Ignition
Metals are capable of burning under the right conditions, similarly to the
combustionCombustion
Combustion or burning is a complex sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat or both heat and light in the form of either a glow or flames, appearance of light flickering.Direct combustion by atmospheric oxygen is a reaction...
process of wood or gasoline. In fact,
rustRust
Rust is a general term for a series of iron oxides, usually red oxides, formed by the reaction of iron and oxygen in the presence of water or air moisture. Several forms of rust are distinguishable visually and by spectroscopy, and form under different circumstances...
is the result of oxidation of
steelSteel
Steel is an alloy consisting mostly of iron, with a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most cost-effective alloying material for iron, but various other alloying elements are used such as manganese, chromium, vanadium, and tungsten...
or
ironIron
Iron is a metallic chemical element with the symbol Fe and atomic number 26. Iron is a group 8 and period 4 element and is therefore classified as a transition metal. Iron and iron alloys are by far the most common metals and the most common ferromagnetic materials in everyday use...
at very slow rates. A thermite reaction is a process in which the correct mixture of metallic fuels are combined and ignited. Ignition itself requires extremely high temperatures.
Ignition of a thermite reaction normally requires only a simple child's
sparklerSparkler
A sparkler, though commonly mistaken for a type of hand-held firework, actually makes up its own category of pyrotechnics that burn slowly while emitting colored flames, sparks, and other effects...
or easily obtainable magnesium ribbon, but may require persistent efforts, as ignition can be unreliable and unpredictable. Thermite reactions require very high temperatures for initiation. These temperatures cannot be reached with conventional black powder fuses,
nitrocelluloseNitrocellulose
Nitrocellulose is a highly flammable compound formed by nitrating cellulose through exposure to nitric acid or another powerful nitrating agent...
rods,
detonatorDetonator
A detonator is a device used to trigger an explosive device. Detonators can be chemically, mechanically, or electrically initiated, the latter two being the most common....
s,
pyrotechnic initiatorPyrotechnic initiator
A pyrotechnic initiator is a device containing a pyrotechnic composition used primarily to ignite other, more difficult to ignite materials, e.g. thermites, gas generators, and solid-fuel rockets...
s, or other common igniting substances. Even when the thermite is hot enough to glow bright red, it will not ignite as it must be at or near white-hot to initiate the reaction. It is possible to start the reaction using a
propane torchPropane torch
A propane torch is a tool for burning the flammable gas propane. The maximum adiabatic flame temperature a propane torch can achieve with air is 2268 Kelvin...
if done correctly. The torch can preheat the entire pile of thermite which will make it explode instead of burning slowly when it finally reaches ignition temperature.
Often, strips of
magnesiumMagnesium
Magnesium is a chemical element with the symbol Mg, atomic number 12 and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the earth's crust by mass, although ninth in the Universe as a whole...
metal are used as fuses. Because metals burn without releasing cooling gases, they can potentially burn at extremely high temperatures. Reactive metals such as magnesium can easily reach temperatures sufficiently high for thermite ignition. Magnesium ignition remains popular among amateur thermite users, mainly because it can be easily obtained.
The reaction between
potassium permanganatePotassium permanganate
Potassium permanganate is the inorganic chemical compound KMnO4, a water soluble salt consisting of equal mole amounts of potassium and permanganate ions. This salt, formerly known as permanganate of potash or Condy's crystals is a strong oxidizing agent...
and glycerine or
ethylene glycolEthylene glycol
Ethylene glycol is an organic compound widely used as an automotive antifreeze and a precursor to polymers. In its pure form, it is an odorless, colorless, syrupy, sweet tasting liquid....
is used as an alternative to the magnesium method. When these two substances mix, a spontaneous reaction will begin, slowly increasing the temperature of the mixture until flames are produced. The heat released by the oxidation of glycerine is sufficient to initiate a thermite reaction. However, this method can also be unreliable and the delay between mixing and ignition can vary greatly due to factors such as particle size and ambient temperature.
Apart from magnesium ignition, some amateurs also choose to use
sparklerSparkler
A sparkler, though commonly mistaken for a type of hand-held firework, actually makes up its own category of pyrotechnics that burn slowly while emitting colored flames, sparks, and other effects...
s to ignite the thermite mixture. These reach the necessary temperatures and provide enough time before the burning point reaches the sample. However, this can be a dangerous method, as the iron sparks, like the magnesium strips, burn at thousands of degrees and can ignite the thermite even though the sparkler itself is not in contact with it. This is especially dangerous with finely powdered thermite.
Similarly, finely-powdered thermite can be ignited by a regular
flint spark lighterFlint spark lighter
A flint spark lighter is a type of lighter used in many applications to safely light a gaseous fuel to start a flame...
, as the sparks are burning metal (in this case, the highly-reactive rare-earth metals
lanthanumLanthanum
Lanthanum is a chemical element with the symbol La and atomic number 57.Lanthanum is a silvery white metallic element that belongs to group 3 of the periodic table and is a lanthanoid. It is found in some rare-earth minerals, usually in combination with cerium and other rare earth elements...
and
ceriumCerium
Cerium is a chemical element with the symbol Ce and atomic number 58. It is a soft, silvery, ductile metal which easily oxidizes in air. Cerium was named after the dwarf planet . Cerium is the most abundant of the rare earth elements, making up about 0.0046% of the Earth's crust by weight. It is...
). Therefore it is unsafe to strike a lighter close to thermite.
A stoichiometric mixture of finely powdered iron(III) oxide and aluminium may be ignited using ordinary red-tipped book matches by partially embedding one match head in the mixture, and igniting that match head with another match, preferably held with tongs in gloves to prevent
flash burnFlash burn
Flash burn can mean:*Arc eye, also called corneal flash burn*The effect that in a nuclear explosion of sufficient magnitude, the majority of damage is done by light and thermal radiation...
s.
Thermite: Facts, Discussion Forum, and Encyclopedia Article
