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Optimized coating adhesion and strength are the advantages of high-power impulse magnetron sputtering (HiPIMS) as an innovative physical vapor deposition (PVD) process. When depositing electrically non-conductive oxide ceramics as coatings with HiPIMS without dual magnetron sputtering (DMS) or mid-frequency (MF) sputtering, the growing coating leads to increasing electrical insulation of the anode. As a consequence, short circuits occur, and the process breaks down. This phenomenon is also known as the disappearing anode effect. In this study, a new approach involving adding electrically conductive carbide ceramics was tried to prevent the electrical insulation of the anode and thereby guarantee process stability. Yttria-stabilized zirconia (3YSZ) with 30 vol.% titanium carbide (TiC) targets are used in a non-reactive HiPIMS process. The main focus of this study is a parameter inquisition. Different HiPIMS parameters and their impact on the measured current at the substrate table are analyzed. This study shows the successful use of electrically conductive carbide ceramics in a non-conductive oxide as the target material. In addition, we discuss the observed high table currents with a low inert gas mix, where the process was not expected to be stable.

Thermal conductivity is a crucial parameter for evaluating the quality and thermal effects of ceramic coatings, especially for thermal barrier coatings. However, measurement by conventional method involves two problems: (a) it is difficult to peel off a ceramic coating from a substrate; (b) even if the coating can be peeled off, it is still hardly used as standard specimen in test. Therefore, the relative method was proposed to evaluate the thermal conductivity of ceramic coating. An analytical relationship among the thermal conductivities of the coating, the substrate, and the coating/substrate composite was established. Experiments on TA4 coated with YSZ coatings were carried out to demonstrate the feasibility of this novel method and to investigate the impact of temperature on the thermal conductivity of YSZ coatings. The experimental results demonstrated the validity and convenience of the relative method. With the increasing testing temperature, the thermal conductivity value of YSZ coatings displayed nonlinearity feature, that is, decreased from 1.4 to 1.3 (W m−1 K−1) in the temperature range of 32‐300°C and then increased up to 1.58 W m−1 K−1 at 1000°C. [ABSTRACT FROM AUTHOR]

This study compared the physical properties of conventional and monolithic yttria-zirconia (Yz) materials after low-temperature degradation (LTD). Bar-shaped specimens (2.0 mm thick × 4.0 mm wide × 16.0 mm in length) were produced. Autoclave aging was executed at 134°C under 2 bar pressure for 5 h. The surface characteristics were assessed using a confocal laser microscope, microstructural phase alterations via an X-ray diffractometer (XRD), 3-point flexural strength using a universal testing machine, Vickers microhardness via a digital microhardness tester, and toughness using a durometer. Fractured specimens and indented surfaces was observed via a scanning electron microscope for fractography characterization. All of the data underwent specific statistical tests considering their distribution and homogeneity. Regarding topography, different Yz materials were very similar after LTD. Conventional Yz materials were smoother. The XRD data support that both materials were mainly composed of tetragonal crystals, whereas slight monoclinic peaks were detected. Monolithic Yz showed higher flexural strength than conventional Yz. All of the fractures started on surface defects at the side where tensile stress was concentrated (opposite to load application) and propagated to the opposite side. Vickers microhardness and toughness analysis found that conventional Yz had higher performance than monolithic Yz. This study has found that there are slight differences in strength, hardness, and toughness between conventional and monolithic yttria-stabilized zirconia ceramics, although both materials demonstrate adequate performance for clinical use. [ABSTRACT FROM AUTHOR]

In this study, we successfully fabricated an yttria-stabilized zirconia (YSZ) aerogel using the sol-gel method and CO 2 supercritical drying. We confirmed the successful thermal insulation function as a thermal barrier coating (TBC) on a high-temperature gas turbine surface. In order to evaluate the performance of the YSZ aerogel, the thermal conductivity and temperature profile were measured in addition to microstructure observation by scanning electron microscopy. The thermal conductivity of the YSZ aerogel was 0.212 W/m·K at 1000 °C, which is significantly lower than the reference values of YSZ materials. The low heat conduction is attributed to heat insulation by the fine pores and low heat conduction through the nanopore spaces in the aerogel structure. The heat insulation of the YSZ aerogel as the TBC was evaluated on a gas turbine blade material by monitoring surface temperature profiles on a heater at 300–700 °C. The heat-blocking performance of the YSZ aerogel coating was superior to that of a conventional YSZ TBC (by 30–50%). By comparison with a numerical calculation, the thermal conductivity of the YSZ aerogel coating was estimated to be 0.05 W/m·K, which is significantly lower (30–40 times) than that of the YSZ TBC used for commercial gas turbines. The porous structure of the aerogel was well preserved even after the high-temperature test confirming the good thermal stability. This study demonstrated that the YSZ aerogel is promising as a gas turbine TBC material. • YSZ aerogel was synthesized using sol-gel method and CO 2 supercritical drying. • YSZ aerogel had significantly lower thermal conductivity than reference YSZ. • YSZ aerogel is applied as a coating layer on commercial gas turbine alloys. • YSZ aerogel coating outperforms APS YSZ used for commercial gas turbine TBC. [ABSTRACT FROM AUTHOR]

Recently, in this journal the phenomenon of ionic conductivity enhancement has again been claimed to boost the electrical characteristics of a solid electrolyte, this time of the classical oxygen ion conductor yttria-stabilized zirconia. It is demonstrated that the arguments to support the claim are flawed and that the criticized article is another example of a fallacy with regard to ionic conductivity enhancement. [ABSTRACT FROM AUTHOR]

Thermal Barrier Coatings (TBCs) play a significant role in improving the efficiency of gas turbines by increasing their operating temperatures. The TBCs in advanced turbine engines are prone to silicate particles attack while operating at high temperatures. The silicate particles impinge on the hot TBC surfaces and melt to form calcia-magnesia-aluminosilicate (CMAS) glass deposits leading to coating premature failure. Fine powder of CMAS with the composition matching the desert sand has been synthesized by solution combustion technique. The present study also demonstrates the preparation of flowable yttria-stabilized zirconia (YSZ) and cluster paired YSZ (YSZ-Ln 2 O 3 , Ln = Dy and Gd) powders by single-step solution combustion technique. The as-synthesized powders have been plasma sprayed and the interaction of the free standing TBCs with CMAS at high-temperatures (1200 °C, 1270 °C and 1340 °C for 24 h) has been investigated. X-ray diffraction analysis of CMAS attacked TBCs revealed a reduction in phase transformation of tetragonal to monoclinic zirconia for YSZ-Ln 2 O 3 (m -ZrO 2 : 44%) coatings than YSZ (m -ZrO 2 : 67%). The field emission scanning electron microscopic images show improved CMAS resistance for YSZ-Ln 2 O 3 coatings than YSZ coatings. [ABSTRACT FROM AUTHOR]

Al 2 O 3 matrix composites containing in-situ formed monoclinic zirconia (m -ZrO 2) and BaO·7.3Al 2 O 3 (one of Ba-β-Al 2 O 3 compounds) were prepared via reactive sintering of Al 2 O 3 and BaZrO 3 powders. When yttria-stabilized zirconia (YSZ) with Y 2 O 3 contents of 1.5 mol% (1.5YSZ), 2 mol% (2YSZ), and 3 mol% (3YSZ) as well as Y 2 O 3 particles were introduced into Al 2 O 3 and BaZrO 3 powder mixtures, the in-situ formed m -ZrO 2 was stabilized, resulting from the migration of Y3+ from YSZ or Y 2 O 3 to m -ZrO 2 during sintering. The incorporation of YSZ contributed to the refinement of Al 2 O 3 grains, whereas Y 2 O 3 -added samples showed larger grain sizes of Al 2 O 3 matrix. The samples with YSZ or Y 2 O 3 addition exhibited high fracture toughness, which is attributed to crack deflection/bridging and transformation toughening of ZrO 2. Although the phase transformation is mainly derived from ZrO 2 formed during sintering, 1.5YSZ particles added in the composites still showed much higher phase transformability compared to 2YSZ and 3YSZ particles. [ABSTRACT FROM AUTHOR]

Commercial yttria-stabilized zirconia Zr 0.8 Y 0.2 O 1.9 (8YSZ), and five synthesized rare-earth aluminates Ln 4 Al 2 O 9 (Ln = Y, Sm, Eu, Gd, Tb), were examined as possible intermediate-temperature barrier materials. The materials were directly deposited on preoxidized Fe-Cr metallic substrate, without bond coating as, using a wet colloidal spray technique. Phase purity and structures for all materials were confirmed by X-ray Diffraction (XRD) and the morphology of these compounds was examined using Scanning Electron Microscopy (SEM). The thermal resistance of the YSZ and Ln 4 Al 2 O 9 (Ln = Y, Sm, Eu, Gd, Tb) layers was compared by the temperature drop method (∆T = T substrate -T substrate with coating), using an in-house built set up. Prior to measurement, the reproducibility and stability of the proposed experiment was confirmed. For the Eu 4 Al 2 O 9 and Tb 4 Al 2 O 9 coatings with thicknesses near 60 μm, the thermal resistance capability (≈180 °C) at 800 °C, was similar to that of the 8YSZ coating (commercial material for Thermal Barrier Coating (TBC) development). The cross-sectional microstructure of the samples, after thermal analysis was also examined, confirming no changes in the microstructure. Given the observed high thermal resistance capability values for the Ln 4 Al 2 O 9 (Ln = Y, Sm, Eu, Gd, Tb) samples, and the possibility to change the porosity of the starting materials by ball milling, the results suggest that these materials have good potential for use as ceramic interlayers for TBCs. • Thermal resistance capabilities of 8YSZ and prepared Ln 4 Al 2 O 9 coatings were studied. • To measure the temperature drop across TBCs a reproducible house built setup was used. • Eu 4 Al 2 O 9 and Tb 4 Al 2 O 9 layers showed the best thermal resistance effect. [ABSTRACT FROM AUTHOR]

The aim of this study was to manufacture zirconia periodic open cellular structures (POCS) (39%–57% porosity) and evaluate their mechanical properties. Zirconia POCS with 39%, 47% and 57% porosity were obtained from a CAD/CAM blank using a CNC milling machine. Specimens with a feldspar-based porcelain infiltrated in the porosities were also produced and tested. The elastic and inelastic properties of the all samples were obtained by compression strength tests. The structures were analyzed using XRD and SEM. FEA was also performed to evaluate the porous structures and for optimization. Zirconia POCS were successfully produced using a CAD/CAM technique. Porous size and distribution can be easily modified to tailor the desired POCS mechanical properties. Elastics and inelastic properties were well fitted by the Gibson-Ashby model, which allows designing POCS with predictable results. [ABSTRACT FROM AUTHOR]

Manufacturability of advanced ceramics has been a challenging issue mainly because of their brittle behaviors and high hardness. One approach to solving this issue is enabling ductile regime cutting, which can also be used to enhance the quality of the surface and accuracy of the final product. There have been many studies investigating how to control and prolong the ductile response regime during cutting; however, it still lacks a straightforward explanation that enables us to predict the transition of the material response from the ductile regime to the brittle regime. In this study, the processing of monocrystalline yttria-stabilized zirconia was investigated to predict material behavior during cutting. Here, it is aimed to confirm that stress intensity factor analysis can be applied with a wide variety of process parameters and investigate the effect of varying the process parameters on the ductile–brittle material response transition. Experimental results showed that negative rake angle and higher cutting speed prolonged the ductile cutting regime. However, the cutting stress at the ductile–brittle transition point remained constant regardless of the process parameters which enabled us to predict the transition point with respect to the stress intensity factor. It is expected that the results of this research can contribute to the development of machining strategies with improved throughput and thus to increasing the utilization of ceramic materials. [ABSTRACT FROM AUTHOR]

YSZ coatings were developed by solution precursor plasma spraying from different solution concentrations. The solutions were characterized and correlated with the rheological properties (specific weight, viscosity and surface tension). The mechanical injection was used therefore a correct injection is essential to get a correct liquid jet break-up inside the plasma plume. The optimal injection pressure must be adjusted for each solution since the solution characteristics affect on the injection process. It was experimentally found out by the observation of the splats' morphology. The particles were not melted at low pressures but solidified prior to the deposition when the injection pressure is high. It was also found out that the optimal static pressure varies with the concentration, but the dynamic pressure is equal for every solution and slightly superior to the dynamic pressure of the plasma plume. After injection optimization, coatings using different solution concentrations were developed and their microstructures were investigated. The liquid jet fragmentations as well as the heat requirements were modified with the concentration so that coating microstructure was affected. The resulting coatings display a lamellar and porous microstructure with the presence of unmelted/unpyrolysed material. Coatings' porosity increased while coatings' grow-up was less intensive when diluted solutions were used as feedstock. • YSZ coatings were developed by solution precursor plasma spraying. • Optimal injection pressure depends on solution characteristics. • Solution concentration affects on splats morphology and coating microstructure. [ABSTRACT FROM AUTHOR]

Suspension plasma spraying process, a relatively new deposition technique in thermal spray coating, has been increasingly applied to deposit high-quality thermal barrier coatings using submicron particles. An accurate simulation of the process includes the development of a realistic model of the plasma both within and outside the torch. In this work, a three-dimensional time-dependent model has been developed to simulate the magnetohydrodynamic fields inside a DC plasma torch including arc fluctuations. The Reynolds stress model is used to simulate the time-dependent turbulent plasma flow. To investigate the effects of plasma arc fluctuation on the trajectory, temperature, and velocity of suspension droplets injected into the plasma jet, a two-way coupled Eulerian–Lagrangian method is employed. Submicron yttria-stabilized zirconia particles, suspended in ethanol, are modeled as multicomponent droplets. The Kelvin–Helmholtz Rayleigh–Taylor breakup model is used to simulate the droplet breakup. Particles are also tracked after the completion of suspension breakup and evaporation to obtain the in-flight particle conditions including the trajectory, size, velocity, and temperature. The arc attachment spots showed a good agreement with the experimental images. It was also shown that the properties of the particles are significantly affected by plasma arc fluctuations. [ABSTRACT FROM AUTHOR]

It is critical for thermal barrier coating (TBC) development that a testing method be used to understand the potential and limitation of a coating's durability and integrity under gas turbine engine operating conditions. To this end, a TBC-coated button is tested using a laser high-heat flux facility. The ceramic coating is ZrO2-8 wt.% Y2O3 applied via the air plasma spraying process on top of a NiCoCrAlY bond coating and an Inconel alloy 617 substrate button of 25.4 mm diameter. The coated button is subject to precisely controlled laser heating on the top side (1150 °C) and a temperature gradient of 63.9 °C/mm through the button overall thickness. The coated button lasts 160.9 h or 570 cycles of laser heating. The void fraction change before and after the test, the thermal conductivity change during the laser test and the failure assessment are presented. After the test, significant horizontal cracks exist in the top coating close to the thermally grown oxide (TGO) layer and near the button center. Based on the cracks and the TGO layer geometry, the stress intensity factor and strain energy release rate are computed. The combined experimental and computational approach can lead to a TBC lifetime model. [ABSTRACT FROM AUTHOR]

Ytrria doped Zirconia can both stabilize structure and bring about oxygen vacancy, which benefits electrochemical ammonia synthesis with a high faradic efficiency (FE) of 12.3% and a large NH 3 yield of 10.84 μg h−1 mg−1 cat. • Fixation of nitrogen to ammonia are achieved by yttria and zirconia nanoparticles. • The electrochemical performance of zirconia for nitrogen fixation is enhanced by yttria doping zirconia. • Yttria stabilized zirconia shows a high selectivity and stability for reducing nitrogen. Ammonia (NH 3) is one of the most essential ingredients on earth as it has been widely applied in fertilizer manufacture and as a source of green energy. Artificial nitrogen fixation exceeds 2% of the world consumption based on the traditional Haber-Bosch process, but it is realized at high temperature and pressure and at a cost of CO 2 emission. Electrochemical reduction of N 2 to NH 3 is thus deemed as an alternative and effective approach for nitrogen fixation at ambient conditions. Nevertheless, efficient and selective catalysts are indispensable to split the strong N N triple bonds. In this work, 8 mol% Y 2 O 3 doped zirconia nanoparticles (8YSZ-NPs) is used as a noble-metal free catalyst for reducing nitrogen to ammonia, which enhances the performances of zirconia and ytrria to a high faradic efficiency (FE) of 12.3% and a large NH 3 yield of 10.84 μg h−1 mg−1 cat in 0.1 M Na 2 SO 4 electrolyte at −0.5 V vs. reversible hydrogen electrode, which also shows a preeminent selectivity and high electrochemical stability even compared with the catalysts running under high temperature and pressure. [ABSTRACT FROM AUTHOR]

• ZrO 2 and YSZ aerogels derived by combining sol-gel method and supercritical drying. • Evolution of crystallinity was observed by in-situ XRD measurements up to 1200 °C. • Phase transformation of zirconia (ZrO 2) is affected by crystallite size growth. • Yttria-stabilized zirconia (YSZ) aerogel forms stable single-phase t -ZrO 2 at 455 °C. Monolithic, structurally stable zirconia (ZrO 2) aerogels can be used in high temperature applications and as medical implants. The macroscopic properties of these solids can be fine-tuned by the appropriate thermal treatment of the amorphous aerogels. Herein, we investigate the thermally induced phase transitions of ZrO 2 and yttria-stabilized zirconia (YSZ) monolithic aerogels. All aerogels were produced by an acid-catalyzed sol-gel technique and subsequent supercritical drying (SCD). A complete reaction mechanism is proposed for the formation of the wet gel network. Also, the phase transformations taking place during calcination were followed as function of temperature by in-situ X-ray diffraction measurements. Composition and size of the forming crystallites were calculated from the XRD data. Phase transition is controlled by the temperature-dependent growth of crystallite size during calcination up to 1200 °C. Both tetragonal and monoclinic zirconia form in pure ZrO 2 aerogels, and a single tetragonal phase forms in YSZ aerogels. [ABSTRACT FROM AUTHOR]

• Aging of Y-TZP influences gingival cell attachment, viability and metabolic activity. • No differences were observed on gingival cell viability among abutment materials. • Lithium disilicate eluates triggered cell metabolic activity. • Surface micro-roughness alterations did not explain differences in biological behavior. This study aimed to investigate the biological effects of yttria-stabilized zirconia (Y-TZP) compared to other dental implant abutment materials, i.e. lithium disilicate (LS2) and titanium alloy (Ti), as well as the effects of aging of Y-TZP on viability/proliferation and attachment properties of Human Gingival Fibroblasts (HGFs). Cylindrical specimens of each material were prepared as per manufacturer's instructions. Y-TZP specimens were divided into three groups: 1. no aging (Zr0), 2. aging for 5 h, 134 °C, 2 bars, 100% humidity (Zr5), 3. aging for 10 h under the same conditions (Zr10). Surface roughness was evaluated by optical profilometry; cell metabolic activity/viability by MTT assay, morphological changes by Scanning Electron Microscopy (SEM) and ratio of live/dead cells by confocal microscopy. Results showed statistically significant reduction of HGF metabolic activity/viability in contact with Y-TZP after aging. Nevertheless, non-aged zirconia showed no significant differences compared with LS2, Ti and control cultures. In contrast, significant stimulation of cell metabolic activity/viability was observed in HGFs exposed to LS2 eluates. Differential morphological patterns were observed for HGF in contact with different materials/treatments, with obviously increased number of dead cells and sparser distribution of HGFs cultured on Zr10 specimens. These effects were not correlated with surface topography, since Y-TZP aging did not alter surface micro-roughness. These findings indicate that Y-TZP shows comparable biological properties to Ti and LS2 as implant abutment material. Nevertheless, Y-TZP aging might influence gingival cell attachment and proliferation properties, providing an alert to a potentially negative effect on the long-term maintenance of gingival architecture. [ABSTRACT FROM AUTHOR]

We have studied the resistive switching in memristive structures based on 40-nm-thick yttria-stabilized zirconia (YSZ) films exposed to 6-keV Si+ ion irradiation to a total dose of 5.4 × 1015 cm–2. It is established that the ion irradiation leads to increased stability of the parameters of resistive switching in YSZ based memristive structures. This effect is related to the fact that the diameter of conducting filaments in irradiated structures is limited by lateral dimensions of the region of atomic displacement cascades (i.e., the region occupied by point defects produced by bombarding ions). The oxidation of ion-modified filaments during resistive switching proceeds more effectively and leads to increasing resistance in the high-resistance state of memristive structures. [ABSTRACT FROM AUTHOR]

This paper presents a comparison of thermal fatigue behavior of sol–gel-derived dip-coated nanostructured nonconventional and conventional air plasma-sprayed seven percent weight of yttria-stabilized zirconia thermal barrier coatings (TBCs). The thermal fatigue test was performed on the thermal cyclic furnace in the temperature range of room temperature and 1100 °C. Microstructural evaluation and elemental analysis were done by using scanning electron microscopy/energy-dispersive spectroscopy, respectively. It was observed that the failure of both nanostructured and conventional TBCs ensured the crack-induced spallation of ceramic top coat. The results demonstrated that spinel oxide (mixed oxide of Cr, Co, Ni) formation over thermally grown oxides layer played a crucial role in both of the case of conventional TBCs and sol–gel-coated nonconventional TBCs. The thermal cyclic fatigue life of the sol–gel coatings was found to be 1.31 times higher than the conventional air plasma. The AFM images also confirmed the coating consisting of nanostructure as well as the surface irregularities which increased with rising temperature. [ABSTRACT FROM AUTHOR]

Thermal barrier coatings (TBCs) consisting of yttria-stabilized zirconia (YSZ) as top coat and NiCrAlY as bond coat were deposited on AZ91D magnesium alloy substrate by atmospheric plasma spraying (APS). In order to improve the stability and prolong the thermal shock life of TBCs, a Ni-P/Al/Ni-P sandwich interlayer between the AZ91D magnesium alloy substrate and the NiCrAlY bond coat was fabricated by electroless plating for Ni-P layer and APS for Al layer. The thermal shock behavior of the YSZ TBCs with the Ni-P/Al/Ni-P sandwich interlayer quenched in water at 400 °C was investigated in detail. The results showed that the thermal shock life of YSZ TBCs with the Ni-P/Al/Ni-P interlayer on the AZ91D substrate was about 226 cycles. The failure of YSZ TBCs in thermal shock test was mainly induced by the corrosion of AZ91D substrate. The results of polarization tests and electrochemical impedance spectroscopy showed that the Ni-P/Al/Ni-P interlayer had better corrosion protection for the magnesium alloy substrate than the Ni-P interlayer, which thus enhanced the thermal shock life nearly two times as compared to that of YSZ TBCs with the Ni-P interlayer. • Ni-P/Al/Ni-P sandwich structured interlayer was used between coating and substrate. • The life of TBC with sandwich interlayer was improved to 226 cycles at 400°C. • The thermal shock failure of the as-prepared coatings was investigated. • Corrosion resistance of substrate with Ni-P/Al/Ni-P was effectively strengthened. • The sandwich interlayer reduced the thermal stress between coating and substrate. [ABSTRACT FROM AUTHOR]

High strength and translucency are generally not coincident in one restorative material and there is still a continuous development for a better balance between these two properties. Zirconia and lithium-disilicate glass-ceramics are currently the most popular alternatives for monolithic restorations. In this work, the mechanical properties and more important, the slow crack growth (SCG) resistance, which rules long-term durability, were thoroughly studied for three zirconia ceramics stabilized by 3, 4 and 5 mol% yttria in comparison to lithium-disilicate glass-ceramic. Translucency versus strength maps revealed that the more translucent zirconia compositions (i.e. with higher yttria contents) fill the gap between the standard 3 mol% yttria stabilized zirconia (3Y-TZP) and lithium-disilicate. Moreover, increasing yttria content did not always result in lower strength, as values for 3 mol% and 4 mol% yttria were the same. Independent on the yttria contents, all zirconia showed similar relative susceptibility to SCG under static and cyclic conditions and were significantly more SCG-resistant than lithium-disilicate glass ceramic. A concern with higher yttria contents (5 and 4 mol%) however could lie in the higher sensitivity to defects, resulting in a larger scatter in strength. In addition to the common investigations on the generally reported strength, toughness and translucency, V-K I diagrams (crack velocity versus stress-intensity factor) from fast fracture to threshold for three newly developed zirconia were directly measured by double torsion methods under static and cyclic loading conditions. The crack-growth mechanisms were analyzed in depth. Results were compared with another popular dental ceramic, namely lithium-disilicate glass-ceramic, revealing the pros and cons of polycrystalline and glass-ceramics in terms of long-term durability. This is the first time that V-K I curves are compared for the major ceramic and glass-ceramic used for dental restorations. Strength versus translucency maps for different CAD/CAM dental restorative materials were described, showing the current indication range for zirconia ceramics. [ABSTRACT FROM AUTHOR]

Abstract For the Fundamental studies on the phase stability of YSZ, we tried to approach the detailed influences of practical conditions through various hypotheses. The phase stability of cubic and tetragonal yttria-stabilized zirconia (YSZ) was studied in the specific electrochemical conditions of current loading and molten salt flux. The degradation of electrochemical performance in the cubic phase occurred more easily than in the tetragonal phase because of yttrium elution in the lattice. The fully stabilized cubic phase showed high electrical performance as an oxide ion-conducting electrolyte, but phase decomposition occurred more easily under applied currents or chemical loading conditions than for the partially stabilized tetragonal phase. When YSZ reacted with a molten salt fluoride flux in solid oxide membrane (SOM) processing, which is used for direct metal reduction, and high-temperature electrolysis in the molten salt, the electrical conductivity of cubic YSZ was decreased by ~37%, while that of tetragonal YSZ showed no change. Our findings have important implications for the use of YSZ as an oxygen conductor in various electrochemical devices. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Vapor-phase dehydration of butanediols was studied over Y-stabilized ZrO 2 catalysts with tetragonal phase. • Unsaturated alcohols were preferentially produced in the dehydration of 1,3-butanediol over Y-stabilized ZrO 2. • Catalytic activity was greatly enhanced by calcination temperature of Y-stabilized ZrO 2 catalysts. • Stable 1,3-butanediol conversion with high unsaturated alcohols selectivity of 96.9% was obtained at 325 oC. • Catalytic activity was sensitively dependent upon the flow rate of nitrogen carrier gas. Abstract Vapor-phase catalytic dehydration of butanediols (BDOs) such as 1,3-, 1,4-, and 2,3-butanediol was investigated over yttria-stabilized tetragonal zirconia (YSZ) catalysts as well as monoclinic zirconia (MZ). BDOs were converted to unsaturated alcohols with some by-products over YSZ and MZ. YSZ is superior to MZ for these reactions in a view point of selective formation of unsaturated alcohols. Calcination temperature of YSZ significantly affected the products selectivity as well as the conversion of BDOs: high selectivity to unsaturated alcohols was obtained over the YSZ calcined at high temperatures over 800 °C. In the conversion of 1,4-butanediol at 325 °C, the highest 3-buten-1-ol selectivity of 75.3% was obtained over the YSZ calcined at 1050 °C, whereas 2,3-butanediol was less reactive than the other BDOs. In the dehydration of 1,3-butanediol at 325 °C, in particular, it was found that a YSZ catalyst with a Y 2 O 3 content of 3.2 wt.% exhibited an excellent stable catalytic activity: the highest selectivity to unsaturated alcohols such as 2-buten-1-ol and 3-buten-2-ol over 98% was obtained at a conversion of 66%. Structures of active sites for the dehydration of 1,3-butanediol were discussed using a crystal model of tetragonal ZrO 2 and a probable model structure of active site was proposed. The well-crystalized YSZ inevitably has oxygen defect sites on the most stable surface of tetragonal ZrO 2 (101). The defect site, which exposes three cations such as Zr4+ and Y3+, is surrounded by six O2− anions. The selective dehydration of 1,3-butanediol to produce 3-buten-2-ol over the YSZ could be explained by tridentate interactions followed by sequential dehydration: the position-2 hydrogen is firstly abstracted by a basic O2− anion and then the position-1 hydroxyl group is subsequently or simultaneously abstracted by an acidic Y3+ cation. Another OH group at position 3 plays an important role of anchoring 1,3-butanediol to the catalyst surface. Thus, the selective dehydration of 1,3-butanediol could proceed via the speculative base-acid-concerted mechanism. [ABSTRACT FROM AUTHOR]

Abstract Optimization of the resistance of thermal barrier coatings (TBCs) to environmental particles is an area of considerable current research. Here, we present a novel methods, incorporating plasma spray physical vapor deposition (PS-PVD), in order to fabricate a novel yttria-stabilized zirconia (YSZ) TBC which is highly phobic (i.e. non-wettable) with respect to CaO-MgO-Al 2 O 3 -SiO 2 (CMAS) particles. At 1250 °C, CMAS particles form liquid droplets which are readily repelled by the TBC surface, diminishing adherence to and penetration into the TBC. This effectiveness of the TBC in resisting wetting by molten CMAS deposits is interpreted to result from its lotus-leaf-like dual-scale microstructure. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Mesoporous WO 3 with high surface area (209 m2/g) prepared using SBA-15. • Mesoporous WO 3 used as sensing electrodes for ppb-level NO 2 detection. • Excellent NO 2 sensitivity, along with high selectivity and stability, was obtained. • The sensors using YSZ sold electrolyte followed the mixed-potential mechanism. Abstract Mesoporous WO 3 with diameter of 7 nm and specific surface area of 209 m2/g was prepared by using SBA-15 as the hard template. Designed for ppb-level NO 2 detection in air, the as-obtained mesoporous WO 3 was employed as the sensing electrode to improve the sensitivity of a mixed-potential-type sensor based on yttria-stabilized zirconia electrolyte. This device showed high sensitivity to NO 2 over the concentration range of 0.06–10 ppm at 500 ℃, and the electric potential difference (ΔV) showed good linear correlation with the logarithm of the NO 2 concentration. The sensor exhibited high NO 2 selectivity, along with excellent repeatability and stability as well. The mixed-potential sensing mechanism was also discussed based on the polarization curves and electrochemical impedances. [ABSTRACT FROM AUTHOR]

Abstract The cathodoluminescence (CL) induced in four oxide single crystals (α-Al 2 O 3 , ZrO 2 : Y or YSZ, MgAl 2 O 4 , and TiO 2) by high-energy electrons from 400 keV to 1250 keV was studied as a function of beam parameters (flux and energy). The main CL bands are related to F center (oxygen vacancy) formation by elastic collisions above the threshold displacement energy of oxygen atoms. The beam-intensity dependence is interpreted on the basis of a kinetic-rate model involving F-center formation and annihilation. The temperature effect was also followed from 110 K to 300 K. A broad maximum is found for all bands at about 200 K for sapphire, whereas a monotonous increase with temperature is observed for YSZ. The plots of CL intensity versus temperature are mainly interpreted by the interplay between the thermal dependence of thermalized free-carrier trapping rates and luminescence efficiency. Finally, the dependence of CL intensity on the primary electron energy for F centers in YSZ showing a maximum at about 600 keV is explained on the basis of the interplay between point-defect formation and secondary-electron energy spectra production. [ABSTRACT FROM AUTHOR]

Abstract The ionic conductivity of flash-sintered, polycrystalline 8 mol% yttria stabilized zirconia (8YSZ) was enhanced compared with that of conventionally-sintered specimens. Flash sintering was carried out at a furnace temperature of 850 °C with an electric field of 100 V cm–1 to initiate flash. The current density limit was varied between 60 and 100 mA mm–2. Post-flash impedance measurements over the range 215–900 °C showed that both bulk and grain boundary conductivities had increased with the increased current density limit which was set prior to flash. The conductivity increases post-flash were ionic, not electronic, although electronic conductivity probably occurred, in addition to ionic conductivity, during flash. The conductivity increases were not attributable to sample densification or microstructural changes. The higher ionic conductivities are attributed to a change in YSZ defect structure that led to an increased concentration of mobile charge carriers; possible explanations for this are discussed. [ABSTRACT FROM AUTHOR]

Abstract Densification mismatch and residual stresses of tri-layered yttria-stabilized zirconia (YSZ) membranes prepared by a non-solvent induced phase separation (NIPS) method were investigated. The tri-layered membrane consisted of sponge-like structures and finger-like voids in macroscale. The densification of the two structures were characterized to elaborate their contribution to the densification mismatch, which led to residual stresses of hundreds of megapascal retained in the sintered membranes. The profile of residual stress suggested that it was related to the strain rate mismatch within the NIPS membranes, which was further quantified with an in-situ monitored camber evolution. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • YSZ-mixed potential sensor using sol-gel derived ZnO was fabricated. • Excellent selectivity and sensitivity to CO at 700 °C in 5–21 vol.% O 2 concentrations. • The sensor showed enduring CO stability with rapid response and recovery. • Nano features of the sol-gel derived ZnO led to high sensitivity and selectivity to CO. Abstract Zinc oxide nanospheres (ZnO) were synthesized by modified sol-gel route using zinc nitrate as precursor and citric acid as gelling agent. Yttria-stabilized zirconia (YSZ)-based sensor was fabricated using the sol-gel derived ZnO nanospheres as sensing electrode and Pt as reference electrode. The sensing characteristics were examined in the temperature range of 600–800 °C under various O 2 concentrations (5, 10, 15 and 21 vol.%). It turned out that the sensor attached with the sol-gel derived ZnO-SE exhibited selective and sensitive response to carbon monoxide (CO) at 700 °C in all measured O 2 concentrations. The sensor using sol-gel derived ZnO-SE showed high response and selectivity to CO at 700 °C in 5 vol.% O 2. The response of the sensor varied linearly with CO concentrations on the logarithmic scale. The sensing mechanism was confirmed to be mixed-potential type. The sensor retained good stability even for about 40 days. The nano features associated with the sol-gel derived ZnO led to high response and selectivity to CO. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Ag/YSZ catalysts show high and stable activity for low Ag loadings. • CO 2 produced by soot combustion participates in the oxygen exchange process. • Isotopic experiments prove that bulk YSZ oxygen species are active for soot oxidation. • Ag promotes the dissociative adsorption and lattice integration of gaseous oxygen. Abstract This study investigates a potential synergy between Ag nanoparticles and Yttria-Stabilized Zirconia (YSZ), an oxygen ionically conducting support, for developing an efficient and stable catalyst for Diesel Particulate Filter regeneration only with oxygen. The catalytic performances as well as the mechanism for soot combustion were thoroughly analyzed through Temperature-Programmed Oxidation and isotopic experiments. We found that Ag/YSZ catalysts reach the highest activity for low contents of Ag, i.e. 2 wt%. Isotopic experiments were carefully performed to prove that active oxygen species originate from YSZ lattice. Silver was shown to promote soot oxidation activity by activating the dissociative adsorption of oxygen that can replenish the YSZ support. [ABSTRACT FROM AUTHOR]

Abstract Y 2 SiO 5 is a promising material for the thermal barrier coatings due to its low thermal conductivity, high temperature stability and exceptional resistance for molten silicate attack. However, it suffers low fracture toughness and low coefficient of thermal expansion compared with yttria-stabilized zirconia (YSZ). In this study, a composite coating approach, i.e., incorporating YSZ into Y 2 SiO 5 coating, was employed to overcome those limitations. The double-layered Y 2 SiO 5 -YSZ/YSZ coatings were fabricated using atomospheric plasma spraying and tested under thermal cycling at 1150 °C. The phase compositions, microstructure, mechanical properties and the failure behavior were evaluated. It was found that the amorphous phase during spraying would crystallize at high temperature accompanied by volume shrinkage, leading to cracks and spallation in the coating. With YSZ addition, the composite coatings exhibited a much longer lifetime than the single phase Y 2 SiO 5 coating due to a lower volume shrinkage and enhanced toughness. [ABSTRACT FROM AUTHOR]

Abstract La 0.6 Ca 0.4 Fe 0.8 Ni 0.2 O 3-δ (LCFN) is synthesized by liquid mixed method. Its crystalline structure is investigated by using X-ray diffraction. The results show that it has an orthorhombic perovskite structure with Pnma space group symmetry. The 8 mol % Y 2 O 3 -Stabilized ZrO 2 (YSZ) is physically mixed with various weight percentages of LCFN to form composite cathodes. High-temperature 4-probe conductivity measurements are performed to investigate the electrical behavior of the system. Electrochemical impedance spectroscopy is carried out using symmetric cells with YSZ substrates under equilibrium condition from 850 °C to room temperature. The electrical conductivity is reduced from 271.3 S cm−1 to 49.5 S cm−1 for LCFN and 10 wt % of YSZ-added LCFN (LCFN-YSZ-9010), respectively. The best area specific resistance among all fabricated composites is 0.0080(1) Ω.cm2 at 850 °C for LCFN-YSZ-9010 which exhibits almost 50% lower value than LCFN. The YSZ-based composites appear to be suitable than the other low temperature electrolyte based composite cathodes. Highlights • Electrical conductivity and electrochemical behaviors of LCFN-YSZ composite cathodes versus temperature were evaluated. • An electrical conductivity and area specific resistance threshold in terms of composite component contents was reported. • YSZ based composite seems to be an effective composite cathode at intermediate temperature ranges. [ABSTRACT FROM AUTHOR]

Abstract The aim of the present work was to investigate the effect of the ultrasonic treatment on the optical and cathodoluminescent properties of translucent ZrO 2 -8 mol.% Y 2 O 3 (YSZ) ceramics obtained by conventional sintering of the pressed compacts. Treatment by intense ultrasound during dry pressing of the YSZ nanopowder leads to an increase in the relative density, a decrease in the pore size and an increase in the grain size of the sintered ceramics. It was shown that when the ultrasonic treatment is applied, the optical absorption cutoff wavelength of the sintered material is shifted to longer wavelengths, while the optical density of the material increases over the whole measurement spectrum. Samples subjected to ultrasonic treatment during pressing show higher intensity of luminescence than those obtained without the use of ultrasound, the shape of the luminescence spectra remaining unchanged. A correlation was obtained between the integral intensity of cathodoluminescence and the vacancy concentration in the sintered YSZ. [ABSTRACT FROM AUTHOR]

Abstract Additive manufacturing represents a revolution due to its unique capabilities for freeform fabrication of near net shapes with strong reduction of waste material and capital cost. These unfair advantages are especially relevant for expensive and energy-demanding manufacturing processes of advanced ceramics such as Yttria-stabilized Zirconia, the state-of-the-art electrolyte in Solid Oxide Fuel Cell applications. In this study, self-supported electrolytes of yttria-stabilized zirconia have been printed by using a stereolithography three-dimensional printer. Printed electrolytes and complete cells fabricated with cathode and anode layers of lanthanum strontium manganite- and nickel oxide-yttria-stabilized zirconia composites, respectively, were electrochemical characterized showing full functionality. In addition, more complex configurations of the electrolyte have been printed yielding an increase of the performance entirely based on geometrical aspects. Complementary, a numerical model has been developed and validated as predictive tool for designing more advanced configurations that will enable highly performing and fully customized devices in the next future. [ABSTRACT FROM AUTHOR]

Abstract In the present study, atmospheric plasma-sprayed yttria-stabilized zirconia coatings were post-remelted by a continuous diode laser to improve the hot corrosion resistance for as-sprayed coatings. The coating surfaces were covered with a salt mixture (V 2 O 5 and Na 2 SO 4) and then subjected to a hot corrosion test at 1100 °C in air. The influence of laser parameters including power and scanning rate on the coating microstructure and corrosion resistance was investigated. Results showed that the hot corrosion resistance can be improved by producing a dense and smooth surface and reducing the coating permeability to the molten salt. The transformation of the hot corrosion mechanisms was clarified on the basis of the observed corrosion behaviors. A laser power of 1500 W and scanning rate of 9 mm/s can produce minimal surface roughness with few segmented cracks, which can provide improved performance of the hot corrosion resistance. [ABSTRACT FROM AUTHOR]

[Display omitted] • Elastic recovery behaviors of LDGC and S-YTZ significantly influenced microground surface profiles. • The more ductile and hydrophobic S-YTZ yielded a larger contact angle and lower bacteria colonization. • The microgrinding surface formation gives accurate average roughness values. • The contact between a droplet and the microground surface was the compound Wenzel-Cassie-Baxter mode. • The contact angle and bacteria colonization were controlled by the microground topographies. Controllable anti-fouling performance associated with the wettability is essential for dental restorations to have a promising reliability. This paper proposed the surface formation modelling for direct end-surface microgrinding of lithium disilicate glass–ceramic (LDGC) and sintered-yttria-stabilized tetragonal zirconia (S-YTZ) incorporating their nanoindentation elastic recovery behaviors, and a compound model of the apparent contact angle to characterize their surface functional characteristics. Nanoindentation was conducted to understand the elastic recovery behaviors at different depths; microgrinding was performed to obtain high-quality LDGC and S-YTZ surfaces; contact angle was tested to describe the wettability; and their anti-fouling performance was examined in MTT tests with streptococcus mutans. The surface formation model accurately calculated the average roughness, the interface area ratio and the relative materials ratio values at different depths of cut d , based on which the profile-controlled coefficient r w · F S for the apparent contact angle compound model was gained to determine the surface wettability. The optical density (OD) values showed strong correlations with the average surface roughness and the apparent contact angle results. Thus, the controlled anti-fouling performance associated with the apparent contact angle can be obtained by the microgrinding conditions-related surface profiles. [ABSTRACT FROM AUTHOR]