Ytrria-stabilized Zirconia Research Articles

Analysis of thermal shock performance of Y2O3 stabilized ZrO2 (YSZ) coating based on residual stress and micro-morphology

Ytrria-stabilized zirconia (YSZ) thermal barrier coatings were prepared via atmospheric plasma spraying, and its thermal shock performance was evaluated. Residual stress was analyzed qualitatively and quantitatively via electron backscatter diffraction (EBSD) and X-ray diffraction (XRD). And image analysis and scanning electron microscopy were used to quantitatively analyze the length, direction, and proportion of the cracks in the coating. A relationship was established between the microstructure of the coating and its thermal shock performance. The results demonstrated that the spraying power altered the microstructure of the coating. The microstructure and residual stresses affected the thermal shock performance of the coating. This may be due to an increase in the spraying power, which led to a decrease in the grain size and service life of the coating.

The resin bond to high-translucent zirconia-A systematic review.

Several systematic literature reviews have assessed the scientific evidence on resin bonding protocols to conventional 3mol% ytrria-stabilized zirconia (3Y-TZP) ceramics. It has been widely discussed, however, that the differing composition and physical properties of new high-translucent zirconia generations (4Y-TZP and 5Y-TZP) may require alternative bonding materials and procedures. This paper reviewed in vitro studies on the success and durability of bonding protocols to high-translucent zirconia. A systematic search of PubMed and Cochrane Library for in vitro studies on bonding to new zirconia generations published until November 2020 was conducted and complemented by a manual search. Studies selected for review fulfilled the applied inclusion and exclusion criteria. The quality of the included studies was assessed with the Cochrane risk-of-bias tool for randomized trials. Of 629 screened articles, 18 were included in this review. They investigated different surface pretreatment methods, primers, resin cements, aging procedures, and bond strength test protocols. The limited number of the identified studies and the heterogeneity of the extracted data did not allow to conduct a meta-analysis. The available evidence suggests that resin bonding protocols successfully applied to conventional zirconia are also the most successful for high-translucent zirconia. Airborne particle abrasion and special phosphate monomer-containing primers or composite resin cements provide long-term durable resin bonds. Durable bonds can be established between high-translucent zirconia and resin cements. The bonding materials and procedures applied do not compromise their physical properties.

Interlayer modification for high-performance and stable solid oxide electrolysis cell

Solid oxide electrolysis cells (SOECs) are an attractive technology that can convert energy into hydrogen or other syngas due to their high energy-conversion efficiency. To improve both performance and stability of SOECs, the effect of the interlayer modification between La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) air electrode and ytrria-stabilized zirconia (YSZ) electrolyte on the high-temperature water electrolysis performance was studied using electrochemical impedance spectroscopy at 1023 K under 40% H2O– 60% H2 fuel flow. Enhancement of the current density from 0.9 A/cm2 to 1.25 A/cm2 was achieved by replacing the porous Ce0.9Gd0.1O1.95 (GDC) interlayer by a dense GDC interlayer. Detailed analysis of the impedance spectra of the cell indicated that utilizing the dense GDC interlayer leads to a significant decrease of the ohmic resistance. Scanning electron microscopy-wavelength dispersive X-ray spectroscopy results show that the dense GDC interlayer could significantly reduce the secondary phase formation of SrZrO3 between the GDC and YSZ interface. Thus, the enhancement of the SOEC current density was also accompanied by good stability of the cell as confirmed over 50 h at 1023 K.

R&D on Surrogate Kernel Fabrication in Support of Reaktor Daya Eksperimental (RDE) Project

R&D program on HTGR fuel to support the RDE project has been outlined and is aimed to develop national capabilities on nuclear fuel technology. The external sol-gel technology has been adopted for the fabrication of kernels. Laboratory scale work has been ongoing at the Center for Nuclear Fuel Technology (PTBBN) BATAN to study various parameters involved in the process of kernel fabrication including tuning of parameters related to droplet formation (feed flow rate, vibrator frequency, NH3 gas flow rate), optimizing chemical formulation in broth preparation, various treatments in aging, washing, drying process, and thermal treatment for densification of kernels. In this early stage, zirconium precursors were used to manufacture surrogate kernels of ytrria-stabilized zirconia. The steps for kernel fabrication include chemical formulation of broth and droplet casting, aging-washing-drying of gel microspheres, calcination and sintering, and characterization of sintered kernels (surface morphology, density, diameter/sphericity, solid phase). Stable cast of droplets from 1 mm nozzle diameter was optimized by adjusting feed flowrate at 30 ml/min, viscosity at 45-60 cP, and vibrating frequency at 100 Hz. Presolidification of gel skin was optimized at a working NH3 flow rate of 3.5 - 4 L/min. Addition of urea with mole ratio urea/metal 2.5/1.0 gave the most preferable results based on SEM examination for crack and morphological structure. Control the opaqueness of the sol can be done by portioning addition of urea, where a portion of urea was added at decomposing temperature around 85°C, while another portion was added at a lower temperature. Addition of urea has a desirable effect on crack reduction during heat treatment of gel microspheres. Increase in metal concentration results in an increase in kernel diameter when other sol-to-gel conversion parameters were kept unvaried. Phase determination by X-Ray Diffractometer indicates that solid phase for ceria-stabilized zirconia prepared with precursor composition of 16% yttrium in zirconium-yttrium sol results in yttria-stabilized zirconia 8YSZ with cubic phase.

Performance of YSZ and Gd2Zr2O7/YSZ double layer thermal barrier coatings in burner rig tests

Double layer thermal barrier coatings (TBCs) consisting of a Gd2Zr2O7 (GZO) top and an ytrria stabilized zirconia (YSZ) interlayer have been tested in a burner rig facility and the results compared to the ones of conventional YSZ single layers. In order to gain insight in the high temperature capability of the alternative TBC material, high surface temperatures of up to 1550 °C have been chosen while keeping the bond coat temperature similar. It turned out that the performance of all systems is largely depending on the microstructure of the coatings especially reduced porosity levels of GZO being detrimental. In addition, it was more difficult in GZO than in YSZ coatings to obtain highly porous and still properly bonded microstructures. Another finding was the reduced lifetime with increasing surface temperatures, the amount of reduction is depending on the investigated system. The reasons for this behavior are analyzed and discussed in detail.

Yttria-Stabilized Zirconia Ceramic Deposition on SS430 Ferritic Steel Grown by PLD - Pulsed Laser Deposition Method

Development of high temperature materials are one of the key issues for the deployment of advanced nuclear reactors due to higher temperature operation. One of the candidate materials for that purpose is ceramic-coated ferritic steel that one of the functions is to be a thermal barrier coating (TBC). Thin films of YSZ (Ytrria-Stabilized Zirconia) ceramic have been deposited on a SS430 ferritic steel using Pulsed Laser Deposition (PLD) at Center For Science and Technology of Advanced Materials laboratory – National Nuclear Energy Agency of Indonesia (BATAN). The thin film was deposited with the chamber pressure range of 200-225 mTorr, the substrate temperature of 800oC, and the number of laser shots of 3×104, 6×104 and 9×104. Afterward, the samples were analyzed using Scanning Electron Microscope – Energy Dispersive X-ray Spectroscope (SEM-EDS), X-Ray Diffractometer (XRD), Atomic Force Microscope (AFM) and Vickers hardness tester. The results showed that the YSZ could homogeneously and sticky deposited on the surface of the ferritic steel. The surfaces were very smoothly formed with the surface roughness was in the range of 70 nm. Furthermore, thickness, composition of Zr4+ dan Y3+, the crystallinity, and hardness property was increased with the increasing the number of the shots.

Deposition of nanostructured YSZ coating from spray-dried particles with no heat treatment

Ytrria stabilized zirconia (YSZ) nanoparticle agglomerates were fabricated by a spray dry method and were directly sprayed using atmospheric plasma spraying (APS) with a current of 300A and 500A. A commercially supplied nanostructured YSZ powder (sintered) was also sprayed under the same conditions for comparison. A scanning electron microscope (SEM), an optical microscope (OM) and X-ray diffraction (XRD) were utilized to characterize the feedstock powder and coatings. Weibull plots were used to analyze the performance of the nanostructured coatings. The lower 300A operating current resulted in a higher portion of nanostructure retention at the expense of coating quality. An approximate 10% increase in porosity and a noticeable decrease in grain size (∼104nm) were obtained by spraying non-heat treated agglomerates with a 500A current. The thermal conductivity (400–600°C) was evaluated using the one-dimensional, steady state Fourier's law of heat conduction. Next, lower thermal conductivity (∼1.3Wm−1K−1 at 600°C) was identified in coatings engineered at 500A from agglomerated powder with no heat treatment.

Barium carbonate nanoparticle to enhance oxygen reduction activity of strontium doped lanthanum ferrite for solid oxide fuel cell

BaCO3 nanoparticles are demonstrated as outstanding catalysts for high-temperature oxygen reduction reaction (ORR) on the La0.8Sr0.2FeO3-δ (LSF) cathode for solid oxide fuel cells (SOFCs) based on ytrria-stabilized zirconia (YSZ) electrolytes. Thermal gravitational and X-ray diffraction measurements show that BaCO3 is stable and chemically compatible with LSF under the fabrication and operation conditions of intermediate-temperature SOFCs. The BaCO3 nanoparticles can greatly reduce the interfacial polarization resistance; from 2.96 to 0.84 Ω cm2 at 700°C when 12.9wt% BaCO3 is infiltrated to the porous LSF electrode on the YSZ electrolyte. Electrochemical impedance spectroscopy shows that there is about one order of magnitude decrease in the low-frequency resistance, indicating that BaCO3 nanoparticles can greatly enhance the surface steps for ORR. Electrical conductivity relaxation investigation indicates about one order of magnitude increase in the chemical oxygen surface exchange coefficient when BaCO3 is applied, directly demonstrating significant increase in the kinetics for ORR. In addition, LSF cathodes with infiltrated BaCO3 nanoparticles have shown excellent stability and substantially enhanced cell performance as demonstrated with single cells, suggesting BaCO3 nanoparticles are very effective in enhancing ORR on LSF.

Waveguide-like structures written in transparent polycrystalline ceramics with an ultra-low fluence femtosecond laser

We present a laser processing study of optically transparent ytrria stabilized zirconia (YSZ) ceramics (ZrO2-8 mol. % Y2O3) using unamplified femtosecond (fs) laser pulses of a few nJ and high repetition rate (70 MHz). The ceramics were fabricated using current activated pressure assisted densification (CAPAD) and have fine grain size and minimal porosity, producing a transparent material. Irradiation using fs laser pulses caused permanent changes in the optical properties of the irradiated zone. These laser written structures were found to confine He-Ne laser light (632 nm) in effect functioning as waveguide like structures and were written into the YSZ ceramics using a remarkably low per-pulse energy (5nJ). The number of passes with the laser i.e total incident pulses per unit area was found to significantly affect the waveguide writing. We believe that waveguides are regions were the concentration of oxygen vacancies and/or their associated free electrons have been altered by laser irradiation. We are not aware of previous reports of low fluence fs laser pulses being used to influence vacancy related defects to produce waveguides in ceramics. This new mechanism opens the door for writing strictures in optical ceramics with lower power than previously thought feasible.

Optimization of an electrochemical cell with an adsorption layer for NOx removal

The structure of a multilayer electrochemical cell with an adsorption layer was optimized by removing an yttria-stabilized zirconia cover layer. It was found that the NOx removal properties of the electrochemical cell were dramatically enhanced through the optimization, especially under conditions of low voltage, intermediate temperature, and high O2 concentration. The pronounced increase in activity and selectivity for NOx decomposition after removing the ytrria-stabilized zirconia cover layer was attributed to the extensive release of selective reaction sites for NOx species and a strong promotion for NOx reduction from the interaction of the directly connected adsorption layer with both the Pt and catalytic layers. The optimized electrochemical cell may provide a promising solution for NOx emission control.

Optimization of Redox Stable Ni-YSZ Anodes for SOFCs by Two-Step Infiltration

Infiltration of a polymeric nickel oxide precursor into a sintered porous ytrria –stabilized zirconia (YSZ) skeleton is a promising approach to achieve redox stable solid oxide fuel cells. In order to ensure that the porous YSZ skeleton was mechanically strong enough to withstand the stresses caused by the volumetric expansion of the Ni phase upon oxidation even at relatively high loadings, a polymeric YSZ precursor was infiltrated into to the porous YSZ skeleton, prior to NiO infiltration. It was shown that infiltration of YSZ precursor strengthened the porous YSZ skeleton without compromising from the porosity or initial YSZ particle size significantly. The amount of infiltrated YSZ and the subsequent heat-treatment temperature were determined to be important processing parameters in achieving redox stable Ni-YSZ anodes. Electrolyte supported SOFC (electrolyte thickness ∼ 180 μm) with redox stable anode prepared by YSZ and NiO infiltrations showed a power density of ∼0.41 Watt/cm2 at 800°C which did not change significantly after 20 redox cycles in 10%H2 – 90% Ar fuel. Impedance spectroscopy measurements at 800°C showed significantly low electrode polarization resistances (anode + cathode ∼ 0.07 Ohm.cm2 at 800°C) which remained stable upon redox cycling.

Hot corrosion of YSZ/Al 2O 3 dispersed NiCrAlY plasma-sprayed coatings in Na 2SO 4–10 wt.% NaCl melt

This study examines the effect of ytrria stabilized zirconia (YSZ) dispersion on hot corrosion behaviour of NiCrAlY bond coat. Hot corrosion studies were conducted on NiCrAlY and NiCrAlY containing 25, 50 and 75 wt.% YSZ coatings obtained through the air plasma spray technique, in Na 2SO 4 + 10 wt.% NaCl environment at 800 °C. The results show that YSZ dispersion lowers the overall hot corrosion tendency of the NiCrAlY, though it enhances the inherent hot corrosion tendency of its metallic constituent (NiCrAlY). Furthermore, there exists a threshold oxide level beyond which it adversely affects the hot corrosion of the coating.

Microstructural modeling of adaptive nanocomposite coatings for durability and wear

Adaptive thin-film nanocomposite coatings comprised of crystalline ductile phases of gold and molybdenum disulfide, and brittle phases of diamond like carbon (DLC) and ytrria stabilized zirconia (YSZ) have been investigated by specialized microstructurally based finite-element techniques. One of the major objectives is to determine optimal crystalline and amorphous compositions and behavior related to wear and durability over a wide range of thermo-mechanical conditions. The interrelated effects of microstructural characteristics such as grain shapes and sizes, local material behavior due to interfacial stresses and strains, varying amorphous and crystalline compositions, and transfer film adhesion on coating behavior have been studied. The computational predictions, consistent with experimental observations, indicate specific interfacial regions between DLC and ductile metal inclusions are critical regions of stress and strain accumulation that can be precursors to material failure and wear. It is shown by varying the composition, resulting in tradeoffs between lubrication, toughness, and strength, the effects of these critical stresses and strains can be controlled for desired behavior. A mechanistic model to account for experimentally observed transfer film adhesion modes was also developed, and based on these results, it was shown that transfer film bonding has a significant impact on stress and wear behavior.

Effective modulus and coefficient of thermal expansion of Ni–YSZ porous cermets

Nickel zirconia, Ni–YSZ, porous cermets used in solid oxide fuel cells can be considered as composite materials consisting of three phases, namely nickel (Ni), ytrria-stabilized zirconia (YSZ), and voids. Based on Ni–YSZ's microstructural features, such as the volume fractions, average particle sizes and their correlations of a physical sample, a three-dimensional stochastic reconstruction method is used to recreate the three-phase composite. The digitally reconstructed microstructure is then transferred into finite element models to obtain the material's corresponding effective elastic modulus and effective coefficient of thermal expansion at various temperatures. Predictions from such a numerical methodology agree well with experimental results.

Effect of powder structure on microstructure and electrical properties of plasma-sprayed 4.5 mol% YSZ coating

Electrolyte coatings by atmospheric plasma spraying were prepared by 4.5 mol% ytrria-stabilized zirconia (YSZ) powders manufactured by agglomerate-sintered (A-S) and fusing-crashed (F-C) processes. Microstructure of the powders and the coatings were characterized using scanning electron microscopy. The electrical conductivity of the coatings was investigated using both impedance spectroscopy and DC methods. The results showed that the electrical conductivity of coating prepared with A-S powder was lower than that with F-C powder. It was found from the impedance analysis that both the grain and grain boundary resistances were large in the coating formed by A-S powder. This fact resulted from deposition of partially melting of spray particles. A model was proposed to explain the effect of powder structure and melting state on the coating microstructure and properties.

Ion Irradiation Effects in Solid Oxide Fuel Cell Electrolytes

ABSTRACTSingle crystal Ytrria-stabilized Zirconia was irradiated with Xe2+ and Xe3+ ions at 320 and 450 keV over a range of doses from 1013 to 1016 ions/cm2. Damage appears as a 150 nm surface layer with a dense dislocation network. The X-ray diffraction pattern shows an increasing lattice expansion with increasing dose that reaches a saturation point. Ion irradiation increases the surface conductance of the material; this effect is removed with certain post-treatments. Preliminary isotope depth profiling indicates enhanced ion diffusion in the damaged layer.

Medium-temperature electrolysis of NO and CH4 under lean-burn conditions using ytrria-stabilized zirconia as a solid electrolyte

Electrolysis of NO and CH4 in the presence of excess O2 has been studied using a single-compartment reactor, constructed from yttria-stabilized zirconia (YSZ), with two palladium electrodes. The palladium electrodes were attached by an electroless plating method. Experiments were conducted between 550 and 900 °C with a mixture of 1000 ppm NO, 1000 ppm CH4, 2% O2, 5% H2O and 5% CO2 in argon at a flow rate of 50 ml min–1. The reduction of NO to N2 and the oxidation of CH4 to CO2 were promoted by applying a direct current between the two palladium electrodes. The current efficiency for the reduction of NO was about 1.5% at all measured temperatures, while that for the oxidation of CH4 decreased from 2.7 to 0.3% with increasing temperature from 550 to 900 °C. The dc resistance of the reactor was mainly due to the ohmic resistance of the electrolyte. The transport properties of O2– through the electrolyte followed Faraday's law under operating conditions. These results were strongly dependent on the morphology and thickness of the palladium electrode.