Position of Fe ions in MgO crystalline structure

Magnesium oxide (MgO) is one of the most important raw materials in many branches of industry. Magnesium oxide is a popular refractory raw material because of its high refractoriness and high resistance to basic slags and environment. In many cases, use of MgO is limited by its properties, especially the presence of secondary phases like iron oxides. The amount and distribution of iron oxides can strongly influence the technological properties of MgO and depend on the manufacturing method, particularly the heat-treatment process. The aim of the study was to evaluate the influence of the heat-treatment process on amount and distribution of iron ions in a magnesium oxide lattice. The ⁵⁷Fe Mössbauer effect measurements of fused and sintered magnesium oxide samples doped by the iron oxide were conducted. Investigation reveals in both cases the presence of Fe²⁺ as well as Fe³⁺ ions. Fe²⁺ ions occupy Mg²⁺ octahedral sites in the MgO lattice, whereas the Fe³⁺ ions are located in highly distorted octahedral coordination. The amount of Fe²⁺ varies from around 66% for fused samples to 30% for sintered samples.