X-RAY-DIFFRACTION - A TOOL FOR THE STUDY OF SOLID-GAS REACTIONS (ADVANTAGES AND DEVELOPMENTS)

Zirconium oxidation mechanism can be studied by X-ray diffraction meth ods : in fact, the interactions between chemical (oxide growth, phases proportion) and physical process (oxide scale texture, mechanical str esses) are observed The oxide formed is composed of two allotropic str uctures, monoclinic ZrO2 (highest proportion) and tetragonal ZrO2 (tra ce). XRD studies show : 1) phases analyses: phases gradient are reveal ed by XRD variable incidence. 2) textures: Spatial evolution of monocl inic zirconia texture through the oxide scale is shown, and quantified 3) mechanical stresses : several relaxations of the oxide compressive stresses occur at different times of the oxidation. They are correlat ed to kinetics breakaway, revealed by other methods. A structural mech anism of the oxide formation is then proposed, which prove the XRD int erest in the heterogeneous kinetics researches.