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The hot‐corrosion behavior of sintered 3 mol.% yttria‐stabilized zirconia (3YSZ) ceramic with significant (1:4 in ratio) variation in grain sizes was investigated. Contrary to the popular perception of the role of grain boundaries, ceramics with smaller grains portrayed remarkable hot‐corrosion resistance despite having ∼450% more grain boundaries compared to their counterpart. The mechanism behind a rather ‘unusual’ role of the grain boundary in deciding the corrosion pathways for 3YSZ ceramic systems was examined. The affinity of NaVO3 to react with Y2O3 was found to be a crucial step for the initiation of corrosion and this process had no potential influence on the fraction of grain boundaries in the system. A phase transformation (tetragonal to monoclinic) induced porosity created easy path for the molten liquid to flow inside the ZrO2 matrix. The ceramic with a smaller grain size resisted such a transformation and resulted in a much lower penetration depth for the corrosion to proceed further inside the matrix. Although grain boundaries are usually portrayed as weak points for corrosion, this study illustrates an alternate pathway using which corrosion can be averted in a fine grained 3YSZ ceramic. [ABSTRACT FROM AUTHOR]

A novel CaO–Al 2 O 3 –SiO 2 –Li 2 O (CASL) glass was developed for bonding yttria–stabilized zirconia ceramics (YSZ). The CASL glass possessed a coefficient of thermal expansion (CTE) that matched with YSZ and exhibited outstanding wettability on the surface of YSZ substrate. During the bonding process, mutual dissolution and diffusion between YSZ and CASL glass took place, which ensured good interface bonding. Furthermore, the rapid cooling speed led to a completely amorphous seam, which allowed the CTE of the seam to correspond with that of the original glass. The optimal flexural strength of YSZ/YSZ joints could reach more than 90 % of that of the YSZ. [ABSTRACT FROM AUTHOR]

Oxygen produced through in‐situ resource utilization (ISRU) is critical to maintaining a permanent human presence on the lunar surface. Molten regolith electrolysis and carbothermal reduction are two promising ISRU techniques for generating oxygen directly from lunar regolith, which is primarily a mixture of oxide minerals; however, both processes require operating temperatures of 1600°C to melt lunar regolith and dissociate the molten oxides. These conditions limit the use of many oxide refractory materials, such as Al2O3 and MgO, due to rapid degradation resulting from reactions between the refractory materials and molten lunar regolith. Yttria‐stabilized zirconia (YSZ) is shown here to be a promising refractory oxide to provide containment of molten regolith while demonstrating limited reactivity. This work focuses on corrosion studies of YSZ powders and dense YSZ crucibles in contact with molten lunar maria and highlands regolith simulants at 1600°C. The interactions between YSZ and molten regolith were characterized using scanning electron microscopy/energy dispersive spectroscopy, X‐ray diffraction, and electron backscatter diffraction. A FactSage thermochemical model was created for comparison with the experimental results. These combined analyses suggest that lunar maria regolith will degrade the YSZ faster than the lunar highlands regolith due to the lower viscosity of the maria regolith. The feasibility of long‐term molten regolith containment with YSZ is discussed based on the YSZ powder and crucible results. [ABSTRACT FROM AUTHOR]

The oxidation resistance of yttria‐stabilized zirconia (YSZ) thermal barrier coatings and conductivity of YSZ solid oxide fuel cells are closely related to the diffusion of oxygen ions (O2−$\text{O}^{2-}$) in YSZ, but the O2−$\text{O}^{2-}$ diffusion behavior in small‐sized YSZ samples under non‐isothermal condition where the temperature gradient (∇T$\nabla T$) could be significant remaining elusive. Herein, we disclose the previously unrevealed effect of extreme ∇T$\nabla T$ on the self‐diffusion behavior of O2−$\text{O}^{2-}$ in both pristine and strained YSZ. It is found that the O2−$\text{O}^{2-}$ self‐diffusion coefficient (D$D$) experiences a nearly one‐fold increase under an extreme ∇T$\nabla T$ around 60 K/Å. The diffusion direction tends to be toward regions of high temperature. Uniaxial stress is revealed to reduce D$D$ due to the increased activation energy of ions, whereas ∇T$\nabla T$ promotes the O2−${\text{O}}^{2-}$ self‐diffusion in the stressed system. These results underscore the role of ∇T$\nabla T$ in influencing the self‐diffusion behavior of YSZ, providing a theoretical guideline for examining ceramics serving in extreme environments. [ABSTRACT FROM AUTHOR]

The development of highly conductive and thermally stable solid electrolytes is crucial for the next generation of intermediate temperature solid oxide fuel cells (IT-SOFCs). This study investigates the influence of copper (Cu) doping on the microstructure and ionic conductivity of 8 mol. % yttria-stabilized zirconia (8YSZ) when sintered at lower temperatures. The mechanochemical synthesized 1, 3, and 5 wt. % Cu-doped 8YSZ compacts were extensively characterized their properties through a suite of analytical techniques like X-ray diffraction, Raman, X-ray photoelectron, UV–Vis diffused reflectance, particle size analyzer, BET surface area, Emission Scanning Electron Microscopy-Energy Dispersive X-Ray, and AC impedance. The results revealed enhanced ionic conductivity and sinterability, at reduced temperature of 1373 K, with the 5 wt. % Cu-doped 8YSZ demonstrating the highest ionic conductivity of 4.18 × 10−3 S cm−1 at 1023 K, alongside reduced activation energy of 1.14 eV. The lower sintering temperatures and consequential benefits in performance metrics suggest Cu-doping as an effective strategy for optimizing 8YSZ-based electrolytes lowering SOFC manufacturing costs without compromising performance for IT-SOFCs. [Display omitted] • 1. Copper -doped 8YSZ synthesized via mechanochemical process results in varied cubic, tetragonal, and monoclinic crystal phases. 2. Copper doping improves 8YSZ's ionic conductivity and sinterability for intermediate -temperature solid oxide fuel cells. 3. 5 wt. % Cu -doped 8YSZ achieves the highest conductivity (4.18 × 10−3 S cm−1 at 1023 K) and lowest activation energy (1.11 eV). 4. Copper doping is suggested to make 8YSZ-based solid oxide fuel cell electrolytes more cost-effective. [ABSTRACT FROM AUTHOR]

The negative electric potential difference observed in a YSZ-based thin film potentiometric sensor at a low operating temperature of 673 K is investigated. The multilayered sensor is grown sequentially using pulsed laser deposition at 998 K with Cu-Cu2O reference electrode, YSZ electrolyte and Pt as working electrode respectively. The thickness of the Cu-Cu2O reference layer is a critical factor in thin film sensors as the Pt3O4 phase stabilized along with Cu-Cu2O can reach the YSZ interface. XRD, μ- Raman and XPS confirm the formation of the Pt3O4 phase on the reference side along with the Cu-Cu2O layer. However, the pure Pt3O4 phase could not be stabilized in the thin film without Cu-Cu2O. The presence of the Pt3O4 phase on the reference side generates a Pt-Pt3O4 reference couple with an equilibrium oxygen partial pressure of ~ 104 ppm higher than the sample oxygen pressure of 10-103 ppm giving rise to a negative electric potential difference with a sensitivity of -7.5 mV/decade. [ABSTRACT FROM AUTHOR]

We prepared yttria‐stabilized zirconia (YSZ) and titania crystalline thin films on polycarbonate (PC) substrates by the sol‐gel transfer technique that we have developed recently. Precursor gel films were deposited by spin‐coating on a polyimide/polyvinylpyrrolidone mixture layer on Si(100) substrates, and then were calcined at 600°C. The spin‐coating and the calcination were cycled, followed by final firing at 600–1000°C, to obtain 140–190 nm thick, YSZ and titania crystalline thin films. The film densification progressed as the final firing temperature increased, where the porosity calculated from the refractive index decreased down to a few percent. The film thus obtained was heated at 190°C on a hot plate, and a PC substrate was pressed on the film to transfer it to the PC substrate. The transferability quantified by image analysis of the film area was found to be significantly different between the YSZ and titania films. In the case of YSZ films, the area of silicon that was fractured and adhered to the transferred film increased significantly with increasing firing temperature, leading to a decrease down to 0% in the fraction of the successful transfer area without such a damage. On the other hand, the fraction of the successful transfer area remained around 90% irrespective of the firing temperature for the titania films. The surface of the titania films that were fired at 800–1000°C and transferred to PC substrates had voids of several tens nm scale, which may have been formed during anatase‐to‐rutile phase transformation. We thought that the reduced titania/Si(100) contact area due to such void formation facilitated the delamination of the titania films from Si(100) substrates. High temperature firing, which promotes crystallization and densification of films, thus affects differently the film transferability to plastic substrates, depending on the type of films. The work also suggested possible use of titania films as release‐assisting layers. [ABSTRACT FROM AUTHOR]

The gradual transition of hydrogen as a fuel for land-based gas turbines has resulted in direct changes to the combustion environment. The inadequate combustion of hydrogen fuel can lead to a transition from an oxidizing environment to a partially reducing environment, and further introduces a new potential failure mode for existing thermal barrier coating materials. In this study, tests were conducted on thermal barrier coating samples at 1000 °C in Ar + 5 % O 2 and Ar + 5 % H 2 environments, in addition to samples subjected to heat-treatment in pure argon and air environments to provide a comparison against low oxygen partial pressure and conventional failure modes. The results demonstrated that the degree of sintering of the top coat decreased gradually with a decreasing oxygen partial pressure, and was significantly inhibited in a reducing environment. Faster cooling rates led to the expansion of vertical cracks in the top coat toward the interface, which was accompanied by the generation of numerous transverse cracks in the reducing environment. In contrast, the structure of the top coat remained intact in the other three environments. Furthermore, effective methods for improving the coating durability in reducing environments are discussed. This study therefore contributes to a comprehensive understanding of the failure behavior of thermal barrier coatings in reducing environments, providing new insights into enhancing the stability under such conditions. [ABSTRACT FROM AUTHOR]

When operating at very high temperatures (starting from 1200 °C), thermal barrier coatings (TBCs) start interacting with oxide particles such as CMAS (CaO-MgO-Al2O3-SiO2), found in sand or volcanic ashes. Namely, CMAS can infiltrate the TBC and tamper the thermal and mechanical properties of said TBC, leading to its deterioration. This study aimed to understand the interaction between yttria partially stabilized zirconia (YSZ) TBCs and CMAS particles under a thermal gradient. The TBC was made through an EB-PVD process. The experimental study was conducted with a laser rig. TBC samples were heated up to 1200 °C and exposed to a cylinder-shaped CAS (CaO-Al2O3-SiO2) deposit for different durations. The study was conducted in presence of a through-thickness thermal gradient of up to 150 °C in the sample. It was observed that the infiltration is a rather quick phenomenon; while, the dissolution of the TBC and the precipitation of the crystalline phases worked on a longer timeline. Both phenomena can then be considered uncoupled under these test conditions and modeled as such. A heat transfer model was implemented as to better understand the different phenomena happening. The model was fitted to experimental data through a test-calculation dialog. [ABSTRACT FROM AUTHOR]

In this work, the deformation behavior of porous ceramics ZrO2–5.5 wt.% Y2O3 with different morphology of the pore space under axial quasi-static compression is studied by the digital image correlation (DIC) method. Two stages of the deformation behavior of the ceramics have been identified, namely, the controlled accumulation of microcracks and the formation of block structures. It has been found that an increase in the average pore size leads to a decrease in the tensile strength, a decrease in the effective elasticity modulus, and an increase in the ultimate deformation, while the nature of the deformation macrolocalization changes from ordered to chaotic one. It is shown that the rate of accumulation of local deformations in the central part of the deformable sample with a pore size of 68 μm is several times higher than in the sample with a pore size of 29 μm. [ABSTRACT FROM AUTHOR]

La2Ce2O7 (LC) has been identified as a promising thermal barrier coating (TBC) for use up to 1250 °C. In this study, a TBC system was deposited on grit-blasted Inconel 738 using atmospheric plasma spraying (APS) with NiCrAlY as the bond coat, followed by YSZ, and then LC as the top layer. The coatings were exposed to a mixture of molten Na2SO4 (45 wt.%) and V2O5 (55 wt.%) at 950 °C for hot corrosion. On the top LC layer, LaVO4, CeVO4 and CeO(1.66–2.00) formed as hot corrosion products after 4 h exposure. A reaction between YSZ and the corrosion products could not be observed due to the absence of YVO4. The hot corrosion mechanism of the LC-based TBC is also discussed in this study. [ABSTRACT FROM AUTHOR]

Higher operating temperatures for gas turbine engines require highly durable thermal barrier coatings (TBCs) with improved insulation properties. A suspension plasma spray process (SPS) had been developed for the deposition of columnar-structured TBCs. SPS columnar TBCs are normally achieved at a short standoff distance (50.0 mm–75.0 mm), which is not practical when coating complex-shaped engine hardware since the plasma torch may collide with the components being sprayed. Therefore, it is critical to develop SPS columnar TBCs at longer standoff distances. In this work, a commercially available pressure-based suspension delivery system was used to deliver the suspension to the plasma jet, and a high-enthalpy TriplexPro-210 plasma torch was used for the SPS coating deposition. Suspension injection pressure was optimized to maximize the number of droplets injected into the hot plasma core and achieving the best particle-melting states and deposition efficiency. The highest deposition efficiency of 51% was achieved at 0.34 MPa injection pressure with a suspension flow rate of 31.0 g/min. With the optimized process parameters, 1000 μm thick columnar-structured SPS 8 wt% Y2O3-stabilized ZrO2 (8YSZ) TBCs were successfully developed at a standoff distance of 100.0 mm. The SPS TBCs have a columnar width between 100 μm and 300 μm with a porosity of ~22%. Furnace cycling tests at 1125 °C showed the SPS columnar TBCs had an average life of 1012 cycles, which is ~2.5 times that of reference air-plasma-sprayed dense vertically cracked TBCs with the same coating thickness. The superior durability of the SPS columnar TBCs can be attributed to the high-strain-tolerant microstructure. SEM cross-section characterization indicated the failure of the SPS TBCs occurred at the ceramic top coat and thermally grown oxide (TGO) interface. [ABSTRACT FROM AUTHOR]

In this work, we have expanded the possibilities of the multiphase-flash sintering (MPFS) technique by investigating several configurations that involve multiple dogbone specimens (ranging from 1 to 3) and multiple phases (also ranging from 1 to 3). Unlike the traditional MPFS approach using complex 3D or cylindrical samples, this new method allows for a direct comparison with the established conventional flash sintering technique. Our experimental results with dense 8-mol% Yttria-stabilized zirconia demonstrate a significant reduction in the onset temperature as the number of phases and dogbones increases. Building on these findings, we achieved the preparation of pure bulk specimens of SrFe 12 O 19 for the first time through reactive multiphase-flash sintering. [ABSTRACT FROM AUTHOR]

The amalgamation of digital light processing (DLP) technology and pressureless sintering has emerged as a promising method for producing delicate, complex, and custom-made yttria-stabilized zirconia (YSZ) components. The procedure consists of fabrication of green part using DLP, debinding to remove the binders and sintering to densify the parts. Explorations in the parameter selection in each step are still far from maturity for producing defect-free densified parts. This study addresses the effect of DLP print parameters on the density of green parts and surface irregularities. DLP printing parameters, such as layer thickness, orientation, and light intensity, were selected, and a central composite design methodology was adopted for the design of experiments to investigate the impact of individual parameter as well as their interactions. The density of the green part decreased with an increase in layer thickness from 10 μm to 70 μm, whereas an increase in density was observed when the part orientation changed from 0 ° to 90°, and the intensity changed from 10 to 50 mW/cm2. The variations in layer thickness and part orientation substantially impact the surface roughness, but variations in intensity have comparatively less influence on the surface roughness. The in-layer and inter-layer voids of the samples fabricated with varying parameters were analyzed using scanning electron microscopy. The minimum surface roughness and maximum green part density responses were obtained using regression equations and a multi-objective optimization strategy. Subsequently, the samples were debinded and sintered to produce high-density zirconia components. To establish the importance of parameter optimization, a comparison of the specimen density and surface irregularity in the green and sintered states was performed for specimens fabricated with optimized parameters and a randomly chosen set of parameters. The novel study provides the parametric relation to fabricate as desired green and sintered density parts along with tuned surface roughness. [ABSTRACT FROM AUTHOR]

The development of advanced thermal barrier coating (TBC) materials with better hot corrosion resistance, phase stability, and residual stresses is an emerging research area in the aerospace industry. In the present study, four kinds of TBCs, namely, single-layer yttria-stabilized zirconia (YSZ), single-layer gadolinium zirconate (GZ), bilayer gadolinium zirconate/yttria-stabilized zirconia (YSZ/GZ), and a multilayer functionally graded coating (FGC) of YSZ and GZ, were deposited on NiCrAlY bond-coated nickel-based superalloy (Inconel 718) substrates using the atmospheric plasma spray technique. The hot corrosion behavior of the coatings was tested by applying a mixture of Na2SO4 and V2O5 onto the surface of TBC, followed by isothermal heat treatment at 1273 K for 50 h. The characterization of the corroded samples was performed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) to identify physical and chemical changes in the coatings. GIXRD was used to analyze the residual stresses of the coatings. Residual stress in the FGC coating was found to be −15.2 ± 10.6 MPa. The wear resistance of TBCs is studied using a linear reciprocating tribometer, and the results indicate that gadolinium zirconate-based TBCs showed better performance when deposited in bilayer and multilayered functionally graded TBC systems. The wear rate of as-coated FGC coatings was determined to be 2.90 × 10−4 mm3/Nm, which is lower than the conventional YSZ coating. [ABSTRACT FROM AUTHOR]

Polymer-infiltrated ceramic network (PICN) materials have gained considerable attention as tooth-restorative materials due to their mechanical compatibility with human teeth, especially with computer-aided design and computer-aided manufacturing (CAD/CAM) technologies. However, the designed geometry affects the mechanical properties of PICN materials. This study aims to study the relationship between manufacturing geometry and mechanical properties. In doing so, zirconia-based PICN materials with different geometries were fabricated using a direct ink-writing process, followed by copolymer infiltration. Comprehensive analyses of the microstructure and structural properties of zirconia scaffolds, as well as PICN materials, were performed. The mechanical properties were assessed through compression testing and digital image correlation analysis. The results revealed that the compression strength of PICN pieces was significantly higher than the respective zirconia scaffolds without polymer infiltration. In addition, two geometries (C-grid 0 and C-grid 45) have the highest mechanical performance. [ABSTRACT FROM AUTHOR]

Abstract:  Currently, around 50% (~178 million) of all Americans are missing at least 1 tooth, with 12% (~40 million) of Americans missing all of their teeth. Dental implants are a common solution to this issue; titanium is the leading material of choice. Zirconia ceramic dental implants are a suitable replacement for titanium, but are often criticized for their brittleness. By developing a tantalum functional gradient coating, we hope to increase the viability of zirconia ceramic materials for dental implants. Two sets of material were chosen to test the proprietary BruxZir tantalum ion solution: yttria stabilized zirconia (3Y-TZP) and alumina toughened zirconia (ATZ). Solutions with varying concentrations of 0%, 10%, 15%, and 30% weight percent tantalum were prepared, and the ceramic samples were coated and sintered. Each sample was analyzed through various characterization methods, including SEM, EDS, XRD, nanoindentation, and Raman spectroscopy to observe how the solution impacted each sample’s microstructure and mechanical properties. Although our results are still in progress, we found evidence of an inverse relationship between tantalum concentration and grain size.

The development of advanced thermal barrier coating (TBC) materials with better hot corrosion resistance, phase stability, and residual stresses is an emerging research area in the aerospace industry. In the present study, four kinds of TBCs, namely, single-layer yttria-stabilized zirconia (YSZ), single-layer gadolinium zirconate (GZ), bilayer gadolinium zirconate/yttria-stabilized zirconia (YSZ/GZ), and a multilayer functionally graded coating (FGC) of YSZ and GZ, were deposited on NiCrAlY bond-coated nickel-based superalloy (Inconel 718) substrates using the atmospheric plasma spray technique. The hot corrosion behavior of the coatings was tested by applying a mixture of Na2SO4 and V2O5 onto the surface of TBC, followed by isothermal heat treatment at 1273 K for 50 h. The characterization of the corroded samples was performed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) to identify physical and chemical changes in the coatings. GIXRD was used to analyze the residual stresses of the coatings. Residual stress in the FGC coating was found to be −15.2 ± 10.6 MPa. The wear resistance of TBCs is studied using a linear reciprocating tribometer, and the results indicate that gadolinium zirconate-based TBCs showed better performance when deposited in bilayer and multilayered functionally graded TBC systems. The wear rate of as-coated FGC coatings was determined to be 2.90 × 10−4 mm3/Nm, which is lower than the conventional YSZ coating.

Polymer-infiltrated ceramic network (PICN) materials have gained considerable attention as tooth-restorative materials due to their mechanical compatibility with human teeth, especially with computer-aided design and computer-aided manufacturing (CAD/CAM) technologies. However, the designed geometry affects the mechanical properties of PICN materials. This study aims to study the relationship between manufacturing geometry and mechanical properties. In doing so, zirconia-based PICN materials with different geometries were fabricated using a direct ink-writing process, followed by copolymer infiltration. Comprehensive analyses of the microstructure and structural properties of zirconia scaffolds, as well as PICN materials, were performed. The mechanical properties were assessed through compression testing and digital image correlation analysis. The results revealed that the compression strength of PICN pieces was significantly higher than the respective zirconia scaffolds without polymer infiltration. In addition, two geometries (C-grid 0 and C-grid 45) have the highest mechanical performance.

In this work, Ce-doped yttria-stabilized zirconia (YSZ) and pure YSZ phases were subjected to irradiation with 14 MeV Au ions. Irradiation studies were performed to simulate long-term structural and microstructural damage due to self-irradiation in YSZ phases hosting alpha-active radioactive species. It was found that both the Ce-doped YSZ and the YSZ phases had a reasonable tolerance to irradiation at high ion fluences and the bulk crystallinity was well preserved. Nevertheless, local microstrain increased in all compounds under study after irradiation, with the Ce-doped phases being less affected than pure YSZ. Doping with cerium ions increased the microstructural stability of YSZ phases through a possible reduction in the mobility of oxygen atoms, which limits the formation of structural defects. Doping of YSZ with tetravalent actinide elements is expected to have a similar effect. Thus, YSZ phases are promising for the safe long-term storage of radioactive elements. Using synchrotron radiation diffraction, measurements of the thin irradiated layers of the Ce-YSZ and YSZ samples were performed in grazing incidence (GI) mode. A corresponding module for measurements in GI mode was developed at the Rossendorf Beamline and relevant technical details for sample alignment and data collection are also presented.

Yttria-stabilized zirconia (YSZ), which exhibits a tetragonal phase, finds widespread application in the realm of high-temperature solid electrolytes. In the context of this research endeavor, a concerted effort was undertaken to procure a stable and controlled tetragonal phase structure within 5 mol% yttria-stabilized zirconia (5 YSZ) by modulating the precipitation rate of YSZ sols in three distinct precipitation environments, namely acidic (AC), near to neutral (NE), and alkaline (AL) conditions. Through the characterization of 5 YSZ compounds synthesized in these various environments, encompassing an assessment of their elemental composition, phase structure, local structure, and microscale morphology, it was discerned that under acidic conditions, the product exhibited non-uniform elemental distribution, pronounced agglomeration, and an abundance of hydroxyl groups, all of which proved detrimental to the stability of the tetragonal phase, resulting in the presence of 40.63% monoclinic phase. Conversely, under alkaline conditions, substantial agglomeration and hydroxyl group presence were also noted, with 34.7% monoclinic phase in the product. In stark contrast, under the condition which is near to neutral, the product demonstrated uniform elemental distribution, excellent dispersion characteristics, and a virtual absence of hydroxyl groups. The tetragonal phase structure remained stable and homogeneous, with almost negligible monoclinic phase content. Subsequent ceramic processing resulted in the highest attainable density (99.7%), coupled with the highest ionic conductivity at 850 °C (35.2 mS/cm). This study underscores that pH control during coprecipitation reactions stands as a robust and effective methodology for achieving a stable tetragonal phase structure.

The paper investigates electrical properties of fully stabilized zirconia, which is widely applied as a solid electrolyte in electrochemical devices such as solid oxide fuel cells. High ionic conductivity of these materials is crucial for effective operating of the devices; however, grain boundary resistivity limits conductivity in polycrystalline ceramics. Thus, optimisation of the microstructure of zirconia is necessary from an application point of view. Based on three-dimensional electron backscatter diffraction (3D EBSD) data, the research employed a complex impedance spectroscopy to establish a correlation between microstructure of cubic zirconia sinters and their conductivity. Samples with different levels of anisotropy in grain boundary plane parameters were investigated. The obtained results indicate that the conduction of ions through the grain boundaries is higher in the sample with the higher representation of the near-(001) grain boundaries. Such a relationship suggests that an over-representation of low-energy grain boundaries in zirconia polycrystals leads to an increase of ionic conductivity. [ABSTRACT FROM AUTHOR]

This study investigated the combination of Direct Ink Writing (DIW) and Flash Sintering of zirconia stabilized with 3 mol. % Y 2 O 3 (3Y-TZP). The samples were printed in two stacking configurations, and flash sintering was performed without current ramp control (FS) and using current ramp (CRFS) for comparison purposes. In both conditions, an electric field of 80 V cm−1 and a current density of 150 mA mm−2 were applied. The physical, microstructural, and mechanical properties of the printed samples were evaluated. The stacking configuration influenced both the grain size gradients and mechanical properties. Furthermore, controlling the current density ramp resulted in a slight homogenization of the grains' size across different regions of the sample (core, edge, and flat surfaces). The presence of zirconia polymorphs, such as ZrO 2 -t and ZrO 2 -c , as well as a distorted form of the tetragonal phase (ZrO 2 -t'), was observed in the samples. These phases were affected by both the printing strategy and the current ramp control during the flash sintering step. In addition, the samples demonstrated typical values of Vickers hardness for 3Y-TZP (ranging from 10.5 to 11.8 GPa) and fracture toughness (ranging from 3.6 to 4.7 MPa m1/2), with a minor current density ramp control influence. Therefore, both FS and CRFS techniques represent viable pathways for producing dense 3D printed ceramic materials. [Display omitted] • Additive Manufacturing and Flash Sintering were combined to produce 3Y-TZP components. • The strategy of stacking the filaments during the 3D printing influenced the mechanical properties. • Current ramp control enhanced the uniformity of grain structure in 3Y-TZP. [ABSTRACT FROM AUTHOR]

In this work, Ce-doped yttria-stabilized zirconia (YSZ) and pure YSZ phases were subjected to irradiation with 14 MeV Au ions. Irradiation studies were performed to simulate long-term structural and microstructural damage due to self-irradiation in YSZ phases hosting alpha-active radioactive species. It was found that both the Ce-doped YSZ and the YSZ phases had a reasonable tolerance to irradiation at high ion fluences and the bulk crystallinity was well preserved. Nevertheless, local microstrain increased in all compounds under study after irradiation, with the Ce-doped phases being less affected than pure YSZ. Doping with cerium ions increased the microstructural stability of YSZ phases through a possible reduction in the mobility of oxygen atoms, which limits the formation of structural defects. Doping of YSZ with tetravalent actinide elements is expected to have a similar effect. Thus, YSZ phases are promising for the safe long-term storage of radioactive elements. Using synchrotron radiation diffraction, measurements of the thin irradiated layers of the Ce-YSZ and YSZ samples were performed in grazing incidence (GI) mode. A corresponding module for measurements in GI mode was developed at the Rossendorf Beamline and relevant technical details for sample alignment and data collection are also presented. [ABSTRACT FROM AUTHOR]

Yttria-Stabilized Zirconia (YSZ) based electrolytes of Solid Oxide Fuel Cell (SOFC) are widely used due to their higher ionic conductivity, stability, and availability. The present study focuses on improving the performance of YSZ-based electrolytes particularly by doping other particles into YSZ. TiO2 was doped into Fe2O3-8YSZ composite and the effects of TiO2 on the mechanical and physical properties of the composites were observed. The concentrations of TiO2 were varied by 0 wt%, 1 wt%, 3 wt%, and 5 wt% for different compositions of the composites. The samples were fabricated by the solid-state reaction method by pressing the powders at 250 MPa for 3 min and were sintered at 1250 °C for 4 h. The sintered samples were then undergone through characterization tests in terms of percentage of volume shrinkage, density, porosity, Diametral Tensile Strength (DTS), and microhardness. The highest values of volume shrinkage (34.83%), relative density (97.83%), DTS (36.58 MPa), hardness (965 HV), and the lowest porosity (2.17%) were found for 5 wt% TiO2 addition. Besides, the lowest values of volume shrinkage (28.44%), relative density (87.94%), DTS (3.24 MPa), microhardness (340 HV), and the highest porosity (12.06%) were found for Fe2O3-8YSZ composites without (0 wt%) TiO2 addition.

The synthesis of yttria‐stabilized zirconia nanoparticles with a fine control on the chemical composition and the distribution of yttrium cations is of major interest to master the mechanical, optical or ionic conduction properties of the final material. However, a fine control of this chemical homogeneity within the particles, especially above 5 mol.% of yttria (Y2O3), is challenging with conventional synthesis routes. In the present study, for the first time the interest of using supercritical sol–gel like synthesis is demonstrated for the continuous production in a single step of high quality zirconia (ZrO2) nanocrystals of 7 nm stabilized with Y2O3 without post‐treatment. Three compositions are investigated, i.e., 1.5, 3, and 8 mol.% of Y2O3 and in‐depth physico‐ chemical characterizations such as X‐ray diffraction, total X‐ray scattering, High‐resolution electron microscopy, Raman and X‐ray photoelectron spectroscopy are performed to asses and thus prove the successful synthesis of these different compositions while keeping a good chemical homogeneity. This enables to confirm that this original process leads to a unique and fine structural control for such small yttria‐doped zirconia nanocrystals. [ABSTRACT FROM AUTHOR]

In thermal barrier coatings (TBCs), the thermal radiative transfer becomes important in the overall heat transfer with higher turbine inlet temperature. The microstructure, including pore size distribution and pore morphology, primarily impacts TBCs' radiative properties. Modifying the microstructure is an effective method to change the radiative and overall heat transfer in TBCs. In this study, a new approach is developed to modify the microstructure of atmospheric plasma sprayed (APS) topcoats by mixing the fugitive polyester powder of various sizes into the base 8 wt.% yttria-stabilized zirconia (8YSZ) powder. By changing the polyester powder size and the volumetric mixing ratio, several 8YSZ films are fabricated, and their scattering coefficients are inverted from the directional-hemispherical transmittance and reflectance measurement in the infrared wavelength range. A detailed discussion of the microstructure changes due to the powder mixture and the resulting scattering coefficient changes is presented. The results show that mixing polyester with the 8YSZ powder is a very effective way to modify the microstructure of the topcoat and increase the scattering coefficient. A preferred microstructure that can result in a higher scattering coefficient will contain a higher fraction of interlamellar pores and large-size pores in the APS topcoat. [ABSTRACT FROM AUTHOR]

Yttria‐stabilized zirconia (t'‐YSZ) thermal barrier coatings (TBCs) were deposited by air plasma spraying (APS) using commercial purity and high‐purity feedstock powders. The coatings were subjected to short‐term, low‐temperature annealing (500–1200°C for 30 min). Significant structural changes were observed by X‐ray diffraction and Raman spectroscopy. These changes were attributed to annihilation of excess oxygen vacancies created by the process. APS induces partial reduction of YSZ due to the reducing potential of the high‐temperature and hydrogen‐rich plasma environment. Laser flash thermal conductivity, impulse excitation elastic modulus, and dilatometric measurements show significant changes in the YSZ during the short‐term low‐temperature thermal exposure, concurrent to the vacancy annealing. The results were analyzed in terms of the coating chemistry and the processing environment. High‐purity coatings exhibited larger increment in thermal conductivity and elastic modulus than commercial purity coatings. [ABSTRACT FROM AUTHOR]

Yield phenomena and bending strength of single crystal 8YSZ were evaluated using microcantilever beam specimens with various crystal orientations. Nonlinearity due to plastic deformation was observed in the stress-strain curves, and the yield stress was found to depend on the crystal orientation. TEM observation revealed many areas of disordered lattice in the region where the maximum tensile stress occurred. Resolved shear stress (RSS) was analyzed for the primary {001}<110> and the secondary {110} < 1 1 ̅ 0 > and {111} < 1 1 ̅ 0 > slip systems as a function of the angle between the specimen's longitudinal direction and the [001] orientation, indicating that the RSS for the secondary ones was the critical RSS in the angle at 10 ° or lower while that for the primary one did so at 20 ° or higher. The measured bending strength, which depended on the crystal orientation, was lower than, but on the same order of magnitude as, the ideal strength. [ABSTRACT FROM AUTHOR]

For the first time, isothermal pressureless flash sintering of 1.5 mol% yttria-stabilized zirconia (1.5YSZ) polycrystals designed for high toughness was performed in a 1-kHz alternating current field (120 V·cm−1). The parameters governing tetragonal phase stability and densification needed to maximize the toughness of 1.5YSZ were investigated by varying the applied current density limit and holding time. A sample with relative density exceeding 98% and indentation toughness of about 13 MPa·m0.5 was sintered at 1100°C by applying 40 mA·mm−2 to the green body for 2 min, where the average steady-state temperature during flash reached 1330°C. Unlike flash sintering of conventional oxide ceramics, the applied current density and densification were not positively correlated despite pore closure. While Joule heating intensified when applying higher current densities, sample densification was hindered as the accelerated grain growth resulted in intergranular cracks which were generated by spontaneous tetragonal-to-monoclinic martensitic phase transformation during cooling. [Display omitted] • First study on flash sintering of high-toughness 1.5 mol% yttria-stabilized zirconia. • Sample with relative density > 98% and toughness of about 13 MPa·m0.5 was produced in 2 min. • Applying higher current density promoted grain growth and hindered densification. • Tetragonal phase stability degraded with increasing grain size. • Cracks formed around monoclinic grains deteriorated sample density and toughness. [ABSTRACT FROM AUTHOR]

The physics behind the switching kinetics of memristors is gradually becoming clearer. The periods required for the onset of electromigration within memristors and the activation or deactivation of the low‐resistance state—referred to as the incubation and switching times—exhibit non‐linearity with applied voltage. This behavior prevails depending on the rate‐limiting step comprising nucleation and filament growth, electron transfer at the electrode/electrolyte interface, and ion migration through the electrolyte. Herein, a model is introduced for ion migration as the rate‐limiting step. This model analyses the incubation time and analytically correlates it with the electric field, diffusion coefficient, and temperature, facilitating the determination of threshold voltage and diffusivity from high to low resistance states for ion migration as the rate‐limiting step. By exploring parallel plate cells with Yttria‐Stabilized Zirconia (YSZ) of nanometer thickness, the application of the model is illustrated and the fundamental equations are applied to outstanding memristive cells in the literature. The applicability of this model to cells of various charge carriers is proposed, ranging from vacancies and electron transport to oxygen ions and metal cations, denoting its potential importance. [ABSTRACT FROM AUTHOR]

Featured Application: Functional surfaces of zirconia with antibacterial properties. Femtosecond pulsed laser irradiation was performed to investigate the feasibility and fundamental characteristics of embedding silver nanoparticles onto zirconia ceramic surfaces. By irradiating laser, nanopores were fabricated on the surface of the yttria-stabilized zirconia (YSZ) substrate, and silver nanoparticles were infiltrated and immobilized into the pores using a commercial nano-silver dispersion solution. Numerous nanopores embedded with silver nanoparticles were successfully obtained on the YSZ surface while keeping the grains' shapes unchanged by controlling laser parameters. Optimizing laser fluence and scanning speed near the ablation threshold made it possible to remove only the excess dispersant that remained on the surface while keeping silver in the pores and without causing machining of the surface of the YSZ substrate. In addition, about 60% embedding in the nanopores was achieved. It was found that the shorter pulse width was suitable to avoid evaporating both dispersant and silver. Cross-sectional observation revealed that the silver nanoparticles were agglomerated to form clumps and were embedded without a gap at the bottom of the pores at a depth of about 600 nm. After laser irradiation, no significant laser-induced phase change was observed in the YSZ substrate, indicating that there was no in-process thermal damage to the bulk. These findings demonstrated the possibility of adding a metal nanoparticle to the zirconia surface by using only a laser process without damaging the properties of the base material during the process. New applications of zirconia, such as the generation of functional surfaces with antibacterial properties, are expected. [ABSTRACT FROM AUTHOR]

This work aims to demonstrate that chronoamperometry is a valuable tool for determining diffusivities in all‐solid‐state nanometer‐thick cells. The transient current in chronoamperometry of electrochemical cells under constant voltage is described by firstly considering purely capacitive processes, defined by RC circuit equations, and then purely diffusive processes, by Cottrell's equations. The physical meaning of the equations has been amply described in liquid cells with porous electrodes but scarcely in solid‐state cells. Thus, we studied Metal/Insulator/Metal nano‐cells with Ru and Au electrodes, Yttria Stabilized Zirconia (YSZ) electrolyte at temperatures between 50 and 170°C and voltages between 0.5 V and 1.5 V, where non‐Faradaic processes occur. The calculated diffusive and capacitive contributions at different temperatures obey the Arrhenius law. The activation energy was associated with vacancies, the major carrier during electrical transport. The analysis discusses other parameters, such as capacitance, effective concentration, and leakage current. The experimental diffusivity of YSZ electrolytes was compared with diffusivity values obtained by the statistical moment method. [ABSTRACT FROM AUTHOR]

The effect of partial SiO2 substitution with Al2O3 and B2O3 on the thermal properties and crystallization of glass sealants in the (50 − x)SiO2–30BaO–20MgO–xAl2O3(B2O3) (wt %) system is studied. It is established that the coefficient of thermal expansion of all obtained glasses lies within a range of 8.2–9.9 × 10−6 K−1. Alumina-doped glasses crystallize after quenching, while samples containing boron oxide are completely amorphous. Magnesium silicates are formed in all glasses after exposure at 1000 °C for 125 h. After 500 h of exposure, a noticeable diffusion of zirconium ions is observed from the YSZ electrolyte to the glass sealant volume, resulting in the formation of the BaZrSi3O9 compound. The crystallization and products of interaction between YSZ ceramics and boron-containing sealants have no significant effects on the adhesion and properties of glass sealants, which makes them promising for applications in electrochemical devices.

The additive manufacturing (AM) of yttria-stabilized zirconia (YSZ) microarchitectures with sub-micrometer precision via two-photon lithography (TPL), utilizing custom photoresin containing zirconium and yttrium monomers is investigated. YSZ 3D microarchitectures can be formed at low temperatures (600 °C). The low-temperature phase stabilization of ZrO2 doped with Y2O3 demonstrates that doping ZrO2 with ≈ 10 mol% Y2O3 stabilizes the c-ZrO2 phase. The approach does not utilize YSZ particles as additives. Instead, the crystallization of the YSZ phase is initiated after printing, i.e., during thermal processing in the air at 600 °C – 1200 °C for one and two hours. The YSZ microarchitectures are characterized in detail. This includes understanding the role of defect chemistry, which has been overlooked in TPL-enabled micro-ceramics. Upon UV excitation, defect-related yellowish-green emission is observed from YSZ microarchitectures associated with intrinsic and extrinsic centers, correlated with the charge compensation due to Y3+ doping. The mechanical properties of the microarchitectures are assessed with manufactured micropillars. Micropillar compression yields the intrinsic mechanical strength of YSZ. The highest strength is observed for micropillars annealed at 600 °C, and this characteristic decreased with an increase in the annealing temperature. The deformation behavior gradually changes from ductile to brittle-like, correlating with the Hall–Petch strengthening mechanism.

Tailoring the electrical conductivity of functional ceramics by introducing dislocations is a comparatively recent research focus, and its merits were demonstrated through mechanical means. Especially bulk deformation at high temperatures is suggested to be a promising method to introduce a high dislocation density. So far, however, controlling dislocation generation and their annihilation remains difficult. Although deforming ceramics generate dislocations on multiple length scales, dislocation annihilation at the same time appears to be the bottleneck to use the full potential of dislocations‐tailoring the electrical conductivity. Here, we demonstrate the control over these aspects using a micromechanical approach on yttria‐stabilized zirconia ‐ YSZ. Targeted indentation well below the dislocation annihilation temperature resulted in extremely dense dislocation networks, visualized by chemical etching and electron channeling contrast imaging. Microcontact‐impedance measurements helped evaluate the electrical response of operating individual slip systems. A significant conductivity enhancement is revealed in dislocation‐rich regions compared to pristine ones in fully stabilized YSZ. This enhancement is mainly attributed to oxygen ionic conductivity. Thus, the possibility of increasing the conductivity is illustrated and provides a prospect to transfer the merits of dislocation‐tuned electrical conductivity to solid oxygen electrolytes. [ABSTRACT FROM AUTHOR]

This study suggests approaches to achieve the desired size and size distribution of highly dense spherical granules by investigating the effect of slurry conditions on size distribution. Highly dense spherical granules were prepared with a solid content of over 77 wt% by spray‐drying the slurry. A prolonged deagglomeration time of 64 h provided adequate flowing ability by breaking up almost all aggregates and improved dispersibility, resulting in reduced granule sizes and narrow size distributions. The optimum slurry conditions for maintaining dispersibility were 1 wt% of the dispersant and a strong basic pH, which had the greatest effect on size distribution. Based on these considerations, the 10.6 µm sized 3 mol% yttria‐stabilized zirconia granules were synthesized with 99.83% density, 97.17% sphericity, and uniform size with fraction yield of 80.01% at 10–20 µm. These dense granules have significantly higher hardness and modulus values of 19.19 and 206.68 GPa, respectively, than that of pellet and film types. To the best of our knowledge, the relationship between the slurries and the span of the size distribution of ceramic granules during spray‐drying has been demonstrated for the first time. [ABSTRACT FROM AUTHOR]

8 mol% yttria-stabilized zirconia nano-powders were synthesized via a novel sol–gel method employing basic zirconium carbonate, acetic acid, and different chelating agents (citric acid, oxalic acid, and ethylenediaminetetraacetic acid (EDTA)). The dried gel and calcined nano-powders were characterized using various techniques to investigate their thermal behavior, phase composition, particle size, microstructure morphology, and electrochemical performance. It was found that the dried gel had different polymeric network structures based on the different molecular structures, number of functional groups, and acidity of the chelating agents, which led to different properties after calcination. The smallest particle size, best dispersion, and narrowest grain size distribution were obtained for the EDTA sample after calcination at 600 °C, which are attributed to the unique functional groups in EDTA. The highest relative density and smallest grain size of the EDTA sample, which resulted in enhanced grain boundary contribution and effective conducting area, led to increased ionic conductivity (0.06 S cm−1). [ABSTRACT FROM AUTHOR]

The effect of partial SiO2 substitution with Al2O3 and B2O3 on the thermal properties and crystallization of glass sealants in the (50 − x)SiO2–30BaO–20MgO–xAl2O3(B2O3) (wt %) system is studied. It is established that the coefficient of thermal expansion of all obtained glasses lies within a range of 8.2–9.9 × 10−6 K−1. Alumina-doped glasses crystallize after quenching, while samples containing boron oxide are completely amorphous. Magnesium silicates are formed in all glasses after exposure at 1000 °C for 125 h. After 500 h of exposure, a noticeable diffusion of zirconium ions is observed from the YSZ electrolyte to the glass sealant volume, resulting in the formation of the BaZrSi3O9 compound. The crystallization and products of interaction between YSZ ceramics and boron-containing sealants have no significant effects on the adhesion and properties of glass sealants, which makes them promising for applications in electrochemical devices. [ABSTRACT FROM AUTHOR]

Femtosecond pulsed laser irradiation of yttria-stabilized zirconia (YSZ) was performed to investigate the feasibility and fundamental characteristics of nanopore structure fabrication. Numerous nanopores were successfully generated on the YSZ surface with only a single laser pulse shot by controlling laser power near the ablation threshold. The nanopore generation mechanism involves light focusing by the convex shape of a crystal grain and ablation inside the grain. By increasing laser power, the number of nanopores increased. Cross-sectional observation revealed that the depth of nanopores was about 500 nm, and nanopores were generated inside the YSZ grains of the top layer while keeping the grains' shapes unchanged. It was found that higher scanning speed and a small number of scans enabled nanopores fabrication without changing the original surface shape, avoiding the removal of the surface layer. Laser-irradiated surfaces of YSZ were characterized by Raman spectroscopy, and it was found that there was no significant phase change in the specimen after nanopore generation compared with the original YSZ surface, confirming that there was no thermal damage to the bulk material. The surface with nanopores showed an enhancement in surface hydrophilicity. These findings demonstrated the possibility of selectively generating nanopores in the top surface of YSZ for use in functional surfaces without serious thermal damage to the workpiece. It is expected that the nanopore generation will lead to new applications of YSZ.

This paper reports the microstructural characteristics and mechanical properties of yttria-stabilized zirconia prepared via fused deposition modelling and slip casting. X-Ray Diffraction peaks indicated that yttria-stabilized zirconia crystallized in tetragonal structure for both slip casted(SC) and fused deposition modelled(FDM) samples. Further, scanning electron microscopy of slip casted sample showcased closely packed structure with fine grains and an average grain size of ∼65 nm whilst fused deposition modelled samples showcased non-homogeneous pores with ∼20 nm grain size. Average relative density of slip casted samples was ∼99.4 % while that of fused deposition modelled sample exhibited ∼96.2 %. The Vickers Hardness of slip casted (∼15.26 ± 0.4 GPa) was ∼10 % higher than the fused deposition modelled samples (∼13.79 ± 0.3 GPa). Likewise, indentation fracture toughness of slip casted (5.78 ± 0.5 MPa m1/2) was 14 % higher than fused deposition modelled samples which could have been due to the change in grain size as well as porosity of the ceramics. Compressive strength of the fused deposition modelled samples was 32 % less than slip casted samples (∼510 ± 10 MPa) due to its non-homogenous pores which led to weakening van der Waals force of attraction.

In this study, yttria-stabilized zirconia (8YSZ, 8 mol%) was flash joined to Ni-Cr-Fe medium-entropy alloy (MEA) within seconds under an electric field (E-field), where the current density was above the threshold (about 100 mA·mm−2) at 750–1000 °C. The maximum joint strength of 103 MPa was achieved at joining temperature of 900 °C under current density of 100 mA·mm−2 for 30 s. The impedance spectrum of the joined sample revealed that there was no impedance barrier to charge transfer between the metal electrode and the ceramic, indicating that the interface was well bonded. Scanning electron microscopy and transmission electron microscopy results show that the joint was formed mainly due to the fast diffusion of Ni into 8YSZ and reduced Zr into MEA. The diffusion of these elements does not change the crystal structure of the ceramic and metal, and leads to only slight increase in the lattice spacing of MEA. [ABSTRACT FROM AUTHOR]

Yttria-stabilized zirconia spherical thin-walled hollow-shell powder (YSZ-STHS) is a highly promising ceramic top-coat materials used in thermal barrier coatings with good homogeneity, a low thickness and no continuous flaws. However, the current technologies for preparing yttria-stabilized zirconia hollow spherical powder (YSZ-HOSP), such as spray drying, inductively coupled plasma spheroidization, and arc plasma spheroidization, face challenges in producing YSZ-STHS due to thick shell thickness and low hollow powder ratio. The triple-cathode plasma torch (TCPT) has characteristics such as high enthalpy and axial powder feeding, making it a promising tool for YSZ-STHS preparation. However, the plasma torch nozzle is often clogged due to powder deposition on the cold anode wall, limiting its application. To address this issue, a novel spheroidization method using a TCPT with hot-wall nozzle is proposed to achieve low shell thickness and high hollow powder ratio in YSZ-STHS powder preparation. Experiments were carried out to investigate the electro-thermal characteristics of the TCPT. The results indicated that the TCPT displayed a high mean enthalpy ranging from 2.37×107 J/kg to 3.36×107 J/kg and a low arc voltage fluctuation of ±1 V, indicating that the proposed TCPT is capable of producing a stable plasma jet with a high temperature. Additionally, experiments and numerical simulations were conducted to reveal the effect of the hot-wall nozzle. The results revealed that the hot-wall nozzle increased the inner wall temperature, decreased the radial temperature gradient of the plasma jet, reduced the nozzle clogging, and extends the high-temperature region and maximum temperature inside the nozzle. Finally, YSZ-STHS preparation by TCPT with hot-wall nozzle was demonstrated through experiments. The results showed that YSZ-STHS with a high spheroidization ratio close to 100%, a high hollow powder ratio of 93.4%, a thin shell thickness with an average value of 3.63 μm, and fully tetragonal phase was successfully prepared, demonstrating the effectiveness of the proposed TCPT with hot-wall nozzle for the preparation of YSZ-STHS. [Display omitted] [ABSTRACT FROM AUTHOR]