Structural evolution of oxidized surface of zirconium-silicide under ion irradiationm

Irradiation-induced structural evolution and compositional alterations on nanometer length scales of ZrO2-SiO2 nanocomposite and crystalline ZrSiO4, produced by oxidation of ZrSi2 at 1000 °C and 1400 °C, respectively, have been investigated. Irradiations were performed with 3.9 MeV Si2+ at 305 °C up to damage levels of 60 displacements per atom (dpa), and post-irradiation characterization was conducted by cross-sectional scanning- and transmission electron microscopy (STEM and TEM) in conjunction with energy dispersive spectroscopy (EDS), as well as glancing-angle X-ray diffraction (XRD). The multilayered nanocomposite oxide showed extensive phase mixing so that the originally distinct interfaces between ZrO2 and SiO2 phases were obliterated resulting in the formation of a single amorphous Zr-Si-O phase. Crystalline ZrSiO4 grains were completely amorphized at damage levels of 5-15 dpa, as evidenced by disappearance of grain boundaries and as confirmed by electron diffraction. The irradiation-induced phase transformation for both types of oxide structures has the potential to dramatically enhance corrosion resistance in high temperature aqueous and steam environments.