Phase transition of iron oxide at high temperature

The structure of iron(III)-oxide was studied at high temperatures up to 1500 degrees C by;X-ray powder diffraction using the furnace type chamber PMP1600. A sharp phase transition between alpha-Fe2O3 (hematite) and a defected spinel-type structure (high-maghemite, s.g. Fd (3) over bar m) could be observed. The transition temperature was found to be highly dependent on the oxygen partial pressure of the environment: 1225 degrees C, 1380 degrees C, and 1425 degrees C in 1 atm nitrogen, normal air and pure oxygen atmosphere, respectively. The phase transition is reversible and has practically no hysteresis. The structure of this spinel-type phase was refined by Rietveld method and showed cation vacancies predominantly at the octahedral position. Based on close relationships between the structures of hematite and spinel-type Fe2O3, a possible mechanism of the transformation is put forward, An overview about the environmentally heated chamber PMP1600 is also presented.