weight. The ingredients should be finely powdered and mixed well.
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Usable metal oxides
- Red iron(III) oxide (Fe2O3, commonly known as rust)
- Black or blue iron (II,III) oxide (Fe3O4)
- Manganese(IV) oxide (MnO2)
- Chromium(III) oxide (Cr2O3)
- Copper(II) oxide (CuO)
Ignition
Ignition of thermite is difficult and requires very high temperatures. The process can be very unpredictable, some times it is very hard to ignite and other time it may ignite prematurely and cause dangerous situations. Even if thermite requires a high temperature to ignite it is possible that small sparks can ignite finely powered thermite.
If you are having difficulty achieving ignition, try placing a 1:1.78 (or just 1:2) mixture of aluminium powder and sulfur powder on top of your main charge. This mixture is easy to ignite with a fuse and relatively tame but burns hot enough to melt steel and ignite thermite mixtures of all sorts.
Magnesium strips as a fuse
Insert a strip of magnesium ribbon into the thermite and light it. The strip itself can be hard to ignite and it needs oxygen (air) to burn.
Potassium permanganate and glycerine or ethylene glycol
When mixed will start a hypergolic reaction that reaches a temperature that is capable of igniting thermite.
Sparkler
A sparkler will ignite thermite but the sparks may cause premature ignition.
Arc
An electric arc is hot enough to ignite thermite.
Where to get aluminium powder
Aluminium is often an alloy (like alloy 6061) that can make ignition very difficult, pure aluminium is better.
- Grinding anything aluminium will work, just make sure the dust keeps cool so it does not burn through the container you collect it in. Remember that aluminium is a reactive metal that can burn and in some cases explode.
- Aluminium powder can be bought in some paint shops as a metallic paint additive.
Where to get metal oxide powder
Iron(III) oxide is the simplest oxide to obtain.
Where to buy iron(III) oxide
- Pottery supply store as pottery glaze.
- Hardware store as cement colourant.
Rusting steel wool
Use a pyrex dish, a small glass plate that fits in the dish, some pennies to space the plate off the bottom of the dish, some water, and steel wool. Place the wool on the glass slide in the dish spaced off the bottom, add some water to wet the wool, and add water so that the wool "wicks" the water.
This will rust quickly. This will give you the Alpha Iron Hydroxide/Iron Oxide....but you want the Gamma species. So take the yellowish orange powder you've let oxidize, put it in a metal pan and heat until the oxide turns deep red. Stirring with a heat resistant rod helps convert all the Alpha to Gamma. You can have several hundred grams in a couple of days with this.
Safety
- The molten metal is extremely hot and emits infrared and ultraviolet radiation that may cause eye damage.
- The reaction releases large amounts of energy and often splash molten metal over a large area. Contaminants may cause explosions. Keep a good distance and never go back to have a closer look if it fails to ignite properely. The reaction contains its own oxygen and can't be extinguised in a normal way. Never throw water or any other substance at burning thermite.
- The oxides can cause serious medical problems at high exposures. Use good ventilation, remember to wash your hands thoroughly. Aluminium is not poisonous like heavy metals but long term exposure is probably not a good idea.
- Aluminium dust can cause fires and explosions and must be handled and stored safely.
