Synthesis and physicochemical properties of a solid oxide nanocomposite based on a ZrO<Subscript>2</Subscript>–Y<Subscript>2</Subscript>O<Subscript>3</Subscript>–Gd<Subscript>2</Subscript>O<Subscript>3</Subscript>–MgO system

A highly dispersive powder with a (ZrO₂)_0.92(Y₂O₃)_0.03(Gd₂O₃)_0.03(MgO)_0.02 composition and specific surface area of 150 m²/g has been synthesized via a method of coprecipitation of hydroxides with the subsequent cryochemical treatment of the gel. Nanoceramics based on the cubic modification of zirconium dioxide with the grain size of ~40–45 nm have been obtained. The temperature dependence of the specific electrical conductance of the nanoceramics within a temperature range of 350–870°C in air has been studied, and the ratio of the ionic and electronic parts of the conductance has been determined. Recommendations for the use of the obtained oxide nanocomposite as an electrolyte for a high-temperature fuel cell have been given.     

Porous ceramics based on the ZrO<Subscript>2</Subscript>(Y<Subscript>2</Subscript>O<Subscript>3</Subscript>)–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> system for filtration membranes

The results of the studies of the process of fabricating ceramic filtration membranes in the system ZrO₂(Y₂O₃)–Al₂O₃ are presented. The phase compositions of the precursor powders and sintered ceramics have been investigated and their porous structures have been determined. Two stages of the implementation of the technology were demonstrated: fabrication of substrates with an open porosity ranging from 20 to 47% and pore sizes in the 100–300 nm range, as well as the deposition of nanocrystalline aluminum oxide layers on them. It has been established that the pore size distribution in the membrane layer of α-Al₂O₃ is unimodal (from 30 to 100 nm).     

Synthesis and comparative studies of xerogels,aerogels, and powders based on the ZrO<Subscript>2</Subscript>–Y<Subscript>2</Subscript>O<Subscript>3</Subscript>–СeO<Subscript>2</Subscript> system

The technology of liquid-phase synthesis of mesoporous xerogels and aerogels based on ZrO₂–Y₂O₃–CeO₂ is developed. Xerogels are obtained by the coprecipitation of hydroxides, while aerogels are obtained in accordance with the sol–gel technology: the average pore size is 1.5–17.2 nm and the specific surface area is 120–878 m²/g. Aerogels are characterized by a high degree of porosity: the pore volume attains 1–4 cm³/g. Based on precursor xerogels, nanopowders of a tetragonal solid solution of the (ZrО₂)_0.92(Y₂О₃)_0.03(CeО₂)_0.05 composition with a particle size of 5–9 nm and S _spec = 74 m²/g were fabricated. Due to the high values of their specific surface area, the synthesized xerogels and aerogels are promising as sorbents, catalysts, or catalyst supports.     

Synthesis and study of mesoporous xerogels and nanopowders of a metastable solid solution 97ZrO<Subscript>2</Subscript>–3Y<Subscript>2</Subscript>O<Subscript>3</Subscript> for the fabrication of catalyst substrates

The—technology of the liquid-phase synthesis of metastable phases in the ZrO₂–Y₂O₃ system has been developed. Mesoporous xerogels with the specific surface area of ~350 m²/g and monophase nanopowders (5–10 nm) of the tetragonal solid solution (ZrO₂)_0.97(Y₂O₃)_0.03 have been obtained and their structural peculiarities have been revealed. The efficiency of the suggested technology and good prospects of the synthesized ZrO₂-based precursors in creating catalysts’ substrates have been demonstrated.     

Synthesis of low-melting eutectic of the CaO–B<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> system in a solid phase

Results are provided for a physicochemical study of processes that occur during synthesis of eutectic composition of the CaO–B₂O₃–SiO₂ system in a solid phase, and the possibility of their activation by using starting calcium-containing components with different chemical and thermal prehistory. It is established that independent of the form of starting components, in all cases there is formation of a crystalline eutectic phase, and the sequence of physicochemical processes that occur is determined by the reaction capacity of the calcium compound introduced.     

Comparative Study of Powders Based on the ZrO<Subscript>2</Subscript>–Y<Subscript>2</Subscript>O<Subscript>3</Subscript>–СeO<Subscript>2</Subscript> System Obtained by Various Liquid Phase Methods of Synthesis

Using the liquid-phase methods of synthesis—the coprecipitation of hydroxides and the hydrothermal method—mesoporous xerogels are obtained based on the ZrО₂–Y₂О₃–CeО₂ system with 5–8-nm particles and powders (after the heat treatment of xerogels at 600°C) with a coherent scattering region (CSR) size of 9 to 10 nm and S_sp = 96–156 m²/g. After calcination at 1400°C, the powders are transformed into tetragonal solid solutions with a CSR size of 65 nm in the synthesis by the coprecipitation method, and they are transformed into solid solutions with a CSR size of 84 nm with a high degree of tetragonality of c/a = 1.438–1.431 in the synthesis by the hydrothermal method.     

Synthesis and properties of binary spinels in a NiO–CuO–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>–Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> system

The conditions for the formation of a spinel structure from a NiO–CuO–Fe₂O₃–Cr₂O₃ oxide mixture using several technological approaches have been examined. Addition of KCl is accompanied with the formation of two spinel-like phases, whereas in the absence of KCl just one solid solution of nickel–copper ferrite–chromite with the structure of a cubic spinel is formed. At the temperature of thermal treatment of 900°C, the presence of an admixture phase of the delafossite (CuCrO₂) type was established. The conditions for the fabrication of samples containing two spinel phases (cubic and tetragonal) characterized with the most developed surface and manifesting = increased catalytic activity in the reaction of the decomposition of an organic substance by hydrogen peroxide have been formulated. The studied features of spinel synthesis can be of interest for developing materials with an active surface promising for application as adsorbents of catalysts and sensors.     

Synthesis and characterization of nanocomposites Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>–SiO<Subscript>2</Subscript>–chitosan based on lbl technology

In this paper, the apparent chain-like core-shell structure Fe₃O₄–SiO₂–chitosan nanoparticles was synthesized by two-step method with cross-linking action of glutaraldehyde based on layer-by-layer technology, the composite particles were characterized by IR, XRD, TEM, SEM, EDS and VSM analytical methods, and the synthesis conditions of the product were studied. The results indicated that the diameter of the composite particles is about 106.5 nm, the parietal layer of chitosan is 20 nm, and after crosslinking action of glutaraldehyde, chitosan uniformaly coated the outer surface of Fe₃O₄–SiO₂.     

Synthesis and research of nanopowders composed of 0.97ZrO<Subscript>2</Subscript> · 0.03La<Subscript>2</Subscript>O<Subscript>3</Subscript>

This work is devoted to the preparation of zirconium oxide nanopowders stabilized by lanthanum oxide using the method of codeposition in the presence of hydrogen peroxide. Nanopowders composed of 0.97ZrO₂ · 0.03La₂O₃ with particles of 10–20 nm are obtained. It is found that in the temperature interval of 500–1100°C the tetragonal and monoclinic points of the zirconium oxide phase crystallize at the same time.     

Effect of the relative volume of the conducting phase on the electroconductivity of glasses in the Na<Subscript>2</Subscript>O–B<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> system

The effect of the relative volume of the conducting phase on the electroconductivity of phase-separated glasses in the ternary system Na₂O–B₂O₃–SiO₂, whose compositions are on the same glass transition isotherm at 550°C, is investigated. It is demonstrated that the electroconductivity of phase-separated sodium borosilicate glasses does not depend on the relative volume of the conducting phase (within the limits from 0.3 to 0.9) under the condition that its composition invariable.     

Synthesis and Physicochemical Properties of Nanopowders and Ceramics in a CeO<Subscript>2</Subscript>–Gd<Subscript>2</Subscript>O<Subscript>3</Subscript> System

Nanopowders with a composition of (СeO₂)_1–x(Gd₂O₃)_x (x = 0.03, 0.05, 0.07, and 0.10) are synthesized by the coprecipitation method using cryotechnologies. The coherent scattering region (CSR) of the powders is 10–14 nm and the specific surface area is 70–81 m²/g. Based on the powders, ceramic nanosized materials with CRS of 64–71 nm are obtained. The dependence of the phase composition, microstructure, and electrical transport properties of the obtained samples on the Gd₂O₃ content is established. In a CeO₂–Gd₂O₃ system, a solid solution with the composition of (CeO₂)_0.90(Gd₂O₃)_0.10 has the highest ionic conductivity with the transfer number of ions of t_i = 0.74 at a temperature of 700°C. It is shown that ceramics of this composition can be used as a solid electrolyte of intermediate-temperature fuel cells due to their physicochemical characteristics.     

Bimetallic Pd–Cu/ZnO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and Pd–Cu/ZrO<Subscript>2</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts for methanol synthesis

Monometallic copper and bimetallic palladium-copper catalysts supported on ZnO–Al₂O₃ and ZrO₂–Al₂O₃ were prepared by conventional impregnation method and tested in methanol synthesis reaction under elevated pressure (3.5 MPa) in gradientless reactor at 220°C. The physicochemical properties of prepared catalytic systems were studied using BET, X-ray, TPR-H₂, TPD-NH₃ techniques. The promotion effect of palladium on catalytic activity and selectivity of copper supported catalyst in methanol synthesis reaction was proven. The highest activity of this system is explained by the Pd–Cu alloy formation.     

Migration processes in the glass forming melts of the Na<Subscript>2</Subscript>O–BaO–Ga<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> system

The specific conductivity and tracer of diffusion of sodium and barium ions have been determined and the values of the transport numbers and correlation factor for diffusion have been calculated in two melts of the Na₂O–BaO–Ga₂O₃–SiO₂ system.