A. K. Ruban

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.

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.

Effect of Coo Microadditive on the Properties of ZrO2–Y2O3–CeO2–Al2O3 Nanocrystalline Powder

The changes in the physical and chemical properties of ZrO2–Y2O3–CeO2–Al2O3 nanocrystalline powder with 0.2 wt.% CoO microadditive during thermal processing in the 400–1300°C temperature range are investigated. It is shown that CoO microadditive reduces the specific surface area of the powder and significantly affects the temperature range of the F-ZrO2 → T-ZrO2 phase transformation. The morphology changes topologically continuously. The phase transformation in the ZrO2–Y2O3–CeO2–Al2O3 system occurs in the 850–1150°C temperature range. In the presence of CoO microadditive, this range is 700–850°C.

Phase Diagrams of Refractory Oxide Systems and Microstructural Design of Materials

It is shown that the phase diagrams of refractory oxide systems based on ZrO2, HfO2, Al2O3, and rare earth oxides underlie the microstructural design of various high-performance materials. Process steps to produce coarse-grained ceramics in the HfO2–ZrO2–Y2O3, ZrO2–Y2O3–Sc2O3, HfO2–ZrO2–Sc2O3, Y2O3–Er2O3, Y2O3–ZrO2, Y2O3–HfO2, Y2O3–Al2O3, Y2O3–SiO2, and Y2O3–La2O3 systems to perform at temperatures up to 2200°C are designed. Process steps to produce high-performance fine-grained composites in the HfO2–ZrO2–Y2O3 (Ln2O3) (Ln–Dy, Ho, Er, Tm, Yb), ZrO2–Y2O3–Sc2O3, ZrO2–Y2O3–Sc2O3, Al2O3–Zr(Hf)O2–Ln(Y)2O3 (Ln–La, Nd, Sm, Gd, Er, Yb), and ZrO2–Y2O3–CeO2–Al2O3 systems are designed as well.

Effect of Mineralizing Agent on the Phase Composition of Nanocrystalline Powder in the System ZrO2 ― Y2O3 ― CeO2

The effect of mineralizing agent (AlF3) on microstructural rebuilding and phase transformation that occurs during heat treatment in the range 600-1000°C for powder of the composition ZrO2 ― 7 mole% CeO2 ― 1 mole% Y2O3 is studied. The original nanocrystalline powder is prepared by high-temperature hydrolysis and sol-gel technology. It is established that during heat treatment there is decomposition of the solid solution based on T-ZrO2 by a eutectoid reaction with formation of M-ZrO2 and Ce2Zr3O10. The compound Ce2Zr3O10 is retained under these conditions at 1000°C. Anisotropic crystals of different chemical composition (M-ZrO2, Ce2Zr3O10, α-Al2O3) form within the sintered matrix of a solid solution based on T-ZrO2.

A method of determining phase-transition temperatures using solar heating

The phase-transition temperatures in oxide systems were determined on the basis of the process of solidification of specimens which were partially melted on the surface in the focus of a solar furnace. In the ZrO/sub 2/-Y/sub 2/O/sub 3/ binary systems, the specimens with intermediate composition were prepared by combined precipitation of zirconium and yttrium hydroxides from nitric acid solutions followed by drying, roasting at 800 C, briquetting, and melting in the solar furnace. The described method of determination of the phase-transition temperatures in the oxide systems on the basis of the surface of the specimens partially melted in the focus of the solar furnace has a number of advantages in comparison with the method of evaluating the temperatures from the radiation of the rotating cavity: it is not necessary to form the cavity with the emissivity properties similar to those of the absolute blackbody; and the oxide melt formed in the course of melting is distributed mainly on the surface of the specimen so that after interrupting the radiation flux the melt solidifies in its entire volume.