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...

Crystal growth,structure and optical properties of Pr^(3+)-doped yttria-stabilized zirconia single crystals

The development of blue semiconductor light-emitting diodes(LEDs)has produced potential applications for Prdoped materials that can absorb blue light,especially crystals,and we now report structure and optical properties for high-quality Pr-doped single crystals of yttria-stabilized zirconia(YSZ)grown by the optical floating zone(FZ)method.X-ray diffraction(XRD)and Raman spectroscopy showed that all of the single crystal samples were in the cubic phase,whereas the corresponding ceramic samples contained a mixture of monoclinic and cubic phases.X-ray photoelectron spectroscopy(XPS)and electron paramagnetic resonance(EPR)spectroscopy showed that Pr was present as the Pr^(3+)ion in ceramic rods and single crystals after heating to high temperatures.The absorption and photoluminescence excitation(PLE)spectra of the Pr-doped YSZ crystals measured at room temperature showed strong absorption of blue light,while their photoluminescence(PL)spectra showed five emission peaks at 565 nm,588 nm,614 nm,638 nm,and 716 nm under450 nm excitation.The optimum luminescence properties were obtained with the crystal prepared using 0.15 mol%Pr_(6)O_(11),and those with higher concentrations showed evidence of quenching of the luminescence properties.In addition,the color purity of Pr-doped YSZ single crystal reached 98.9%in the orange–red region.

Particle growth mechanism of nanocrystalline zirconia powder during high temperature heat treatment

Agglomerated nanocrystalline ZrO2-8%Y2O3 powder prepared by spray drying was heat-treated in air at temperatures from 1200 ℃ to 1400 ℃ for 2 h. Scanning electron microscopy was used to examine the changes of particle size and morphology, and X-ray diffraction was used to analyze the change of constituent phases before and after the high temperature heat treatment. Nano-particle growth behavior was also investigated. The results show that the major constituent phase of the agglomerated nanocrystalline powder is tetragonal, and non-uniform growth of the nano-particles occurs while the heat treatment temperature reaches 1 300 ℃. This non-uniform growth phenomenon is related with the inhomogeneous distribution of Y2O3 in ZrO2. Nano-particles grow into micron particles through the mechanisms of gradual merging of nano-particles in some areas and sudden merging of nano-particles in other areas.

Effect of particle size on phase structure of ZrO_2 produced by hydrolysis of ZrOCl_2 solution

A method to produce ZrO2 nano-particles is developed and the effect of particle size on the phase structure of ZrO2 is studied. The method is based on the hydrolysis of ZrOCl2 solution in the reverse micelles of a liquid-liquid two-phase system, in which AOT （sodium 2-ethylhexyl sulfosuccinite） and toluene are chosen as the surfactant and organic phase, respectively. The reverse micelles prevent the aggregation of primary particles, the nano-particle size increases as the AOT content decreases. The TEM, XRD and particle-size analysis results show that the occurrence of metastable tetragonal ZrO2 is attributed to the effect of the particle size other than the effect of the crystallite size. The ratio of t-phase to m-phase increases as the particle size decreases, and 28 nm is the critical size for t-phase to m-phase transformation.

Luminescence intensification of lanthanide complexes by silver nanoparticles incorporated in sol-gel matrix

We present how the luminescence of europium RR-2-P-oxides complexes can be increased by interaction of electronic levels of the complex with the radiation field of silver nanoparticles （NPs）. The procedure by which silver NPs are formed in a sol-gel polyurethane matrix precursor was elaborated. The formed Ag NPs were combined with Eu complex incorporated in ormocer matrix. The emission spectra of the complexes without silver NPs were compared with spectra of the same complexes with addition of silver NPs. As the result of the interaction of the electronic levels of lanthaaide ligands with silver plasmons, dramatic increase of luminescence was observed.

Preparation and Mechanical Properties of Zirconia Ceramics Doped with Different Y_(2)O_(3)Contents

The sintering behavior and mechanical properties of zirconia doped with 2.0mol%-3.0mol%Y_(2)O_(3)were studied by pressure-less sintering.The experimental results show that the densification temperature of zirconia ceramics increases gradually with the decrease of Y_(2)O_(3)doping content by which decreases the sintering driving force due to the lower oxygen vacancy concentration of the systems.Furthermore,the bending strength and fracture toughness of the prepared zirconia ceramics increase with the decrease of Y_(2)O_(3)doping content.It can be attributed to the fact that the phase stability of tetragonal zirconia decreases with the decrease of Y_(2)O_(3)doping content,which is easier to induce"phase transformation toughening"and dissipate impact energy.The relative density,bending strength and fracture toughness of 2.0 mol%Y_(2)O_(3)doped zirconia ceramics(2.0Y-ZrO_(2))sintered at 1525℃are 99.00%,1256.65±20.82 MPa and 9.85±0.13 MPa·m^(1/2),respectively.

The first observation of Ni nanoparticle exsolution from YSZ and its application for dry reforming of methane

Ni nanocatalysts produced through exsolution have shown strong resistance to particle sintering and carbon coking in a beneficial dry reforming of methane(DRM)reaction utilizing greenhouse gases such as CH_(4)and CO_(2).However,most of the existing oxide supports for exsolution have been limited to perovskite oxide,while studies on fluorite support have been rarely conducted due to the limited solubility despite its excellent redox stability.Here we demonstrate that 3 mol%Ni can be successfully dissolved into the yttria-stabilized zirconia(YSZ)lattice and be further exsolved to the surface in a reducing atmosphere.The YSZ decorated with exsolved Ni nanoparticles shows enhanced catalytic activity for DRM reaction compared to the conventional cermet type of bulk Ni-YSZ.Moreover,the catalytic activity is extremely stable for about 300 h without significant degradation.Overall results suggest that the YSZ-based fluorite structure can be utilized as one of the support oxides for exsolution.

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.

Influence of characteristics of stabilized zirconia electrolyte on performance of cermet supported tubular SOFCs

Ni-Al_(2)O_(3)cermet supported tubular SOFC was fabricated by thermal spraying.Flame-sprayed Al_(2)O_(3)-Ni cermet coating plays dual roles of a support tube and an anode current collector.4.5mol.%yttria-stabilized zirconia(YSZ)and 10mol.%scandia-stabilized zirconia(ScSZ)coatings were deposited by atmospheric plasma spraying(APS)as the electrolyte in present study.The electrical conductivity of electrolyte was measured using DC method.The post treatment was employed using nitrate solution infiltration to densify APS electrolyte layer for improvement of gas permeability.The electrical conductivity of electrolyte and the performance of single cell were investigated to optimize SOFC performance.The electrical conductivity of the as-sprayed YSZ and ScSZ coating is about 0.03 and 0.07 S·cm^(-1)at 1000℃,respectively.The ohmic polarization significantly influences the performance of SOFC.The maximum output power density at 1000℃increases from 0.47 to 0.76 W·cm^(-2)as the YSZ electrolyte thickness reduces from 100μm to 40μm.Using APS ScSZ coating of about 40μm as the electrolyte,the test cell presents a maximum power output density of over 0.89 W·cm^(-2)at 1000℃.

颗粒级配对直写成型氧化锆陶瓷机械性能的影响研究

利用颗粒级配理论将平均粒径分别为50 nm和300 nm的ZrO_(2)粉体以不同级配比例制备出了适用于直写成型的固含量为58 vol.%的低黏度陶瓷浆料,分析了颗粒级配对ZrO_(2)陶瓷浆料流变特性的影响,研究了不同级配比例对直写成型ZrO_(2)陶瓷的致密度、微观结构和力学特性的影响。结果表明:在不改变陶瓷浆料固含量的情况下,通过对不同粒径ZrO_(2)粉体的颗粒级配,相较级配前单一粒径陶瓷浆料流变性能更好;颗粒级配的引入产生了钉扎作用,有效抑制了晶粒的异常生长。当亚微米和纳米ZrO_(2)粉末的级配比例为95∶5时,ZrO_(2)陶瓷具有最佳的机械性能,相对密度、抗弯强度、断裂韧性分别为99.1%、(691±12)MPa、(9.65±0.30)MPa·m^(1/2),分别提高0.40%、2.50%、50.78%。

基于SPH方法的氧化锆陶瓷正交切削仿真研究

为深入研究氧化锆陶瓷切削加工质量的影响因素并揭示其切削去除机理,开展基于光滑质点流体动力学(SPH)方法的氧化锆陶瓷正交切削仿真研究,模拟材料去除时的大变形行为,揭示了裂纹发展和切屑形成过程。结果表明:脆延转变取决于切削深度,临界转变深度为0.75~1.00μm,其裂纹形式存在明显差异;切屑形态主要分为不连续带状和崩脆粉末状,延性去除时材料变形量与切削深度和切削速度正相关,脆性去除时稳定于极大值;切削力与切削深度正相关,但仅在延性去除时与切削速度正相关,脆性去除时切削力的时序分布与裂纹的发展密切相关。

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.

Thermal Transport in Nanoporous Yttria-Stabilized Zirconia by Molecular Dynamics Simulation

Yttria-stabilized zirconia(YSZ) is widely used as thermal barrier coatings(TBCs) to reduce heat transfer between hot gases and metallic components in gas-turbine engines. Porous structure can generally reduce the lattice thermal conductivity of bulk material, so porous YSZ can be potentially used as TBCs with better thermal performance. In this work, we investigate the thermal conductivity of nanoporous YSZ using the nonequilibrium molecular dynamics(NEMD) simulation, and comprehensively discuss the effects of cross-sectional area, pore size, structure length, porosity, Y_2O_3 concentration and temperature on the thermal conductivity. To compare with the results of the NEMD simulation, we solve the heat diffusion equation and the gray Boltzmann transport equation(BTE) to calculate the thermal conductivity of the same porous structure. From the results,we find that the thermal conductivity of YSZ has a weak dependence on the structure length at the length range from 10 to 26 nm, which indicates that the majority of heat carriers have very short mean free path(MFP) but there exists small percentage(about 3%) of phonons with longer MFP(larger than 10 nm) contributing to the thermal conductivity. The thermal conductivity predicted by NEMD simulation is smaller than that of solving heat diffusion equation(diffusive limit) with the same porous structure. It shows that the presence of pores affects phonon scattering and further affects the thermal conductivity of nanoporous YSZ. The results agree well with the solution of gray BTE with a average MFP of 0.6 nm. The thermal conductivity of nanoporous YSZ weakly depends on the Y_2O_3 concentration and temperature, which shows the phonons with very short MFP play the major contribution to the thermal conductivity. The results help to better understand the heat transfer in porous YSZ structure and develop better TBCs.

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.

Impact-abrasive Wear Behavior of ZTA and NbC Reinforced Fe60 Matrix Composites

The impact-abrasive wear behavior of ZTA(zirconia toughened alumina)particle(ZTAp)and NbC particle(NbCp)reinforced Fe60 matrix composites(ZTAp-NbCp/Fe60)were investigated.Specimens of pure Fe60 matrix material,NbCp reinforced Fe60 composite(NbCp/Fe60)and ZTAp-NbCp/Fe60 with different contents of ZTAp were prepared through vacuum sintering and tested on an MLD-10B Impact Wear Rig.As revealed by the results,NbCp could strengthen Fe60 matrix,and had fine grain strengthening effect on Fe60matrix.When the mass fraction of ZTAp was 5%-15%,the impact-abrasive wear performance of ZTAp-NbCp/Fe60 composites was better than that of Fe60 and NbCp/Fe60.When the mass fraction was 15%,the ZTApNbCp/Fe60 had the best performance.ZTAp could weaken the impact and wear effect of abrasive particles on the composite and protect the matrix.Cracks occured at the interface and at defects in the ZTAp.The former leaded to ZTAp shedding,while the latter leaded to ZTAp fracturing.In both cases,the performance of the composite material would decrease.

Hot corrosion mechanism of yttria-stabilized zirconia powder in the presence of molten Na_(2)SO_(4)+V_(2)O_(5) salts

The hot corrosion behavior of yttria-stabilized zirconia(YSZ)powder specimens exposed to Na_(2)SO_(4)/V_(2)O_(5) salts mixtures at high temperature was evaluated.Initial tests were carried out at 1000℃ for 10 h,the salt concentrations varied from 0.1 wt%to 1.00 wt%,and the Na_(2)SO_(4)/V_(2)O_(5) mass ratios were between 0.20 and 0.44 following a factorial design 22.X-ray diffraction(XRD)analyses of the tested samples showed with a confidence of95%that the mixture composed of 32 wt%Na_(2)SO_(4)+68 wt%V_(2)O_(5),and 1.00 wt% salt concentration led to high destabilization of the t’-YSZ phase and formation of YVO_(4) products.A second set of experiments were conducted to assess the influence of temperature on the hot corrosion response of the YSZ in the range between 490 and 1100℃.Thermogravimetric analysis(TGA)experiments and Rietveld adjustments of XRD patterns showed that the mass loss of the samples varied with testing temperature and also that the major destabilization of tetragonal phase occurred at 900℃.

Fabrication,microstructure,and properties of 8 mol%yttria-stabilized zirconia(8YSZ)transparent ceramics

Fine grained 8 mol%yttria-stabilized zirconia(8YSZ)transparent ceramics with high optical and mechanical properties were fabricated by air pre-sintering and hot isostatic pressing(HIP)using commercial 8YSZ powders as the raw material.The pre-sintered ceramics with fine grains and appropriate relative density play a key role to achieve high transparency and suppressed grain size after HIP post-treatment at relatively low temperatures.With the increase of HIP temperature from 1350 to 1550℃,the in-line transmittance of 8YSZ ceramics at 600 nm increases from 56.9%to 71.5%(2.5 mm in thickness),and the average grain size increases from 2.4 to 16.3μm.The corresponding bending strength of 8YSZ transparent ceramics decreases from 328±20 to 289±19 MPa,the hardness(H)decreases from 12.9±0.1 to 12.5±0.2 GPa,and the fracture toughness(KIC)decreases from 1.30±0.02 to 1.26±0.03 MPa·m^(1/2).Systematical investigations were carried out to study the combination of high optical transparency and excellent mechanical properties in 8YSZ ceramics.

Self-supported yttria-stabilized zirconia mesocrystals with tunable mesopores prepared by a chemi-thermal process

Mesoporous mesocrystals are highly desired in catalysis,energy storage,medical and many other applications,but most of synthesis strategies involve the usage of costly chemicals and complicated synthesis routes,which impede the commercialization of such materials.During the sintering of dense ceramics,coarsening is an undesirable phenomenon which causes the growth of the grains as well as the pores hence hinders the densification,however,coarsening is desired in the sintering of porous ceramics to expand the pore sizes while retaining the total pore volume.Here we report a chemi-thermal process,during which nanocrystallite aggregates were synthesized by hydrothermal process and then converted to the product by sintering.Through this strategy,we synthesized mesoporous self-supported mesocrystals of yttria-stabilized zirconia with tunable pore size and the process was then scaled-up to industrial production.The thermal conductivity measurement shows that the mesoporous powder is a good thermal isolator.The monolith pellets can be obtained by SPS sintering under high pressure and the mesoporosity is retained in the monolith pellets.This work features facile and scalable process as well as low cost raw chemicals making it highly desirable in industrial applications.

STUDIES ON THE WET CHEMICAL PREPARATION AND REGULARITY OF PHASE TRANSFORMATION OF ZIRCONIA ULTRAFINE PARTICLES

Zirconia is an important material of transformation toughening. Consequently, a clear understanding of the regularity of phase transformation, a full realization of all forms of zirconia, and a deep investigation into the methods of preparation and even dispersion of high purity ZrO2 ultrafine particles （henceforth simplified as ZrO2 UFP ） will undoubtedly stimu-

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.