Thermite Mixtures

Aluminium powder ignites in chlorine without heating, and foil reacts vigorously with liquid bromine at 15°C, and incandesces on warming in the vapour [1], The metal and iodine react violently in the presence of water, either as liquid, vapour or that present in hydrated salts [2], Moistening a powdered mixture causes incandescence and will initiate a thermite mixture [3],... 

In demonstrating the use of powdered aluminium to reduce the oxide in a thermite-type reaction, the mixture must be heated behind a safety screen because of the small explosion produced [1]. Consolidation of the thermite mixture into a high-density composite gives chemical heat sources which are safe to handle [2],... 

The mixture ( silicon thermite ) attains a very high temperature when heated, producing molten iron like the usual thermite mixture. 

Crozier, T. H., HMInsp. Expl. Spec. Rept. 237, London, HMSO, 1929 A 20 t quantity of an incendiary bomb mixture of the finely powdered oxide, aluminium and sulfur became accidentally ignited and burned with almost explosive violence. It is similar to thermite mixture. 

Bentzinger, von R. et al Praxis Naturwiss. Chem., 1987, 36, 38 A priming mixture of magnesium powder and barium peroxide to ignite thermite mixture was to be prepared, but as no barium peroxide was available, sodium peroxide was used instead. Some time after preparation, the mixture ignited spontaneously, because sodium peroxide, unlike barium peroxide, is very hygroscopic and forms hot cone, hydrogen peroxide from contact with atmospheric moisture. See Carbon dioxide, etc., above... 

Thermite mixtures have foimd application as incendiary compositions and spot-welding mixtures. They are also used for the intentional demolition of machinery and for the destruction of documents. Thermites are usually produced without a binder (or with a minimum of binder), because the gaseous products resulting from the combustion of the organic binder will carry away heat and cool the reaction. 

Iron oxide (Fe 2O 3 or FesO 4) with aluminum metal is the classic thermite mixture The particle size of the aluminum should be somewhat coarse to prevent the reaction from being too rapid. Thermites tend to be quite safe to manufaeture, and they are rather insensitive to most ignition stimuli. In faet, the major problem with most thermites is them to ignite, and a... 

Calorific data for a variety of aluminum thermite mixtures are given in Table 6.9. 

Oxidizers Formula % Active oxygen by weight %Alby weight in thermite mixture -Hreaetion, kcal/gram... 

A study of burning rate for a series of conventional thermite mixtures (Fe203[s]-Al[s] [micron-sized]) and nanocomposites (Fe203[s]-UFG[s] [nanosized]) indicates that nanocomposites appear to burn much more rapidly and are more sensitive to thermal ignition than conventional thermite mixtures. At the same time, it is interesting to observe that most of the nanocomposites are found insensitive during standard impact, spark and friction tests [103]. 

As particle sizes decrease, the sensitivity of the thermite mixture to impact and friction increases. The micron scale thermites are usually quite insensitive to impact and shock, but thermites on the nanoscale can be quite sensitive to both or one of the two depending on the metal oxide. This is exemplified in the work of Spitzer, where a tungsten(VI) oxide and aluminum thermite was prepared by mixing nano and micron aluminum with nano and micron W03. The results of this are presented in Table 13.2. 

Naud et al. have preformed extensive work on the use of the Mo03/A1 nanothermite for application in electric matches. Electric matches prepared from this thermite mixture have been shown to have lower friction, impact, thermal and ESD sensitivities than the currently used matches, which contain toxic lead compounds making them both safer and more environmentally friendly to use. 

This reaction of aluminium with ifon(lll) Oxide is called the thermite reaction. It is used to make molten steel for mending and welding broken railway lines the temperature reached is about 2000 °C. The thermite mixture was often used in World War II incendiary bombs, such as those which devastated London, Hamburg and Dresden. 

---