Oxygen Storage Capacity, Specific Surface Area, and Pore-Size Distribution of Ceria–Zirconia Solid Solutions Directly Formed by Thermal Hydrolysis

The oxygen storage capacity (OSC) of CeO₂–ZrO₂ solid solutions that were directly formed as nanocrystals by thermal hydrolysis of acidic aqueous solutions of (NH₄)₂Ce(NO₃)₆ and ZrOCl₂ at 150°C increased from 94 μmol of O₂/g for pure CeO₂ to >400 μmol of O₂/g for compositions of CeO₂/ZrO₂ with molar ratios (C/Z) from 74.1/25.9 to 41.7/58.3 (maximum value of 431 μmol O₂/g was reached at the composition C/Z = 51.7/48.3) and then decreased with increased ZrO₂ content in the solid solutions. As compared with pure CeO₂, the CeO₂–ZrO₂ solid solutions that contained <84.8 mol% ZrO₂ maintained high specific surface area and large pore volume with nanosized pores (pore size at maximum pore volume) <10 nm in diameter after heat treatment at 700°C.     

Effect of the Presence of Ammonium Peroxodisulfate on the Direct Precipitation of Ceria and Ceria–Zirconia Solid Solutions from Acidic Aqueous Solutions

Direct precipitation of nanometer-sized particles of ceria–zirconia (CeO₂–ZrO₂) solid solutions with cubic and tetragonal structures was successfully attained from acidic aqueous solutions of cerium(III) nitrate (Ce(NO₃)₃) and zirconium oxychloride (ZrOCl₂) through the addition of ammonium peroxodisulfate ((NH₄)₂S₂O₈), because of promotion of the hydrolysis via the oxidation of Ce³⁺ ions, together with the simultaneous hydrolysis of ZrOCl₂ under hydrothermal conditions. Ultrafine CeO₂ particles also could be formed from relatively concentrated aqueous solutions of the same trivalent cerium salt in the presence of (NH₄)₂S₂O₈ via hydrolysis. The crystallite size and lattice strain of as-precipitated solid solutions varied, depending on the composition within the CeO₂–ZrO₂ system. Creation of a solid solution of ZrO₂ into a fluorite-type CeO₂ lattice clearly introduced lattice strain, as a consequence of the decreasing crystallite size. Both the direct precipitation process and the effectiveness of the presence of (NH₄)₂S₂O₈ for the synthesis of CeO₂–ZrO₂ solid solutions were discussed.     

Phase Equilibria in the Hafnia–Yttria–Lanthana System

The HfO₂–Y₂O₃–La₂O₃ system was studied in the wide range of temperatures (1250°–2800°C) and concentrations by methods of X-ray analysis at 20°C, petrography, differential thermal analysis in helium at temperatures to 2500°C, thermal analysis in air using a solar furnace at temperatures to 3000°C, and electron microprobe X-ray analysis. The complete phase diagram was constructed. The liquidus and solidus projections, crystallization paths for the alloys, isothermal (1250°, 1600°, and 1900°C) and polythermal sections are presented. The structure of the boundary binary systems defines the phase equilibria in the ternary system. No ternary compounds were found. Ternary solid-solution regions were determined based on constituent oxides and intermediate phases.     

1000°C Phase Relations and Superconductivity in the (Nd-Ce-Cu)-O Ternary System

The phase relations involving the 24 K n -type Nd_{2- x} Ce _x CuO₄ superconductor were investigated at 1000°C in air. The terminal solid solubility was confirmed to be x = 0.2. This solid solution is the only ternary phase in the Nd₂O₃–CeO₂–CuO diagram. A binary (1 − y )CeO₂– y NdO_1.5 solid solution exists out to y = 0.4. Phase diagrams for NdO_1.5–CeO₂–CuO (1000°C) and NdO_1.5–CeO₂ (900° to 1500°C) are presented.     

Subsolidus Phase Relations and Transparent Conductors in the Cadmium-Indium-Tin Oxide System

Subsolidus phase relations have been determined in the CdO–InO_1.5–SnO₂ system at 1175°C. A cubic-bixbyite solution In_{2−2 x} (Cd,Sn)_{2 x} O₃ (0 < x < 0.34), a cubic spinel solution (1− x )CdIn₂O₄– x Cd₂SnO₄ (0 < x < 0.75), and an orthorhombic-perovskite solution Cd_{1− x} Sn_{1− x} In_{2 x} O₃ (0 < x < 0.045) having the GdFeO₃ structure have been discovered. The CdO phase field exists over a small range of InO_1.5 (<3%) and SnO₂ (<1%). Orthorhombic Cd₂SnO₄ (Sr₂PbO₄ structure) and rutile SnO₂ appear to be point compounds with negligible solubility. The vertical section between spinel CdIn₂O₄ and orthorhombic Cd₂SnO₄ was determined between 900° and 1175°C. The spinel phase field (1− x )CdIn₂O₄– x Cd₂SnO₄ was found to extend between x = 0 and x = 0.75 at 1175°C or x = 0.78 at 900°C. All of the phases in this system appear to allow small excess quantities of the donors In and/or Sn (vs cation stoichiometry) which may be the source of the electrons that give these oxides their n-type character. The electrical and optical properties of bulk and thin-film specimens in this system are compared and contrasted with each other and the relative merits of each are assessed.     

Thermal Expansion Behavior of Titanium-Doped La(Sr)CrO3 Solid Oxide Fuel Cell Interconnects

La_0.8Sr_0.2Cr_0.9Ti_0.1O₃ perovskite has been designed as an interconnect material in high-temperature solid oxide fuel cells (SOFCs) because of its thermal expansion compatibility in both oxidizing and reducing atmospheres. La_0.8Sr_0.2Cr_0.9Ti_0.1O₃ shows a single phase with a hexagonal unit cell of a = 5.459(1) Å, c = 13.507(2) Å, Z = 6 and a space group of R -3 C . Average linear thermal expansion coefficients of this material in the temperature range from 50° to 1000°C were 10.4 × 10⁻⁶/°C in air, 10.5 × 10⁻⁶/°C under a He–H₂ atmosphere (oxygen partial pressure of 4 × 10⁻¹⁵ atm at 1000°C), and 10.9 × 10⁻⁶/°C in a H₂ atmosphere (oxygen partial pressure of 4 × 10⁻¹⁹ atm at 1000°C). La_0.8Sr_0.2Cr_0.9Ti_0.1O₃ perovskite with a linear thermal expansion in both oxidizing and reducing environments is a promising candidate material for an SOFC interconnect. However, there still remains an air-sintering problem to be solved in using this material as an SOFC interconnect.     

High-Temperature Phase Relations in the System Y2O3-Ta2O5

The phase relations for the system y₂o₃–Ta₂o₅ in the composition range 50 to 100 mol% Y₂O₃ have been studied by solid-state reactions at 1350°, 1500°, or 17000C and by thermal analyses up to the melting temperatures. Weberite-type orthorhombic phases (W2 phase, space group C222₁), fluorite-type cubic phases (F phase, space group Fm3m )and another orthorhombic phase (O phase, space group Cmmm )are found in the system. The W2 phase forms in 75 mol% Y₂O₃ under 17000C and O phase in 70 mol% Y₂O₃ up to 1700°C These phases seem to melt incongruently. The F phase forms in about 80 mol% Y₂O₃ and melts congruently at 2454° 3°C. Two eutectic points seem to exist at about 2220°C 90 mol% Y²O₃, and at about 1990°C, 62 mol% Y₂O₃. A Phase diagram including the above three phases were not identified with each other.     

In_2W_3O_(12)陶瓷的相变特性及其负热膨胀性能(英文)

以分析纯In2O3和WO3为原料,采用固相反应法制备In2W3O12陶瓷。利用X射线衍射仪、场发射扫描电子显微镜、热重分析仪、差示扫描量热仪和热机械分析仪对样品的物相组成、微观结构、相变和热膨胀特性进行了表征。结果表明:在900℃烧结6h可制备出纯的单斜相In2W3O12陶瓷,In2W3O12陶瓷断面晶粒均匀,平均尺寸为4～6μm。In2W3O12陶瓷在253.34℃发生单斜相到斜方相的相转变,单斜相的In2W3O12陶瓷显示正热膨胀,在27～249℃,其平均热膨胀系数为16.51×10-6℃-1,斜方相的In2W3O12陶瓷显示负热膨胀,在273～700℃,其平均热膨胀系数为-3.00×10-6℃-1。     

Fabrication of Transparent Yttria Ceramics by the Low-Temperature Synthesis of Yttrium Hydroxide

Thin flakes of yttrium hydroxide agglomerated in a manner resembling houses of cards with aging at 10°C. The agglomerate then dissociated into fine yttria particles with calcination at >800°C. The particle size of the calcined powder increased appreciably as the calcination temperature increased. The shrinkage curve indicated similar densification behavior among undoped yttria powders calcined at 800°–1000°C, despite considerable particle growth as the calcination temperature increased. Increasing the calcination temperature to >1000°C shifted the shrinkage curve appreciably to the high-temperature region. Sulfate-ion-doped yttria particles had round edges, irrespective of calcination temperature, in contrast to the sharp edges of the undoped yttria particles. A calcination temperature of <1000°C resulted in skeleton yttria particles, which exhibited poor sinterability. At a calcination temperature >1000°C, the skeleton particles dissociated into monodispersed particles that densified easily. When the calcination temperature was >1000°C and the average particle sizes were similar, the undoped and sulfate-ion-doped yttria showed similar densification rates. The transparency of the sintered yttria ceramics was dependent on both the calcination temperature and sulfate-ion doping: that is, sulfate-ion doping and calcining at 1100°C were both necessary conditions for the fabrication of a transparent body.     

Phase Relations and Volume Changes of Hafnia under High Pressure and High Temperature

Using multi-anvil high-pressure devices and synchrotron radiation, X-ray in situ observations of HfO₂ under high pressure and high temperature have been performed to investigate its phase relations and compression behavior. An orthorhombic phase (orthoI) is stable from 4 to 14.5 GPa below 1250°–1400°C and transforms to a tetragonal phase, which is one of the high-temperature forms of HfO₂, above these temperatures. Another orthorhombic phase (orthoII) with a cotunnite-type structure appears above 14.5 GPa. OrthoII is stable up to 1800°C at 21 GPa. OrthoII is quenchable to ambient conditions. The orthoI-to-orthoII transition is accompanied by ∼8 vol% decrease. The bulk moduli of orthoI and orthoII at room temperature are 220 and 312 GPa, respectively. This low compressibility of orthoII indicates that it is a potential candidate for very hard materials.     

Phase Composition and Compatibilities in the Bi-Sr-Ca-Cu Quaternary Oxide System at 800°C in Air

Subsolidus phase relations in the system (Bi-Sr-Ca-Cu)-O at 800°C were investigated via powder X-ray diffraction and electron probe microanalysis of solid-state reaction products. Two recently reported (Bi-Sr-Ca)-O phases were detected in quaternary assemlages and had the approximate cation stoichiometries of 9 11 5 and 825. The only truly quaternary compound detected is the superconducting phase with the cation stoichiometry 2212. Tie lines, tie triangles, and compatibility tetrahedra involving this phase and the 2201 superconducting phase were determined. Both superconducting compounds exhibit small but detectable Sr-to-Ca solubility and are Sr-deficient with respect to the "ideal" formulas.     

Phase Transformation in EB-PVD Yttria Partially Stabilized Zirconia Thermal Barrier Coatings during Annealing

Electron-beam physical-vapor-deposited thermal barrier coatings consisting of ZrO₂ stabilized by 7 wt% Y₂O₃ were investigated in regard to phase transformation after annealing. Free-standing ceramic layers were heat-treated in air, for up to 200 h, in the temperature range 1200°—1400°C and then analyzed by X-ray diffractometry. Based on information obtained from the {111} and {400} peaks, the phase composition and the Y₂O₃ content in the phases were calculated. At the start of transformation, small grains of a low-Y₂O₃ t phase and a c phase formed. After >30 h at 1300°C and at 1400°C, a mixture of a t phase deficient in Y₂O₃, an m phase, and a c phase formed after cooling, with the Y₂O₃ contents in the phases roughly predicted by the phase diagrams. The results of the present study are discussed here in detail and compared with data for plasma-sprayed coatings.     

Stable and Metastable Phase Relations in the System Alumina–Zirconia–Yttria

The Al₂O₃ZrO₂Y₂O₃ system was studied in the range of temperatures 1600°–2800°C by methods of X-ray analysis at 20°C, petrography, DTA in He at temperatures to 2500°C, thermal analysis in air using a solar furnace at temperatures to 3000°C, and electron microprobe X-ray analysis. The stable and metastable phase diagrams were constructed. The liquidus and solidus projections, crystallization paths for the alloys, and polythermal sections are presented in the article. The structure of the restricting systems defines the phase equilibria in the ternary system. No ternary compounds were found. The metastable phase relations were caused by the ambivalent behavior of Y₃Al₅O₁₂ during crystallization.     

Thermal Conductivity and Thermal Expansion Coefficients of the Lanthanum Rare-Earth-Element Zirconate System

To enhance the insulating properties of a thermal barrier coating, one has to focus on new materials with lower intrinsic thermal conductivity than established yttria-stabilized zirconia. Substances with pyrochlore structure were investigated. Starting from lanthanum zirconate, substitutions of the lanthanum by other trivalent rare-earth elements were made, and the thermal conductivity and the thermal expansion coefficient of the manufactured materials were measured. A complete substitution of the lanthanum led to increased thermal expansion coefficients, whereas the partial substitution did not show an appreciable effect. The thermal conductivities of the modified materials were lower than that of the pure lanthanum zirconate for temperatures <1000°C for all amounts and elements of substitution. A comparison of the observed values with calculated values of the thermal conductivities showed a relatively good agreement.     

CeO2−CoO Phase Diagram

Phase equilibria in the CeO₂−CoO system at temperatures above 1500°C were investigated. The microstructures and the phase compositions of the DTA (differential thermal analysis) samples and the quenched solid pellets were analyzed using SEM (scanning electron microscope), EDX (energy dispersive X-ray), and WDX (wavelength dispersive X-ray). A eutectic reaction was found at 1645 ± 5°C. The eutectic point was calculated to be at 82 ± 1.5 mol% CoO. The eutectic phases were the CeO₂-rich phase (containing <5 mol% CoO) and the CoO-rich phase (containing ∼0.5 mol% CeO₂). At 1580°C, the solubility of CoO in CeO₂ was ∼3 mol%.     

(Sm0.7Yb0.3)2Ce2O7陶瓷的热膨胀系数及热导率

以Sm2O3、Yb2O3和CeO2为原材料,采用固相反应法制备了(Sm0.7Yb0.3)2Ce2O7陶瓷材料,用X射线衍射(XRD分析了其相结构,采用扫描电子显微镜(SEM)和电子能谱(EDS)分析其显微组织和元素组成,用推杆膨胀法和激光脉冲法测试了其热膨胀系数和热导率.结果表明,所制备的(Sm0.7Yb0.3)2Ce2O7具有典型的萤石结构,其微观组织致密,晶界清晰.Yb3+离子较小的离子半径使其热膨胀系数低于Sm2Ce2O7,基质原子与取代原子之间质量及尺寸之间的差别,使其具有比Sm2Ce2O7更低的热导率,该材料有潜力用作新型热障涂层表面陶瓷层材料.     

Negative Thermal Expansion in (HfMg)(WO4)3

A single-phase material (HfMg)(WO₄)₃ with an orthorhombic structure, A₂ (WO₄)₃-type tungstate, has been successfully prepared for the first time by the calcination of HfO₂, MgO, and WO₃, substituting Hf⁴⁺ and Mg²⁺ for A³⁺ cations in A₂(WO₄)₃. The new material shows a negative thermal expansion coefficient of approximately −2 ppm/°C from room temperature to 800°C. The mechanism of negative thermal expansion is assumed to be the same as that of Sc₂(WO₄)₃.     

固-固相变储能材料的研究

研究了四氯合金属 ( )酸二正十八烷胺 ( n- C18H37NH3) 2 MCl4 ( M=Mn2 +、Cu2 +、Fe2 +、Cd2 + 、Ni2 + 、Zn2 + 和 Co2 + )和二氯二正十八烷胺合铜 ( ) ( n- C18H37NH2 ) 2 Cu Cl2 类化合物的合成、表征和固 -固相转变的研究 ,并测定了该类化合物的热分解反应动力学参数。在 35 0～ 390 K温度区间 ,该类化合物具有 80～ 1 0 0 k J/mol的固 -固摩尔相变焓 ,是一类具有开发前途的固 -固相变低温储能材料。     

Modeling of complex interfaces: Gadolinium‐doped ceria in contact with yttria‐stabilized zirconia

Gadolinium‐doped ceria (GDC) and yttria‐stabilized zirconia (YSZ) are well‐known electrolyte materials in solid oxide fuel cells (SOFCs). Although they can be used independently, it is common to find them in combination in SOFCs, where they are used as protective layers against the formation of secondary phases or electron conduction blockers. Despite their different optimum operating temperatures, it appears that oxygen conduction is not affected by their interface. However, the intrinsic mechanisms of oxygen diffusion at these interfaces still remain unclear. One of the main difficulties when modeling the contact between different materials, or indeed different particles of the same material, is caused by the structural complexity of these systems. If we wish to evaluate the properties of the materials, we first need to obtain a model that includes the main features of the GDC/YSZ interface, such as large‐scale defects or cation interdiffusion in the contiguous phase. Since the generation of such a mixed system is complicated, we show here how the “amorphization and recrystallization” strategy can help us to obtain realistic systems. In this, the first of our papers on the structure and properties of layered GDC/YSZ materials, we discuss the structural features of the grain boundary between GDC and YSZ obtained by molecular dynamics simulations.     

Y2-xLaxMo3O12陶瓷的制备及其热膨胀性能

以分析纯Y2O3、La2O3和MoO3为原料,采用固相反应法制备Y2–xLaxMo3O12(0≤x≤2.00)系列陶瓷。利用X射线衍射仪、场发射扫描电子显微镜、能谱仪、热重分析仪和热机械分析仪对样品的物相组成、微观结构、吸湿性和热膨胀特性进行了表征。结果表明:在750℃烧结10 h可制备得到Y2–xLaxMo3O12(0≤x≤2.00)系列陶瓷;Y2–xLaxMo3O12(0≤x≤2.00)陶瓷断面晶粒呈不规则多边形,为多孔结构。热重分析发现:Y2Mo3O12陶瓷易吸湿,掺入La后吸湿现象消失。在178～600℃测试温度范围内,随La掺入量增加,Y2–xLaxMo3O12(0≤x≤2.00)系列陶瓷样品的热膨胀系数呈增大趋势。