Pyrophoric Iron

Mention has already been made of the fact that reduction of iron oxide, carbonate, or oxalate in a current of hydrogen or carbon monoxide results in the formation of a very pure iron in the form of a black powder. If the temperature is kept low throughout the experiment - namely at about 435° C., - the resulting iron powder, usually contaminated with more or less ferrous oxide, is pyrophoric, becoming incandescent when exposed to the air in consequence of the heat set free by the rapid oxidation of the metal. Complete reduction to metallic iron at this temperature, however, is exceedingly slow in taking place. Ferrous oxide is first formed, and it was not until the passage of hydrogen had been continued for ninety-six hours that Moissan was, in his experiments, able to obtain the iron entirely free from oxide. At 600° C. the reaction proceeds fairly rapidly, but the reduced iron is not pyrophoric.

Pyrophoric iron decomposes water rapidly at 50° to 60° C., and its action is perceptible even below 10° C. Its reactivity appears to be independent of the presence of occluded gases or the presence of carbon, and to be solely dependent upon its fine state of division.