Thermite
From PyroGuide
Thermite is a high-temperature incendiary composition that can successfully reach temperatures of 2500 degrees Celsius. A thermite reaction--sometimes called a "Goldschmidt reaction"--refers to the very exothermic process occurring between a metal oxide such as Iron (III) oxide, Manganese (IV) oxide, or Copper (II) oxide, and a more reactive pure metal, such as Magnesium or Aluminium. The more reactive pure metal reduces the metal Oxide, Oxidizing itself and releasing a substantial amount of energy during the reaction. Usually the mixture is made by simply combining the ingredients, and then igniting it, which takes very high temperatures. The reaction releases so much energy, molten metal is produced as one of the products. This can often times become airborne when the reaction is sufficiently energetic, and poses major health hazards.
Contents |
Thermite Compositions
Red Iron oxide
| Aluminium | 1 |
| Iron (III) oxide | 2.96 |
Black Iron oxide
| Aluminium | 1 |
| Iron (II, III) Oxide (Black) | 3.22 |
Black Copper oxide
| Aluminium | 1 |
| Copper (II) oxide | 4.42 |
Red Copper oxide
| Aluminium | 1 |
| Copper (I) oxide | 7.96 |
Black Manganese oxide
| Aluminium | 1 |
| Manganese (IV) oxide | 2.42 |
Black Cobalt oxide
| Aluminium | 1 |
| Cobalt (II) oxide | 4.17 |
Silicon dioxide & Sulphur
| Aluminium | 10 |
| Silicon dioxide (Sand) | 9 |
| Sulphur | 12 |
Reaction Formulas
Iron (III) oxide (Red):
- Fe2O3(s) + 2Al(s) → Al2O3(s) + 2Fe(l); ΔH = -851.5 kJ/mol
According to the reaction's stoichiometry, the ratio of Iron (III) oxide to Aluminum powder--by weight--is about 3:1, or more exactly, 2.96:1.
Iron (II,III) oxide (Black):
- 3Fe3O4(s) + 8Al(s) → 4Al2O3(s) + 9Fe(l); ΔH = -3347.6 kJ/mol
Though the ΔH for this reaction as balanced is higher than that for Fe2O3 thermite, a given mass of Fe2O3 thermite will generate more energy than the same mass of Fe3O4 thermite. According to the reaction's stoichiometry, the ratio of Iron (II,III) oxide to Aluminum powder by weight is about 3.2:1, or more exactly, 3.22:1.
Copper (II) oxide (Black):
- 3CuO(s) + 2Al(s) → Al2O3(s) + 3Cu(l); ΔH = -1203.8 kJ/mol
While this thermite mixture does not produce the same amount of energy as some other compositions--like Iron (II,III) oxide--it does have an incredibly fast burn rate. Additionally copper has a comparatively low melting point, and this mix should be treated as extremely dangerous. Due to the amount of molten copper produced, and the mixtures tendency to explode--caused by the high burn rate, this mixture is known for sending out thousands of drops of liquid metal, and it is recommended that you be very careful when attempting to ignite this compound. According to the reaction's stoichiometry, the ratio of Copper (II) Oxide to Aluminum powder by weight is about 4.4:1, or more exactly, 4.42:1.
Copper (I) oxide (Red):
- 3Cu2O(s) + 2Al(s) → Al2O3(s) + 6Cu(l); ΔH = -1169.8 kJ/mol
While this thermite mixture does not produce the same amount of energy as some other compositions--like Iron (II,III) oxide--it does have an incredibly fast burn rate. Additionally copper has a comparatively low melting point, and this mix should be treated as extremely dangerous. Due to the amount of molten copper produced, and the mixtures tendency to explode--caused by the high burn rate, this mixture is known for sending out thousands of drops of liquid metal, and it is recommended that you be very careful when attempting to ignite this compound. According to the reaction's stoichiometry, the ratio of Copper (I) oxide to Aluminum powder by weight is about 8:1, or more exactly, 7.96:1.
Manganese (IV) oxide (Black):
- 3MnO2(s) + 4Al(s) → 2Al2O3(s) + 3Mn(l); ΔH = -1788.7 kJ/mol
According to the reaction's stoichiometry, the ratio of Manganese (IV) oxide to Aluminum powder by weight is about 2.4:1, or more exactly, 2.42:1.
Cobalt (II) oxide (Black):
According to the reaction's stoichiometry, the ratio of Colbalt (II) oxide to Aluminum powder by weight is about 4.2:1, or more exactly, 4.17:1.
Silicon dioxide (Sand) & Sulphur:
- 3SiO2(s) + 4Al(s) → 2Al2O3(s) + 3Si(l); ΔH = -? kJ/mol
- 3S(s) + 2Al(s) → Al2S3(s); ΔH = -? kJ/mol
or According to the reaction's stoichiometry, the ratio of Silicon dioxide to Aluminium powder by weight is about 1.7:1, or more exactly, 1.67:1. This thermite will work, but is extremely difficult to ignite. The remedy this, you can add in additional Aluminium and Sulphur to the mixture. These two elements will also burn very very hot, and are easier to ignite. They burn hot enough to start the other reaction. A mixture of Silicon dioxide, Aluminium powder, and Sulphur in the ratio of 9:10:12 works well and makes ignition manageable.
Thermate
Thermate is a slightly more powerful version of thermite which is made by combining 68.7% regular thermite, 29.0% Barium Nitrate, 2.0% sulfur, and 0.3% dextrin (as a bonding agent) together. Warning: Thermate is more unstable than thermite, when experimenting with thermate, give yourself ample time to clear the area.
Tutorial
It is best to use materials that are as fine as possible for all thermite--the finer the powder is, the faster the burn rate. Screen the chemicals together by passing the mixture several times through a mesh screen, but do not ball mill or grind the materials together. A very intimate mixing is well-worth the effort, as it will yield the best performance.
Ignition
The ignition temperature of thermite is extremely high. Therefore, traditional ignition methods like fuse, matches, and electrical igniters do not work. There are several ways to safely light a thermite mixture, the most common being:
Magnesium Ribbon
- Magnesium metal burns in the presence of air, in a very bright, exothermic reaction. Magnesium ribbon can burn at several thousand degrees, easily igniting thermite. This is a very good option, as the ribbon acts like a fuse, giving you plenty of time before the thermite is lit.
Potassium perchlorate and visco
- A mixture of potassium perchlorate and icing sugar will burn with a hot enough flame to ignite all thermite mixtures and can itself be ignited by safety fuse. This is useful if the desired ignition point is below the surface of the thermite and because magnesium ribbon can fragment as it burns, causing premature ignition which can be very dangerous with some of the more energetic thermites (for example copper oxide based thermites).
Potassium permanganate Reaction
- The reaction between Potassium permanganate and Glycerin is both simple and safe, while producing sufficient heat to light thermite mixtures. Additionally, this method gives you time to retreat to a safe distance. A pile of Potassium permanganate, which is an extremely powerful oxidizer that should be treated carefully, is placed atop the thermite composition, and a few drops of glycerin are added. After a short delay, the mixture reacts violently, producing enough heat to light the thermite mixture.
Magnalium + Iron Oxide
- For the lucky people who have easy access to Magnaluim, a very easy and safe option is to simply mix Magnalium and Red Iron Oxide in the ratio 1:3. this mix is easily ignited by visco, and even matches, while still producing temperatures in excess of 2000 degrees centigrade. The mixture is not explosive, and can be made in under a minute. A point to note is DO NOT use magnalium with ANY thermite components other than red iron oxide. such mixtures, especially with copper (II) oxide, are as explosive as flash powders, with the added danger of throwing molten metal around.
Several other ignition methods are possible, but not recommended. Safety is the key issue here, and thermite can very realistically hurt you if you try to employ these other types of ignition. Flash powders will light thermite, but they can send debris flying, and themselves require an ignition source. Also, sparklers and other very hot heat sources can ignite thermite, but these are also dangerous, as you have to be close to apply this heat to the thermite. Botched ignitions can be disasterous, and thermite should only be made and used by serious hobbyists. Underestimating its power is a one of the worst ideas you can have.
Video
250g of Thermite - 1.5meg - A backyard test of 250 grams of thermite. The heat generated was enormous and the flame was over 15 foot high (out of camera range). At the end of the very energetic burn you can see the white hot metal remaining.