Calcia Stabilized Ceria Doped Zirconia Nanocrystalline Ceramic

Calcia-stabilized cerium doped cubic zirconia nanocrystalline ceramic was synthesized using poly (vinyl alcohol) as a polymeric precursor. Obtained ceramic was pressed into a cylindrical pellet and sintered at 850 °C. The calcined and sintered ceramics were characterized by XRF, XRD, BET and SEM. The XRD pattern of the calcined ceramic shows that the ceramic has a face centered cubic crystal structure. The SEM results show that the grain size of the ceramic was increased after sintering. The BET surface areas were determined as 13.236 and 4.397 m² g^?1 for the calcined and sintered ceramics, respectively.     

添加Li_2O对YSZ电解质性能影响

8%（摩尔分数,下同）Y2O3稳定的ZrO2（8YSZ）是固体氧化物燃料电池（SOFC）中最常用的电解质材料,本文研究了在8YSZ基体中加入n%Li2O（n=0,0.25,0.50,1.00,1.50,1.70,2.00,2.50,3.00）后（记为n%Li2OYSZ）对其晶相结构、晶格常数、烧结性能、微观形貌、电导率及其作为SOFC电解质性能的影响。结果表明,Li2O中的Li＋可以固溶到YSZ的晶格内使其晶格常数减小;Li2O的加入量n〈1.70时,瓷体在烧结过程中不会发生相变。加入少量的Li2O（n=0.25,0.50）可以提高YSZ的致密度和电导率,0.25%Li2OYSZ和0.50%Li2OYSZ样品800℃的电导率分别高达0.030 2 S/cm和0.027 6 S/cm,分别是纯YSZ的1.35和1.24倍;当Li2O含量n≥1.00时,相同条件下烧结体致密度随Li2O加入量的增大而逐渐减小;当n≥1.70时,样品在烧结过程中虽然出现相变,但在高于1400℃可以烧结致密,并得到纯立方相YSZ。将1250℃烧结制得的0.25%Li2OYSZ和0.50%Li2OYSZ作为SOFC电解质的单电池,800℃时的开路电压高于1.0V,说明YSZ中没有出现电子电导,具有比纯YSZ为电解质的单电池更高的性能输出,表现出了良好的应用前景。     

Electrical Conductivity of Zirconia Stabilized with Scandia and Yttria

Electrical conductivity of zirconia stabilized with scandia and yttria (Sc₂O₃+Y₂O₃= 8 mol%) has been measured by the complex impedance method in the temperature range 573 to 1173 K. With increasing Sc₂O₃ concentration, electrical conductivity increases at temperatures above 640 K, but it decreases below this temperature. Electrical conductivity in the electrolytes examined is a result of two processes: an activation energy of 59 to 79 kJ·mol⁻¹ predominant at high temperatures and an activation energy of 109 to 125 kJ·mol⁻¹ predominant at low temperatures.     

钇稳定氧化锆的制造方法及应用

介绍了钇稳定氧化锆的性质、用途及各种制造工艺,包括预烧结法、机械混合法、包裹沉淀法、中和共沉淀法、加水分解法和水热法等.     

Fundamental Optical Absorption Edge of Sputter-Deposited Zirconia and Yttria

Zirconia and yttria films were sputter deposited onto unheated fused silica substrates using a metal target and rare gas-oxygen discharges. Double-beam spectrophotometry was used to measure the transmission and reflection as a function of incident photon energy, E , from which the absorption coefficient, α( E ), was calculated. An indirect interband transition at E _i= 4.70 eV and two direct interband transitions at E _g1= 5.17 eV and E _g2= 5.93 eV occur in monoclinic zirconia. Two direct interband transitions at E _g1= 5.07 eV and E _g2= 5.73 eV occur in cubic yttria. The absorption edge structure is modified when unusual phases, such as tetragonal zirconia, and zirconia and yttria with no longrange crystallographic order, are present.     

氧化钇稳定氧化锆的制备及电性能测试

氧化钇稳定氧化锆(yttria-stabilized zirconia,YSZ)是目前使用最多的电解质材料,探索了以YSZ纳米粉体为原料,采用固相法制备YSZ电解质薄片。采用X射线衍射(XRD)测试了它的微结构;采用交流四端子法测瓷体的电导率。实验表明,最佳烧结温度在1300℃,气孔含量少、晶粒均匀,电导率高,800℃时为0.08 S.m-1,是理想的高温电解质材料。     

Quantification of Yttria in Stabilized Zirconia by Raman Spectroscopy

The relationship between Y₂O₃ content in tetragonal and cubic ZrO₂ phases and the shift of the Raman band at ～645/cm was investigated. With increasing Y₂O₃ content, the 645/cm Raman band position decreases to lower Raman shift values. A fit of x = Y₂O₃ content in wt% and y = Raman band position in per cm, was found to be valid for low Y₂O₃‐stabilized t‐ZrO₂, t′′‐ZrO₂ transition, and fully stabilized c‐ZrO₂. Modeling the change in lattice parameters due to the incorporation of Y₂O₃ in ZrO₂ as obtained from Rietveld‐refined XRD data confirms that the peculiar sigmoidal form of the band shift with Y₂O₃ content is mainly due to a variation of the amount of oxygen vacancies. The resultant method is highly attractive in fields of Y₂O₃ determination in ZrO₂ materials where a fast, spatially resolved, and nondestructive analysis is required.     

Extra-Large Grains in the Silicon Nitride Ceramics Doped with Yttria and Hafnia

Microstructural development of silicon nitride doped with Y₂O₃ and HfO₂ was investigated to determine how extra-large grains develop during gas pressure sintering. Grains as long as 200 µm and a few tens of micrometers wide developed at high temperatures (>2173 K) in a fine-grained matrix containing a limited amount of liquid which had a poor propensity to spread. A small number of grains could grow quite large before their growth was halted by neighboring grains of comparable size.     

Microstructural Evolution during Sintering of Aluminum Nitride Ceramics Doped with Alumina and Yttria

The microstructural evolution of AlN sintered at >1950°C was studied in a specimen doped with 10 wt% Al₂O₃ and 5 wt% Y₂O₃. The constituent phases of the specimen were AlN, YAG, γ-AlON, and AlON polytypoids (compositional polytypes). Transmission and scanning electron microscopy revealed the microstructural characters: platelike 7AlN·Al₂O₃ first crystallized with concurrent formation of a residual liquid, then spherical AlN crystals formed. The liquid itself changed composition with the progress of the crystallization and reached the eutectic composition in the pseudobinary system AlN–YAG, and crystallized to an aggregate of AlN and YAG during cooling. As a product of the reaction of 7AlN·Al₂O₃, γ-AlON was formed.     

Analytical Electron Microscopy of Yttria Partitioning in the Yttria-Partially-Stabilized Zirconia Crystal

Yttria-partiaUy-stabilized zirconia was grown frcm the melt by the arc-image floating zone technique and annealed at 1700'C. The yttria concentration of the crystal was measured by analytical electron microscopy. The crystal, which contained 8.6 mol% YO_{1. 5}, consists of tetragonal and cubic phases with yttria concentrations of 3.9 and 9.7 mol% YO_1.5, respectively. There is a small difference between this result and the composition expected from the ZrO₂-Y₂O₃ phase diagram.     

Effect of Yttria on Interfacial Reactions Between Titanium Melt and Hot-Pressed Yttria/Zirconia Composites at 1700°C

Various Y₂O₃/ZrO₂ samples were fabricated by hot pressing, whereby Y₂O₃ was mutually dissolved or reacted with ZrO₂ as a solid solution or Zr₃Y₄O₁₂. Hot-pressed samples were allowed to react with Ti melt at 1700°C for 10 min in argon. Microstructural characterization was conducted using X-ray diffraction and analytical electron microscopy. The Y₂O₃/ZrO₂ samples became more stable with increasing Y₂O₃ because Y₂O₃ was hardly reacted and dissolved with Ti melt. The incorporation of more than 30 vol% Y₂O₃ could effectively suppress the reactions in the Ti side, where only a very small amount of α-Ti and β'-Ti was found. When ZrO₂ was dissolved into Ti on the zirconia side near the original interfaces, Y₂O₃ reprecipitated in the samples containing 30%–70 vol% Y₂O₃, because the solubility of Y₂O₃ in Ti was very low. In the region far from the original interface, α-Zr, Y₂O₃, and/or residual Zr₃Y₄O₁₂ were found in the samples containing more than 50 vol% Y₂O₃ and the amount of α-Zr decreased with increasing Y₂O₃.     

铝掺杂纳米氧化锆的合成与改性研究

氧化锆是一种具有特殊作用的氧化物并受到越来越多的关注。作者利用阳离子表面活性剂(CTAB)的辅助途径,通过前期的制备工艺成功实现了金属铝对纳米氧化锆的掺杂改性。借助XRD,TEM,EDS,Uv-vis以及N2吸附-脱附等方法对样品进行了表征分析;研究表明:金属铝离子能成功地进入氧化锆当中,掺杂改性后的氧化锆相对未掺杂的氧化锆有明显的蓝移,热稳定性显著提高,并且有一定的微孔结构。     

Experimental Assessment of Plasticity of Nanocrystalline 1.7 mol% Yttria Tetragonal Zirconia Polycrystals

High temperature mechanical behavior of nanocrystalline 1.7 mol% (3 wt%) yttria tetragonal zirconia polycrystals (nc-YTZP) was characterized by compression creep tests. The hot isostatically pressed nc-YTZP with mean grain size of 120 nm was subjected to grain growth to obtain grain sizes in the range of 120–310 nm. Direct measurements of the creep parameters were performed in the temperature range 1150°–1300°C and stress range 5–400 MPa. The strain rates at 1150°C ranged between 2 × 10⁻⁷ and 9 × 10⁻⁵ s⁻¹ when increasing the stress from 15 to 400 MPa. Values of the stress exponent, n =2.0±0.3, and the activation energy, Q =630±40 kJ/mol, were obtained for all test conditions. A value of the grain size exponent, p =1.5±0.3, was obtained at 1150°C in the stress range studied. Detailed microstructural observations revealed the absence of glassy phase at the grain boundaries. The creep parameters were compared with those from the literature, and the results were discussed in terms of the model recently developed by the authors, with a reasonable agreement.     

Composites Derived from Zirconia Nanopowders Stabilized with Yttria and Containing Alumina Particles Incorporated Physically or Chemically

Two methods of incorporating Al₂O₃ inclusions into a polycrystalline matrix of tetragonal zirconia stabilized with yttria (3Y-TZP) were used, and their influence on the microstructure and properties of TZP/Al₂O₃ composites has been studied. The first method consisted in the physical mixing of the component powders by means of intensive milling. The second method utilized the possibilities of the coprecipitation method of chemically homogeneous deposits followed by their calcination. An aqueous solution of zirconium, yttrium, and aluminum salts was used. Green compacts were shaped by cold isostatic pressing under a pressure of 300 MPa, and then they were sintered under no pressure for 2 h at 1500–1650°C in air. The powders were also consolidated using hot pressing under 25 MPa in argon and under the same heating cycle as in the case of pressureless sintering. The composites studied contained from 0 to 20 vol % of alumina inclusions, whose sizes depended on the powder preparation method. The morphology and phase composition of the powders and the microstructure of the green compacts and sintered materials were characterized. Bending strength, fracture toughness, and wear were measured. The coprecipitation method enabled us to produce composites that contained nanosize alumina inclusions. The inclusions derived from this method were much smaller than those derived from the physical mixing method (d ₅₀ = 0.21 ± 0.01 and 0.32 ± 0.2 µm, respectively). The reduction in the alumina inclusion size nearly to the nanometer level did not increase the fracture strength and fracture toughness of the composites. The density of the composites and the size of microstructural flaws were the critical factors controlling the fracture strength. The highest strength value, namely, 1.7 ± 0.2 GPa, was measured for the TZP containing 5 vol % of alumina particles incorporated by means of the physical mixing process. The 20 vol % content of alumina particles increased the wear resistance of the 3Y-TZP materials by 51 and 41% for the physical and chemical methods of inclusion incorporation, respectively.Original English Text Copyright © 2005 by Fizika i Khimiya Stekla, W. Pyda, Brzezinska-Miecznik, Bucko, Pedzich, A. Pyda.This article was submitted by the authors in English.     

Impedance Spectroscopy and Dielectric Properties of Flash Versus Conventionally Sintered Yttria‐Doped Zirconia Electroceramics Viewed at the Microstructural Level

The defect chemistry‐modulated dielectric properties of dense yttria‐doped zirconia ceramics prepared by conventional sintering (at 1350°C–1500°C) and electric field‐assisted flash sintering (55 V/cm at 900°C) were studied by impedance spectroscopy. While the bulk dielectric properties from both sets of samples showed only small and insignificant changes in conductivity and permittivity, respectively, a huge increase of these properties was measured for the grain boundaries in the flash sintered specimens. A close analysis of these results suggests that flash sintering reduced grain‐boundary thickness (by about 30%), while increasing the concentration of oxygen vacancies near these interfaces (by about 49%). The underlying mechanism proposed is electric field‐assisted generation and accommodation of defects in the space‐charge layers adjacent to the grain surface. The changes in measured permittivity are attributed to the boundary thickness effect on capacitance, while conductivity involved variations in its defect density‐dependent intrinsic value, accounting for changes also observed in grain‐boundary relaxation frequencies. Therefore, in terms of modifications to the specific dielectric properties of these materials, the overall consequence of flash sintering was to considerably lower the semi‐blocking character of the grain boundaries.     

Low-Temperature Sintering and Mechanical Property Evaluation of Nanocrystalline 8 mol% Yttria Fully Stabilized Zirconia

Fully stabilized zirconia containing 8 mol% yttria (8Y-FSZ) in nanocrystalline form has been synthesized by the coprecipitation method. The formation of an easily filterable hydroxide is facilitated by the addition of ammonium sulfate and polyethylene glycol during precipitation. The precipitate is then calcined to produce nanocrystalline powder. Using this powder, it has been possible to obtain a sintering density of more than 95% at a temperature as low as 1150°C by following a conventional sintering schedule. Adoption of a two-stage sintering schedule, in which heat treatment of the powder compact has been carried out initially to a high temperature, followed by a long holding at a lower temperature, resulted in further lowering of the sintering temperature. Hardness and toughness values have been found to be dependent on the microstructure in low-temperature-sintered samples.     

Contact Properties of Yttria Partially Stabilized Zirconia Up To 1000°C

The mechanical properties of a commercial polycrystalline yttria partially stabilized zirconia (Y-PSZ) are evaluated as a function of temperature up to the onset of creep. Hertzian indentation tests in combination with finite element modeling (FEM) are used to determine its elastic–plastic properties up to 1000°C. Vickers hardness measurements are also performed at selected temperatures to complement the mechanical characterization. In addition, critical loads for radial and ring crack initiation are determined from postmortem inspection of test surfaces. The results reveal a dramatic hardening and strengthening of Y-PSZ as the temperature decreases below 600°C, effects that are attributed to the tetragonal-to-monoclinic ( t → m ) transformation. Above the transformation temperature, the material strength continues to decrease with increasing temperature but at a lower rate, an effect that is explained by a gradual grain boundary degradation.