7b. Thermite ------------ The thermite reaction is a redox reaction that produces a lot of heat and light. In its usual configuration, temperatures can exceed 3000 degrees C, and molten iron is produced. It is therefore mainly used for welding, and by the Army in incendiary grenades. There are many possible configurations - basically it is the reaction between a reactive metal and the oxide of a less reactive metal. The most common is as follows: Aluminium powder, Al (coarse) 1 volume part or 3 weight parts Iron (III) Oxide, Fe203 1 volume part or 1 weight part A stoichiometric mixture will provide best results. The powders are mixed together and ignited with a suitable fuse. Many people use magnesium ribbon - I don't recommend this, as magnesium ribbon is not all that easy to light, and quite prone to going out due to oxygen starvation. A much better fuse for thermite is a common sparkler. The mixture should be shielded with aluminium foil or similar to prevent sparks from the sparkler igniting the thermite prematurely. Reaction: 2Al + Fe O ---> Al O + 2Fe + lots of heat (s) 2 3(s) 2 3(s) (l) The mixture can be varied easily, as long as the metal oxide you are using is of a less reactive metal than the elemental one you are using, e.g. copper oxide and zinc. Adjust the ratios accordingly. Safety aspects: Reaction: Make sure you no longer need whatever you are igniting the thermite on - the reaction will melt and/or ignite just about anything. If you ignite the thermite on the ground, make sure the ground is DRY and free of flammable material. If the ground is wet a burst of steam may occur, scattering 3000 degree metal everywhere. Be careful when igniting the thermite - use adequate shielding to prevent premature ignition. Don't get close to the mixture once ignited - it has been known to spark and splatter. Don't look at the reaction directly. It produces large amounts of ultraviolet light that can damage the eyes. Use welder's goggles, 100% UV filter sunglasses or do not look at all. Aluminium: Chemical dust in the lungs is to be avoided. As always, wear a dust mask. Make sure the environment you are working in is dry - aluminium powder can be dangerous when wet. Fine aluminium dust is pyrophoric - this means it can spontaneously ignite in air. For this reason aluminium powder with a large particle size is recommended. Iron Oxide: This is not directly toxic, but any particulate matter in the lungs is not good. Again, the dust mask is important.
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