Y2O3-stabilized ZrO2 (YSZ) ceramics have been used for various engineering applications or as a solid electrolyte in oxygen sensors and fuel cells. The performance in YSZ strongly depends on the microstructure which is directly determined by the characteristic of raw powder. In this paper, the synthetic methods of YSZ powder and its starting material are first overviewed, and then the formation mechanism of YSZ powder is explained, focusing the hydrolysis process which is industrially adopted. Next, microstructural development during sintering of the hydrolytic YSZ powder is summarized, focusing Y2O3-stabilized tetragonal ZrO2 polycrystal (Y-TZP) with excellent mechanical properties among YSZ. The author finally introduces that based on the hydrolytic process technique and microstructural knowledge, low temperature degradation that is fatal shortcoming of Y-TZP can be resolved by controlling the grain-boundary nanostructure and chemical composition distribution in Y-TZP.
In this paper, regarding colloidal shaping in a rotating magnetic field, the fabrication and evaluation were described for various crystal-oriented ceramics including c-axis oriented ZnO, piezoelectric ceramics with tungsten bronze crystals as Sr2KNb5O15, (Sr,Ca)2NaNb5O15 (SCNN) and (Sr,Ba)Nb2O6. In order to shorten the shaping time, which is the problem of this method, a shaping method was proposed in which a slurry was prepared with a solution containing an ultraviolet (UV) curing monomer, and the slurry was solidified by UV irradiation after orientation treatment in a magnetic field. Crystal-oriented SCNN and Ca10(PO4)6(OH)2 compacts were prepared by holding for several tens of seconds. The experimental results were examined based on the theory regarding the UV curing depth and rotation time, and it was confirmed that the experimental results follow the theory. In addition, regarding the fabrication of laminated ceramics by the stereolithography method, c-axis oriented SCNN ceramics with a thickness of 600 μm were produced, and the piezoelectric property were also confirmed. In the future, particle orientation in a low magnetic field were achieved, which would be thought to enhance versatility.
Pure oxygen is mainly produced by separating oxygen from the air. Oxygen separation membranes using mixed oxide ionic-electronic conductor (MIEC) selectively separate high-purity oxygen via oxide ions using the oxygen partial pressure difference on both sides of the membrane as a driving force. It is expected to be industrially put into practical use as a device suitable for on-site oxygen production. In order to improve the oxygen separation efficiency, it is important to increase the surface reaction area and reduce the thickness of the membrane. A multi-layered structure composed of “porous layer / dense thin layer / porous support layer” is suitable for the purpose. Electrophoretic deposition (EPD) is a very suitable method for forming such a multilayered structure. This review introduces the processing viewpoints to optimize various conditions such as suspension preparation conditions, EPD conditions, and co-sintering conditions. Finally, the oxygen separation performance is tested for the obtained membrane and the importance of microstructural design and process selection in improving oxygen separation performance is discussed.