Thermite Thermite is a pyrotechnic composition of metal powder fuel and metal oxide . When ignited by heat , thermite undergoes an exothermic oxidation - reduction reaction . Most varieties are not explosive but can create brief bursts of high temperature in a small area . Its form of action is similar to that of other fuel - oxidizer mixtures , such as black powder . Thermites have diverse compositions . Fuels include aluminium , magnesium , titanium , zinc , silicon , and boron . Aluminium is common because of its high boiling point . Oxidizers include boron ( III ) oxide , silicon ( IV ) oxide , chromium ( III ) oxide , manganese ( IV ) oxide , iron ( III ) oxide , iron ( II , III ) oxide , copper ( II ) oxide , and lead ( II , IV ) oxide . Chemical reactions . The aluminium reduces the oxide of another metal , most commonly iron oxide , because aluminium forms stronger bonds with oxygen than iron : The products are aluminium oxide , free elemental iron , and a large amount of heat . The reactants are commonly powdered and mixed with a binder to keep the material solid and prevent separation . The reaction is used for thermite welding , often used to join rail track s . Other metal oxides can be used , such as chromium oxide , to generate the given metal in its elemental form . Copper thermite , using copper oxide , is used for creating electric joints in a process called cadwelding : Some thermite - like mixtures are used as pyrotechnic initiator s such as fireworks . Thermites with nanosized particles are described by a variety of terms , such as metastable intermolecular composite s , super - thermite , nano - thermite , and nanocomposite energetic materials . History . The thermite ( " thermit " ) reaction was discovered in 1893 and patented in 1895 by German chemist Hans Goldschmidt . Consequently , the reaction is sometimes called the " Goldschmidt reaction " or " Goldschmidt process " . Goldschmidt was originally interested in producing very pure metals by avoiding the use of carbon in smelting , but he soon discovered the value of thermite in welding . The first commercial application of thermite was the welding of tram tracks in Essen , Germany , in 1899 . Types . Red iron ( III ) oxide ( FeO , commonly known as rust ) is the most common iron oxide used in thermite . Magnetite also works . Other oxides are occasionally used , such as MnO in manganese thermite , CrO in chromium thermite , or copper ( II ) oxide in copper thermite , but only for specialized purposes . All of these examples use aluminium as the reactive metal . Fluoropolymers can be used in special formulations , Teflon with magnesium or aluminium being a relatively common example . Magnesium / teflon / viton is another pyrolant of this type . In principle , any reactive metal could be used instead of aluminium . This is rarely done , however , because the properties of aluminium are nearly ideal for this reaction : Although the reactants are stable at room temperature , they burn with an extremely intense exothermic reaction when they are heated to ignition temperature . The products emerge as liquids due to the high temperatures reached ( up to 2500 °C with iron ( III ) oxide ) — although the actual temperature reached depends on how quickly heat can escape to the surrounding environment . Thermite contains its own supply of oxygen and does not require any external source of air . Consequently , it cannot be smothered and may ignite in any environment , given sufficient initial heat . It will burn well while wet and cannot be easily extinguished with water , although enough water will remove heat and may stop the reaction . Small amounts of water will boil before reaching the reaction . Even so , thermite is used for welding underwater . The thermites are characterized by almost complete absence of gas production during burning , high reaction temperature , and production of molten slag . The fuel should have high heat of combustion and produce oxides with low melting point and high boiling point . The oxidizer should contain at least 25 % oxygen , have high density , low heat of formation , and produce metal with low melting and high boiling point ( so the energy released is not consumed in evaporation of reaction products ) . Organic binders can be added to the composition to improve its mechanical properties , however they tend to produce endothermic decomposition products , causing some loss of reaction heat and production of gases . The temperature achieved during the reaction determines the outcome . In ideal case , the reaction produces a well - separated melt of metal and slag . For this , the temperature has to be high enough to melt both the reaction products , the resulting metal and the fuel oxide . Too low temperature will result in a mixture of sintered metal and slag , too high temperature – above boiling point of any reactant or product – will lead to rapid production of gas , dispersing the burning reaction mixture , sometimes with effects similar to a low - yield explosion . In compositions intended for production of metal by aluminothermic reaction , these effects can be counteracted . Too low reaction temperature ( e . g . when producing silicon from sand ) can be boosted with addition of a suitable oxidizer ( e . g . sulfur in aluminium - sulfur - sand compositions ) , too high temperatures can be reduced by using a suitable coolant and / or slag flux . The flux often used in amateur compositions is calcium fluoride , as it reacts only minimally , has relatively low melting point , low melt viscosity at high temperatures ( therefore increasing fluidity of the slag ) and forms a eutectic with alumina . Too much of flux however dilutes the reactants to the point of not being able to sustain combustion . The type of metal oxide also has dramatic influence to the amount of energy produced ; the higher the oxide , the higher the amount of energy produced . A good example is the difference between manganese ( IV ) oxide and manganese ( II ) oxide , where the former produces too high temperature and the latter is barely able to sustain combustion ; to achieve good results a mixture with proper ratio of both oxides should be used . The reaction rate can be also tuned with particle sizes ; coarser particles burn slower than finer particles . The effect is more pronounced with the particles requiring being heated to higher temperature to start reacting . This effect is pushed to the extreme with nano - thermite s . The temperature achieved in the reaction in adiabatic conditions , when no heat is lost to the environment , can be estimated using the Hess ' s law – by calculating the energy produced by the reaction itself ( subtracting the enthalpy of the reactants from the enthalpy of the products ) and subtracting the energy consumed to heating the products ( from their specific heat , when the materials only change their temperature , and their enthalpy of fusion and eventually enthalpy of vaporization , when the materials melt or boil ) . In real conditions , the reaction loses heat to the environment , the achieved temperature is therefore somewhat lower . The heat transfer rate is finite , so the faster the reaction is , the closer to adiabatic condition it runs and the higher is the achieved temperature . Iron thermite . The most common composition is the iron thermite . The oxidizer used is usually either iron ( III ) oxide or iron ( II , III ) oxide . The former produces more heat . The latter is easier to ignite , likely due to the crystal structure of the oxide . Addition of copper or manganese oxides can significantly improve the ease of ignition . The original mixture , as invented , used iron oxide in the form of mill scale . The composition was very difficult to ignite . Copper thermite . Copper thermite can be prepared using either copper ( I ) oxide ( CuO , red ) or copper ( II ) oxide ( CuO , black ) . The burn rate tends to be very fast and the melting point of copper is relatively low so the reaction produces a significant amount of molten copper in a very short time . Copper ( II ) thermite reactions can be so fast that copper thermite can be considered a type of flash powder . An explosion can occur and send a spray of copper drops to considerable distance . Copper ( I ) thermite has industrial uses in e . g . welding of thick copper conductors ( " cadwelding " ) . This kind of welding is being evaluated also for cable splicing on the US Navy fleet , for use in high - current systems , e . g . electric propulsion . Thermates . Thermate composition is a thermite one enriched with a salt - based oxidizer ( usually nitrates , e . g . barium nitrate , or peroxides ) . In contrast with thermites , thermates burn with evolution of flame and gases . The presence of the oxidizer makes the mixture easier to ignite and improves penetration of target by the burning composition , as the evolved gas is projecting the molten slag and providing mechanical agitation . This mechanism makes thermate more suitable than thermite for incendiary purposes and for emergency destruction of sensitive equipment ( e . g . cryptographic devices ) , as thermite ' s effect is more localized . Ignition . Metals are capable of burning under the right conditions , similar to the combustion process of wood or gasoline . In fact , rust is the result of oxidation of steel or iron 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 a sparkler or easily obtainable magnesium ribbon , but may require persistent efforts , as ignition can be unreliable and unpredictable . These temperatures cannot be reached with conventional black powder fuses , nitrocellulose rods , detonator s , pyrotechnic initiator 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 torch if done correctly . Often , strips of magnesium 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 permanganate and glycerol or ethylene glycol 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 . Apart from magnesium ignition , some amateurs also choose to use sparkler 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 lighter , as the sparks are burning metal ( in this case , the highly reactive rare - earth metals lanthanum and cerium ) . 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 burns . Civilian uses . Thermite reactions have many uses . Thermite is not an explosive ; instead it operates by exposing a very small area of metal to extremely high temperatures . Intense heat focused on a small spot can be used to cut through metal or weld metal components together both by melting metal from the components , and by injecting molten metal from the thermite reaction itself . Thermite may be used for repair by the welding in - place of thick steel sections such as locomotive axle - frames where the repair can take place without removing the part from its installed location . Thermite can be used for quickly cutting or welding steel such as rail tracks , without requiring complex or heavy equipment . However , defects such as slag inclusions and voids ( holes ) are often present in such welded junctions and great care is needed to operate the process successfully . Care must also be taken to ensure that the rails remain straight , without resulting in dipped joints , which can cause wear on high speed and heavy axle load lines . A thermite reaction , when used to purify the ore s of some metals , is called the thermite process , or aluminothermic reaction . An adaptation of the reaction , used to obtain pure uranium , was developed as part of the Manhattan Project at Ames Laboratory under the direction of Frank Spedding . It is sometimes called the Ames process . Copper thermite is used for welding together thick copper wires for the purpose of electrical connections . It is used extensively by the electrical utilities and telecommunications industries ( exothermic welded connection s ) . Military uses . Thermite hand grenade s and charges are typically used by armed forces in both an anti - materiel role and in the partial destruction of equipment ; the latter being common when time is not available for safer or more thorough methods . For example , thermite can be used for the emergency destruction of cryptographic equipment when there is a danger that it might be captured by enemy troops . Because standard iron - thermite is difficult to ignite , burns with practically no flame and has a small radius of action , standard thermite is rarely used on its own as an incendiary composition . It is more usually employed with other ingredients added to enhance its incendiary effects . Thermate - TH3 is a mixture of thermite and pyrotechnic additives which have been found to be superior to standard thermite for incendiary purposes . Its composition by weight is generally about 68 . 7 % thermite , 29 . 0 % barium nitrate , 2 . 0 % sulfur , and 0 . 3 % of a binder ( such as PBAN ) . The addition of barium nitrate to thermite increases its thermal effect , produces a larger flame , and significantly reduces the ignition temperature . Although the primary purpose of Thermate - TH3 by the armed forces is as an incendiary anti - material weapon , it also has uses in welding together metal components . A classic military use for thermite is disabling artillery pieces , and it has been used for this purpose since World War 2 ; such as at Pointe du Hoc , Normandy . Thermite can permanently disable artillery pieces without the use of explosive charges , and therefore thermite can be used when silence is necessary to an operation . This can be done by inserting one or more armed thermite grenades into the breech and then quickly closing it ; this welds the breech shut and makes loading the weapon impossible . Alternatively , a thermite grenade discharged inside the barrel of the gun will foul the barrel , making the weapon very dangerous to fire ; thermite can also be used to weld the traversing and elevation mechanism of the weapon , making it impossible to aim properly . Thermite was used in both German and Allied incendiary bomb s during World War II . Incendiary bombs usually consisted of dozens of thin thermite - filled canisters ( bomblet s ) ignited by a magnesium fuse . Incendiary bombs destroyed entire cities due to the raging fires that resulted from their use . Cities that primarily consisted of wooden buildings were especially susceptible . These incendiary bombs were utilized primarily during nighttime air raids . Bombsights could not be used at night , creating the need to use munitions that could destroy targets without the need for precision placement . Hazards . Thermite usage is hazardous due to the extremely high temperatures produced and the extreme difficulty in smothering a reaction once initiated . Small streams of molten iron released in the reaction can travel considerable distances and may melt through metal containers , igniting their contents ( see images ) . Additionally , flammable metals with relatively low boiling points such as zinc ( with a boiling point of 907 °C , which is about 1 , 370 °C below the temperature at which thermite burns ) could potentially spray superheated boiling metal violently into the air if near a thermite reaction . Preheating of thermite before ignition can easily be done accidentally , for example by pouring a new pile of thermite over a hot , recently ignited pile of thermite slag . When ignited , preheated thermite can burn almost instantaneously , releasing light and heat energy at a much higher rate than normal and causing burns and eye damage at what would normally be a reasonably safe distance . The thermite reaction can take place accidentally in industrial locations where abrasive grinding and cutting wheels are used with ferrous metal s . Using aluminium in this situation produces a mixture of oxides which is capable of a violent explosive reaction . Mixing water with thermite or pouring water onto burning thermite can cause a steam explosion , spraying hot fragments in all directions . Thermite ' s main ingredients were also utilized for their individual qualities , specifically reflectivity and heat insulation , in a paint coating or dope for the German zeppelin " Hindenburg " , possibly contributing to its fiery destruction . This was a theory put forward by the former NASA scientist Addison Bain , and later tested in small scale by the scientific reality - TV show " MythBusters " with semi - inconclusive results ( it was proven not to be the fault of the thermite reaction alone , but instead conjectured to be a combination of that and the burning of hydrogen gas that filled the body of the " Hindenburg " ) . The " MythBusters " program also tested the veracity of a video found on the Internet , whereby a quantity of thermite was allowed to drop onto a block of ice of similar mass , causing a sudden explosion . They were able to confirm the results , finding chunks of ice as far as 150m from the point of explosion . Co - host Jamie Hyneman conjectured that this was due to the thermite mixture aerosol izing , perhaps in a cloud of steam , causing it to burn even faster . Hyneman also voiced skepticism about another theory explaining the phenomenon : that the reaction somehow separated the hydrogen and oxygen in the ice and then ignited them . A far more likely explanation is that the explosion is due to the reaction of high temperature molten aluminium with water . Aluminium reacts violently with water or steam at high temperatures , releasing hydrogen and oxidizing in the process . The speed of that reaction and the ignition of the resulting hydrogen can easily account for the explosion verified . < ref name = " Aluminium Times Vol 11 n 3 Jul / Aug 2009 " > < / ref > This process is akin to the explosive reaction caused by dropping metallic potassium into water .