A. V. Shevchenko

Interactions in the Al2O3-ZrO2-Y2O3 system

The phase diagram of the Al2O3-ZrO2 system was replotted over a broad range of concentrations (0–100 mole %) and temperatures (1150–2800°C). The polymorphic transformation of zirconium F ⇄ T occurs via the metatectic reaction F ⇄ T + L at 2260°C. Phase triangulation was employed to plot the diagrams of the partially quasibinary sections in the Al2O3-ZrO2-Y2O3 system. Since there is a wide solubility range based on ZrO2 in the binary ZrO2-Y2O3 system, the triangulation conodes are displaced in the F-solid solution corners. The two-phase regions Y3A5-F are quite broad. The reactions in all three are of the eutectic type. The ternary solid solution fields in the Al2O3-ZrO2-Y2O3 system had no observable width.The phase diagram of the Al{sub 2}O{sub 3}-ZrO{sub 2} system was replotted over a broad range of concentrations (0-100 mole %) and temperatures (1150-2800{degrees}C). The polymorphic transformation of zirconium F {r_reversible} occurs via the metatectic reaction F {r_reversible}T + L at 2260{degrees}C. Phase triangulation was employed to plot the diagrams of the partially quasibinary sections in the Al{sub 2}O{sub 3}-ZrO{sub 2}-Y{sub 2}O{sub 3} system. Since there is a wide solubility range based on ZrO{sub 2} in the binary ZrO{sub 2}-Y{sub 2}O{sub 3} system, the triangulation conodes are displaced in the F-solid solution corners. The two-phase regions Y{sub 3}A{sub 5}-F are quite broad. The reactions in all three are of the eutectic type. The ternary solid solution fields in the Al{sub 2}O{sub 3}-ZrO{sub 2}-Y{sub 2}O{sub 3} system had no observable width.

Synthesis and properties of nanocrystalline 90 wt % ZrO2〈Y2O3, CeO2〉-10 wt % Al2O3 powder

Using hydrothermal treatment of coprecipitated hydroxides, we have prepared nanocrystalline ZrO2-rich ZrO2-Y2O3-CeO2-Al2O3 powder. The effect of heat treatment on the properties of the powder has been studied in the temperature range 400–1300°C. The powder has been shown to have a metastable phase composition, which is attributable to structural and size factors and also to the fact that the ZrO2 and Al2O3 crystallites inhibit the growth of each other. Sintering the powder under various conditions, we have obtained ceramics with fracture toughnesses from 6.4 to 16.8 MPa m1/2.

Liquidus surface in the HfO2-Y2O3-La2O3 system

The liquidus surface in the HfO2-Y2O3-La2O3 system was studied by differential thermal analysis in helium at temperatures of up to 2500°C, derivative thermal analysis in air at temperatures of up to 3000°C, x-ray diffraction, optical microscopy, and electron microscopy. The liquidus surface was found to comprise five primary crystallization fields-those of theH-Y2O3-,C-Y2O3-,F-HfO2-, andX-La2O3-based solid solutions and the pyrochlore phase La2Hf2O7. Three invariant equilibria were identified in the system studied-two peritectics and one eutectic.

Effect of heat treatment on the properties of nanocrystalline 80 wt % Al2O3-20 wt % ZrO2〈CeO2, Y2O3〉 powder

We have studied the evolution of nanocrystalline 80 wt % Al2O3-20 wt % ZrO2〈CeO2, Y2O3〉 powder prepared through hydroxide coprecipitation followed by hydrothermal decomposition of the hydroxides and firing at temperatures from 400 to 1300°C. α-Al2O3 has been shown to form at 850°C. The metastable phase F-ZrO2 persists up to this temperature. The variation in the morphology of the powder is topologically continuous. The processes induced by heat treatment of the nanocrystalline powder are interpreted in terms of the evolution of an open system.

Microstructural Design of Bioinert Composites in the ZrO2–Y2O3–CeO2–Al2O3–CoO System

It is shown that a scientifically sound approach to each stage of producing ZrO2-based bioinert implants (from the synthesis of starting powders to their sintering) is a necessary condition for promoting the optimum structure and high mechanical properties. Conditions for producing bioinert implants with regular, laminar, and highly porous microstructures are found. The research results serve as a scientific basis for microstructural design of various bioinert implants in the ZrO2–Y2O3–CeO2–Al2O3-CoO system.

Properties of Nanocrystalline ZrO 2 -Y 2 O 3 -CeO 2 -CoO-Al 2 O 3 Powders

We have studied the properties of nanocrystalline ZrO2-Y2O3-CeO2-CoO-Al2O3 powders prepared via hydrothermal treatment of a mixture of coprecipitated hydroxides at 210°C. A number of general trends are identified in the variation of the properties of the synthesized powders during heat treatment at temperatures from 500 to 1200°C. Our results demonstrate that the addition of 0.3 mol % CoO to nanocrystalline ZrO2-based powders containing 1 to 5 mol % Al2O3 allows one to obtain composites with good sinterability at a reduced temperature (1200°C).

Effect of Al2O3 on the properties of nanocrystalline ZrO2 + 3 mol % Y2O3 powder

We have studied the properties of nanocrystalline ZrO2〈3 mol % Y2O3〉 and 90 wt % ZrO2〈3 mol % Y2O3〉-10 wt % Al2O3 powders prepared via hydrothermal treatment of coprecipitated hydroxides at 210°C. The results demonstrate that Al2O3 doping raises the phase transition temperatures of the metastable low-temperature ZrO2 polymorphs and that the structural transformations of the ZrO2 and Al2O3 in the doped material inhibit each other.

Change in the Physicochemical Properties of Nanocrystalline Powder Based on ZrO2 in the Presence of a Mineralizing Agent

The change in physicochemical properties of nanocrystalline powder of the composition ZrO2 ― 3 mole% Y2O3 in the presence of aluminum fluoride is studied. The starting powder is prepared by a complex method including elements of hydrothermal synthesis and sol-gel technology. It is established that these conditions expand the temperature limits for the existence of ZrO2 monoclinic solid solution. Transformation is connected with adsorption of fluorine at the ZrO2 surface, diffusion in the solid phase, and a reduction in anion vacancy concentration.

Sintering of ultradisperse powders based on zirconium dioxide (review)

We consider the effect of the starting powder characteristics (purity, grain size and shape, size distribution, sintering aids content, etc.), green compact microstructure (density and porosity distribution), and processing parameters (including temperature, exposure time, rate of heating or cooling of the medium) on sintering of ultrafine ZrO2-based powders. We discuss various sintering techniques: hydrothermal sintering, microwave sintering, hot pressing, sinter—forging, sinter-HIP, and gas-pressure sintering.

Liquidus Surface of the ZrO2–Y2O3–Eu2O3 Phase Diagram

The derivative thermal analysis in air up to 3000 °C, X-ray diffraction, petrography, and electron microscopy are employed to examine phase equilibria on the liquidus surface of the ZrO2–Y2O3–Eu2O3 phase diagram. It is established that the liquidus surface of the system is formed by four primary solidification fields of the phases: solid solutions based on hexagonal (N) and cubic (C) crystalline modifications of Y2O3, cubic ZrO2 modification with fluorite (F) structure, and high-temperature cubic modification (X) of Eu2O3. Two four-phase invariant incongruent equilibria are found in the ternary system.