Über pyrophores Eisen

Abstract

If iron oxides are reduced at temperatures ranging from 300° to 500°C, Fe3O4, is first formed, if not already present, and this goes directly over into iron. The nucleation of iron is slow, and if the oxide is finely crystalline, the iron nuclei grow by diffusion of iron atoms from many oxide crystals already at a temperature of approximately 300°C. The iron crystals sinter together to form irregular secondary particles. ‐ Responsible for the pyrophorous behaviour is the specific surface. Self‐ignition occurs when this surface is greater than approximately 3 m2/g. Pyrophorous iron can be inactivated with a mixture of N2 low in 02, an oxide layer being formed approximately 13 Å, i.e. ca. 6 02−‐layers, thick. An estimation of the heat produced on forming this layer and of the resulting temperature increase leads to a value which is in agreement with the ignition temperature of inactivated iron powder with a specific surface of approx. 3 m2/g.

Properties and sintering behaviour of fine spherical iron powders produced by new hydrogen reduction process

“…For this reason, the powder is classified as pyrophoric and cannot be used in practice. 7 Higher reduction temperatures lead to higher oxygen contents, but only very high temperatures (>1000°C) reduce the oxygen content to acceptable values. 8 At these high temperatures the fine powder particles are mostly sintered to strong cake that is difficult to break down.…”