THERMITE
Updated 04-May-2020.
Mondo shtuff from around the internet, all about THERMITE!
Thermite reactions: their utilization in the synthesis and processing of materials
Water/magma interaction: some theory and experiments on peperite formation: Experiments, using molten thermite as a magma analog, produce peperite when the melt interacts with wet sand. These experiments also show explosive behavior, developing Strombolian- and Surtseyan-like bursts. The results demonstrate that the application of fuel-coolant interaction (FCI) theory is appropriate for interpretation of peperites. The theory described includes discussion of the importance of mass interaction ratios of wet sediment and magma ( Rs), which determine thermal equilibrium temperature limits and contact interface dynamics. The dynamics of the interface between magma and wet sediments involves heat transfer over a wide range of rates from passive quenching to explosive fragmentation. A vapor film layer develops at the interface and acts both as an insulating barrier, promoting passive quenching, as well as a potential energy reservoir that can cause magma fragmentation, mingling of the magma with wet sediments, and explosive quenching when the vapor film becomes unstable. An important parameter in determining the behavior of the vapor film is the value of Rs, which controls whether heat can be convectively removed from the layer as more is being added from its contact with magma. If Rs>1 for fully saturated sediments, there is enough water in the sediments to make convective heat flow effective in quenching the magma, but below that value, there is the potential that the vapor film will be unstable, producing highly dynamic phenomena, including explosive fragmentation. At values of Rs<0.1 there is insufficient water to allow the escalation of explosive fragmentation.
Generation of fast propagating combustion and shock waves with copper oxide/aluminum nanothermite composites: Nanothermite composites containing metallic fuel and inorganic oxidizer are gaining importance due to their outstanding combustion characteristics. In this paper, the combustion behaviors of copper oxide/aluminum nanothermites are discussed. CuO nanorods were synthesized using the surfactant-templating method, then mixed or self-assembled with Al nanoparticles. This nanoscale mixing resulted in a large interfacial contact area between fuel and oxidizer. As a result, the reaction of the low density nanothermite composite leads to a fast propagating combustion, generating shock waves with Mach numbers up to 3.
My botty best at summarizing from Wikipedia: when ignited by heat, thermite undergoes an exothermic reduction-oxidation reaction . most varieties are not explosive, but can create brief bursts of heat and high temperature in a small area fuels include aluminium, magnesium, titanium, zinc, silicon, and boron . thermites have also been used in metal refining, disabling munitions, and in incendiary weapons reactants are powdered and mixed with a binder to keep the material solid and prevent separation . other metal oxides can be used, such as chromium oxide, to generate the given metal in its elemental form other oxides are occasionally used, but only for specialized purposes . all of these examples use aluminium as the reactive metal . a cryo-thermite is detonated when the ingredients are finely divided and confined in a pipe . a portion of the carbon liberated in the reaction emerges in the form of diamond . its relatively low melting point (660 °C) means that it is easy to melt the metal . high boiling point (2519 °c) enables the reaction to reach very high temperatures . low density of aluminium oxide reactants burn with intense exothermic reaction when heated to ignition temperature . thermite contains its own supply of oxygen and does not require any external source of air . it burns well while wet, and cannot be easily the thermites are characterized by almost complete absence of gas production during burning . the fuel should have high heat of combustion and produce oxides with low melting point . organic binders can be added to the composition to improve its reaction produces well-separated melt of metal and slag . too low a temperature produces a mixture of sintered metal . high temperature leads to rapid production of gas, dispersing reaction mixture . too much flux dilutes 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 . reaction rate can be tuned with particle sizes; coarser the temperature achieved in the reaction in adiabatic conditions can be estimated using the Hess’s law . in real conditions, the reaction loses heat to the environment, the achieved temperature is therefore somewhat lower . the faster the density of prepared thermite is often as low as 0.7 g/cm3 . this, in turn, results in relatively poor energy density . rapid burn times and spray of molten iron due to expansion pressed themite has higher melting power . it can melt a steel cup where a low density thermite would fail . the original mixture, as invented, used iron oxide in the form of mill scale . the burn rate tends to be very fast and the melting point of copper is relatively low . copper(II) thermite reactions can 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” aluminium oxide is molten and copper in both liquid and gaseous form . 77.6 g of copper vapor per kg of this thermite is produced . the energy content is 575.5 thermate is more suitable than thermite for incendiary purposes . rust is the result of oxidation of steel or iron at very slow rates . ignition requires extremely high temperatures . 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 a piece of the burning strip can fall off into the mixture resulting in premature ignition . the reaction between potassium permanganate and glycerol or ethylene glycol is used as an alternative to the magnesium method iron sparks, like magnesium strips, burn at thousands of degrees and can ignite thermite . this is especially dangerous with finely powdered thermites . match heads enveloped with aluminium foil and a thermite operates by exposing a very small area to extremely high temperatures . great care is needed to operate the process successfully . defects such as slag inclusions and voids (holes) are often present the numerical analysis of thermite welding of rails has been approached similar to casting cooling analysis . Increasing weld gap has been shown to reduce shrinkage cavity formation and cold lap welding defects . increasing preheat and thermite is used for welding together copper wires for the purpose of electrical connections . standard iron-thermite is difficult to ignite and burns with practically no flame . it is rarely used on its own as an in thermate-TH3 is a mixture of thermite and pyrotechnic additives . it’s composition by weight is generally about 68.7% therite, 29.0% barium thermate-TH3 is an incendiary anti-materiel weapon . it can permanently disable artillery pieces without the use of explosive charges . thermite can be used when silence is necessary to an thermite can weld the traversing and elevation mechanism of the weapon, making it impossible to aim properly . incendiary bombs created massive damage in many cities due to fires started by thethermit small streams of molten iron released in the reaction can travel considerable distances . flammable metals with relatively low boiling points could potentially spray superheated boiling metal violently into the air if near a thermit preheating of thermite before ignition can easily be done accidentally . reaction can take place accidentally in industrial locations where workers use ferrous metals . theory put forward by former NASA scientist Addison Bain . huge chunks of ice found as far as 50m from point of explosion . co-hosts speculate explosion is due to thermite mixture aerosolizing . another theory claims reaction separated hydrogen and oxygen in ice the speed of that reaction and the ignition of the resulting hydrogen can easily account for the explosion verified . this process is akin to the explosive reaction caused by dropping metallic potassium into water . Encyclopedia Americana. 1920.