Title: Processing and Properties of Macroporous Nanocrystalline Yttria-stabilised Zirconia- JRC-ITU-TN-2009/05
Authors: SANTA-CRUZ Hernan
Publisher: European Commission - Joint Research Centre - Institute for Transuranium Elements
Publication Year: 2009
JRC N°: JRC51274
URI: http://publications.jrc.ec.europa.eu/repository/handle/JRC51274
Type: PhD Theses
Abstract: A laboratory scale route to produce defect-free monolithic ceramic specimens with tailored pore/grain microstructure has been developed. The target configuration consisted of isolated individual pores 0.5-1 µm size, immersed in a matrix of 200-300 nm sized grains with total porosity levels of 10 to 20 %. This type of microstructure is of special interest in the nuclear energy field because of its appearance at the periphery of Light Water Reactor UO2 fuel at high burn-up 1. A commercial 4 mol% yttria stabilised ZrO2 (Y-PSZ) nanopowder with modified surface was used to replicate the structure observed in nuclear fuel. The target microstructure was achieved via a novel colloidal consolidation technique based on the gel-casting process. Polymethylmethacrylate microspheres, introduced as sacrificial templates for the pore formation, were co-dispersed and stabilised with the powder before consolidation. The steps of drying and debinding were critical for the fabrication. Drying was optimised as a lengthy process involving stepwise controlled decrease of humidity. In addition, a debinding program in air was developed using very low heating rates during the critical temperature intervals, where weight loss and shrinkage occur. Furthermore, it was found favourable to continue with the sintering directly after debinding to avoid stresses from cooling and re-heating. For the nanopowder a very low sintering activation energy was determined. The porous specimens showed a slight tendency to an even further reduced sintering activation energy. In contrast, a reference micro-powder revealed in agreement with the literature data a much higher (by factor 5) sintering activation energy. Thereby, the ability of the nanomaterial to sinter at lower temperatures than its coarse-grained counterpart while grain growth is efficiently hindered was demonstrated.
JRC Directorate:Nuclear Safety and Security

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