Crystallization studies in mullite and mullite–YSZ beads

Mullite and mullite/Y-ZrO2 (25 and 50 vol.%) beads were produced by thermal spraying in water the corresponding atomised compositions. The amount of amorphous phases in the as-sprayed beads was comparatively determined by X-ray diffraction (XRD) and differential thermal analysis (DTA) methods. Characteristic XRD peaks associated to crystallization of the mullite and Y-ZrO2 (t) phases were compared with the intensity of the exothermic events in the DTA for each composition. A direct linear relationship between the amount of amorphous phases estimated by XRD methods and the area under DTA peaks per unit mass was found. The crystallization microstructure of the different composition beads after heat treatments was followed by scanning electron microscopy (SEM).