Self-Igniting Iron

The best-known corrosion process is the rusting of iron. Luckily this process, which economically speaking Is a disaster, occurs only slowly. As is well knowm, it is due to the conversion of iron atoms fixed in the crystal lattice into hydrated irun(III) oxide, the rust , in the presence of air and water. If the stable lattice is destroyed, the oxygen molecules of the air can react freely with the finely-divided iron particles, so that the corrosion process appears to occur without any energy being supplied. 

4 widc-ncckcd test tubes with rubber bungs, fire-resisiaiu support, gas burner, safety glasses, protective gloves. 

The four open test tubes are filled to about 1/5 of their height with yellow iron oxalate, l eC204 1.5 1LO and each tube is heated until the latter has been converted to a black residue. Any water vapor which condenses at the top.s of the I ubes is carefully removed with a soft filter paper. The test tubes are then tightly closed with the rubber bungs and put aside for the demonstration. After show- 

The lecturer and his assistant (or two spectators) now stand on the demon-straring table, hold the test tubes upside down and remove the bungs simultaneously. A brilliant shower of red sparks demonstrates that the iron oxidises spon-laiieouslv. 

Iron oxalate decomposes on heating to give a pyrophoric mixture of iroii(Il) oxide and metallic iroiij which reacts with oxygen according to the highly exothermic reaction described by the following equation  

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During roller-blending to disperse iron red pigment (iron(III) oxide) into plasticised cellulose nitrate, the mixture became a gel after 15 passes and tended to self-ignite. 

Compared to pure oxygen, chlorine is even more reactive. The self-ignition temperature of gaseous mixtures of organic vapours with chlorine is much lower than that of their mixtures with oxygen. Natural light can split the chlorine molecule to produce reactive chlorine radicals. Many reactions of chlorine take place near the ambient temperature. The combustion of iron in chlorine can be initiated at temperatures slighly above 100°C. 

ETHANE PENTACHLORIDE (76-01-7) CHCljCClj Noncombustible liquid. Incompatible with water, producing dichloroacetic acid. May self-ignite in air. Incompatible with strong oxidizers. Contact with aluminum, cadmium, mercury, hot iron, alkalis, alkali metals causes dehologenation, forming chloroacetylene gas which is spontaneously explosive in air. Contact with potassium may explode (after a short delay) or form shock- and friction sensitive materials. Incompatible with potassium-sodium alloy + bromoform reaction may be violent. 

Pyrophoric materials are self-igniting when exposed to air (oxygen). The most common pyrophoric in the process industries is iron sulfide, FeS (also known as pyrite). It forms as a scale in piping, vessels, tanks, and equipment when H2S reacts with iron and moisture in a low oxygen environment according to the following equation ... 

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