lumina-based nanocrystalline powders with different ZrO 2 amounts were produced for the first time by hydrothermal synthesis in an alkaline environment for designing zirconia toughened alumina (ZTA) composites. In ZTA composites, ZrO 2 solid solution particles codoped with ceria and yttria are distributed in a rigid Al 2 O 3 matrix. To examine the physicochemical properties, 90 wt.% Al 2 O 3 –10 wt.% ZrO 2 (Y 2 O 3 , CeO 2 ) and 58.5 wt.% Al 2 O 3 –42.5 wt.% ZrO 2 (Y 2 O 3 , CeO 2 ) powders were used. The ZrO 2 solid solution had composition 90 mol.% ZrO 2 –2 mol.% Y 2 O 3 –8 mol.% CeO 2 . The hydrothermal powders were heat treated in the temperature range 400–1450°C and examined by X-ray diffraction, differential thermal analysis, and electron microscopy. The powder specific surface area was determined by the BET method. The sizes of primary particles were determined with the Scherrer equation. The AMIC software (Automatic Microstructure Analyzer) was employed to process the morphology analysis results. The phase transformations and active sintering of the ZTA powders determined the dependences showing the sizes of primary particles and the specific surface area of the powders versus the heat treatment temperature. With higher ZrO 2 content, temperature of the F-ZrO 2 → T-ZrO 2 phase transformation decreased, the likelihood of M-ZrO 2 to emerge increased, and the sequence of Al 2 O 3 phase transformations changed after the boehmite had decomposed. The variation in the morphology and specific surface area of the powders in the heat treatment process indicated that their sintering activity increased. The dependence of the shape factor characterizing the nanocrystalline 90AZG and 58.5AZG powders on the heat treatment temperature was studied. The starting nanosized 90AZG and 58.5AZG powders had a similar distribution of agglomerates according to the shape factor. Round agglomerates and multifaceted regular agglomerates were predominant. The way in which the shape factor of the agglomerates varied with temperature was associated with a topochemical memory effect manifested by the 90AZG and 58.5AZG powders were examined. With increasing ZrO 2 content, the microhardness of the ZTA composites decreased from 195 to 160 MPa, fracture toughness (KIc) increased from 6 to 8 MPa · m0.5, and Vickers hardness decreased from 8.3 to 5.6 GPa. The improvement in consolidation methods for ZTA composites will allow tool, structural, and functional ceramics with the required properties to be produced.

Alumina-based nanocrystalline powders with different ZrO2 amounts were produced for the first time by hydrothermal synthesis in an alkaline environment for designing zirconia toughened alumina (ZTA) composites. In ZTA composites, ZrO2 solid solution particles codoped with ceria and yttria are distributed in a rigid Al2O3 matrix. To examine the physicochemical properties, 90 wt.% Al2O3–10 wt.% ZrO2 (Y2O3, CeO2) and 58.5 wt.% Al2O3–42.5 wt.% ZrO2 (Y2O3, CeO2) powders were used. The ZrO2 solid solution had composition 90 mol.% ZrO2–2 mol.% Y2O3–8 mol.% CeO2. The hydrothermal powders were heat treated in the temperature range 400–1450°C and examined by X-ray diffraction, differential thermal analysis, and electron microscopy. The powder specific surface area was determined by the BET method. The sizes of primary particles were determined with the Scherrer equation. The AMIC software (Automatic Microstructure Analyzer) was employed to process the morphology analysis results. The phase transformations and active sintering of the ZTA powders determined the dependences showing the sizes of primary particles and the specific surface area of the powders versus the heat treatment temperature. With higher ZrO2 content, temperature of the F-ZrO2 → T-ZrO2 phase transformation decreased, the likelihood of M-ZrO2 to emerge increased, and the sequence of Al2O3 phase transformations changed after the boehmite had decomposed. The variation in the morphology and specific surface area of the powders in the heat treatment process indicated that their sintering activity increased. The dependence of the shape factor characterizing the nanocrystalline 90AZG and 58.5AZG powders on the heat treatment temperature was studied. The starting nanosized 90AZG and 58.5AZG powders had a similar distribution of agglomerates according to the shape factor. Round agglomerates and multifaceted regular agglomerates were predominant. The way in which the shape factor of the agglomerates varied with temperature was associated with a topochemical memory effect manifested by the 90AZG and 58.5AZG powders were examined. With increasing ZrO2 content, the microhardness of the ZTA composites decreased from 195 to 160 MPa, fracture toughness (KIc) increased from 6 to 8 MPa · m0.5, and Vickers hardness decreased from 8.3 to 5.6 GPa. The improvement in consolidation methods for ZTA composites will allow tool, structural, and functional ceramics with the required properties to be produced.

Досліджено фізико-хімічні властивості нанодисперсного ZTA-порошку складу (мас.%): 80 Al2O3 – 20 ZrO2 (Y2O3,CeO2), синтезованого гідротермальним методом у лужному середовищі. Склад твердого розчину на основі ZrO2 (мол.%): 90 ZrO2 – 2 Y2O3 – 8 CeO2. Методи дослідження: рентгенофазовий аналіз, диференційно-термічний аналіз, електронна мікроскопія та метод БЕТ.

The standard material of the ceramic layer in thermal barrier coatings (TBCs)—a solid solution of ZrO 2 stabilized with (6–8 wt.%) Y 2 O 3 (YSZ)—approaches the temperature limit of its application (<1200°C) because the ZrO 2 t′ phase sinters and undergoes t′-ZrO 2 → T-ZrO 2 + F-ZrO 2 phase transformations to form M-ZrO 2 at elevated temperatures. Ceramic materials for a new generation of TBCs need to be developed to increase the operating temperature (up to 1600°C), efficiency, and productivity of gas-turbine engines. The overview paper analyzes research efforts focusing on the development of TBCs using solid solutions of ZrO 2 with rare-earth metal and titanium oxides. When Y 2 O 3 in YSZ is partially substituted by CeO 2 , TiO 2 , La 2 O 3 , Sc 2 O 3 , Gd 2 O 3 , Nd 2 O 3 , Yb 2 O 3 , Er 2 O 3 , and Ta 2 O 5 , ceramics with high phase stability (ZrO 2 t′ phase being retained in the coating) up to 1500°C, lower thermal conductivity, and required fracture toughness and sintering resistance but shorter thermal fatigue life than that of standard YSZ are produced. The concepts of greater tetragonality of the ZrO 2 t′ phase (ceramics in the ZrO 2 –CeO 2 –TiO 2 system) and a ‘multicomponent defective cluster’ (ceramics in the ZrO 2 –Y 2 O 3 –Nd 2 O 3 (Gd 2 O 3 , Sm 2 O 3 )–Yb 2 O 3 (Sc 2 O 3 ) system) explain how the operating temperature of the TBC ceramic layer increases to 1350°C and 1600°C, respectively. The thermal conductivity of TBC ceramics in the binary ZrO 2 –CeO 2 , ZrO 2 –Er 2 O 3 , ZrO 2 –Sm 2 O 3 , ZrO 2 –Nd 2 O 3 , ZrO 2 –Gd 2 O 3 , ZrO 2 –Dy 2 O 3 , and ZrO 2 –Yb 2 O 3 systems is lower than that of YSZ. Ceramics with high phase stability and low thermal conductivity have been produced in the ternary ZrO 2 –Sc 2 O 3 –Gd 2 O 3 , ZrO 2 –CeO 2 –Gd 2 O 3 , ZrO 2 –YbO 1.5 –TaO 2.5 , and ZrO 2 –Yb 2 O 3 –TiO 2 systems. An integrated approach is needed to choose the composition of the ceramic layer based on the ZrO 2 solid solution, select the coating technique, and improve the coating architecture to design effective TBCs with balanced properties.

Variations in the phase composition, specific surface area, and morphology of structural components in the ultrafine powder of composition (wt.%) 70 (90 ZrO 2 (3 Y 2 O 3 , 2 CeO 2 )–10 Al 2 O 3 )–30 CoAl 2 O 4 (70ZA30CoA), produced by hydrothermal synthesis combined with mechanical mixing, were studied in the heat treatment process up to 1300°C. The study employed Xray diffraction, scanning and transmission electron microscopy, petrography, and BET. The formation of CoAl 2 O 4 in the 70ZA30CoA powder in the heat treatment process was accompanied by reversible phase transformations: T-ZrO 2 → M-ZrO 2 → T-ZrO 2 . The M-ZrO 2 content increased from 15% to 46% in the temperature range 850–1000°C and decreased to 13% after heat treatment to 1150°C. The process involved slight coarsening of the primary T-ZrO 2 particles, while the size of the primary M-ZrO 2 particles remained practically unchanged. The phase transformation was due to a decrease in the free energy of the ultrafine 70ZA30CoA powder, representing a thermodynamically nonequilibrium system. The phase composition changed color of the 70ZA30CoA powder in the following sequence: gray → gray blue → dark cyan → bright blue. Morphological analysis of the structural components showed that the CoAl 2 O 4 formation and reversible T-ZrO 2 → M-ZrO 2 phase transformation were accompanied by shape change, loosening, and subsequent sintering of the agglomerates. The chain-like agglomerates of various shapes and sizes indicate that the 70ZA30CoA powder sinters actively at 1300°C. The decrease in the specific surface area from 46 to 1 m 2 /g depending on the heat treatment temperature was determined by the development of three structural transformation processes: formation of CoAl 2 O 4 , phase transition of the ZrO 2 solid solution, and sintering of the 70ZA30CoA powder. The established regularities are of fundamental importance for the microstructural design of ZrO 2 composites such as ZrO 2 –Y 2 O 3 –CeO 2 –Al 2 O 3 –CoO materials of blue and other colors for various applied purposes.

One of the main directions of the modern materials development science is the development of new oxide ceramic materials for engineering, energy, chemical, aerospace, electronic and other industries in multi component systems, including containing TiO2, Al2O3 and rare earth oxides. The Al2O3‒TiO2‒Yb2O3 system attracts the attention of researchers because possibility of design of structural high-temperature materials with low coefficient of thermal expansion, as well as refractory ceramic materials. The basis of new materials creation is the study of physical and chemical interaction, which is reflected in the phase diagrams of the systems. The purpose of this study is the construction of phase diagram isothermal section for the Al2O3−TiO2−Yb2O3 system at 1400 °С, which is the part of the interaction systematic study of the Al2O3−TiO2−Ln2O3 systems, where Ln = (La, Nd, Gd, Er, Yb and Y). The samples were prepared by a chemical method. Annealed in air at 1400°С for 80 hour sand cooled in the furnace. Phase content of the samples was determined by XRD analysis. New multicomponent phases and appreciable homogeneity regions based on components and binary compounds were not found. Isothermal section consists of four narrow two-phase Al2TiO5+Yb2Ti2O7, Al2O3+Yb2Ti2O7, Yb3Al5O12+Yb2Ti2O7, Yb3Al5O12+Yb2TiO5 regions and five threephase Al2TiO5+TiO2+Yb2Ti2O7, Al2TiO5+Yb2Ti2O7+Al2O3, Al2O3+Yb2Ti2O7+Yb3Al5O12, Yb2Ti2O7+Yb3Al5O12+Yb2TiO5, Yb3Al5O12+Yb2TiO5+С-Yb2О3 fields. In addition, in the system we expects the existence of new three-phase and two-phase eutectics, which can be obtained in the form of high-temperature structural materials by the directional solidification. This fact opens up the possibility to find and establish the coordinates of new three-phase and two-phase eutectics for directional solidification and to obtain new high-temperature structural materials in the Al2O3–TiO2–Yb2O3 system.

Zirconates of rare earth elements with a pyrochlore-type structure, as a class of ceramics with low thermal conductivity, are among the most promising materials for a ceramic layer in thermal barrier coatings (TBCs) for gas turbine engines with operating temperatures above 1200°C. The paper presents an overview of studies focusing on the development of the upper Gd2Zr2O7 TBC layer. The microstructural design of these materials is based on the ZrO2–Gd2O3–Al2O3 phase diagram. Methods for increasing the fracture toughness of Gd2Zr2O7 materials and preventing the interaction of Gd2Zr2O7 and Al2O3 formed in TBC operation are presented. The features of multilayer and functional gradient coatings are addressed. Complex improvement of the composition, architecture, and deposition of the coatings ensures the properties required for long-term operation of Gd2Zr2O7 TBCs.

Transformation toughening, based on the martensitic T-ZrO2 → M-ZrO2 phase transformation, causes the high strength of ZrO2-based composites. The reversible martensitic phase transformation of fine-grained composites ZrO2–12 mol% CeO2 occurs below ambient temperature. Bulk material 12Се-TZP is characterized by “shape memory”, high fracture toughness (К1с up to 35 МПа·м 0,5) and tolerance to aging. Properties of composites depend on the properties of the starting powders. Hydrothermal synthesis in an alkaline medium is perspective for producing nanocrystalline powders of ZrO2-based solid solutions . Variations of physico-chemical properties of hydrothermal nanocrystalline 88 ZrO2–12CeO2 (mol%) powder after synthesis and thermal treatment in the 400–1300 °C range were investigated. It was found that after hydrothermal synthesis the thermodynamically non-equilibrium system consisting of a low temperature metastable cubic solid solution based on ZrO2 (F-ZrO2) and an X-ray amorphous phase were formed. The primary particles size was ≈ 10 nm. The powder specific surface area was 107 m2/g. Low-temperature F-ZrO2 remained up to 700 °C. Temperature increase up to 850 °C was accompanied by the F-ZrO2→T-ZrO2 phase transformation. This transformation is completed at 1000 °C. The powder specific surface area decreases from 107 m2/g to 0.27 m2/g during thermal treatment. Variation of powder specific surface area depends on both the ZrO2- based solid solution phase transformations and the sintering of freely poured powders. The primary particles size of the ZrO2-based solid solution increased to 20 nm. Morphology of powder varies topologically continuously during thermal treatment. The unit cell volume of T-ZrO2 phase decreased from 135.32 to 135.20 A after thermal treatment in the 1150–1300 °C range. Under these conditions the T-ZrO2 tetragonality increases from 1.0137 to 1.0139. Powder was characterized by high activity to sinter ing. The investigation results will be used for microstructural design of high-performance ZrO2-based composites.

The changes in the physical–chemical properties of ZrO 2 –Y 2 O 3 –CeO 2 –Al 2 O 3 –CoC nanocrystalline powders, produced by hydrothermal synthesis combined with mechanical mixing, are investigated. It is found out that, in the presence of cobalt compounds, the temperatures of phase transformations of ZrO 2 -based solid solution decrease. The powders are characterized by increased activity to sintering. AMIS software is used for processing the research results on the powder morphology. The flame atomic absorption spectrometry is used to confirm that the probability of cobalt wash-out from ZrO 2 –Y 2 O 3 –CeO 2 –Al 2 O 3 –CoO composites does not exceed 0.2 mg/l. The research results will be used for the microstructural design of blue ZrO 2 -based composites.

The aim of this investigation is the construction of isothermal sections for the Al2O3-TiO2-Y(Gd)2O3 phase diagrams at 1400oС as part of systematic investigations of Al2O3-TiO2-Ln2O3 (Ln=lanthanides, Y) systems. The 1400°C was taken as the temperature, at which no liquid phases are expected in the both systems. The isothermal sections at 1400 °С for the Al2O3 – TiO2 – Y(Er)2O3 phase diagrams were constructed for the first time. Samples were prepared by a chemical method. Samples were annealed in air at 1400°С for 80 hours and cooled in the furnace. This temperature value was selected with a view to provide possibility of phase transformations character studies. New phases and appreciable solubility regions based on the components and binary compounds were not found, as predicted. Triangulation of the systems is determined by the phase Y(Er)2T2O7, which is in equilibria with compounds Al2TiO5, Y(Er)3Al5O12, Y(Er)AlO3, Y(Er)4Al2O9 and components TiO2 and Al2O3. The structures of isothermal sections of the both systems are similar. The systems are triangulated into six secondary triangles, in which three-phase eutectic are expected. In five quasibinary sections two-phase eutectic should expect to exist. The obtained results will make a significant contribution to the understanding of interactions between the components in the systems studied.This systems offer a number of promising opportunities such as high-temperature structural composites based on directionally solidified two-phase and three-phase eutectic materials, solid electrolytes (SOFCs, oxygen sensors, film for electronic devices, etc.), promising to accumulate water, immobilizing materials for nuclear industry, tough ceramics, catalysts carriers, wear- and corrosion-resistant ceramic coatings and super refractories.

The aim of this investigation is the construction of isothermal sections for the Al2O3-TiO2-Y(Gd)2O3 phase diagrams at 1400ºС as part of systematic investigations of Al2O3-TiO2-Ln2O3 (Ln=lanthanides, Y) systems. The 1400°C was taken as the temperature, at which no liquid phases are expected in the both systems. The isothermal sections at 1400 °С for the Al2O3– TiO2–Y(Er)2O3 phase diagrams were constructed for the first time. Samples were prepared by a chemical method. Samples were annealed in air at 1400°С for 80 hours and cooled in the furnace. This temperature value was selected with a view to provide possibility of phase transformations character studies. New phases and appreciable solubility regions based on the components and binary compounds were not found, as predicted. Triangulation of the systems is determined by the phase Y(Er)2T2O7, which is in equilibria with compounds Al2TiO5, Y(Er)3Al5O12, Y(Er)AlO3, Y(Er)4Al2O9 and components TiO2 and Al2O3. The structures of isothermal sections of the both systems are similar. The systems are triangulated into six secondary triangles, in which three-phase eutectic are expected. In five quasibinary sections two-phase eutectic should expect to exist. The obtained results will make a significant contribution to the understanding of interactions between the components in the systems studied.This systems offer a number of promising opportunities such as high-temperature structural composites based on directionally solidified two-phase and three-phase eutectic materials, solid electrolytes (SOFCs, oxygen sensors, film for electronic devices, etc.), promising to accumulate water, immobilizing materials for nuclear industry, tough ceramics, catalysts carriers, wear- and corrosion-resistant ceramic coatings and super refractories.

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.

A technology for synthesizing a high-purity nanocrystalline powder of zirconia doped with yttrium oxide and ceric oxide, namely ZrO2 (5% Y2O3 and 3% CeO2), is developed. The powder is characterized by high activity during sintering and the absence of hard agglomerates. The technology can be used to synthesize powders for manufacturing structural, functional, and medical purpose non-ageing ceramics.

The paper examines the low-temperature gamma-Al2O3 -> alpha-Al2O3 phase transformation in gamma-Al2O3 powder for chromatography with AlF3 mineralizer. Changes in the AlF3 amount (2-3 wt.%) and isothermal holding time at 850A degrees C allow variation in the powder phase composition, specific surface area (from 85.5 to 0.2 m(2)/g), and morphology (from spheroids to lamellas). The experimental results serve as a basis for designing precipitation-strengthened composites consisting of a ZrO2 solidsolution matrix and a strengthening alpha-Al2O3 phase.

The paper examines the low-temperature γ-Al2O3 → α-Al2O3 phase transformation in γ-Al2O3 powder for chromatography with AlF3 mineralizer. Changes in the AlF3 amount (2–3 wt.%) and isothermal holding time at 850°C allow variation in the powder phase composition, specific surface area (from 85.5 to 0.2 m2/g), and morphology (from spheroids to lamellas). The experimental results serve as a basis for designing precipitation-strengthened composites consisting of a ZrO2 solidsolution matrix and a strengthening α-Al2O3 phase.

Nanocrystalline powder of ZrO2 (5 % Y2O3, 3 % CeO2) has been synthesized. The powder is developed for manufacture of ceramic implants for bone surgery. Physico-chemical properties of the powder and its radioactivity have been examined. It is shown that the proposed technology allows to produce the nanocrystalline ZrO2 based powder of high chemical purity and high activity for sintering. Ceramics made of the powder provides the high reliability and assures long term service in the aggressive environment of a living organism. The specific radioactivity of the powder is (1.3 +/- 0.4) Bq/kg and is caused by the presence in the powder of natural radionuclide Ra-226. Radioactivity of the synthesized powder is more than 100 times below the norm accepted by the international standards for ceramic materials based on T-ZrO2 for surgical implants.

The physicochemical properties of ZrO 2 -based composite in the ZrO 2 –Y 2 O 3 –CeO 2 –CoO system, which is intended for the development of bioinert implants, are examined. To produce the starting nanocrystalline powder, hydrothermal synthesis in alkaline medium and mechanochemical treatment were successively used. The samples were consolidated by cold uniaxial pressing, sintering in air, and barothermal treatment in argon. This resulted in the fine-grained composite consisting of (mol.%): 96.3 ZrO 2 –2.8 Y 2 O 3 –0.6 CeO 2 –0.3 CoO. The composite has properties that comply with international standards and is not prone to ageing.

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.

Matrix (mol.%) 95ZrO2-3Y2O3-2CeO2 was produced by hydrothermal synthesis from a mixture of previously precipitated hydroxides. α-Al2O3 and Co(NO3)3 were added by mechanical mixing. The properties of nanocrystalline powders with a complex chemical composition (wt.%) [90 (ZrO2-CeO2-Y2O3)-10Al2O3]-(0,1Al2O3-0,1CoO) after heat treatment in the temperature range from 400 to 1300 °C were investigated by XRD phase analysis and BET measurements. During heat treatment powders retained in nanocrystallite state (primary particle size of the zirconia solid solution varies from 14 to 83 nm), and its specific surface area decreases from 99,7 m2/g to 1.51 m2/g.

It is shown that a scientifically sound approach to each stage of producing ZrO 2 -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 ZrO 2 –Y 2 O 3 –CeO 2 –Al 2 O 3 -CoO system.