Hydrothermal synthesis of nanocrystalline powders in the ZrO2-Y2O3-CeO2 system

The paper examines the properties of the nanocrystalline powder 95 mole% ZrO₂-2 mole% CeO₂-3 mole% Y₂O₃, synthesized using a combination of two methods: coprecipitation and hydrothermal decomposition. It is established that coprecipitation produces an x-ray amorphous gel consisting of hard agglomerates from 5 to 10 μm and having a specific surface area of 120 m²/g and a bottle density of 2.94 g/cm³. Hydrothermal synthesis results in a low-temperature metastable cubic solid solution based on ZrO₂ (F-ZrO₂). Its specific surface area is 101.6 m²/g and bottle density is 4.65 g/cm³. Soft agglomerates (0.5–10 μm) consist of primary particles with sizes to 10 nm. The change in hydrothermal suspension processing steps results in soft agglomerates with branched internal porosity. This method allows synthesizing powders of needed compositions in the ZrO₂-CeO₂-Y₂O₃ system. __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 1–2(453), pp. 23–30, 2007.     

Diffusion Interaction during Preparation of Nanocrystalline Powders in the System ZrO2-Y2O3

The properties of ZrO₂ - 3 mole% Y₂O₃ nanocrystalline powder prepared by diffusion impregnation are studied. The original nanocrystalline powder of M-ZrO₂ is prepared with hydrothermal treatment of aqueous zirconium hydroxychloride solution by different regimes. It is found that after diffusion impregnation for all of the powders with yttrium oxide two solid solutions are formed (F-ZrO₂ and M-ZrO₂) in mixture. It is established that the morphological features typical for the original powders are retained. The efficiency of diffusion impregnation is determined by the slightly-agglomerated powder with a high degree of crystallinity.__________Translated from Poroshkovaya Metallurgiya, Nos. 3–4(442), pp. 3–11, March–April, 2005.     

Electrical properties of phases in the ZrO2 - Y2O3 - La2O3 system

An investigation was made of the electrical properties of phases with the cubic fluorite, pyrochlor, and C-Y₂O₃ structures, and the tetragonal ZrO₂ structure (T-ZrO₂) in the ternary system ZrO₂ - Y₂O₃ - La₂O₃. For comparison, the electrical conductivity of a number of specimens with the fluorite structure in the binary system ZrO₂ - Y₂O₃ and with the pyrochlor structure in the ternary system HfO₂ - Y₂O₃ - La₂O₃ was also studied. The specimens were prepared from nanocrystalline powders synthesized by the hydrolysis of zirconium salts in an acid medium at high temperatures. Conductivity was measured over the range 300–950°C in air. It was shown that phases with the fluorite and T-ZrO₂ structures in the investigated systems possess the highest electrical conductivities. Translated from Poroshkovaya Metallurgiya, Nos. 3/4(412), pp. 40–46, March–April, 2000.     

Phase equilibria in the system HfO2-Y2O3-La2O3 AT 1900°C

We have used x-ray phase analysis, electron-probe microanalysis, petrography, and electron microscopy on annealed specimens to study phase equilibria in the ternary system HfO₂-Y₂O₃-La₂O₃ at 1900 °C over the entire concentration range. We have plotted the isothermal cross section of the phase diagram for this system at the indicated temperature. We found 23 phase regions. A typical feature of the system is formation of solid solutions based on different crystal modifications of the starting components (A-and H-La₂O₃, C-Y₂O₃, T-and F-HfO₂) and also the compounds La₂Hf₂O₇, LaYO₃. We did not observe new phases in the system. The nature of the phase equilibria in the system is consistent with the high relative thermodynamic stability of lanthanum hafnate (ΔH °La₂Hf₂O₇ ≈ 100 kJ/mole) compared with LaYO₃. We established that adding a third component extends the thermal stability region for the ordered phase of LaYO₃ toward higher temperatures. __________ Translated from Poroshkovaya Metallurgiya, Nos. 1–2(447), pp. 73–87, January–February, 2006.