Yttria-Tetragonally Stabilized Zirconia: Aqueous Synthesis and Processing
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In the field of structural ceramics, yttria-tetragonally stabilized zirconia (Y-TZP) is of great interest because of its high strength and toughness and good wear resistance. Previous studies have demonstrated that wet processing routes provide the best possible mechanism for obtaining “bulk” nanocrystalline ceramics because wet processing does not call for extremely high pressures for consolidation as are needed with conventional dry forming techniques. The chief problem with wet processing is aqueous attack on Y-TZP. Aqueous degradation can lead to processing dilemmas as the dissolution of yttrium ions from the surface of the powder changes the surface chemistry of the powder while leading to a lack of control over suspension pH values. Furthermore, dissolution of the yttrium-stabilizing agent can lead to catastrophic degradation of the ceramic in service as a result of the tetragonal to monoclinic phase change which leads to spallation of the ceramic because of stresses produced by the 5–6 vol.% expansion associated with the phase change. It is the aim of this review to summarize the current scientific understanding about the aqueous chemistry of Y-TZP and the implications toward synthesis, dispersion, and processing of nanosized Y-TZP. After reviewing the wealth of knowledge in the literature, elucidation of the techniques that will allow for the aqueous synthesis and processing of nanosized Y-TZP will be apparent. Improvement and utilization of these techniques will lead to the accomplishment of a universal goal in structural ceramics which is the production of bulk ceramics from nanosized ceramic powders.