The efficiency of using the collector pressing scheme in the Spark Plasma Sintering (SPS) process has been confirmed in improving the optical, physical, and mechanical properties of yttria-stabilized zirconia (YSZ) ceramics with an increased shape factor. An approach for developing a seal surface and determining the optimal method of increasing pressure and temperature during SPS on this surface was used to optimize the consolidation modes of the materials. It has been shown that transparent/translucent YSZ ceramics with an increased shape factor (14 mm in diameter and up to 5 mm in height, h/d = 0.36) can be successfully fabricated by the SPS technique combined with the collector pressing scheme. The optical properties and microhardness of ceramics obtained using the collector scheme are better to the optical properties of ceramics obtained using the conventional uniaxial pressing scheme.

In the present study, nearly fully dense monolithic ZrC samples are produced and broadly characterized from microstructural, mechanical and optical points of view. Specifically, 98% dense products are obtained by Spark Plasma Sintering (SPS) after 20 min dwell time at 1850 degrees C starting from powders preliminarily prepared by Self-propagating High-temperature Synthesis (SHS) followed by 20 min ball milling. A prolonged mechanical treatment up to 2 h of SHS powders does not lead to appreciable benefits. Vickers hardness of the resulting samples (17.5 +/- 0.4 GPa) is reasonably good for monolithic ceramics, but the mechanical strength (about 250 MPa up to 1000 degrees C) could be further improved by suitable optimization of the starting powder characteristics. The very smoothly polished ZrC specimen subjected to optical measurements displays high absorption in the visible-near infrared region and low thermal emittance at longer wavelengths. Moreover, the sample exhibits goodspectral selectivity (2.1-2.4) in the 1000-1400 K temperature range. These preliminary results suggest that ZrC ceramics produced through the two-step SHS/SPS processing route can be considered as attractive reference materials for the development of innovative solar energy absorbers.

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Dense fully stabilized cubic zirconia, sintered by the spark plasma sintering (SPS) method, was characterized through hardness, fracture toughness, and electrical impedance measurements. The effect of sintering temperature on hardness and fracture toughness was evaluated. Samples sintered at 1200 °C for 5 min, which had crystallite size of <100 nm, exhibited the highest hardness. Impedance measurements showed an increase in bulk contribution relative to grain boundaries as sintering temperature is increased. Calculation of the activation energy for conduction gave a value, 1.13 eV, in agreement with previously published results.