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In this study, a citrate–nitrate combustion method was applied to synthesize composite Y 2 O 3 –MgO nanopowders. In order to optimize the synthesis condition to support sufficient combustion, the molar ratio of citric acid to nitrate (c/n molar ratio) used in the reaction mixtures was varied between 0.17 and 0.34. Nanopowders with an average particle size of 17 nm were achieved. The properties of these nanopowders indicated that the higher molar ratios decreased the unreacted organic components and increased the amount of carbide on the surface of the oxides, which helped to inhibit the formation of carbonate groups. The amount of carbonate groups was reduced with the increasing c/n molar ratio. Y 2 O 3 –MgO nanocomposites fabricated through hot-isostatic-pressing sintering showed a uniform distribution of Y 2 O 3 and MgO grains, which had an average size of ∼180 nm. In addition, the absorption peaks at 1410 and 1511 cm −1 disappeared until the c/n molar ratio reached 0.28. A high average infrared transmittance of 83% in the range of 4000–1667 cm −1 (2.5–6 μm) was obtained in the nanocomposites. [ABSTRACT FROM AUTHOR]

Y 2 O 3 –MgO nanocomposites are appropriate materials for hypersonic infrared windows and domes because of their low emissivity and improved mechanical properties. In this study, the synthesized Y 2 O 3 –MgO nanopowders are investigated to evaluate the influence of moisture absorption on the manufacturing process and properties of the resulting nanocomposites. It is shown that MgO plays a more significant role than Y 2 O 3 in the moisture absorption of the composite nanopowders, and the absorbed moisture leads to a lowering IR transmittance of the final Y 2 O 3 –MgO nanocomposites. A higher calcination temperature improves the resistance to moisture absorption of Y 2 O 3 –MgO nanopowders, which is beneficial for IR transmittance of the final nanocomposites. In addition, increasing the sintering temperature to 1100 °C during spark plasma sintering (SPS) minimizes the influence of absorbed moisture on the IR transmittance of the final nanocomposites. In the water resistance test, the Y 2 O 3 –MgO nanocomposites demonstrate severely eroded surfaces and degraded IR transmittance after water erosion, suggesting the requirement for necessary water-proof treatments on such materials in practical applications. [ABSTRACT FROM AUTHOR]

In this study, pure and fine composite nanopowders with equal volume fractions of Y 2 O 3 and MgO were synthesized via thermal decomposition of nitrate mixtures at a relatively low temperature (600 °C). To improve the performance of the synthesized nanopowders, thermal decomposition under different heating rates were performed and the influence of milling conditions were investigated. Fully dense Y 2 O 3 –MgO composites were prepared by pre-sintering the Y 2 O 3 –MgO nanopowders in air, followed by hot isostatic pressing. The prepared Y 2 O 3 –MgO composites did not contain carboxylate groups and exhibited excellent infrared transmittance over the 3–7.5 μm range. [ABSTRACT FROM AUTHOR]

Highly transparent ZrO 2 -doped Y 2 O 3 ceramics were successfully synthesized using the hot isostatic pressing (HIP) process. The effects of the ZrO 2 content on the sintering behaviors, optical transmission spectra, Vickers hardness, grain size, size distribution, and Raman spectra were determined. The results indicated that decreased ZrO 2 content could promote increased transmittance, red-shifted infrared cutoff wavelength, increased thermal conductivity, decreased Vickers hardness, and increased lattice ordering. According to the optical transmission spectra, the optimized ZrO 2 content was 0.50 at%, at which point the ceramic exhibited a larger pre-sintering temperature range of 1650–1750 °C and the average grain size of 3.35 µm at 1750 °C. The grain size was significantly decreased at lower pre-sintering temperatures. Furthermore, a moderate Vickers hardness of 8.42 GPa and high thermal conductivity of 10.85 W/m K at room temperature were obtained for the optimized ceramic. [ABSTRACT FROM AUTHOR]

ZrO 2 is considered an efficient sintering additive for transparent Y 2 O 3 ceramics. However, the doping of tetravalent Zr 4+ ions leads to a dark brown color of the ceramic after vacuum sintering. In this study, the optical properties of vacuum-sintered and air-annealed ceramics were characterized using transmittance spectra and a Commission International de l’Eclairage (CIE) diagram. The corresponding defects are investigated by electron paramagnetic resonance (EPR) spectra. The band gap of the vacuum-sintered samples is 2.72 eV, which is much smaller than that of the annealed sample. The results reveal that the V O + (F + center) and Zr 3+ defects form transition energy levels near the top of the valence band and at the bottom of the conduction band, respectively. The color-related absorption is mainly attributed to the electronic transfer from the Zr 3+ level to the conduction band and from the F + center to the Zr 3+ level. [ABSTRACT FROM AUTHOR]