Yttria stabilized zirconia solid electrolyte surface modification with ZrO<Subscript>2</Subscript>, Y<Subscript>2</Subscript>O<Subscript>3</Subscript>, and ZrO<Subscript>2</Subscript> + 9 mol % Y<Subscript>2</Subscript>O<Subscript>3</Subscript> films

The surface of ceramic electrolyte ZrO₂ + 9 mol % Y₂O₃, hereinafter referred to as YSZ (abbreviated yttria stabilized zirconia), was modified with 0.1 to 0.2 μm oxide films of ZrO₂, Y₂O₃, and YSZ (same composition as substrate) by dip coating in alcohol solutions of the relevant salts and further annealing. The results of scanning electronic microscopy and X-ray diffraction evidence epitaxial film growth. By means of impedance spectroscopy at the temperatures of 500 to 600°C, the effect of YZS electrolyte surface modification with ZrO₂, Y₂O₃, and YSZ films to the polarization resistance of silver electrode was studied.     

Na2SO4 + NaCl molten salts corrosion mechanism of thermal barrier coatings used in ships

6–8 mass% Y₂O₃ stabilized ZrO₂ (6–8YSZ) thermal barrier coatings (TBCs) are widely applied to protect the hot ends of gas turbines in large navy ships. In this work, the 8YSZ TBCs were prepared by air plasma spraying technique, and their microstructure and phase composition were investigated. The hot corrosion mechanism of YSZ TBCs in molten salts consisting of 80% Na₂SO₄?+?20% NaCl at 900 °C was comprehensively analyzed. The results showed that the corrosion product Y₂(SO₄)₃ was formed due to the reaction between Na₂SO₄ media and the stabilizer Y₂O₃. As the result of the depletion of Y₂O₃ phase, the transformation from the tetragonal phase to monoclinic phase of ZrO₂ could not been totally inhibited, which consequently induced the 4–6 vol.% expansion and more cracks of YSZ TBCs. Meanwhile, the cracks could work as transfer paths for oxygen and molten salts. The kinetic analysis on hot corrosion also showed that more reaction products (from 2 to 8.1 mg cm^?1) were generated from 20 to 60 h due to more cracks generated by molten salts and oxygen infiltrating. More thermal grown oxides generated between ceramic layer, bonding layer and substrate, and the volume expansion caused by phase transition, increased the stresses in the coatings. Consequently, the peeling-off failure of 8YSZ TBCs could happen.

     

EPMA of interfaces applied to the solid oxide fuel cell

Chemical interactions at the phase boundaries of materials applied for the solid oxide fuel cell (SOFC) have been studied by EPMA. The chemical reactivity at the interface of La_y-xSr_xMnO₃/ZrO₂-Y₂O₃ is dependent on the stoichiometry (y) and the Sr content (x) of the perovskite. Typical reaction products (zirconates) and a diffusion zone in the ZrO₂–Y₂O₃ have been observed. The extension of cation release (Mn) is related to the increasing chemical activity of Mn oxide in the perovskite by the Sr substitution for La. The wettability of the metal/oxide interface in the anode cermet (Ni/ZrO₂–Y₂O₃) has been found to be influenced by chemical reactions resulting from the applied reducing atmosphere with high carbon activity. The disintegration of ZrO₂–Y₂O₃ in contact with molten Ni or Ni-Ti and Ni-Cr alloys leads to the redeposition of Y₂O₃-enriched oxides and also to Zr-rich intermetallic compounds and eutectics.     

(ZrO2)0.86(Sm2O3)0.14纳米粉体的水热法合成及其烧结体的电性能

以湿化学法制得Zr(OH)₄和Sm(OH)₃的共沉淀为前驱体, 在碱性介质中用水热法合成了(ZrO₂)_0.86(Sm₂O₃)_0.14及(ZrO₂)_0.88(Sm₂O₃)_0.12纳米粉体. 将纳米粉体在较低温度(1450 ℃)下烧结制得了致密的固体电解质陶瓷样品, 比通常高温固相反应法采用的烧结温度(＞1600 ℃)降低了150 ℃以上. XRD测定结果表明, (ZrO₂)_0.86(Sm₂O₃)_0.14纳米粉体及其烧结体均为立方相, 但(ZrO₂)_0.88(Sm₂O₃)_0.12纳米粉体为立方相, 它的烧结体为立方相和单斜相的混合相. 用交流阻抗谱法、氧浓差电池法及氧泵(氧的电化学透过)法研究了(ZrO₂)_0.86(Sm₂O₃)_0.14陶瓷样品在600～1000 ℃下的离子导电特性. 结果表明, 该陶瓷样品在600～1000 ℃下氧离子迁移数为1, 氧离子电导率的最大值为3.2×10^－2 S•cm^－1, 是一个优良的氧离子导体; 它的氧泵性能明显地优于YSZ.     

Total Oxidation of Propene and Toluene on Copper/Yttrium Doped Zirconia

The catalytic oxidation of propene and toluene has been investigated on pure ZrO₂, pure Y₂O₃, and ZrO₂ doped with 1, 5, and 10 mol % Y₂O₃ in the presence or absence of copper (0.5, 1, and 5 wt%). A synergetic effect has been detected since ZrO₂ and Y₂O₃ exhibit significantly lower activities than the mixed oxides. The higher surface areas, related to structural change from mononoclinic (ZrO₂) to tetragonal (ZrO₂–;;Y₂O₃), partly explained the higher activity of ZrO₂–;;Y₂O₃. However, it has been shown that the number of anionic vacancies, created by the substitution of Zr⁴⁺ by Y³⁺, in yttria-stabilized zirconia solids depends on the yttrium contents. Their effect on propene and toluene oxidation activity is significant. The anionic vacancies should induce better activity of the ZrO₂—5 mol % Y₂O₃ catalyst with or without copper, which presents the higher number of Zr³⁺ species. This support should favor the formation of CuO particles, which should be the most active catalytic sites in the studied reaction.     

Effect of Modifying Additives on the Sintering and Properties of SiC/SiC<Subscript>w</Subscript> Ceramic Composite Material

Spark plasma sintering and hot compaction methods were used to obtain experimental samples of a composite material of the SiC?SiC_w system with various modifying additives (AlN, B₄C, HfB₂, Y₂O₃, Al₂O₃, Si₃N₄). The effect of the modifying additives on the sintering process, physicomechanical, and thermal properties of the ceramic composite material was examined. The introduction of the modifying additives lowered the sintering temperature of silicon carbide produced by the hot compaction method by 200°C and that formed with spark plasma spark sintering by 300?450°C as compared with the sintering temperature of silicon carbide without additives.     

A study of conduction band edge states in complex oxides by X-ray absorption spectroscopy

Conduction band edge d-states are compared for complex oxides: (i) mixed tetravalent–trivalent ZrO₂–Y₂O₃ alloys, (ii) tetravalent Zr(Hf)O₂–TiO₂ alloys, and (iii) trivalent La scandate and aluminate. Low Y₂O₃ content cubic ZrO₂–Y₂O₃ alloys display two crystal-field split 4d-features in O K₁ spectra. Alloys with higher Y₂O₃ content, as well as Zr(Hf)O₂–TiO₂ alloys display increased d-state multiplicity. O K₁ spectra of perovskite-structured LaScO₃ and LaAlO₃ indicate Jahn–Teller d-state term-splittings with contributions from both trivalent atomic species.     

The influence of the method of addition of Al2O3 to 3YSZ material on its thermal and electrical properties

The properties of tetragonal yttria-stabilized zirconia composites with the small addition of alumina (Al₂O₃?Y₂O₃?ZrO₂ composite) obtained on two ways of synthesis were studied in terms of usability for anode materials in solid oxide fuel cell. Both methods were based on citric synthesis: in the first one, Al₂O₃ was coprecipitated with the tetragonal ZrO₂ in the form of citrate by citric acid, while in the second Al₂O₃ was impregnated in the form of aluminium nitrate precursor on tetragonal ZrO₂ matrix. The obtained materials were analysed by X-ray diffraction, dilatometry and impedance spectroscopy. The results of measurements show that regardless of synthesis method, the addition of Al₂O₃ influences the conductivity of samples by increasing their grain boundaries conductivity as an effect of removing of SiO₂ and decreasing of conductivity activation energy. The impregnation of Al₂O₃ on tetragonal ZrO₂ and sintering of this material above shrinking temperature cause, however, radical decrease of porosity of materials, which disqualifies these samples as anode materials. In the case of samples obtained by coprecipitation the significant decrease of porosity is not observed.     

Ceramic membranes modified with catalytic oxide films as ensembles of catalytic nanoreactors

Hybrid catalytic membrane systems have been produced by modifying porous ceramic membranes with metal oxide films. A two-layer cermet membrane consisting of a flexible stainless steel layer and an overlying porous TiO₂ ceramic layer and a ceramic titanium carbide membrane are examined. The membrane surfaces have been modified by the alkoxide method using colloidal organic solutions of metal complex precursors. Producing a tetragonal single-phase ZrO₂/Y₂O₃ coating on the cermet surface increases the abrasion strength of the ceramic layer. CO oxidation and the oxidative conversion of methane into synthesis gas and light hydrocarbons can be markedly intensified by modifying the membrane channels with Cu_0.03Ti_0.97O_2±δ and La + Ce/MgO catalysts, respectively. A method has been developed for depositing, onto the geometrical surface of a membrane, a film of the new single-phase oxide P_0.03Ti_0.97O_2±δ with an anatase structure and uniform pores of mean diameter 〈d〉 ～ 2 nm. Blocks of zeolite-like silicalite can be formed on the surface of the phosphorus-titanium oxide film. The resulting hybrid membrane is characterized by an anisotropic permeability depending on the flow direction. This property has an effect on conversion and selectivity in the nonoxidative dehydrogenation of methanol.     

Solid-state spreading of oxides: Morphology and conductivity of In2O3-based films

Spontaneous solid-state spreading of In₂O₃ over the surface of ceramic and single crystal substrates of Al₂O₃, ZrO₂(0.08Y₂O₃), Y₃Al₅O₁₂ and YAlO₃ at 1380 and 1500 °C has been investigated. The films structure, element and phase composition were studied by means of XRD and SEM/EDS. The phase compositions of all films correspond to that of powder In₂O₃. The most films are dense with monolithic “film/substrate” interface. AC-conductivity in the range 25–250 °C is reported. Depending on the substrate material, the films demonstrate a whole set of conductivity types (semi-conductive, metallic) and wide range of magnitudes (more than 3 orders).Thermodynamic and kinetic aspects of oxide spreading and subsequent crystallization on the surface of primary border film are discussed. It is shown, in particular, that the solid-state spreading is facilitated in systems with high chemical affinity (mutual solubility, formation of intermediate interface compounds). In the case of eutectic-type systems, heteroepitaxy of diffusant at substrate surface results in formation of dense films.     

Sintering behavior and thermal expansion of zirconia–titanium composites

The dilatometric and thermogravimetric methods were used to investigate the sintering conditions of 3Y–ZrO₂ and 3Y–ZrO₂–Ti composites. For the materials preparation, the nanometric zirconia stabilized by 3 mol% Y₂O₃ powder and micrometric titanium powder (3 and 10 vol%) were used. The green body samples were formed by slip casting method. The morphology of samples microstructures was determined by SEM observations. The stereological analysis of zirconia and zirconia–titanium composites was carried out using computer program. The density was measured using the Archimedes method. The hardness of sinters was also investigated. Addition of Ti into ZrO₂ influenced the sintering behavior and thermal expansion of obtained composites. The analysis of the sintering process and characteristic temperatures confirmed the increase of onset and final temperature of shrinkage with the increase in Ti content. The changes of the thermal expansion curves for the pure zirconia and 3Y–ZrO₂–Ti composites were the result of the αTi → βTi transformation and the transition temperature of the zirconia m → t transformation. The zirconia and composite samples were characterized by relative density about 98%, close to theoretical density. The slight growth of zirconia grains was observed.     

Composite solid electrolyte based on (Ca2+, Al3+)-infiltrated ZrO2(MgO) for direct sulfur determination in the liquid iron

Magnesium-stabilized zirconia [ZrO₂(MgO)] with calcium aluminate (CaO–Al₂O₃) ceramic composite electrolyte based on (calcium ion [Ca²⁺], aluminum ion [Al³⁺])-infiltrated zirconia-magnesia [ZrO₂(MgO)] porous backbone was prepared for direct sulfur ([S]) determination in the liquid iron. Effect of amylum content on the phase composition, microstructures and mechanical properties of the composite electrolyte was detected and correlated to the electrochemical performance. The results indicated that the ZrO₂(MgO)-(CaO–Al₂O₃) composite electrolyte simultaneously inherited the mechanical and electrochemical properties of ZrO₂(MgO), and unique physical and chemical properties of CaO–Al₂O₃. The compressive strength of the composite electrolyte reached above 250 MPa and the conductivity reached up to 0.003 S/cm^-, meeting the requirements of the sensor for the electrolyte. The assembled sensor could respond to sulfur activity and showed fine response characteristics. Among the tested compositions, the composite electrolyte with 6.0 wt% of amylum added in ZrO₂(MgO) porous backbone exhibited the best properties and was more suitable for application in sulfur determination.     

Electrophoretic deposition of Al2O3/ZrO2 layer with controllable thickness in ethanol medium

ZrO₂ toughened Al₂O₃ (Al₂O₃/ZrO₂) ceramic layers with required thickness were prepared by electrophoretic deposition (EPD) method using ethanol suspensions with stabilizing agent of polyethyleneimine (PEI) under constant-voltage mode in this paper. The deposition of Al₂O₃/ZrO₂ ceramic powders occurred on the titanium alloy cathode. A stable suspension with 1wt% PEI in ethanol at pH 5 was prepared in terms of the zeta potential and sedimentation of the suspension. The effects of the suspension concentration, applied voltage, deposition time and processing method of titanium alloy cathode on the coating thickness and morphology were investigated. The deposition layers on titanium alloys with smooth surfaces and thickness of 0.35?C1.2 mm could be obtained by adjusting the aforementioned parameters. In addition, after being sintered at 1500°C for 3 h in air atmosphere, ZrO₂ toughened Al₂O₃ ceramic layers became smooth and dense.     

Preparation of polyzirconoxane from zirconium oxychloride octahydrate and ethylene glycol as a precursor for zirconia ceramics

An Erratum has been published for this article in Applied Organometallic Chemistry 2001; 15(4):317. The preparation of polyzirconoxanes (EG‐PZO) was investigated by a one‐pot reaction of zirconium oxychloride octahydrate with ethylene glycol. Triethylamine was added dropwise into a mixture of zirconium oxychloride octahydrate, ethylene glycol and methanol to give EG‐PZO with a good spinnability and stability to self‐condensation. The ¹H NMR spectrum, IR spectrum, analytical data and expanded X‐ray absorption fine‐structure analysis indicated that EG‐PZO consisted of Zr < (OH)₂ > Zr linkages as a main chain with pendant 2‐hydroxyethoxy groups, chloro groups and water. The 3Y₂O₃–97ZrO₂ ceramic fibers were prepared by sintering the precursor fibers after the addition of <?tw=97%>Y(acac)₃ (acac = acetoacetate) to EG‐PZO. Copy‐<?tw>­right © 2000 John Wiley & Sons, Ltd.     

Preparation of Y2Ba4Cu7O15-δ Superconductor without High Oxygen Pressure

The synthesis of bulk Y₂Ba₄Cu₇O_15-δ superconductor at atmospheric oxygen pressure via solid state sintering is reported. Temperature ranging from 860 to 890 °C as well as time interval over 2 to 15 days were used to investigate the formation of the Y₂Ba₄Cu₇O_15-δ phase. A time-temperature profile characterizing the conditions for the preparation of Y₂Ba₄Cu₇O_15-δ phase suggests the optimal condition to be sintering at 890 °C for over 10 days. Detailed results of X-ray diffraction, electrical resistivity, iodometric titration and magnetization measurements are described.     

Mechanosynthesis of nanopowders of the proton-conducting electrolyte material Ba(Zr, Y)O3−δ

The formation of perovskite nanopowders of the common proton-conducting, electrolyte material Ba(Zr_1−xY_x)O_3−δ is demonstrated by room temperature mechanosynthesis for the compositional range x=0, 0.058 and 0.148. This is achieved with a planetary ball mill at 650 rpm in zirconia vials, starting from BaO₂ with ZrO₂, (ZrO₂)_0.97(Y₂O₃)_0.03 or (ZrO₂)_0.92(Y₂O₃)_0.08 precursors, respectively. Powder X-ray diffraction (XRD) reveals the formation of the perovskite phase in the early stages of milling with phase purity being achieved after milling times of 240 min for composition x=0.058 whereas 420 min is necessary for composition x=0.148. In contrast, traces of ZrO₂ are apparent in composition x=0 even after milling times of 420 min. The use of BaCO₃ as precursor does not allow the formation of the perovskite phase for any composition. The perovskite crystallites are spherical in shape with an average size determined from XRD of ca. 30 nm in agreement with transmission electron microscopy observations. FTIR spectra demonstrate that contamination levels of BaCO₃ in the mechanosynthesized powders are very low. The spherical shape and nanoscale of the crystallites allow densification levels that are highly competitive when compared to BaZrO₃-based materials formed by alternative synthesis techniques documented in the literature.     

Preparation, crystal structure and electrorheological performance of nano-sized particle materials containing ZrO2

A series of nano-sized particle materials containing ZrO₂ was prepared and their compositions were determined by elemental analysis and thermogravimetric analysis (TGA). The effect of particle size and crystal structure type (lattice and space group) on the ER performance of these materials was investigated by X-ray diffraction (XRD) analysis, Raman spectra, the particle size analysis and rheological measurement. Their electrorheological (ER) effects show that the ER activities of the ZrO₂ materials doped with rare earth (RE=Y, La, Ce, Gd, Tb), whose grain sizes were less than that of pure ZrO₂, were lower than that of pure ZrO₂, which belongs to the tetragonal crystal system. The ER activity of Y₂O₃-ZrO₂ is the strongest among all the RE-doped ZrO₂ materials. The ER activity of the tetragonal phase ZrO₂ is higher than that of the monoclinic phase ZrO₂.     

Synthesis of Er3+:Y3Al5O12 and its effects on the solar light photocatalytic activity of TiO2–ZrO2 composite

The Er³⁺:Y₃Al₅O₁₂ as an upconversion luminescence agent, which can transform visible light into ultraviolet light, was synthesized by nitrate?Ccitrate acid and calcined method. Then, a novel photocatalyst, Er³⁺:Y₃Al₅O₁₂/TiO₂?CZrO₂, was prepared using ultrasonic dispersion and liquid boiling method. The samples were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). In succession, the degradation process of organic dye was monitored by UV?CVis spectrum and ion chromatography for verifying the photocatalytic activity of Er³⁺:Y₃Al₅O₁₂/TiO₂?CZrO₂. The influences on its photocatalytic activity such as Ti/Zr molar ratio, heat-treated temperature, and time were studied. In addition, the influences of initial concentration, Er³⁺:Y₃Al₅O₁₂/TiO₂?CZrO₂ amount, solar light irradiation time, and organic dye category on the photocatalytic degradation efficiency were also investigated. It was found the photocatalytic activity of Er³⁺:Y₃Al₅O₁₂/TiO₂?CZrO₂ was superior to Er³⁺:Y₃Al₅O₁₂/TiO₂ and Er³⁺:Y₃Al₅O₁₂/ZrO₂. Therefore, the Er³⁺:Y₃Al₅O₁₂/TiO₂?CZrO₂ is a useful photocatalytic material for the wastewater treatment duo to efficient utilization of solar light.     

Basicity and catalytic activity of ZrO2?Y2O3 mixed oxides in the oxidation of cyclohexanol

Acidity/basicity of mixed oxides of ZrO₂−Y₂O₃ activated at various temperatures were determined by a titration method using Hammett indicators. The activity of these oxides towards liquid phase oxidation of cyclohexanol are also reported. The activity data parallel the basicity of these oxides.     

Two-Layer Nano-Oxide Composite Films on Fe-18Cr Alloys

A two-layer film composed of a reactive element (RE) oxide (ZrO₂, Y₂O₃, CeO₂, or La₂O₃) and aluminum oxide (Al₂O₃) was prepared on the surface of Fe-18Cr alloys by an electrochemical process combined with sintering. High-resolution field emission scanning electron microscopy (FE-SEM) was used to characterize the two-layer film, which showed nanostructure. SEM, EDS and mass gain measurement were used to study the oxidation resistance of the film on Fe-18Cr alloy. It is proved that this kind of film is effective in protecting the substrate from oxidation. The results also indicated that the two-layer film possesses superior oxidation resistance than a single Al₂O₃ film. The mechanisms accounting for such effects have been discussed.