Yttria-stabilized Zirconia Research Articles

Investigation of microstructure and thermal expansion behaviour of a functionally graded YSZ/IN718 composite produced by laser-powder bed fusion

Yttria-stabilized zirconia (YSZ) has been extensively used as a thermal barrier coating (TBC) for high-temperature alloys. In this research, the microstructural attributes and thermal expansion behavior of an additively manufactured functionally graded composite (YSZ/IN718 FGC) were investigated. First, a powder mixture of IN718 and YSZ (ranging from 1 wt% to 4 wt%) was achieved via low-energy ball-milling at 100 rpm. Differential scanning calorimetry (DSC) analysis depicted the melting behaviour of the powder mixtures of different YSZ content. The endothermic peaks in the DSC curve, at ∼1360 ℃, suggested that the energy needed to melt the powder mixture increases with increasing YSZ content. These varying powder compositions were used to fabricate FGC samples using L-PBF. The study investigated the effects of laser power variation along the YSZ gradient, successfully mitigating the fusion defects that had been initially observed in FGC samples. Microscopic analyses, comprising scanning electron microscopy (SEM) and transmission electron microscopy (TEM), depicted the elemental segregation of Nb and Mo at the solidification subgrain boundaries (SSBs). Furthermore, the electron backscattered diffraction (EBSD) results demonstrated the refinement of grains and a reduction in textural intensity, particularly along the YSZ gradient. Energy dispersive spectroscopy (EDS) and electron probe micro analysis (EPMA) were used to validate the uniform dispersion of YSZ particles throughout the composite matrix, with the EPMA line scan affirming a predominantly linear YSZ content variation. Lastly, the coefficients of thermal expansion (CTEs) were evaluated, both parallel and perpendicular to the build direction. A decrease of approximately ∼6 % in CTE was noted along the building or gradation direction. Notably, perpendicular to the building direction, the CTE values for specimens containing 4 wt% and 2 wt% YSZ witnessed significant reductions of ∼32 % and ∼12 %, respectively. This research significantly contributes to the understanding of the microstructural intricacies and thermal behavior of YSZ/IN718 FGC produced by L-PBF process.

A critical investigation of the effect of silver migration at the silver | alumina scandia doped zirconia electrolyte interface in solid oxide fuel cell conditions

In this work, a critical evaluation of silver ion migration at the surface of Al0.04Sc0.06Zr0.9O1.95 (AlScZrO) electrolyte is explored in intermediate temperature solid oxide fuel cells (IT-SOFCs). The behaviour of silver is systematically studied at the operating conditions of silver as a cathode, anode, or sealant in IT-SOFCs. The results to those obtained at the surface of other electrolytes (gadolinia doped ceria, samaria doped ceria and yttria-stabilized zirconia) are also analysed. In the case of cathodic polarization, a thick silver deposit is formed around the electrode on the surface of the electrolyte, which may lead to the short-circuiting of the electrodes. While for the anodic polarization, oxygen bubbles are formed between the electrode and electrolyte, leading the delamination of electrode. Silver can also migrate from unpolarized parts of the cell such as sealants. Therefore, Issues related to the application of silver in IT-SOFCs should be concerned by the scientific community.

Spectroscopic Elucidation of Phase Evolution in NiO/YSZ Under Oxidative and Reductive Gas Environments

High temperature co-electrolysis of CO2 and H2O serves a viable, energy efficient, and scalable route to produce syngas (CO+ H2), which can be used to generate a variety of utility hydrocarbons. Solid oxide electrolysis cell (SOEC) has proven to be a promising technology for CO2 utilization and a carbon neutral route to curb CO2 emissions. The design of cathode catalyst is critical as it must facilitate the activation of CO2 and H2O and also exhibit high electronic and oxygen ion conductivity. The state-of-the-art cathode material used in SOECs is Ni/YSZ (8 mol% Yttria Stabilized Zirconia) ceramic composite (known as cermet), whose performance is dependent on various operating factors including temperature, composition of feed gas stream, presence of contaminants like SOx/NOx etc. There is a very limited number of studies on the evolution of the cathode materials under process level conditions. To begin with, effect of different oxidative and reductive gas environments and temperature over Ni/YSZ is studied using in situ Raman spectroscopy.Typical flue gas composition is chosen as the basis for the concentration of different components like 15% CO2, 10% H2O, 5% O2 with argon. Under oxidative conditions (O2, CO2, H2O) with temperature variation range of RT-800 0C, NiO/YSZ vibrational modes revealed that it is composed of NiO and YSZ phases. It is seen that there is thermal broadening in the bands of NiO and YSZ, thermal effects reversible upon cooling down and red shift in the NiO bands exemplified the lattice expansion. Exposing the NiO/YSZ to 5% H2 at high temperature resulted in the formation of metallic Ni, which is corroborated by the absence of the Ni-O vibrational modes in Raman spectrum at 400 0C. YSZ phase is quite stable in H2 at elevated temperature.After reduction of NiO/YSZ to get Ni/YSZ, exposure to oxidative environments (i.e., O2, CO2, H2O) aided in the formation of defect laden NiOx phase on YSZ. Specifically, NiOx formation starts at 350 0C under oxygen and at 450 0C under CO2 and H2O. Under 15% CO2, there is an overlap between the bands associated to the carbonate like species and the NiO phase but there is no formation of coke at these conditions as D and G bands were not observed (Fig. 1). It could be due to the oxidation of Ni that obliterated coke formation. The blue shift at 1046 cm-1 (2P mode of NiO) signifies the shortening of bond length in Ni-O with gradual conversion of Ni to NiOx. Compared to the NiOx phase formed under 5% O2 and 15% CO2 which has a sharp feature in Raman spectra, there is a broad band of NiOx phase formed under 10 % H2O in the region 480-580 cm-1 . This observation demonstrates the variation in the microcrystalline size of the defect laden NiOx phase formed under exposure to different oxidizers.Another set of experiments were done with the dry hydrogen (5 % H2) and humidified hydrogen (5% H2 + 10 % H2O) to study the role of presence of water on the reduction of NiO/YSZ with temperature variation between 120 – 800 0C. It was found that reduction of NiO to Ni is not affected by the presence of water. Under both conditions this transformation occurs between 400-600 0C. The results from the current study provide the key information on the effects of temperature and gas compositions over Ni/YSZ which serves as a guide for the process level design and operation of SOECs. References Juliana Carneiro et al, Industrial & Engineering Chemistry Research 2020 59(36), 15884-15893.John Kirtley et al, The Journal of Physical Chemistry C2013, 117 (49), 25908-25916.A. Naumenko et al, Phys Chem Solid State 2008, 9, 121–125. Figure 1

(Invited) Solid Oxide Cell Design for High Power Density and Reliability: Applications in Power and Fuels Production

Solid oxide fuel cells (SOFC) offer a carbon-neutral solution to power generation, fuel flexibility, and robust design suitable for stationary and air transportation applications. OxEon Energy developed an air electrode supported (AES) cell design that demonstrated 63% increase in power density compared with its heritage cell design in short stack tests.OxEon Energy team has been advancing solid oxide technology for over three decades and the stacks operate fully reversibly in fuel cell and electrolysis cell modes. The SOEC/SOFC technology builds on the success of the SOEC stack installed on NASA’s Mars Perseverance Rover as part of the MOXIE (Mars Oxygen In-situ resource utilization Experiment) mission. The MOXIE stack produced propellant grade, high-purity O2 by electrolyzing Mars atmosphere CO2. MOXIE stack used an electrolyte supported design to meet the reliability requirements for a space mission.An infiltrated air electrode cell design was developed to increase fuel cell stack specific power (kW/kg). Electrolyte thickness, the most resistive element of the SOFC, was reduced from ~250 microns to 70 microns. The fabrication process results in a bi-layer of dense scandia stabilized zirconia (ScSZ) electrolyte and a porous yttria stabilized zirconia (YSZ) matrix for air electrode infiltration. Fuel electrodes are screen printed. The reduced thickness of the electrolyte offers a compromise between improved performance over electrolyte supported design, while meeting robustness required for aerospace applications.Producing infiltrated electrodes with well-adhered and homogeneous distribution of active material is a challenge that requires multiple infiltration-calcination cycles to deposit sufficient material. Key variables are precursor chemistry to reduce the number of infiltrations and prevent interaction between electrode layers; intermediate calcination temperatures; and process development using infiltration equipment that enables volume production. OxEon partnered with National Energy Technology Laboratory (NETL) for electrode infiltration process development and PNNL for button cell and short stack validation testing.SOFC fuel flexibility was demonstrated in button cells and stacks previously; performance was nearly identical among hydrogen, ammonia, and reformed natural gas. Durability testing shows similarly stable performance in each fuel.A 10-cell AES stack was tested in SOFC mode at 800 °C in H2 and NH3 fuel feeds at 0.7 V/cell, and the same stack was operated in steam electrolysis to produce H2. SOFC testing demonstrated powder density of 0.35 W/ cm2 at 0.7 V/cell in the AES stack in ammonia feed; an electrolyte supported stack with equivalent materials measured 0.20 W/cm2 at 0.7 V. Long term testing in steam electrolysis showed stable performance at 800 °C and 1.2 V/ cell.Button cell tests show the thin electrolyte cell structure is capable of an area specific resistance (ASR) of 0.25 Ω-cm2 in H2- and NH3 fuel feeds. OxEon’s continued AES cell development is focused on improving manufacturability, infiltrated electrode stability, and implementing degradation mitigation strategies developed for electrolyte supported cell structures. Improved performance with AES cell design has critical implications for future integration in OxEon’s technology suite: SOEC systems to generate H2 and syngas from renewable energy, and Fischer-Tropsch to produce synthetic fuels.This material is based on research sponsored by Air Force Research Laboratory under agreement number FA8649-22-P-0792. The views expressed are those of the authors and do not necessarily reflect the official policy or position of the Department of the Air Force, the Department of Defense, or the U.S. government. Approved for public release; distribution is unlimited. Figure 1

Efficient mixed-potential acetone sensor with yttria-stabilized zirconia and porous Co3O4 nanofoam sensing electrode for hazardous gas monitoring and breath analysis

For hazardous gas monitoring and non-invasive diagnosis of diabetes using breath analysis, porous foams assembled by Co3O4 nanoparticles were designed as sensing electrode materials to fabricate efficient yttria-stabilized zirconia (YSZ)-based acetone sensors. The sensitivity of the sensors was improved by varying the sintering temperature to regulate the morphology. Compared to other materials sintered at different temperatures, the porous Co3O4 nanofoams sintered at 800 °C exhibited the highest electrochemical catalytic activity during the electrochemical test. The response of the corresponding Co3O4-based sensor to 10 ppm acetone was –77.2 mV and it exhibited fast response and recovery times. Moreover, the fabricated sensor achieved a low detection limit of 0.05 ppm and a high sensitivity of –56 mV/decade in the acetone concentration range of 1–20 ppm. The sensor also exhibited excellent repeatability, acceptable selectivity, good O2/humidity resistance, and long-term stability during continuous measurements for over 30 days. Moreover, the fabricated sensor was used to determine the acetone concentration in the exhaled breaths of patients with diabetic ketosis. The results indicated that it could distinguish between healthy individuals and patients with diabetic ketosis, thereby proving its abilities to diagnose and monitor diabetic ketosis. Based on its excellent sensitivity and exhaled breath measurement results, the developed sensor has broad application prospects.

Simulation of Electrical Conductivity of Porous Composite Electrodes for Solid Oxide Cells Using a Monte Carlo 3D Equivalent Electronic Circuit Networks

Solid oxide cells (SOCs) show high potential in energy conversion applications necessary for the decarbonization of the economy. Their advantage consists in ability to operate at high temperatures, reaching up to 900 °C. Firstly, it results in accelerated electrode reactions kinetics, secondly, in favorable thermodynamic conditions decreasing the equilibrium voltage of the water splitting. As a result, SOCs are attractive candidates for both efficient electrolysis and fuel cell applications, offering a robust solution in the pursuit of clean energy. However, the elevated operational temperature also introduces material challenges that hinder the competitiveness of SOCs.Porous gas diffusion electrodes are used to accomplish the desired electrode reactions. Considering conventional exclusively electron-conductive electrode materials, triple phase boundary (TPB) is required for the reactions to take place – a simultaneous contact of electron-conductive, ion-conductive and gaseous phase. While the electrode and electrolyte phases are solid, the gaseous phase is represented by open porosity in the electrode body. TPB is located exclusively at the contact area of electrode and electrolyte components in the case of single-phase electrodes, limiting the electrode electrocatalytic performance. To avoid the limitation by TPB length, composite electrodes are frequently used. Due to the involvement of the ionically conductive phase, they exhibit improved electrocatalytic capabilities.Electrolyte phase, however, usually exhibits 4 orders of magnitude lower electrical conductivity than the electron-conductive phase, while gaseous phase is electrically non-conductive. Thus, an improper phase composition and morphology of the composites can lead to a significant drop in their electrical conductivity and thus in the cell performance. Simple and reliable method for the conductivity value prediction is up to now missing. At the same time, experimental determination is both expensive and time-consuming. The goal of this study was to develop simple, fast and reliable method for prediction of electrical conductivity of the porous electron-ion conductor composites.The key feature of the presented approach lies in the minimal requirements for input parameters. Only electrode phase composition and bulk electrical conductivity of each phase are required. Based on the input composition, the model generates a 3D artificial specimen, a domain discretized into cubic voxels each assigned randomly to a specific phase. The resulting structure is substituted with an equivalent circuit network with electric elements corresponding to the electrochemical properties of the material components: specific resistivity of electrical conductors and polarization resistance / capacitance of electrochemical reaction at material interface. In-silica electrochemical impedance spectroscopy measurement is performed by solving charge balance following Kirchhoff’s current law for multiple frequency values. Resulting impedance spectrum is fitted in order to obtain Ohmic and polarization resistance and the capacitance of the artificial specimen. This procedure is averaged over a large number of artificial specimens in a Monte Carlo manner.Conventionally used oxygen electrode composite material lanthanum strontium manganite (LSM) mixed with yttria-stabilized zirconia (YSZ) was used to produce validation dataset. LSM:YSZ powder mixtures of compositions between 1:0 and 0:1, chosen to produce samples of various degree of LSM percolation, were homogenized. The mixtures were fired at 1150 °C. Electrical conductivity of the pellets was determined at temperatures between 600 and 800 °C using electrochemical impedance spectroscopy.Experimental data obtained were confronted to the model results. The model demonstrated very good accuracy for a porosity value of up to 55%. Significant error was observed in the porosity range between 55% and 68%. Finally, the model failed to generate an artificial specimen with a porosity of 75%. As it was found, the limited applicability of the model for the materials characteristic for high porosity was caused by the coalescence of the void phase. This shortcoming of the model was solved by implementing morphological parameter describing degree of void phase coalescence in the electrode structure. Due to this modification, model allows to gain valuable information on the microstructure of the studied composite material on the base of the experimentally determined conductivity data.This work introduces a novel modelling approach with minimal amount of input parameters, streamlining the prediction of electrical conductivity of porous electron-ion conductor composites. This simplified yet effective methodology holds great promise for efficiently characterizing and optimizing materials for energy conversion applications, offering a valuable tool for advancing research in the field.This publication was supported by the project "The Energy Conversion and Storage", funded as project No. CZ.02.01.01/00/22_008/0004617 by Programme Johannes Amos Commenius, call Excellent Research.

Comparative study of random and block SPEEK copolymers for high-temperature proton exchange membrane electrolysis

Traditionally, High-temperature proton Exchange Membrane Electrolysis (HT-PEME) has relied on costly and exceptionally hydrogen-permeable PFSA ionomers like Nafion®, Flemion®, and Aciplex®. Sulfonated Poly (ether ether ketone) (SPEEK) membranes have been developed as potential substitutes for the highly hydrogen permeable Nafion® membranes. The ion exchange capacity (IEC) of SPEEK membranes has been varied, ranging from 0.5 to 2.2 meq/g, to enhance their performance. Furthermore, the incorporation of ion-conducting units into these polymers is explored using both random and block copolymerization approaches. At 75 °C, SPEEK membranes exhibit significantly lower hydrogen diffusivity (35–50 barriers) compared to Nafion® and Flemion® membranes (∼202 barriers). Among SPEEK yttria-stabilized zirconia membranes (YSZM), those produced through random copolymerization exhibit marginally greater proton-to-hydrogen selectivity than YSZM derived from block SPEEK copolymers with a similar ion exchange capacity (IEC). This could be ascribed to the improved hydrogen-blocking capability resulting from an underdeveloped hydrophilic component. Among the SPEEK membranes tested, the random SPEEK membrane with an IEC of approximately 1.9 meq/g demonstrates superior performance (6.8 A/cm2) compared to a similarly thick (∼45 μm) Flemion® membrane (4.4 A/cm2) at 2.2 V. However, during an accelerated stress test involving 410 successive fluctuating flow densities of 2.8 and 0.04 A/cm2 imitating the alternating period's cycles of a water electrolyzer, the random SPEEK membrane exhibits a higher degradation rate (860 μV/h) compared to Flemion® and Nafion® (505 μV/h).

Micro-cold Spray Deposition of YSZ Films from Ultrafine Powders Using a Pressure Relief Channel Nozzle

The use of ultrafine powders in the micro-cold spray (MCS) process, also referred to as the aerosol deposition method, typically results in porous and/or poorly adhering films because the particles do not impact at a high enough velocity for sufficient plastic deformation and interparticle bonding to occur. Under typical operating conditions, particles < 100 nm accelerate to high velocities but then are slowed by the stagnant gas in the bow shock that forms just upstream of the substrate. Using larger particles reduces particle slowing, but large particles can cause erosion of the film at high impact velocity, decreasing deposition efficiency. In this study, a pressure relief channel nozzle using helium as a carrier gas is proposed such that high-velocity deposition of yttria-stabilized zirconia particles as small as 10 nm in diameter is possible. This is well below the size range of powders previously used for MCS. The proposed nozzle design increases impact velocities for 10, 20, and 50 nm particles by ~ 880, 560, and 160 m/s, respectively, when compared to a conventional nozzle. Experimental deposition of ultrafine 8YSZ powder shows that the pressure relief channel nozzle results in lower porosity and more uniform deposits, with a ∼ 186% increase in deposition efficiency.

Effect of different precipitants on the formation of ultrafine 3 mol% yttrium-stabilized zirconia nanopowders by reverse precipitation

This study proposes a simple method for preparing highly dispersed ultrafine 3 mol% yttrium-stabilized zirconia nanopowders (3YSZ NPs), which provide high-quality powders for use in high-performance ceramics. First, 3YSZ NPs were prepared using a reverse precipitation method with different precipitants: NaOH, NH3·H2O and (NH3)2CO3. The thermal decomposition, phase evolution, morphology and chemical composition of the precursor particles and 3YSZ NPs were analysed. The effects of precipitant and reaction conditions on 3YSZ NPs were systematically studied. The results show that there are differences in the mechanism of powder synthesis using the co-precipitation method among the three precipitants. In addition, ultrafine 3YSZ NPs with minimum agglomeration and high sphericity can be prepared using NaOH. Y3+ and ZrO2+ cannot coprecipitate in solution according to the designed molar ratio in the NH3·H2O and (NH4)2CO3 methods. Considering agglomeration, crystallinity and elemental distribution, NaOH is the best precipitant. The prepared zirconia powder exhibits high crystallinity, good dispersion, a narrow particle size distribution and a tetragonal phase structure. By investigating the effects of calcination temperature, titration end point pH and NaOH concentration, 3YSZ NPs with an average particle size of 22.29–38.94 nm are obtained.

Al2O3 enhanced bi-phase high-entropy ceramic composites

One limitation of high-entropy ceramics is the low toughness that could hinder their implementations in the relevant industries despite the diverse potential applications. This challenge is increasingly attempted in recent years with high-entropy ceramic composites which consisted of high-entropy ceramic matrix and secondary phase. A suitable secondary phase candidate is Al2O3 which to-date has not been reported for such ceramic composites. In this work, bi-phase high-entropy ceramic composites of cubic fluorite oxide matrix and Al2O3 secondary phase were in situ synthesized from HfO2, ZrO2, CeO2, CaO and Al2O3 nano powders via solid-state reaction method. Variation of thermal and mechanical properties of the composites with Al ratio was due to the combined effects of the inherent properties of Al2O3, concentrations of grain boundary and of oxygen vacancies. The high-entropy ceramic composites enhanced by Al2O3 were also compared with yttria-stabilised zirconia for potential application as thermal barrier coating material.

Design and optimization of a novel patient-specific subperiosteal implant additively manufactured in yttria-stabilized zirconia

ObjectiveTo design a patient-specific subperiosteal implant for a severely atrophic maxillary ridge using yttria-stabilized additively manufactured zirconia (3YSZ) and evaluate its material properties by applying topology optimization (TO) to replace bulk material with a lattice structure. MaterialsA contrast-based segmented skull model from anonymized computed tomography data of a patient was used for the initial anatomical design of the implant for the atrophic maxillary ridge. The implant underwent finite element analysis (FEA) and TO under different occlusal load-bearing conditions. The resulting implant designs, in bulk material and lattice, were evaluated via in-silico tensile tests and 3D printed. ResultsThe workflow produced two patient-specific subperiosteal designs: a) an anatomically precise bulk implant, b) a TO lattice implant. In-silico tensile tests revealed that the Young’s modulus of yttria-stabilized zirconia is 205 GPa for the bulk material and 83.3 GPa for the lattice. Maximum principal stresses in the implant were 61.14 MPa in bulk material and 278.63 MPa in lattice, both tolerable, indicating the redesigned implant can withstand occlusal forces of 125–250 N per abutment. Furthermore, TO achieved a 13.10 % mass reduction and 208.71 % increased surface area, suggesting improved osteointegration potential. SignificanceThe study demonstrates the planning and optimization of ceramic implant topology. A further iteration of the implant was successfully implanted in a patient-named use case, employing the same fabrication process and parameters.

Strengthening Ti3SiC2/Cu brazed joint assisted with cold spray additive manufacturing: Lower brazing temperature through interdiffusion and graded reinforcement for stress relaxation

Graded composite fillers exhibit unique advantages in alleviating residual stress in ceramic/metal brazed joints. However, traditional methods for preparing graded composite fillers are often complex and may deplete their strengthening phases. In this study, cold spray additive manufacturing was employed to fabricate yttria-stabilized zirconia (YSZ)-Ti25Zr25Ni25Cu25-Ag graded composite coatings on Cu substrates to serve as fillers. The graded composite coatings and the resultant Ti3SiC2/Cu brazed joints were systematically characterized to elucidate the deposition mechanism of the coatings and its residual stress-relaxed mechanism. The bondings between particles in the coatings, based on their plastic deformation ability, were classified into noncrystalline weak bonds and homogeneous strong bonds. Both bondings facilitated the elemental interdiffusion between filler and Cu substrate during the heating process, which contributed to the formation of Ag-Cu eutectic. This significantly reduced the required brazing temperature and its induced residual stress. Furthermore, the solid phase transformation of graded-distributed YSZ within the brazing seam from tetragonal to monoclinic achieved a smooth thermal transition and releasing residual stress at the same time. Consequently, the shear strength of the brazed joint reached to the highest value of 110.23 ± 3.45 MPa, which was Much higher than the previously reported values. This study introduces a novel method for residual stress relaxation assisted with cold spray technology and broadens its application in the brazing field.

Does dental material type influence bacterial adhesion under the same polishing conditions? Direct observation using a fluorescent staining technique: An in vitro study.

Highly polished 3, 4, and 5 mol% yttria-stabilized zirconia and CAD/CAM composite resin samples were prepared, and the influence of surface roughness (Ra and Sa, 21 areas/group), wettability (contact angle and surface energy, 3 samples/group), and surface chemical composition (2 samples/group) on single-strain bacterial adhesion models (Porphyromonas gingivalis, Streptococcus oralis, Streptococcus sanguinis, Streptococcus gordonii, and Streptococcus mutans) were compared via fluorescent staining with graphical analysis (21 areas/group). Statistical analysis was performed using the Shapiro-Wilk test followed by one-way analysis of variance with Tukey's test or the Kruskal-Wallis test with Dunn's test (α=0.05) and linear regression. For dental zirconia with the same surface roughness, the yttria content did not significantly influence the initial bacterial adhesion. However, higher bacterial adhesion was detected for the composite resin owing to its high C, O, and Si contents. There was no correlation between surface energy and bacterial adhesion for any bacterial strain (p<0.005).

CMAS Corrosion Resistance of Plasma-Sprayed YSZ and Yb2O3-Y2O3-Co-Stabilized ZrO2 Coatings under 39–40 KW Spraying Power

This study uses atmospheric plasma spraying (APS) technology to prepare thermal barrier coatings (TBCs) with yttrium-stabilized zirconia (YSZ) and Yb2O3-Y2O3-co-stabilized ZrO2 (YbYSZ) materials at different spraying powers. It analyzes the differences and changes in the microstructure, thermodynamic properties, and mechanical properties of the TBCs. The CaO-MgO-Al2O3-SiO2 (CMAS) resistance of coatings was tested using thermal cycling-CMAS experiments and isothermal corrosion experiments. Compared to YSZ coatings, YbYSZ coatings have lower thermal conductivity, a higher hardness and elastic modulus, a longer lifetime under thermal cycling-CMAS conditions, and lower penetration and degradation depths. Under thermal cycling-CMAS coupling conditions, the optimal power range for the longest thermal cycling lifetime for both coatings is 39–40 kW. Overall, compared to the YSZ material, the YbYSZ material exhibits superior properties.

Phase Evolution of Yttria-Stabilized Zirconia During Hybrid Microwave Sintering

Phase Evolution of Yttria-Stabilized Zirconia During Hybrid Microwave Sintering

A Dynamic Testing Approach for Particulate Erosion–Corrosion for Gas Turbine Coatings

Abstract Particle interactions in engines can be complex phenomena leading to degradation of thermal (TBCs) and environmental barrier coatings (EBCs) meant to protect engine components. Ingestion of particles into the engine can lead to recession of coatings due to particle erosion. Similarly, these particles can become molten, adhere to coatings, and result in thermochemical corrosion of coating materials. Erosion testing is often carried out where particles are injected into a gas stream, accelerated within a nozzle, and impinge on samples. Conversely, most molten particle corrosion testing is often done in static furnaces, which does not capture the dynamic nature of deposition. Nevertheless, these damage mechanisms are often tested separately, and no standard exists to test both erosive/corrosive particle interactions with coating materials under relevant turbine operating conditions. Understanding the synergies of particle interactions is crucial in determining operating lifetimes of potential coating materials. Such considerations emphasize the need for realistic approaches in standardizing particle interaction testing in combustion environments. This study outlines efforts at NASA Glenn's Erosion Burner Rig Facility in improving dynamic erosion/corrosion testing methods by assessing the durability of state-of-the-art (SOA) TBC 7 wt % yttria-stabilized zirconia (7YSZ) as a function of particle deposition rate, burner temperature, and particle size. Calibration data to determine particle deposition rate will be presented, and mass and optical profilometry measurements were utilized to estimate mass/volume loss versus deposition per increment of particulate used. Electron microscopy analyses were then carried out to assess coating damage after testing.

Tribo-Chemical Reactions in DLC-Zirconia Sliding under Ethanol Gas Environment.

A reactive force field (ReaxFF) molecular dynamics simulation is performed for the sliding of diamond-like carbon (DLC) and yttria-stabilized zirconia (YSZ) under an ethanol gas environment, motivated by the previous experiment of ultralow friction phenomenon (friction fade-out). We observe (i) dissociation of ethanol into ethoxy and hydrogen, both of which simultaneously adsorb on the YSZ surface, and (ii) dissociation of ethanol into ethyl and hydroxy, the former of which forms a bond with another ethanol molecule and the latter of which adsorbs on the DLC surface. Reaction (i) is enhanced by the sliding motion, but occurs even without it, while reaction (ii) only occurs during sliding with a sufficiently high load pressure. The potentials of mean force for the two reactions are also calculated combining the steered MD and Jarzynski equality. It is shown that the activation energies of reactions (i) and (ii) are significantly lowered by the YSZ and DLC surfaces, respectively, as compared to those in a vacuum. The resultant activation energy is higher for reaction (ii) than for reaction (i).

Improved Reversibility of Thin-Film Solid Oxide Cells at 500 °C by Tailoring Sputtering Processes for Depositing Yttria-Stabilized Zirconia Electrolyte.

The present study investigates the impact of sputtering configurations on the microstructure and crystallinity of thin-film yttria-stabilized zirconia electrolytes for anodized aluminum oxide-supported all-sputtered thin-film reversible solid oxide cells. Employing various sputtering parameters, such as target-substrate distance and substrate rotation speed, the present study reveals distinct surface characteristics and crystalline structures of thin-film yttria-stabilized zirconia. The microstructure analysis includes scanning electron microscopy and atomic force microscopy examinations, uncovering the influence of the process parameters on the surface morphology, roughness, and grain size. X-ray diffraction data illustrate the texture preferences and crystallite characteristics. The electrochemical characterization of the reversible solid oxide cells demonstrates that the optimized sputtering configuration significantly outperforms the others in both SOFC and SOEC modes, showing exceptional current densities of 964 mA/cm2 at 1.3 V in electrolysis mode at 500 °C. Electrochemical impedance spectroscopy further reveals improved charge transfer reactions at the interface of the electrolyte. The enhanced electrochemical performance is attributed to the unique microstructure and crystallinity of the thin film of yttria-stabilized zirconia. The record-breaking electrolysis performance of this work at 500 °C underscores the potential of tailored sputtering parameters in optimizing the reversible solid oxide cell performance.

Formation of {111} oriented domains during the sputtering epitaxy growth of (001) oriented Iridium films

In the wafer-scale growth of Ir(001) on yttria-stabilized zirconia (YSZ) by magnetron sputtering epitaxy two kinds of {111} oriented domains are observed. One consists of sharp ‘fjord’-shaped features in which four 90° alternated rotational variants of {111} are possible and the second one consists of islands with less defined shapes in which eight 45° alternated rotational variants can be found. Their formation occurs directly at the Ir/YSZ interface along incoherent grain boundaries, likely nucleating at local defects of the YSZ surface. In order to avoid these misoriented domains, process separation and proper etching pretreatment of the wafers both before and between the sputtering processes have been found to be the key strategy for achieving reproducibility and overall better material quality.

Zirconia toughened fluorosilicate glass-ceramics for dental prosthetic restorations

BackgroundDental glass-ceramics have limited strength and are unsuitable for high-stress-bearing areas. Zirconia stands out as a popular choice for reinforcing dental glass-ceramics due to its biocompatibility and high fracture toughness. ObjectivesThe objective of the study is to investigate the effect of an increase in zirconia (25, 30, 35 and 50 wt%) on microstructure, chemical solubility, hardness, fracture toughness, and brittleness index of fluorosilicate glass systems for dental restorative applications. Material and methodsThe fluorosilicate glass frit was obtained through the melt-quench technique. The glass frit was ball-milled with 25, 30, 35 and 50 wt % of 3 mol % yttria-stabilized zirconia (G-25Z, G-30Z, G-35Z, and G-50Z). The composites were sintered to 1000 °C for 48h at a heating rate of 5 °C/min. The glass frit was subject to differential scanning calorimetry. Phase analysis and microstructural characterization were carried out. The crystallite size of zirconia and glass-ceramics, micro-hardness, indentation fracture toughness, brittleness index, and chemical solubility were evaluated. ResultsPhase analysis reveals tetragonal and monoclinic zirconia with minor peaks of forsterite, fluorphlogopite, norbergite, and spinel. Their microstructures reveal the characteristic house-of-cards arrangement of fluorophlogopite crystals with dispersed zirconia. The results of hardness and fracture toughness show a statistically significant improvement with an increase in zirconia content. The crystallite size of zirconia and fluorophlogopite crystals with aspect ratio, brittleness index, and chemical solubility declined as the zirconia content increased. ConclusionsIncrease in zirconia content from 25 wt % to 50 wt % in heat-treated fluorosilicate glass systems reveals non-reactive zirconia with a stable glass matrix and limits the growth of fluorphlogopite crystals with a house-of-cards microstructure. This results in a range of properties suitable for dental restorations of enhanced hardness, and improved fracture toughness. Despite these improvements, the material maintains its machinability with reduced chemical solubility.