L. M. Lopato

Al2O3–HfO2–Y2O3 phase diagram. I. Isothermal sections at 1250 and 1650°C

The isothermal sections of the Al2O3–HfO2–Gd2O3 phase diagram at 1250 and 1650°C are constructed for the first time and phase equilibria at these temperatures are established. No ternary compounds or appreciable solid solution regions based on components or binary compounds are found in the ternary system. Interaction in the system is determined by the most thermodynamically stable compound, HfO2, which equilibrates with all phases in the system. In the region with Gd2O3 content up to ~65%, the sections are similar, only width of the regions changes. This is connected with changes in the extension of M and F solid solutions in the HfO2–Gd2O3 binary bounding system. The presence of AL + F, GA + GH2, and G2A + F two-phase regions at the isothermal sections suggests that there are triangulating sections of the Al2O3–HfO2–Gd2O3 system in them. Since the F and GH2 phases are of variable composition, these sections can be qualified as conditionally quasibinary. In wide three-phase regions, like in the Al2O3–ZrO2–Gd2O3 system, ternary eutectic points are expected to exist.

Interaction of Cerium Oxide with Hafnium, Zirconium, and Yttrium Oxides at 1500°C

Using the methods of x-ray diffraction and petrographic analysis as well as electron microscopy, phase relationships in the ternary systems ZrO2 ― Y2O3 ― CeO2 and HfO2 ― Y2O3 ― CeO2 were investigated over the entire range of concentrations at 1500°C. The accuracy of the phase relationships of the binary systems HfO2 ― CeO2, ZrO2 ― CeO2, and CeO2 ― Y2O3 at this temperature was improved. Isothermal sections of the ternary phase diagrams at 1500°C were constructed. Specimens of various compositions were prepared from nitrate solutions by evaporating, drying, and heat treating at 1500°C. These systems are characterized by the formation of broad ranges of solid solutions based on C-Y2O3, F-CeO2, F-HfO2 and ZrO2, and narrow ranges based on T-ZrO2 and M-HfO2. No new phases were detected. The course of isoparametric lines in the solid solution ranges of F-HfO2 (ZrO2) leads to the assumption that yttrium and cerium ions substitute for each other, but no appreciable substitution by them for zirconium or hafnium ions occurs.

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.

Functional Graded Materials Based on ZrO2 and Al2O3. Production Methods

The various methods for producing functional graded materials based on ZrO2 and Al2O3 are reviewed: dry pressing followed by thermal treatment, diffusion welding, co-extrusion, chemical infiltration, electrophoretic deposition, centrifugal deposition, sedimentation, tape casting, slip casting, direct ceramic ink-jet printing.

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.

Phase Equilibria during Solidification of Alloys of the Ternary System HfO2 ― Y2O3 ― La2O3

Phase equilibria in the region of alloy solidification have been studied in the system HfO2 ― Y2O3 ― La2O3. A melting-point diagram is constructed for this system. It is established that in the system HfO2 ― Y2O3 ― La2O3 there are seven monovariant three-phase and three invariant four-phase processes with participation of liquid of eutectic (1) and peritectic (2) types. The last three correspond to isothermal planes on the solidus surface at 2230, 2170, and 2040°C.

Interactions in the Al2O3 ― ZrO2 ― La2O3 System at 1250 and 1650°C

Triangulation has been determined for the Al2O3 ― ZrO2 ― La2O3 system, and 1250 and 1650°C isothermal sections of the phase diagram have been constructed. The LaAlO3 ― La2Zr2O7 section is quasibinary, while the LaAlO3 ― T-ZrO2 and La2O3 ·11Al2O3 ― T-ZrO2 ones are partially quasibinary. The triangulation of the ternary system is based on ZrO2 and a phase containing it. No ternary compounds or regions of ternary solid solutions have been identified.

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.