1 Because +3 valence iron has strong oxidation, simple iron can be oxidized to +2 valence iron at high temperature. In addition, iron oxide will be decomposed into ferrous oxide and oxygen at high temperature.

4Fe+3O2====2Fe2O3

Fe2O3+Fe== high temperature ==3FeO

2Fe2O3== high temperature ==4FeO+O2

There is also a reaction that is carried out under the condition of ignition.

3Fe+2O2== Ignition ==Fe3O4

Fe3O4 can also be written as FeO*Fe2O3.

2 Iron is heated in oxygen to form iron oxides: iron oxide (Fe2O3) and iron oxide (Fe3O4), namely (Fe2O3 FeO).

What iron oxide is produced when iron is heated in oxygen is mainly related to the concentration of oxygen. The greater the concentration of oxygen, the more complex the composition of iron oxide. For example, iron is violently burned in pure oxygen to generate ferric oxide (Fe3O4), that is, (Fe2O3 FeO), which is heated in air to generate iron oxide (Fe2O3). It is not only related to the concentration of oxygen, but also related to the reaction conditions. For example, there are two kinds of heating: slow heating and intensive heating. When iron is slowly heated in oxygen (meaning that the reaction temperature is not very high), iron oxide (Fe2O3) is generated. The enhancement of heat by iron in oxygen is equivalent to the ignition of iron in pure oxygen, resulting in ferroferric oxide (Fe3O4), namely (Fe2O3 FeO).