Physicochemical properties of nanocrystalline composites based on ZrO<Subscript>2</Subscript>, Al<Subscript>2</Subscript>O<Subscript>3</Subscript>, and rare-earth oxides

Powder precursors have been prepared by means of the sol-gel technique and codeposition, and nanoceramics in the ZrO₂-Al₂O₃-rare-earth (RE) oxide system (RE = Ce, Sc, or Y) based on them have been obtained. Physicochemical properties of the resulting ceramic composites have been investigated. The energy model for oxygen-ionic transport processes in a solid solution based on ZrO₂, which relies on computer simulation procedure, has been proposed, and the structural, strength, and electrophysical characteristics of the solid solution have been calculated. The obtained materials are promising as high-melting electrochemical sensors in molten oxides.     

Phase separation in melts of the ZrO<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> system

The morphology of the quenched and slowly crystallized samples in the ZrO₂-Al₂O₃ system is investigated in the composition range 25–70 wt % ZrO₂. It is revealed that, irrespective of the cooling rate, the samples contain large baddeleyite (or corundum) crystals, eutectic mixtures, and characteristic regions of intergrown elongated baddeleyite and corundum grains with micron sizes. These regions have the same phase composition at any initial ratio between zirconium and aluminum oxides and at any cooling rates of the melt. A hypothesis is put forward that these regions are products of the decomposition of ZrO₂ · 2Al₂O₃ associates.     

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 of nickel catalysts supported on Zr-doped ordered mesoporous Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and their catalytic performance for low-temperature CO<Subscript>2</Subscript> reforming of CH<Subscript>4</Subscript>

A series of Zr-doped ordered mesoporous Al₂O₃ with various Zr contents were synthesized by evaporation-induced self-assembly strategy and the Ni-based catalysts supported on these Al₂O₃ materials were prepared by impregnation method. These catalysts with large specific surface area, big pore volume, uniform pore size possess excellent catalytic performance for the low-temperature carbon dioxide reforming of methane. The activities of these catalysts were tested in carbon dioxide reforming of methane reaction with temperature increasing from 500 to 650?°C and the stabilities of these catalysts were evaluated for long time reaction at 650?°C. It was found that when Zr/(Zr?+?Al) molar ratio?=?0.5%, the Ni/0.5ZrO₂–Al₂O₃ catalyst showed the highest activity, and exhibited superior stabilization compared to the Ni-based catalyst supported on traditional ordered mesoporous Al₂O₃. The “confinement effect” from mesoporous channels of alumina matrix is helpful to stabilize the Ni nanoparticles. As a promoter, Zr could stabilize the ordered mesoporous framework by reacting with Al₂O₃ to form ZrO₂–Al₂O₃ solid solution. Since ZrO₂ enhances the dissociation of carbon dioxide, more oxygen intermediates are given to remove the carbon formed during the reaction.     

ZrO<Subscript>2</Subscript>-and HfO<Subscript>2</Subscript>-based electrochemical sensors intended for investigation of glass-forming oxide melts

A theoretical analysis was made of the possible use of solid electrolytes with oxygen-ion conductivity for investigation of the relative basicity of silicate melts, and the optimum design of the electrochemical cell was chosen. Glasses in the SiO₂-Na₂O system were synthesized, and ceramic sensory membranes based on the cubic solid solution (ZrO₂)_0.92(Y₂O₃)_0.08 were prepared. An electrochemical cell based on ZrO₂ and HfO₂ and intended for investigation of glass-forming melts with the use of a platinum electrode and a reference electrode with oxygen-ion conductivity was designed and fabricated. The concentration dependence of the electromotive force of the electrochemical cells was examined for melts in the SiO₂-Na₂O system containing alkali oxide in different concentrations. A mathematical treatment of the obtained dependence of the electromotive force on the Na₂O concentration in this system was performed. The results obtained were used to calculate the relative oxygen ion activities and the corresponding pO values for alkali silicate melts under investigation.     

Fusion-Cast Refractories in the High-Zirconia Region of the ZrO<Subscript>2</Subscript> - SiO<Subscript>2</Subscript> - Cao System

The synthesis and properties of fused materials in the ZrO₂ - SiO₂ - CaO system (83.1 – 91.7% ZrO₂, 0.3 – 9.2% SiO₂, and 0.6 – 7.8% CaO) are reported. CaO-assisted stabilization of ZrO₂ to yield a cubic modification is reached at a SiO₂ concentration of ≤ 4.3%. The arc furnace technology developed can be used to fabricate crucibles, tubes, rings (of diameter 320 mm and height 310 mm), and other shaped components from high-zirconia refractory materials with more than 90% ZrO₂. __________ Translated from Novye Ogneupory, No. 3, pp. 37 – 40, March, 2005.     

Evaluating the ability of separation and adsorption of SO<Subscript>2</Subscript> by nano-CuO-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>/TiO<Subscript>2</Subscript> in high concentrations and moderate temperatures

Nano CuO-Fe₂O₃/TiO₂ adsorbents were made with different compositions of metal oxides using precipitation- desorption method. The adsorbents were applied for adsorption of SO₂ at high concentrations ranging from 10,000 to 30,000 ppm and temperatures between 523 and 627 K. Adsorption experiments were applied for adsorbents in a laboratory fixed bed adsorption column. The adsorption capacity was measured by calculating the area under the adsorption curve using the integral method. The results showed that temperature is the most affecting factor on the adsorption capacity. The highest adsorption capacity was obtained by using 17, 8 and 75 wt% of CuO, Fe₂O₃ and nano TiO₂, respectively. Characteristics of the best sorbent were determined by using Fe-SEM, XRD and nitrogen adsorption-desorption analyses.     

Infrared and raman characterization of V<Subscript>2</Subscript>O<Subscript>5</Subscript> on zirconia modified with WO<Subscript>3</Subscript> and activity for acid catalysis

Vanadium oxide supported on zirconia modified with WO₃ was prepared by adding Zr(OH)₄ powder into a mixed aqueous solution of ammonium metavanadate and ammonium metatungstate followed by drying and calcining at high temperatures. The characterization of prepared catalysts was performed by using FTIR, Raman, and XRD. In the case of calcination temperature at 773 K, for samples containing low loading V₂O₅ below 18 wt%, vanadium oxide was in a highly dispersed state, while for samples containing high loading V₂O₅ equal to or above 18 wt%, vanadium oxide was well crystallized due to the high V₂O₅ loading on the surface of ZrO₂. The ZrV₂O₇ compound was formed through the reaction of V₂O₅ and ZrO₂ at 873 K, and the compound decomposed into V₂O₅ and ZrO₂ at 1,073 K, these results were confirmed by FTIR and XRD. Catalytic tests for 2-propanol dehydration and cumene dealkylation have shown that the addition of WO₃ to V₂O₅/ZrO₂ enhanced both catalytic activity and acidity of V₂O₅-WO₃/ZrO₂ catalysts. The variations in catalytic activities for both reactions are roughly correlated with the changes of acidity.     

Investigation into the phase formation in the ZrO<Subscript>2</Subscript>-CeO<Subscript>2</Subscript> system

Nanopowders of solid solutions with different compositions are prepared in the zirconia-enriched region of the ZrO₂-CeO₂ system. The crystallization of these powders and the formation of the monoclinic, cubic, and tetragonal solid solutions of the composition (Zr_{1 – x} Ce_x)O₂ are investigated. It is found that the unit cell parameters of the solid solutions increase as the cerium content increases. This confirms the fact that cerium ions [r(Ce⁴⁺) = 1.11 ] substitute for zirconium ions [r(Zr⁴⁺) = 0.98 ] in these solid solutions. The average size of crystallites of the solid solutions under investigation increases from 5 to 60 nm in the temperature range 500–1200°C.Original Russian Text Copyright © 2005 by Fizika i Khimiya Stekla, Panova, Glushkova, Nefedova.     

Synthesis of Titanates with a Ramsdellite-Type Tunnel Structure Crystallizing in the Li<Subscript>2</Subscript>O-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-TiO<Subscript>2</Subscript> System in Different Gaseous Media

The ramsdellite-type phases crystallizing in the Li₂O-Fe₂O₃-TiO₂ system in the course of synthesis in gaseous media at different oxygen partial pressures are studied. Solid solutions based on the ramsdellite structure with the composition Li₂Ti_3?xFe _x O_{7 ? δ} (0 ≤ x ≤ 0.7) are prepared in an oxidizing medium (P_O2 = 1 atm) for the first time. Analysis of the results obtained by electron paramagnetic resonance and Mossbauer spectroscopy revealed that, in these solid solutions, all iron ions are in the oxidation state Fe⁺³.     

A structural study of Y<Subscript>2</Subscript>O<Subscript>3</Subscript>-partially stabilized zirconia ceramics

Partially stabilized zirconia ceramics ZrO₂ (Y₂O₃) of different structures and phase compositions are tested for thermal stability and thermal shock. The ceramics can be used as solid electrolytes in oxygen activity sensors for fluid heat transfer agents (lead).__________Translated from Novye Ogneupory, No. 10, pp. 56 – 59, October, 2004.     

Direct conversion of methane to synthesis gas using lattice oxygen of CeO2–Fe2O3 complex oxides

Three kinds of complex oxides oxygen carriers (CeO₂–Fe₂O₃, CeO₂–ZrO₂ and ZrO₂–Fe₂O₃) were prepared and tested for the gas–solid reaction with methane in the absence of gaseous oxidant. These oxides were prepared by co-precipitation method and characterized by means of XRD, H₂-TPR and Raman. The XRD measurement shows that Fe₂O₃ particles well disperse on ZrO₂ surface and Ce–Zr solid solution forms in CeO₂–ZrO₂ sample. For CeO₂–Fe₂O₃ sample, only a small part of Fe³⁺ has been incorporated into the ceria lattice to form solid solutions and the rest left on the surface of the oxides. Low reduction temperature and low lattice oxygen content are observed over ZrO₂–Fe₂O₃ and CeO₂–ZrO₂ samples, respectively by H₂-TPR experiments. On the other hand, CeO₂–Fe₂O₃ shows a rather high reduction peak ascribed to the consuming of H₂ by bulk CeO₂, indicating high lattice oxygen content in CeO₂–Fe₂O₃ complex oxides. The gas–solid reaction between methane and oxygen carriers are strongly affected by the reaction temperature and higher temperature is benefit to the methane oxidation. ZrO₂–Fe₂O₃ sample shows evident methane combustion during the reducing of Fe₂O₃, and then the methane conversion is strongly enhanced by the reduced Fe species through catalytic cracking of methane. CeO₂–ZrO₂ complex oxides present a high activity for methane oxidation due to the formation of Ce–Zr solid solution, however, the low synthesis gas selectivity due to the high density of surface defects on Ce–Zr–O surface could also be observed. The highly selective synthesis gas (with H₂/CO ratio of 2) can be obtained over CeO₂–Fe₂O₃ oxygen carrier through gas–solid reaction at 800 °C. It is proposed that the dispersed Fe₂O₃ and Ce–Fe solid solution interact to contribute to the generation of synthesis gas. The reduced oxygen carrier could be re-oxidized by air and restored its initial state. The CeO₂–Fe₂O₃ complex oxides maintained very high catalytic activity and structural stability in successive redox cycles. After a long period of successive redox cycles, there could be more solid solutions in the CeO₂–Fe₂O₃ oxygen carrier, and that may be responsible for its favorable successive redox cycles performance.     

Combustion of Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>/TiO<Subscript>2</Subscript>/Al thermit mixtures in steel tubes

Explored was the combustion of Fe₂O₃/TiO₂/Al thermit mixtures in steel tubes upon variation in green composition and with special emphasis on the dependence of combustion temperature T _c and burning velocity U on reaction heat Q. Special attention was given to incompleteness of combustion for compositions with low Q.     

Preparation and characterization of spindle-like Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> mesoporous nanoparticles

Magnetic spindle-like Fe₃O₄ mesoporous nanoparticles with a length of 200 nm and diameter of 60 nm were successfully synthesized by reducing the spindle-like α-Fe₂O₃ NPs which were prepared by forced hydrolysis method. The obtained samples were characterized by transmission electron microscopy, powder X-ray diffraction, attenuated total reflection fourier transform infrared spectroscopy, field emission scanning electron microscopy, vibrating sample magnetometer, and nitrogen adsorption-desorption analysis techniques. The results show that α-Fe₂O₃ phase transformed into Fe₃O₄ phase after annealing in hydrogen atmosphere at 350°C. The as-prepared spindle-like Fe₃O₄ mesoporous NPs possess high Brunauer-Emmett-Teller (BET) surface area up to ca. 7.9 m² g^-1. In addition, the Fe₃O₄ NPs present higher saturation magnetization (85.2 emu g^-1) and excellent magnetic response behaviors, which have great potential applications in magnetic separation technology.     

Oxygen permeability and structural stability of La<Subscript>0.6</Subscript>Sr<Subscript>0.4</Subscript>Co<Subscript>0.2</Subscript>Fe<Subscript>0.8</Subscript>O<Subscript>3−<Emphasis Type="Italic">δ</Emphasis></Subscript> membrane

La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ oxides were synthesized by citrate method and hydrothermal method. The oxides prepared by citrate method are perovskite type structure, while the oxides by hydrothermal method have a small amount of secondary phase in the powder. Pyrex glass seal and Ag melting seal provided reliable gas-tight sealing of disk type dense membrane in the range of operation temperature, but commercial ceramic binder could not be removed from the support tube without damage to the tube or membrane. Though the degree of gas tightness increases in the order of glass>Ag>ceramic binder, in the case of glass seal, the undesired spreading of glass leads to an interfacial reaction between it and the membrane and reduction of effective permeation area. The oxygen flux of La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ membrane increases with increasing temperature and decreasing thickness, and the oxygen permeation flux through 1.0 mm membrane exposed to flowing air (P _h =0.21 atm) and helium (P₁=0.037 atm) is ca. 0.33 ml/cm²·min at 950 °C. X-ray diffraction analysis for the membrane after permeation test over 160 h revealed that La₂O₃ and unknown compound were formed on the surface of membrane. The segregation compounds of surface elements formed on both surfaces of membrane irrespective of spreading of glass sealing material. This paper was presented at the 6 ^th Korea-China Workshop on Clean Energy Technology held at Busan, Korea, July 4–7, 2006.     

Synthesis and thermal behavior of Fe<Subscript>3</Subscript>O<Subscript>2</Subscript>(BO<Subscript>4</Subscript>) oxoborate

Iron oxoborate Fe₃O₂(BO₄) has been first produced in solid-phase chemical reactions. Its thermal behavior in the temperature range 20–900°C is studied with the use in-situ high-temperature powder X-ray diffraction. It is shown that Fe₃O₂(BO₄) begins decomposing with the formation of Fe₂O₃ in the temperature range 660–900°C. Thermal expansion is sharply anisotropic at room temperature (α_max/α_min = 7) and becomes more isotropic with an increase in the temperature (α_max/α_min = 1.2). The degree of oxidation of Fe³⁺ has been confirmed by Mössbauer spectroscopy (at a room temperature), and two nonequivalent positions in the structure have been detected, which are occupied by iron atoms with the octahedral environment of the oxygen atoms.     

Effect of surface modification of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles on the preparation of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/polystyrene composite particles via miniemulsion polymerization

Fe₃O₄ nanoparticles were modified by n-octadecyltrimethoxysilane (C18TMS) and 3-trimethoxysilylpropylmethacrylate (MPS). The modified Fe₃O₄ nanoparticles were used to prepare Fe₃O₄/polystyrene composite particles by miniemulsion polymerization. The effect of surface modification of Fe₃O₄ on the preparation of Fe₃O₄/polystyrene composite particles was investigated by transmission electron microscopy, Fourier transform infrared spectrophotometer (FT-IR), contact angle, and vibrating sample magnetometer (VSM). It was found that C18TMS modified Fe₃O₄ nanoparticles with high hydrophobic property lead to the negative effect on the preparation of the Fe₃O₄/polystyrene composite particles. The obtained composite particles exhibited asymmetric phase-separated structure and wide size distribution. Furthermore, un-encapsulated Fe₃O₄ were found in composite particles solution. MPS modified Fe₃O₄ nanoparticles showed poor hydrophobic properties and resulted in the obtained Fe₃O₄/polystyrene composite particles with regular morphology and narrow size distribution because the ended C=C of MPS on the surface of Fe₃O₄ nanoparticles could copolymerize with styrene which weakened the phase separation distinctly.     

Kinetics of the nanocrystal formation in the ZrO<Subscript>2</Subscript>-In<Subscript>2</Subscript>O<Subscript>3</Subscript>-H<Subscript>2</Subscript>O system under hydrothermal conditions

The hydrothermal synthesis of nanocrystals in the ZrO₂-In₂O₃-H₂O system is investigated kinetically. The presence of indium hydroxide results in an increase in the dehydration temperature of this system. The size of nanocrystals is equal to 20–30 nm and virtually does not depend on the temperature and time of hydrothermal treatment or on the type of crystalline modification of ZrO₂. An increase in the synthesis temperature leads to an increase in the fraction of the monoclinic zirconia modification.Original Russian Text Copyright © 2005 by Fizika i Khimiya Stekla, Artamonova, Almjasheva, Mittova, Lavrushina, Gusarov.     

Synthesis and properties of flux-cast refractories in the Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-MgO-B<Subscript>2</Subscript>O<Subscript>3</Subscript> system

Details are given of the synthesis and testing of flux-cast refractory materials in the alumina-rich region of the Al₂O₃-MgO-B₂O₃ system; XRD and petrography indicate that the main structure-forming phases are corundum and magnesian spinel. In subordinate amounts there are the boroaluminate 9Al₂O₃·2B₂O₃ and the previously unknown compound 4Al₂O₃·MgO·2B₂O₃, whose composition has been established by microprobe analysis. Corrosion tests showed that three-component systems containing magnesium and boron oxides at levels of 5–10% do not increase the corrosion resistance of refractories in molten sodium-calcium-silicate glass and electrovacuum borosilicate glass. __________ Translated from Novye Ogneupory, No. 3, pp. 161–163, March, 2008.     

Effect of TiO<Subscript>2</Subscript> loading on the activity of V/TiO<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> in the catalytic oxidehydrogenation of ethylbenzene with carbon dioxide

TiO₂-Al₂O₃ mixed oxides with different compositions ranging from 40wt-% to 95wt-% of TiO₂ were prepared by sol-gel method and impregnated with different amounts of VO _x . Supports and catalysts were characterized by X-ray diffraction (XRD), physisorption, temperature preprogrammed reduction (H₂-TPR), and ammonia temperature programmed desorption (NH₃-TPD). TiO₂ content in the support had obvious effect on the crystal structure, texture characteristic, acid property, and catalytic activity in dehydrogenation of ethylbenzene (EB) with carbon dioxide. The highest catalytic activity was acquired when the TiO₂ content was 50 wt-%.