V. B. Glushkova

Nanocrystalline ceramics based on the ZrO2-HfO2-Y2O3 system

The formation of nanopowders of cubic solid solutions in the ZrO2–HfO2–Y2O3 system is investigated using the coprecipitation method. Conducting ceramic materials are prepared from the powders at 1450°C.

Preparation of nanodisperse solid solutions based on ZrO2 and HfO2 from hydroperoxides

A procedure for preparing solid solutions based on zirconium and hafnium hydroperoxides is developed. This procedure is based on the coprecipitation of components in the presence of hydrogen peroxide. Amorphous nanopowders (Ssp = 80–90 m2/g, dmean = 2–3 nm) without any indication of the agglomeration of particles are synthesized. After the decomposition of complex hydroperoxides at a temperature of 500°C, the compacted powders undergo an active sintering at a temperature of 1450°C. The particle size after heat treatment does not exceed 50 nm. As follows from the electrical and physical characteristics obtained for these materials, they can be recommended for the use as solid electrolytes and sensors of oxygen partial pressure.

Synthesis of nanocrystalline solid solutions based on zirconia and hafnia

Nanosized (2–8 nm) amorphous powders of the solid solution based on zirconia and hafnia are synthesized through back coprecipitation upon treatment of gels at temperatures from +20 to −77°C. Heat treatment of these powders at temperatures up to 1000 and above 1100°C leads to the formation of cubic (fluorite type, Oh5 = Fm3m) and tetragonal phases of the Zr82Hf10Y3Ce5Ox composition, respectively. It is revealed that a decrease in the synthesis temperature (from +20°C to −6°C) results in a decrease in the size of gel agglomerates from 30 to 1 μm. Recrystallization processes in the gels prepared using cryochemical treatment are developed very slowly in the temperature range 500–1200°C (the crystallite size does not exceed 25 nm).

Ceramics based on monoclinic hafnia

A procedure combining the advantages of mechanochemical and sol-gel processes is developed for preparing highly refractory materials based on the monoclinic hafnia modification. The ceramic materials produced at temperatures in the range 1500–1700°C have a density equal to 80–90% of the theoretical density, a strength of 80–120 MPa, and a total (open and closed) porosity of less than 10–20%.

Phase Formation in the ZrO2 – Nd2O3 (Y2O3) – Al2O3 (Cr2O3) SYSTEMS AND PROPERTIES OF MATERIALS BASED ON THEM

The nature and degree of completeness of phase transformations that occur at 1100 – 1750°C in ZrO2 – Nd2O3 (Y2O3) – Al2O3 (Cr2O3) compositions rich with ZrO2 are studied. It is shown that the zirconium-yttrium cubic solid solution has a maximum resistance to the action of Al2O3 and Cr2O3. The sinterability and other properties of parts from ZrO2 can be controlled within a quite wide range by adding Al2O3, Cr2O3, and NdCrO3 to ZrO2 stabilized by Nd2O3.

Preparation and Properties of a Ceramic in the ZrO2 – CeO2 System

The ZrO2 – CeO2 solid solution (88 mol.% – 12 mol.%) is synthesized by coprecipitation. The effect of dry mechanical grinding on the dispersity of the solid solution is studied. Combining methods of coprecipitation and mechanical grinding intensifies the sintering process and allows preparation of compact ceramic materials in the ZrO2 – CeO2 system.

Electrtic transport properties and the size effect in ZrO2-based ceramic materials

Amorphous nanomaterials in the ZrO2-CeO2 system are synthesized. The aging and crystallization processes in a complex zirconium-cerium hydrogel are investigated. Powders with a crystal size of 45–100 nm are prepared. Samples having a porosity of less than 2.2% are produced from the powders. It is demonstrated that tetragonal zirconia-based solid solutions Zr1−xCexO2−δ sintered at a temperature of 1500°C possess ionic conductivity in air and in noble gasses. The assumptions are made regarding the mechanisms of ionic (surface anionic) and electronic (hopping) conduction in samples of the 88ZrO2 · 12CeO2 (mol %) composition. The solid solutions prepared can be used at a temperature of 720°C as high-strength inexpensive solid electrolytes.

Formation and stability of fluorite-like solid solutions in the Zr — Mg — Y — Al — O system

The method of x-ray phase analysis is used to study the kinetics of the interaction of ZrO2 Y2O3, MgO, and A12O3 and the succession of the formation of phases in synthesis of a cubic solid solution of fluorite-like Zr1-x(Y, Mg)x Oz in the range 1100–1500°C. The effect of Y2O3 and A12O3 on the composition and stability of the obtained material is investigated. The kinetic parameters of the oxide interaction are determined. The solid solution is shown to behave unusually in the synthesis.