TEM in-situ observation of SiO2 Doped TZP at High Temperatures

Chemical reaction of SiO₂ and TZP(Tetragonal Zirconia Polycrystal) was directly observed by using TEM in-situ heating technique in order to understand the behavior of SiO₂ to TZP at high temperatures. The dynamic interaction of SiO₂ and TZP was recorded up to about 1400°C by the CCD camera-video system which was connected to TEM. It was found that most of SiO₂ phase is dissolved into ZrO₂ grains at above 1300°C. On the other hand, during cooling from the high temperature to around 400°C, amorphous SiO₂ reprecipitated from the surface of ZrO₂ grains and formed a thin layer around the ZrO₂ grains. This result agrees well with the fact that silicon segregates in the vicinity of the grain boundaries in SiO₂-doped TZP. In order to confirm the grain boundary segregation at high temperatures, the grain boundaries in the quenched specimen were investigated by high resolution electron microscopy (HREM), energy dispersive X-ray spectroscopy (EDS) and electron energy loss spectroscopy (EELS). It was found that no amorphous phase was present between two adjacent grains even in the quenched samples. EDS analysis revealed that silicon segregated at the grain boundaries and its width was larger than that in as-sintered specimen. Electron energy loss near edge structure (ELNES) of O-Kedge was measured from both grain boundary and grain interior in the quenched specimen.