Industrial growth of yttria-stabilized cubic zirconia crystals by skull melting process

We reported the development of a Ф100 cm growth apparatus for skull melting growth of yttria-stabilized cubic zirconia(YSZ) crystals and more than 1000 kg crystals have been grown in the furnace each time.The growth conditions were optimized and the structure of the as-grown crystals was characterized by X-ray diffraction.The transmittance of 15 mol.% yttria-stabilized cubic zirconia crystal was nearly 80% in the range of 400–1600 nm.The refractive indices were measured and fitted the Sellmeier equation whi...

SURFACE ELECTRICAL PROPERTIES AND STRUCTURE OF YTTRIA-PARTIALLY-STABILIZED ZIRCONIA IMPLANTED WITH ^(57) Fe IONS

Sintered plates of 5mol% yttria-partially-stabilized zirconia have been implanted at room temperature with 5 ×1015to 2 ×1017 Fe+ ions/cm2 at 140 KeV. Electrical measurement, Rutherford backscattering spec-troscopy(RBS), Raman spectroscopy and X-ray photoelec-tron spectroscopy(XPS) have been used to study the surface electrical properties and the structure of the implanted layer before and after thermal annealing treatment in N2.

Preparation of alumina-doped yttria-stabilized zirconia nanopowders by microwave-assisted peroxyl-complex coprecipitation

Alumina-doped yttria-stabilized zirconia (ADYSZ) nanopowders were prepared by microwave-assisted peroxyl-complex coprecipitation (MAPCC) using ZrOCl2·8H2O, Y2O3 and AlCl3·6H2O as starting materials, NH3·H2O as precipitant and H2O2 as complexant. The effects of adding H2O2 and microwave drying on the preparation and properties of ADYSZ were investigated. The precursors and nanopowders were studied by EDX, XRD, SEM and TEM techniques. The results show that the uniformity of component distribution within ADYSZ nanopowders is improved by adding appropriate dosage of H2O2. Complexing reaction between H2O2 and Zr4+ ion restrains the hydrolyzation and precipitation of Zr4+ ion. With the addition of H2O2, Al3+, Y3+ and Zr4+ ions can be precipitated synchronously in a relatively narrow range of pH value. H2O2 also improves the filterability of the wet precipitate. The highly hydrophilic precipitates can be quickly and effectively separated from aqueous solution. During microwave drying process, the moisture of wet precursors is selectively heated. Quick expansion of steam vapor within the wet colloidal particles causes the aggregations burst into numerous tiny lumps. Compared with oven drying, microwave drying can not only shorten drying time but also reduce aggregation intensity of the resultant ADYSZ nanopowders.

A review of C_1 chemistry synthesis using yttrium-stabilized zirconia catalyst

C1 chemistry based on synthesis gas, methane, and carbon dioxide offers many routes to industrial chemicals. The reactions related to the synthesis of gas can be classified into direct and indirect approach for making such products, such as acetic acid, dimethyl ether, and alcohol. Catalytic syngas processing is currently done at high temperatures and pressures, conditions that could be unfavorable for the life of the catalyst. Another issue of C1 chemistry is related to the methane-initiated process. It has been known that direct methane conversions are still suffering from low yields and selectivity of products resulting in unprofitable ways to produce products, such as higher hydrocarbons, methanol, and so on. However, many experts and researchers are still trying to find the best method to overcome these barriers, for example, by finding the best catalyst to reduce the high-energy barrier of the reactions and conduct only selective catalyst-surface reactions. The appli- cation of Yttria-Stabilized Zirconia （YSZ） and its combination with other metals for catalyzing purposes are increasing. The existence of an interesting site that acts as oxygen store could be the main reason for it. Moreover, formation of intermediate species on the surface of YSZ also contributes significantly in increasing the production of some specific products. Understanding the phenomena happening inside could be necessary. In this article, the use of YSZ for some C1 chemistry reactions was discussed and reviewed.

Resistive Switching in Stabilized Zirconia Films Studied by Conductive Atomic Force Microscopy

We have applied Conductive Atomic Force Microscopy (CAFM) to study the microscopic mechanism of resistive switching in the ultrathin (3 - 5 nm) yttria stabilized zirconia (YSZ) films. Using CAFM, we were able to trace the growth of the individual conductive filaments, which are considered now to be responsible for the resistive switching effect in the transition metal oxides. The growth of the filaments has been proven to be initiated by the defects in the film material including the ones, which are the concentrators of the electric field, in particular, by the roughness (hillocks) of the film/substrate interface. The electron transport via individual filaments has been studied. Besides the butterfly-type hysteresis in the current-voltage (I-V) curves of the probe- to-sample contact typical for the bipolar resistive switching, we have observed the I-V curves with resonant peaks attributed to the resonant electron tunneling via the localized electron states in the filaments.

Composite ceramics thermal barrier coatings of yttria stabilized zirconia for aero-engines

Composite ceramics thermal barrier coatings(TBCs) are widely used in the aero-engines field due to their excellent thermal insulation, which improves the service life and durability of the inherent hot components. The most typical, successful and widely used TBCs material is yttria stabilized zirconia(YSZ). In this paper, fabrication methods, coating structures, materials, failure mechanism and major challenges of YSZ TBCs are introduced and reviewed. The research tendency is put forward as well. This review provides a good understanding of the YSZ TBCs and inspires researchers to discover versatile ideas to improve the TBCs systems.

Microstructure and thermal cycling behavior of nanostructured yttria partially stabilized zirconia (YSZ) thermal barrier coatings

Nanostructured yttria partially stabilized zirconia(YSZ) coatings were prepared by atmospheric plasma spraying(APS) using the conglomeration made by zirconia nanoparticle as the raw materials.The measurement methods,which consisted of scanning electron microscopy(SEM),transmission electron microscopy(TEM) and thermal cycling behavior,were used to character the morphology,composition and thermal oxidation behavior of the powder and the coatings.From the results,it was shown that the YSZ coating was the laminar structure,and the elements distribution in the bond and top coat were well-proportioned.The YSZ coatings were composed of fine grains with size ranging from 30 to 110 nm.The laminar layers with columnar grains were surrounded with unmelted parts of the nanostructured powder and some equiaxed grains.In the as-sprayed nanostructured zirconia coatings,there existed pores that were less than 1 μm.The cracks were observed on some of the crystal border.The cyclic oxidation experiment showed that the nanostructured coating had longer thermal cycling lifetime to exhibit the promising thermal cyclic oxidation resistance.The failure of the nanostructured TBC was similar to the failure of conventional APS TBC.

Densification behavior of yttria-stabilized zirconia powders for solid oxide fuel cell electrolytes

Yttria-stabilized zirconia(YSZ) is the most common electrolyte material for solid oxide fuel cells. Herein, we conducted a comparative study on the densification behavior of three different kinds of commercial 8 mol% YSZ powders:(i) TZ-8Y(Tosoh, Japan),(ii) MELox 8Y(MEL Chemicals, UK), and(iii) YSZ-HT(Huatsing Power, China). The comparison was made on both the selfsupporting pellets and thin-film electrolytes coated onto a NiO–YSZ anode support. For the pellets, MELox 8Y showed the highest densification at lower sintering temperatures with 93% and 96% of the theoretical density at 1250 and 1300 ℃, respectively. Although YSZ-HT showed a higher sintering rate than TZ-8Y, a sintering temperature of 1350 ℃ was required for both the powders to reach 95% of the theoretical density. For the thin-film electrolytes, on the other hand, YSZ-HT showed the highest sintering rate with a dense microstructure at a co-sintering temperature of 1250 ℃. Our results indicate that besides the average particle size, other factors such as particle size distribution and post-processing play a significant role in determining the sintering rate and densification behavior of the YSZ powders. Additionally, a close match in the sintering shrinkage of the electrolyte and anode support is important for facilitating the densification of the thin-film electrolytes.

Aging performances for resisting low-temperature of three dental yttria-stabilized zirconia ceramic core materials

Background The low-temperature resistance aging performance of Yttria-stabilized tetragonal zirconia polycrystal （Y-TZP） is the key effective factor that influences the long-term success rate of prosthesis. The objective of this study was to test and compare the aging performances for resisting low temperature of Lava Frame, Cercon Smart, and Upcera Yttria-stabilized zirconia core materials, via analyzing the micro and the crystal phases of the materials, and measure the three-point bending strength and the fracture toughness. Methods The three zirconia green bodies were prepared as 60 test samples for three-point bending strength and as 60 test samples for fracture toughness. The test samples for three-point bending strength and fracture toughness were assigned to five groups and were treated respectively for 0, 5, 10, 15, and 20 hours to observe the micro and the crystal phases of the test samples. Then the three-point bending strength and fracture toughness were tested by X-ray diffraction （XRD）. Results The m phase content of Lava Frame was raised from 7.70% to 13.01%; the m phase content of Cercon Smart was raised from 4.95% to 8.53%; and Lava Frame is raised from 10.84% to 35.18%. The three-point bending strengths of the three zirconia core materials were higher than 1100 MPa and the fracture toughness was higher than 3 MPa.m^1/2. The three-point bending strength and the fracture toughness of Upcra zirconia decreased the most, followed by Lava Frame, and then by Cercon Smart. Conclusion The aging resistance sequences of the three zirconia core materials are, from strong to weak, Cercon Smart, Lava Frame, and Upcera.

Theoretical Aspects on Doped-Zirconia for Solid Oxide Fuel Cells:from Structure to Conductivity

Solid oxide fuel cells(SOFCs)are regarded to be a key clean energy system to convert chemical energy(e.g.H_(2) and O_(2))into electrical energy with high efficiency,low carbon footprint,and fuel flexibility.The electrolyte,typically doped zirconia,is the"state of the heart"of the fuel cell technologies,determining the performance and the operating temperature of the overall cells.Yttria stabilized zirconia(YSZ)have been widely used in SOFC due to its excellent oxide ion conductivity at high temperature.The composition and temperature dependence of the conductivity has been hotly studied in experiment and,more recently,by theoretical simulations.The characterization of the atomic structure for the mixed oxide system with different compositions is the key for elucidating the conductivity behavior,which,however,is of great challenge to both experiment and theory.This review presents recent theoretical progress on the structure and conductivity of YSZ electrolyte.We compare different theoretical methods and their results,outlining the merits and deficiencies of the methods.We highlight the recent results achieved by using stochastic surface walking global optimization with global neural network potential(SSW-NN)method,which appear to agree with available experimental data.The advent of machine-learning atomic simulation provides an affordable,efficient and accurate way to understand the complex material phenomena as encountered in solid electrolyte.The future research directions for design better electrolytes are also discussed.

Mechanical Behaviors of ZrO_2-Al_2O_3 Ceramic Composites with Y_2O_3 as Stabilizer

The ZrO2-Al2O3 ceramic composites were prepared by appropriate techniques with commercial ZrO2 and Al2O3 powders as raw materials and Y2O3 as stabilizer. The results indicate that with the introduction of Al2O3 into the ZrO2 matrix where the quantity of additive Y2O3 is 3.5% (mole fraction), the growth of ZrO2 grains is efficiently inhibited, which helps the ZrO2 grains exist in a metastable tetragonal manner; thus higher strength and toughness are acquired. When the content of alumina is 20% (mass fraction), the bending strength and fracture toughness of the composites are 676.7 MPa and 10 MPa·m1/2 respectively, the mechanical behaviors are close to those prepared with ZrO2 and Al2O3 powders synthesized through wet chemical approach. The mechanical behaviors of the composites are well improved owing to the dispersion toughening of alumina grains and phase transformation toughening of zirconia grains.

Electrical property of 8-mol% yttria-stabilized zirconia electrolyte by spark-plasma sintering

Spark-plasma sintering (SPS) process was used to sinter ZrO2 (8Y) powders, and a relative density of 99% has been reached at a low temperature (1350°C) and short dwelling time (10 min) compared to the conventional sintered identical samples (1450°C 4 h)(CS). By the X-ray diffraction (XRD) patterns, the microstructure of the SPS pellet and CS pellet are both indexed by the cubic unit cell (Fm3m). The finer crystallite size (D111) of the SPS pellet is 154 nm and D111 of the CS pellet is more than 1 μm. The AC impedance spectroscopy shows that the ionic conductivity of SPS pellet is different from that of CS pellet. The activation energy for the SPS ceramics, estimated from the slope in the range of 400–800°C, was 91 kJ mol?1, which is in good agreement with CS pellet (96 kJ mol?1), indicating that the conduction mechanism in SPS ceramics is similar to that in CS ceramics.

Investigation on the thermo-chemical reaction mechanism between yttria-stabilized zirconia （YSZ） and calciummagnesium-alumino-silicate （CMAS）

Thermal barrier coatings （TBCs） with Y2O3-stabilized ZrO2 （YSZ） top coat play a very important role in advanced turbine blades by considerably increasing the engine efficiency and improving the performance of highly loaded blades. However, at high temperatures, environment factors result in the failure of TBCs. The influence of calcium-magnesium-alumino-silicate （CMAS） is one of environment factors. Although thermo-physical effect is being paid attention to, the thermo-chemical reaction becomes the hot-spot in the research area of TBCs affected by CMAS. In this paper, traditional twolayered structured TBCs were prepared by electron beam physical vapor deposition （EB- PVD） as the object of study. TBCs coated with CMAS were heated at 1240℃ for 3 h. Additionally, 15 wt.% simulated molten CMAS powder and YSZ powder were mixed and heated at 1240℃ or 1350℃ for 48 h. SEM and EDS were adopted to detect morphology and elements distribution. According to XRD and TEM results, it was revealed that CMAS react with YSZ at high temperature and form ZrSiO4, Ca0.2Zr0.8O1.8 and Ca0.15Zr0.85O1.85 after reaction, as a result, leading to the failure of TBCs and decreasing the TBC lifetime.

锆基陶瓷热障涂层的腐蚀研究进展

近年来随着航空与航海工业的迅速发展,具有耐高温、长寿命、耐腐蚀等优势的发动机叶片成为开发新一代航空发动机和涡轮发动机的重要一环。热障涂层(TBCs)作为常用的热防护技术,一方面可为发动机叶片部分金属基底提供隔热保护,使其免受高温气体的影响;但另一方面,更高的发动机工作温度使得叶片及其表面TBCs遭受严重的环境沉积物腐蚀,造成过早失效,腐蚀类型主要有热腐蚀、CMAS腐蚀、熔盐腐蚀等。腐蚀已成为限制TBCs工作温度和服役寿命的难题,抗腐蚀防护是目前TBCs领域研究的重点。本文首先简述了以氧化钇稳定氧化锆陶瓷(YSZ)为主的热障涂层材料的主要特性,再简述了TBCs的不同腐蚀的反应机理,重点从涂层的微观结构设计、梯度涂层的设计、涂层成分改性及掺杂改性等方面与涂层腐蚀过程之间的影响关系出发,阐述了TBCs改性方法与涂层腐蚀的特点。提出未来涂层改进与防护的几种方法,最后对TBCs的腐蚀防护发展方向进行了展望。

可用于氧气传感器的新型高离子电导YSZ薄膜制备方法

基于微机电系统的氧化钇稳定氧化锆(YSZ)薄膜氧气传感器因其小型化、集成化优势而成为新一代氧气传感器的最佳技术路线.集成化小型化的关键在于获取工作温度低,离子电导率高的YSZ薄膜.本工作探究了脉冲激光沉积技术在降低YSZ薄膜工作温度和提高其离子电导率方面的应用;通过在高真空下采用脉冲激光沉积技术,多次沉积与原位氧退火交替实施获取了厚度约为200 nm的YSZ薄膜,分析了沉积与退火温度对薄膜结构、成分、电学性能和氧气气敏性能的影响.此外,本文还验证了氧离子在氧空位中传输是薄膜的主要传导机制,且具有较低的氧离子激活能0.227 eV,最后进行了氧气敏感测试.结果表明:采用PLD法可将YSZ薄膜的工作温度从1073 K降低至873 K,这为基于MEMS的微型YSZ薄膜氧气传感器的研发进行了有效探索.

MOCVD技术制备In_(2)O_(3)紫外光电探测器研究

采用金属有机化学气相沉积(MOCVD)方法分别在蓝宝石、氧化钇稳定氧化锆(YSZ)和蓝宝石上p-GaN衬底上生长In_(2)O_(3)薄膜,生长温度为600℃。利用高分辨X射线衍射仪(HRXRD)、原子力显微镜(AFM)、X射线光电子能谱(XPS)、霍尔系统对3种薄膜进行了表征,结果表明YSZ基In_(2)O_(3)薄膜的最小半峰宽(FWHM)为0.23°,表面粗糙度为1.99 nm,霍尔迁移率为39.9 cm^(2)/(V·s);蓝宝石基In_(2)O_(3)薄膜中氧空位缺陷最少,占总缺陷比为29.37%,霍尔迁移率达到58.3 cm^(2)/(V·s),实现了FWHM为0.31°、表面粗糙度为3.08 nm的高质量薄膜。最终采用蓝宝石基In_(2)O_(3)薄膜制备出具有1.74×10^(14 )Jones高探测率以及光暗电流比约9165.7的紫外光电探测器。

Blister defect formation within partially stabilized zirconia film during constrained sintering

Yttria stabilized zirconia(YSZ)film has been screen printed and sintered on a rigid substrate.The constrained sintering caused the formation of multiple microcracks and most critically large“blister”defects.The morphology of such defects has been characterized by scanning electron microscopy(SEM).It was revealed that the film surface exhibits noticeable roughness.Microhardness testing revealed little variation in green density distribution.Rheological measurement,however,showed that some agglomerations are present in the YSZ ink.The existence of agglomerations in the screen printing ink in combination with debonding at the film/substrate interface is potentially the cause for the formation of blister defects.

钇稳定氧化锆纳米粉体烧结工艺的研究

实验研究了钇全稳定氧化锆(8YSZ)纳米粉体的烧结工艺,根据阿基米德原理测瓷体密度,通过测定烧结前后瓷片尺寸获得烧结线收缩率,使用扫描电子显微镜观测样品微观形貌,并探讨了纳米粉体烧结的致密化过程,分析了烧结工艺对致密度和晶粒大小的影响,得到了8YSZ纳米粉体合理的烧结工艺为:采用两步烧结,首先升温到1500℃,升温速率为3℃/min,然后降低温度到1450℃,烧结时间为4h。结果显示,采用该工艺,可以得到相对密度98%,晶粒尺寸小于3μm的性能优异的8YSZ瓷体。研究发现,粉体粒度对烧结性能影响较大,纳米粉体比普通粉体具有较低的开始烧结温度,双粒度混合粉体可以进一步提高其烧结性能。

微波水热合成ZrO_2-8%Y_2O_3纳米粉体

以Zr(OH)4和Y(OH)3的共沉淀为前驱体,在碱性介质中用微波水热法合成摩尔分数为8%的氧化钇稳定氧化锆(yttria stabilized cubic zirconia,YSZ)纳米粉体.通过X射线粉末衍射仪、透射电镜和等离子发射光谱等表征粉体的性能.研究了微波水热法的反应温度、时间和前驱物浓度对反应产物形貌、粒度等的影响.获得了制备具有纳米立方相结构的YSZ粉体的最佳工艺参数:粉体粒度为5～10 nm,产物纯度为99%.结果表明:温度为200℃时,产物粒径较小且均匀.微波水热制备YSZ的最佳反应时间为20～40 min.前驱物中Zr4+的最佳浓度为0.2 mol/l.增大碱性介质KOH的浓度对产物的晶型和粒度影响不大.

低温烧结3Y-TZP陶瓷的微观结构与力学性能

在 3Y -TZP(tetragonalzirconiapolycrystalsstabilizedwith 3 %Y2 O3inmole)中 ,采用LAS (Li2 O -Al2 O3-SiO2 )玻璃粉料为添加剂 ,在13 0 0～ 15 0 0℃下烧结 ,材料抗弯强度可达 85 0MPa ,断裂韧性可达 8.7MPa·m1 /2 .讨论了添加剂对微观结构及材料力学性能的影响 ,得出了采用LAS作为添加剂 ,不但能显著地降低材料的烧结温度 ,又不会明显削弱材料的力学性能的结论 .