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Development, characterization and degradation behavior of cubic zirconia doped with rare earth oxides processed through spark plasma sintering

University of British Columbia

Stabilized zirconia ceramics are candidate materials for high temperature applications due to their chemical inertness, high thermal stability and low thermal conductivity. These ceramics also exhibit superior stability under radiation exposure and thus there has been a rising interest in utilizing these materials in nuclear applications, particularly Supercritical Water Reactors (SCWRs). Compared to present day nuclear technologies, SCWRs boast improved thermal efficiencies, lower operating costs and enhanced safety. The fundamental idea behind this promising technology is the use of supercritical water as a coolant. Existing at temperatures and pressures above 374 °C and 22.1 MPa, respectively, supercritical water is an exceptionally aggressive and corrosive environment which many current nuclear materials cannot withstand. However, preliminary studies demonstrate that zirconia ceramics have improved stability under a supercritical water environment and, as such, there has been interest in using these ceramics as a thermal and protective insulating material in the SCWR system. However, the applications of zirconia ceramics are severely limited by their degradation behaviour. To date, there has been little progress in effectively controlling this behaviour and, as such, further development is essential for the application of zirconia ceramics in supercritical water. In this research, 8 mol% Yttria Stabilized Zirconia (YSZ) as well as YSZ ceramics containing various amounts of CeO₂ and Nd₂O₃ additions were fabricated via a novel technique called Spark Plasma Sintering (SPS). The sintered ceramics were then subjected to a supercritical water environment at a temperature and pressure of 400 °C and 31 MPa, respectively. Weight loss and microstructural changes associated with supercritical water exposure were characterized with a Scanning Electron Microscope X-ray Energy Dispersive Spectroscopy (SEM-XEDS), X-ray Diffraction (XRD) and Optical Microscopy (OM) systems. It was found that both CeO₂ and Nd₂O₃ additives improved the degradation resistance of the YSZ ceramic. Microstructure observations suggested that this improvement was related to the prevention of a phase change of the zirconia polymorphs in the CeO₂ and Nd₂O₃ containing YSZ ceramics.

Text

2014-08-13

Attribution-NonCommercial-NoDerivs 2.5 Canada

http://hdl.handle.net/2429/50011

Mechanical Engineering

University of British Columbia

UBCO

http://creativecommons.org/licenses/by-nc-nd/2.5/ca/