Yttria-stabilized Zirconia Nanoparticles Research Articles

Attaining translucency in binder/additive-free, nanograined, tetragonal 1.5 mol.% yttria-stabilized zirconia ceramics

In the quest of minimum yttria content to stabilize tetragonal zirconia system, we report the synthesis of ultrafine (∼9 nm), near-spherical, phase-pure tetragonal 1.5 mol.% yttria-stabilized zirconia (1.5YSZ) nanoparticles. The pressureless sintering process (at 1100 °C) involved of 1.5YSZ nanopowders (without any slurry processing) and did not need any binders, additives, or sintering aid to attain high-density (>98.5%) and refined grain size (∼50 nm) for the consolidated fully tetragonal 1.5YSZ nanoceramics. A promising transmittance value of 46% (at 630 nm) was obtained, making it comparable/higher in optical properties with respect to the transmittance values of existing 3 mol.% yttria-doped ZrO2 compositions. This result is credited to our synthesized phase-pure (validated via X-ray Diffraction and Raman analysis) near-spherical nanoparticles with improved tetragonality (c/a ratio = 1.439, obtained via Rietveld analysis) that paved the way for low-temperature conventional sintering for possible large-scale industrial applications.

Ionic Conductivity of Electrolytes Composed of Oleate-Capped Yttria-Stabilized Zirconia Nanoparticles.

Yttria-stabilized zirconia (YSZ) is a highly promising electrolyte material for solid oxide fuel cells (SOFCs). We investigated the conductivity-enhancing effect of nanosized YSZ to explore key techniques to decrease the operating temperature. YSZ nanoparticles ranging from 2 to 4 nm were synthesized with oleate groups by the hydrothermal method at various oleate/metal ion ratios (Ole/M = 1.00, 0.75, and 0.50). The nanoparticles were sintered, and the ionic conductivities were evaluated. The 1.00 Ole/M sample exhibited high dispersibility in cyclohexane and showed a nearly monodispersed distribution. The other samples possessed agglomerated nanoparticles. The sintered YSZ nanoparticles had densities of 3.36-2.80 g/cm3 and ionic conductivities of 2.52-1.16 mS/cm at 750 °C, which are higher than those of commercial 8 mol % YSZ. Furthermore, the sintered YSZ nanoparticles exhibited higher activation energies than the commercial samples in the lower temperature range (550-650 °C). The ionic conductivity enhancement despite the high activation energy is likely due to the increased grain boundary volume. This study demonstrated the successful production of YSZ with high ionic conductivity and sinterability upon sintering at 1050 °C using YSZ nanoparticles.

Hot corrosion and thermal shock performance of nanoparticulate YSZ coatings deposited via suspension plasma spraying (SPS)

In this research, the preparation, and some thermal behaviors of nanoparticulate yttria stabilized zirconia (YSZ) coatings were assessed. Aqueous suspensions containing YSZ nanoparticles were produced and then used to deposit thermal barrier coatings through the suspension plasma spraying (SPS) method. Cyclic hot corrosion and thermal shock experiments were performed on the coatings in a Na2SO4–Na2VO3 molten salt at 880 °C and under rapid cycles at 1100 °C, respectively. The coating obtained from spraying of the optimal suspension, which includes YSZ nanoparticles dispersed with α-Terpineol as a surfactant, promisingly has a columnar-shaped structure. The lifetimes of this columnar SPS-YSZ coating during the hot corrosion and thermal shock experiments were measured to be 380 h and 120 cycles, respectively, whereas they were 240 h and 100 cycles for a laminar coating obtained from spraying of nonoptimized YSZ. It is concluded that by optimizing the water-based suspension of YSZ nanoparticles, novel thermal barrier coatings with an optimal microstructure can be achieved, which improves the properties of the coating and increases its lifetime.

Yttria-Stabilized Zirconia Nanoparticles─Carbon Nanotube Composite as a Polysulfide-Capturing Lithium–Sulfur Battery Separator

The shuttle phenomenon of polysulfides is a huddle that needs to be overcome to commercialize Li–S batteries. In this study, a composite membrane based on 15 mol % yttria-stabilized zirconia nanoparticles (15YSZ) and carbon nanotubes (CNTs) is coated on a commercial separator (SV718) to fabricate a functional separator that effectively suppresses the shuttle phenomenon while enhancing the performances of Li–S batteries. Compared with the pristine SV718 separator, the functional separator with 15YSZ-CNT composite coating layer significantly enhances the cyclic stability of the Li–S cell by more than 4 times. Furthermore, slight enhancements in specific capacities are observed up to 1C from the Li–S cells incorporating 15YSZ-CNT. The mechanism behind inhibition of the shuttle phenomenon by 15YSZ-CNT is investigated via electrochemical (EIS) and surficial (XPS) characterization, which shows that Frenkel defects, such as oxygen vacancies, in YSZ can effectively capture polysulfides.

Effect of nano yttria-stabilized zirconia on properties of Ni-20Cr composite coatings

In the present work, 5 wt.% and 10 wt.% yttria-stabilized zirconia (YSZ) nanoparticles were reinforced in Ni-20Cr powder and deposited on boiler tube steel using a high-velocity oxy-fuel spraying process. The effect of YSZ reinforcement on microhardness, surface roughness and porosity was investigated. The hardness was the highest for nanocomposite coating reinforced with 10 wt.% YSZ and hardness was found to increase with a decrease in porosity. The coating microstructure and elements were characterized using field emission scanning electron microscopy (FE-SEM) with an energy dispersive spectroscope (EDS). The constituents of the coating were identified using X-ray diffractometer. It was found that the composite coating with 10 wt.% YSZ reinforced nanocomposite coating has the highest microhardness, in the range of 1008-1055 hv. During the coating process, nano YSZ particles were dispersed in the gaps between the micrometric Ni-20Cr particles, providing a better coating matrix than conventional Ni-20Cr. The Ni-20Cr with 10 wt.% of YSZ nanoparticles showed better results in terms of mechanical and microstructural properties during the investigation.

Decomposition behavior of yttria-stabilized zirconia and its effect on directed energy deposited Ti-based composite material

• The present study focuses on the rule of YSZ nanoparticles in the refined both α and β grains and increased strength of additively manufactured Ti-6Al-4 V (Ti64). • The YSZ nanoparticles decomposed during the deposition process and led to the formation of Y 2 O 3 and some excess oxygen in the Ti64 matrix. • The decrease in the sizes of the prior β grains could be attributed to the increasing amount of dissolved oxygen and yttrium, which promoted constitutional supercooling. • The reduction in the size of the α grains could be ascribed to a shift of the onset of the β → α+β transformation to a higher temperature and shorter time with increasing concentration of dissolved oxygen. • The contributions of the underlying strengthening mechanisms (α grain size, oxygen solid solution, Y 2 O 3 precipitate) for the as-deposited specimens were quantitatively determined. We report on the microstructure and the strengthening mechanisms of additively manufactured parts fabricated by directed energy deposition of Ti-6Al-4V (Ti64) powders blended with yttria-stabilized zirconia (YSZ) nanoparticles. These specimens showed refined microstructures as compared to bare as-deposited Ti64, where the α and columnar prior β grain sizes decreased with increasing YSZ content. The YSZ nanoparticles decomposed during the deposition process and led to the formation of yttrium oxide and some excess oxygen in the Ti64 matrix. The decrease in the sizes of the prior β grains could be attributed to the increasing amount of dissolved oxygen and yttrium, which promoted constitutional supercooling. Furthermore, the reduction in the size of the α grains could be ascribed to a shift of the onset of the β → α+β transformation to a higher temperature and shorter time with increasing concentration of dissolved oxygen. Finally, the contributions of the underlying strengthening mechanisms for the as-deposited specimens were quantitatively determined.

Mechanical and microstructural properties of yttria-stabilized zirconia reinforced Cr3C2-25NiCr thermal spray coatings on steel alloy

In this research work, nano yttria-stabilized zirconia (YSZ) reinforced Cr3C2-25NiCr compo­site coatings were prepared and successfully deposited on ASME-SA213-T-22 (T22) boiler tube steel substrates using high-velocity oxy-fuel (HVOF) thermal spraying method. Different nanocomposite coatings were developed by reinforcing Cr3C2-25NiCr with 5 and 10 wt.% YSZ nanoparticles. The nanocomposite coatings were analysed by scanning elec­tron microscope (SEM)/Energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) technique. The porosity of YSZ- Cr3C2-25NiCr nanocomposite coatings was found to be decreasing with the increase in YSZ content, and hardness has been found to be increasing with an increase in the percentage of YSZ in the composite coatings. The coating of 10 wt.% YSZ-Cr3C2-25NiCr showed the lowest porosity, lowest surface roughness, and highest microhardness among all types of coatings. This may be due to the flow of YSZ nanoparticles into the pores and gaps that exist in the base coatings, thus providing a better shield to the substrate material.

Mechanical and microMechanical and microstructural characterization of yttria-stabilized zirconia (Y2O3/ZrO2; YSZ) nanopartstructural characterization of yttria stabilized zirconia (Y2O3/ZrO2; YSZ) nanoparticles reinforced WC-10Co-4Cr coated turbine steel

The aim of this paper is to investigate the WC-10Co-4Cr coatings reinforced with 5 % and 10 % of yttria-stabilized zirconia (Y2O3/ZrO2; YSZ) nanoparticles deposited on the CA6NM turbine steel by using the high-velocity oxy-fuel (HVOF) thermal spraying technique. In the HVOF technique, the hot jet of the semi-solid particles strikes against the workpiece and creates a layer of coating of varying thickness on the substrate material. The coatings fabricated with HVOF were analyzed by scanning electron microscope (SEM) / energy-dispersive x-ray spectroscopy (EDS). The phase identification of a crystalline material was made with the x-ray diffraction (XRD) technique. The mecha­nical properties in terms of porosity, surface roughness and microhardness of the nanocomposite coatings were also evaluated. The SEM/EDS analysis showed that dense and homogeneous coatings were developed by the reinforcement of YSZ nanoparticles. The peaks of XRD graphs of WC-10Co-4Cr coating reinforced with 5 and 10 % of YSZ nanoparticles revealed that the WC was present as a major phase and W2C, Co3W3C, Co, Co6W6C, Co6W and Y2O3/ZrO2 nanoparticles were observed as a minor phase. The porosity level decreased up to 42 and 56 % by the addition 5 and 10 % of YSZ nanoparticles as compared with conventional WC-10Co-4Cr coating. The surface roughness values for WC-10Co-4Cr conventional coating, 95 % (WC-10Co-4Cr) + 5 % YSZ and 90 % (WC-10Co-4Cr) + 10 % YSZ nanocomposite coated samples were found to be 5.03, 4.89 and 4.28 respectively. The nanocomposite coatings reinforced with 10 % YSZ nanoparticles exhibited the highest microhardness value (1278 HV). The WC-10Co-4Cr coatings reinforced with 10 % of YSZ nanoparticles resulted in low porosity, low surface roughness and high microhardness. During the coating process, the nanoparticles of YSZ flow into the pores and are dispersed in the gaps between the micrometric WC particles and provide a better shield to the substrate material. The WC-10Co-4Cr with 10 % of YSZ nanoparticles showed better results in terms of mecha­nical and microstructural properties during the investigation.

Thermal energy evolution and mechanical deformation of monocrystalline yttria-stabilized zirconia nanoparticles in aerosol deposition processes

Aerosol deposition (AD) is a coating process wherein aerosol particles are impacted on a target substrate. There are fundamental differences between the AD process (cold impact), where particle translational kinetic energy is high and thermal energy is low, and thermal spray deposition (thermal impact), where translational energy is lower but thermal energy is high. To better compare cold and thermal impact effects on particles, we carried out molecular dynamics simulations using yttria-stabilized zirconia (YSZ) nanoparticles on YSZ substrates as a model system. We performed cold impact simulations at 300 K with variable impact velocity in the 500 ms−1–1500 ms−1 range to understand how increasing translational kinetic energy affects thermal energy and mechanical evolution. We then performed thermal impact simulations at variable temperature and impact velocity, but where the total kinetic energy of the nanoparticle was equivalent to that of a 300 K, 1000 ms−1 impact. In cold impact, the temperature increases in YSZ nanoparticles at a rate of 1013–1014Ks−1, and large temperature gradients result. Conversely, in thermal impact, nanoparticle temperatures remain uniform. The temperature gradients during cold impact coincide with plastic deformation in nanoparticles, while with larger thermal energies, plastic deformation is reduced.

Effect of Yttria-Stabilized Zirconia (Y2O3/ZrO2) Nanoparticles Reinforced Cr3C2-25NiCr Coatings on the Microstructural and Mechanical Properties of Turbine Steel

Abstract The present work is mainly focused on the investigation of Cr3C2-25NiCr coatings reinforced with 5 % and 10 % of yttria-stabilized zirconia (YSZ) nanoparticles deposited on the CA6NM turbine steel by using the high-velocity oxy-fuel technique. The coatings were analyzed by scanning electron microscope (SEM)/energy-dispersive X-ray spectroscopy (EDS). The phase identification of a crystalline material was done with the X-ray diffraction (XRD) technique. The SEM/EDS analysis showed that dense and homogeneous coatings were developed by the reinforcement of YSZ nanoparticles. The peaks of XRD graphs of Cr3C2-25NiCr coating reinforced with 5 % and 10 % of YSZ nanoparticles revealed that the chromium and carbon were present as a major phase, and the presence of nickel, yttrium, and zirconium was observed as a minor phase. The porosity level decreased up to 32 % and 45 % by the addition 5 % and 10 % of YSZ nanoparticles as compared with conventional Cr3C2-25NiCr coating. The surface roughness values for coated samples were found to be 5.03, 4.89, and 4.28. The nanocomposite coatings reinforced with 10 % YSZ nanoparticles exhibited the highest microhardness value (1,251 HV). The Cr3C2-25NiCr coatings reinforced with 10 % of YSZ nanoparticles resulted in low porosity, low surface roughness, and high microhardness. During the coating process, the nanoparticles of YSZ flow into the pores and gaps that exist in the coatings and provide a better shield to the substrate material. The Cr3C2-25NiCr with 10 % of YSZ nanoparticles showed better results in terms of mechanical and microstructural properties during the investigation.

Yttria Stabilized Zirconia Nanoparticles – Carbon Nanotubes Composite as a Polysulfide Capturing Lithium-Sulfur Battery Separator

Yttria Stabilized Zirconia Nanoparticles – Carbon Nanotubes Composite as a Polysulfide Capturing Lithium-Sulfur Battery Separator

Fabrication of microstructured yttria-stabilized zirconia electrolyte surface using centrifugal molding for high-performance solid oxide fuel cells

This study replicated the surface of yttria-stabilized zirconia (YSZ) microstructures by centrifugal filling to improve the performance of solid oxide fuel cells. A slurry with YSZ nanoparticles were filled with centrifugal force in polymer replica mold, solvent dried, and then transferred and sintered onto a bulk YSZ electrolyte plate. 3 m-pitch pillar structure was successfully replicated with a centrifugal acceleration of 2,500 G, and the polarization resistance of the electrodes was reduced by approximately 25%. Similarly, a line-and-space structure was formed to investigate the structure dependence, and resistance reduction was confirmed. Furthermore, a distribution relaxation time analysis confirmed that the reduction in resistance was due to decreasing tortuosity factor of YSZ.

Effect of Yttria-Stabilized Zirconia Concentration in an Electroless Bath on Microstructure and Composition of Ni/Yttria-Stabilized Zirconia Nanocomposite.

The effect of the yttria-stabilized zirconia (YSZ) nanoparticle loading in an electro-less bath was considered as one of the vital synthesis variables for control Ni content and microstructure of prepared nanocomposite particles, which are two crucial factors to achieving high-performance SOFC anode. Nanocomposite particles were prepared using a simple electroless method without any expensive pretreatment of sensitizing by Sn²+ ions as well as activating by Pd2+ ions that are usually used to apply nickel coating on the surface of a non-conductive substrate. The process was performed by adding YSZ nanoparticles into NaOH solution, separating them from the solution by the centrifugal method, then providing several water-based nanofluids with different concentrations of activated YSZ nanoparticles, mixing them with NiCI₂ solution, followed by adding the hydrazine and then NaOH solution. X-ray diffraction and scanning electron microscopy coupled with energy dispersive X-ray analysis were used to analyze the prepared nanocomposite particles. It is observed that after adding YSZ nanoparticles into the NaOH solution, the pH of the solution varied gradually from a starting pH of 10.2 to 9. Also, by increasing the YSZ nanoparticles loading in the electroless bath from 76 mg/l to 126 mg/l, the grain size of Ni deposits, the Ni content and the average size of the prepared nanocomposite particles decreased. The electrochemical mechanism previously proposed for the nickel ion reduction was modified, and a novel analytical model was proposed for variation of the efficiency of Ni deposition with YSZ nanoparticles loading.

Preparation and Optimization Green Gel Casting Technique for Manufacturing Near-Net-Shape Ceramics Using Genetic Algorithm

Gel casting technique is a promising technology that has ability to produce near-net shape ceramics via using toxic and non-ecofriendly agents. The current work aim to develop green gel casting technique using water as a solvent, agar as a gelling agent, and the microwave thermal treatment instead of cross linker. 8mo l% Yttria stabilized zirconia was selected as a case study to produce near-net shape ceramics. The experimental work involved the preparation of Yttria stabilized zirconia nanoparticles via chemical precipitation method. The effect study of agar ratio, Yttria stabilized zirconia solid loading percent on the physical, mechanical, surface properties of the prepared ceramics and selecting of suitable casting conditions. The study has been found that the microwave thermal treatment develops thermally activated cross linking in the agar aqueous solution leading to higher glass transition temperature for agar. The green combination (agar aqueous solution and microwave treatment) can be used as alternative to (monomer, solvent, cross linker) Companion. Also, using the ultrasonic treatment can effectively eliminate needs for dispersants, also the vacuum de-airing treatment. Yttria stabilized zirconia ceramic with high dimensional accuracy, low surface roughness (Ra=2. 81 nm) can be obtained using an agar ratio of (0.4%) and solid loading of (65%). The sample can be moulded with complex shape and the green gel, also the pre-sintered body is machineable. The sintered samples have a porosity of (31%) and compressive strength of (234MPa). Regression analysis and genetic algorithm are showed that the obtained microhardness, compressive strength, and surface roughness are predictable.

Sol-Gel Synthesis and Characterization of YSZ Nanofillers for Dental Cements at Different Temperatures.

Background: Yttria-stabilized zirconia nanoparticles can be applied as fillers to improve the mechanical and antibacterial properties of luting cement. The aim of this study was to synthesize yttria-stabilized zirconia nanoparticles by the sol–gel method and to investigate their composition, structure, morphology and biological properties. Methods: Nanopowders of ZrO2 7 wt% Y2O3 (nY-ZrO) were synthesized by the sol–gel method and were sintered at three different temperatures: 800, 1000 and 1200 °C, and their composition, size and morphology were investigated. The biocompatibility was investigated with human gingival fibroblasts (hGFs), while reactive oxygen species (ROS) production was evaluated through fluorescence analysis. Results: All synthesized materials were composed of tetragonal zirconia, while nanopowders sintered at 800 °C and 1000 °C additionally contained 5 and 20 wt% of the cubic phase. By increasing the calcination temperature, the crystalline size of the nanoparticles increased from 12.1 nm for nY-ZrO800 to 47.2 nm for nY-ZrO1200. Nano-sized particles with good dispersion and low agglomeration were received. Cell culture studies with human gingival fibroblasts verified the nanopowders’ biocompatibility and their ROS scavenging activity. Conclusions: the obtained sol–gel derived nanopowders showed suitable properties to be potentially used as nanofillers for dental luting cement.

Measuring Radiation Enhanced Diffusion Through <i>in situ</i> Ion Radiation Induced Sintering of Oxide Nanoparticles

Radiation enhanced diffusion often contributes significantly to the evolution of microstructures subject to radiation but can be challenging to predict in complex nonmetallic material systems. Here, microstructural evolution in the presence of ion radiation was leveraged to explore the underlying transport phenomenon. Specifically, in situ ion irradiation of nanoparticles reveal rapid densification at room temperature for nanoparticles of cerium oxide (CeO2) and yttria stabilized zirconia (YSZ) but not for magnesium oxide (MgO) or silicon carbide (SiC). This is attributed to rapid diffusion of radiation induced interstitial defects to the high density of free surfaces in the nanoparticle agglomerates. When these observations are combined with image processing and application of a simple two-sphere sintering model, radiation enhanced diffusivity values can be calculated. In situ irradiation of YSZ nanoparticles over a broader temperature range, 50 K to 1073 K, clearly revealed a transition between three distinct rate limiting regimes: (i) low temperature, sink-limited kinetics, (ii) intermediate temperature, recombination-limited kinetics, and (iii) at high-temperature the densification is consistent with thermally activated diffusion kinetics. The high spatial and temporal resolution provided by the in situ methodology is critical to confidently distinguishing these regimes in nonmetallic oxides. While only four nonmetallic nanoparticle systems are presented here (YSZ, CeO2, SiC, and MgO), application of this methodology to the readily accessible, diverse catalog of nanoparticle chemistries and morphologies will allow for rapid exploration of radiation-enhanced diffusion behavior in a broader range of complex nonmetallic systems without the need for tracers.

Kinetic evaluation of YSZ/Al2O3 nanocomposite coatings fabricated by electrophoretic deposition on a nickel-based superalloy

In the current study, the evolution of deposition yields with time for yttria stabilized zirconia (YSZ)/Al2O3 nanocomposite coatings deposited by electrophoretic technique was described by a kinetic model. Aluminium powder was used as a sintering aid and also the source for the formation of Al2O3 during sintering. A mixture of ethanol and acetylacetone was utilized as the solvent. In order to prepare a stable suspension, surface charges and electrostatic interaction between particles in suspensions were evaluated through analyses of pH, zeta potential, and particles size. Electrophoretic deposition (EPD) on Inconel 718 electrodes was successfully carried out by employing three well-dispersed suspensions including nanostructured YSZ with 0, 30 and 50 wt.% of Al particles. The influences of three different applied voltages (25, 45 and 65 V), deposition time and the weight percent of Al particles on the EPD kinetic at a time interval of 0-300 s were studied and quantified based on the Baldisserri equation. It was shown that the results achieved from the Baldisserri model were almost well matched with the experimental data within a wide range of time. It was found that the deposition rate declines with the increase in YSZ nanoparticles content and time. The coated substrates in the final step were dried and sintered at 1150 ?C. The coating quality and surface morphology were characterized by field emission scanning electron microscopy (FE-SEM).

High Performance Commercial SOFC Cathodes Achieved with YSZ Nanoparticles

The electrochemical performance of solid oxide fuel cell (SOFC) cathodes was improved via integration of ultra-high surface area ceramic nanoparticles, up to 115 m2·g-1, generated with a novel processing method herein introduced. The processing method generates the high surface area nanoparticles at traditional SOFC sintering temperatures in two steps. In the first step, a hybrid inorganic-organic material comprising the ceramic precursors is sintered in an inert atmosphere at any temperature between 850°C-1350°C. During this step, an amorphous carbon template is generated in situ, preventing coarsening of the ceramic nanoparticles. The carbon template is then removed during the second step by a mild calcination in air at 700°C. Yttria-stabilized zirconia (YSZ), lanthanum strontium cobalt ferrite (LSCF), gadolinium-doped ceria (GDC), and strontium titanate (STO) have all been successfully prepared by this method. YSZ nanoparticles (nYSZ) were incorporated into a lanthanum strontium manganite-YSZ (LSM-YSZ) cathode of a commercial cell, resulting in a 90% increase in maximum power density. Impedance spectroscopy indicates the large improvement in power density was attributed to a combination of significant improvement in polarization resistance, a 45% decrease, and ohmic resistance, a 35% decrease. Remarkably, the performance of the cell modified with nYSZ was higher than cells modified with two mixed ionic electronic conductors (MIEC): PrxBa1-xCo3-δ (PBC) and LaxSr1-xCoyFe1-yO3-δ (LSCF). Both MIECs enhanced the density of active sites, but, unlike nYSZ, did not significantly improve ohmic resistance. The results demonstrate a novel pathway to achieve high performance in commercial SOFCs.

Quasi-solid-state electrolyte for rechargeable high-temperature molten salt iron-air battery

Molten salts are a unique type of electrolyte enabling high-temperature electrochemical energy storage (EES) with unmatched reversible electrode kinetics and high ion-conductivities, and hence impressive storage capacity and power capability. However, their high tendency to evaporate and flow at high temperatures challenges the design and fabrication of the respective EES devices in terms of manufacturing cost and cycling durability. On the other hand, most of these EES devices require lithium-containing molten salts as the electrolyte to enhance performances, which not only increases the cost but also demands a share of the already limited lithium resources. Here we report a novel quasi-solid-state (QSS) electrolyte, consisting of the molten eutectic mixture of Na2CO3-K2CO3 and nanoparticles of yttrium stabilized zirconia (YSZ) in a mass ratio of 1:1. The QSS electrolyte has relatively lower volatility in comparison with the pristine molten Na2CO3-K2CO3 eutectic, and therefore significantly suppresses the evaporation of molten salts, thanks to a strong interaction at the interface between molten salt and YSZ nanoparticles at high temperatures. The QSS electrolyte was used to construct an iron-air battery that performed excellently in charge-discharge cycling with high columbic and energy efficiencies. We also propose and confirm a redox mechanism at the three-phase interlines in the negative electrode. These findings can help establish a simpler and more efficient approach to designing low-cost and high-performance molten salt metal-air batteries with high stability and safety.

Spray pyrolysis of yttria-stabilized zirconia nanoparticles and their densification into bulk transparent windows

We describe an aerosol spray pyrolysis system for the synthesis of yttria-stabilized zirconia (YSZ) nanoparticles with precisely tunable composition. Extensive structural and compositional characterization confirm that this technique gives access to particles with combined size and composition that are not commercially available. We have densified these particles via spark plasma sintering to investigate the mechanical and optical properties of the resulting bulk samples. Direct transmittance of the densified samples was measured to determine the role of grain size, porosity, oxygen vacancies, and crystal structure on the transparency of the samples. Small grain sizes and low porosity are commonly suggested as the essential property to obtain transparency. We have found that the transparency strongly correlates with crystal structure, with isotropic crystal structure having the highest transparency. Finally, to determine the mechanical properties of the densified samples, we used Vickers hardness testing confirming that YSZ in a tetragonal crystal structure is both harder and tougher than in a cubic crystal structure. This study suggests that aerosol spray pyrolysis is a promising synthetic approach for the synthesis of small YSZ nanocrystals with controllable composition. This could enable the optimization of both the optical and mechanical properties of bulk YSZ.