X-ray diffraction and near edge studies of iron oxides and alumina at hightemperatures using aerodynamic levitation and laser heating

A new high temperature chamber using aerodynamic levitation and laser heati ng has been used to study spheres of oxide materials at temperatures up to 2100 degrees C. Near edge studies of Fe3O4 (MP : 1597 degrees C) and FeO (M P 1377 degrees C) have been performed by fluorescent XANES and in situ X-ra y Diffraction (XRD). Both iron oxides reveal a shift in the Fe K-absorption edge on melting to lower energies by between 2 and 3 eV. This is accompani ed by an increase in the threshold resonance. Experiments with neutral and oxidising levitating gases show the same behaviour and suggest a physical o rigin. A possible explanation is an increase in the Fe-O bond length with a consequent reduction in physical density on melting. This would naturally result in a narrower energy gap which would lead to the observed shift in t he absorption threshold to lower energies in passing from the solid to the liquid state. This would also account for the rise in the threshold resonan ce on melting. By performing high temperature XRD, the thermal expansion co efficients alpha of Al2O3 (MP 2054 degrees C) have been obtained crystallog raphically by measuring the increase of the unit cell parameters. XRD curve s have been recorded at several temperatures From 800 degrees C up to the m elting point. The measured coefficients are ia agreement with literature da ta. On the technical side, some problems relating to the levitation state a nd temperature measurements are discussed indicating the need for improveme nt of the chamber.