In situ and time resolved study of the γ/α-Fe2O3 transition in nanometric particles

In situ and real-time study of the γ to α-Fe2O3 transition is carried out on the H10 beamline at LURE (France). γ-Fe2O3 particles are synthesized by soft chemistry. These particles have an average diameter evaluated by X-ray diffraction of 9±1nm and a specific surface area of 116m2g-1. The size of produced α-Fe2O3 particles is determined by in situ and time resolved X-ray diffraction measurements at different temperatures. An amazing evolution of size with time is revealed: an abrupt doubling of the α-Fe2O3 particle size is observed whatever the heating temperature. Some assumptions are given in order to explain this phenomenon which implies at the same time surface energy, granulometric distribution and coalescence of particles. -- A brutal increase of the X-rays coherent domain sizes of the α-Fe2O3 particles during the γ/α transition at nanometric scale. Maghemite γ-Fe2O3 particles (φ=9±1nm) were heated at 723 K. First germs (or grains) of α-Fe2O3 were detected with a size of 2 nm