Effect of technological parameters on optical and mechanical properties of Spark Plasma Sintered transparent YSZ ceramics
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Spark Plasma Sintering
Transparent ceramics
Porous yttria-stabilised zirconia ceramics have been gaining popularity throughout the years in various fields, such as energy, environment, medicine, etc. Although yttria-stabilised zirconia is a well-studied material, voided yttria-stabilised zirconia powder particles have not been demonstrated yet, and might play an important role in future technology developments. A sol-gel synthesis accompanied by a freeze-drying process is currently being proposed as a method of obtaining sponge-like nano morphology of embedded faceted voids inside yttria-stabilised zirconia particles. The results rely on a freeze-drying stage as an effective and simple method for generating nano-voided yttria-stabilised zirconia particles without the use of template-assisted additives.
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The phase transformation process of zirconia–8 mol % yttria powder mixtures during a high energy ball milling process has been studied by means of x-ray diffraction analysis. It has been found that the m-ZrO2 (monoclinic zirconia) transforms first to m-ZrO2 solid solution and then to t-ZrO2 (tetragonal zirconia) solid solution. Finally, a single cubic zirconia solid solution phase forms after prolonged milling. The structural transformation is discussed and explained in terms of the phase relations in zirconia-yttria ceramics and the nonequilibrium nature of the mechanical alloying.
Monoclinic crystal system
Tetragonal crystal system
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Monoclinic crystal system
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The sintering behavior of α‐alumina powders doped with magnesia (500 or 1500 ppm) and yttria (0, 500, or 1500 ppm) was investigated using constant‐heating‐rate dilato‐metric experiments. The apparent activation energies for the intermediate stage of sintering were 740, 800, and 870 kJ/mol for 0, 500, and 1500 ppm yttria doping levels, respectively; these were independent of magnesia doping. Yttria‐doped powder compacts exhibited systematic anomalous second peaks in the densification rate curves at certain grain sizes which were determined only by yttria doping levels. Before the anomalous peak, with lower yttrium contents at grain boundaries, yttrium in an atomic state delays densification and raises the apparent activation energy. Beyond the peak, with higher yttrium contents at grain boundaries, yttria‐rich precipitation delays the densification. Within the peak, yttrium segregation near the saturation level enhances densification.
Saturation (graph theory)
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Thermal Stability
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Transparent ceramics
Hot pressing
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Scandium
Transparent ceramics
Nanocrystalline material
Holmium
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The phase relationships in the zirconia‐yttria system have been established up to 2000°C. The addition of 0 to 5 mole per cent yttria lowers the temperature at which zirconia transforms from the tetragonal to the monoclinic form. From 7 to 55 mole per cent yttria is soluble in zirconia and this solid solution is cubic (stabilized zirconia). A two‐phase region appears between 55 and 76 mole per cent yttria. With more than 76 per cent yttria, zirconia is soluble in yttria. These phase boundaries refer to the specimens rapidly cooled from 2000°C. The effect of lowering the temperature to 1375°C is to increase the width of the two‐phase region between cubic zirconia and yttria solid solution. A tentative phase diagram of the zirconia‐yttria system is presented. The mechanism of stabilization of zirconia by an oxide of the yttria type is discussed in relation to the crystal structure of these two oxides. It is concluded that scandia, as well as other oxides of the rare earth group from element 62 to element 71, should stabilize zirconia by the same mechanism. Experimental results obtained on scandia, gadolinia, and samaria indicate that, as for yttria, the minimum amount of these oxides necessaryto produce stabilization is about 6 mole per cent.
Tetragonal crystal system
Monoclinic crystal system
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Transparent ceramics
Hot isostatic pressing
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